The Project Gutenberg eBook of Aeroplanes, by James Slough Zerbe

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Aeroplanes

by J. S. Zerbe

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AEROPLANES

This work is affordable interactive globes under 30 dollarsnot intended to set forth the exploits of aviatorsnor to give a history of the Art. It is a book of instructionsintended to point out the theories of flying, as given by thepioneers, the practical application of power to the variousflying structures; how they are built, the different methods ofcontrolling them; the advantages and disadvantages of the typesnow in use; and suggestions as to the directions in whichimprovements are required.

It distinctly points out wherein mechanical flight differsfrom bird flight, and what are the relations of shape, form, sizeand weight. It treats of kites, gliders and model aeroplanes,and has an Interesting chapter on the aeroplane and its uses Inthe great war. All the illustrations have been specially preparedfor the work.

Every Boy's Mechanical Library

AEROPLANES

BY
J. S. ZERBE, M. E.
Author of Automobiles—Motors

COPYRIGHT, 1915, BY
CUPPLES & LEON COMPANY
NY

CONTENTS

INTRODUCTORY

CHAPTER I. THEORIES AND FACTS ABOUT FLYING

The "Science" of Aviation. Machine Types. Shape
or Form not Essential. A Stone as a Flying Machine.
Power the Great Element. Gravity as Power. Mass
and Element in Flying. Momentum a Factor. Resistance.
How Resistance Affects Shape. Mass and Resistance.
The Early Tendency to Eliminate Momentum.
Light Machines Unstable. The Application of
Power. The Supporting Surfaces. Area not the Essential
Thing. The Law of Gravity. Gravity. Indestructibility
of Gravitation. Distance Reduces Gravitational
Pull. How Motion Antagonizes Gravity. A
Tangent. Tangential Motion Represents Centrifugal
Pull. Equalizing the Two Motions. Lift and Drift.
Normal Pressure. Head Resistance. Measuring Lift
and Drift. Pressure at Different Angles. Difference
Between Lift and Drift in Motion. Tables of Lift and
Drift. Why Tables of Lift and Drift are Wrong.
Langley's Law. Moving Planes vs. Winds. Momentum
not Considered. The Flight of Birds. The
Downward Beat. The Concaved Wing. Feather Structure
Considered. Webbed Wings. The Angle of Movement.
An Initial Movement or Impulse Necessary. A
Wedging Motion. No Mystery in the Wave Motion.
How Birds Poise with Flapping Wings. Narrow-
winged Birds. Initial Movement of Soaring Birds.
Soaring Birds Move Swiftly. Muscular Energy
Exerted by Soaring Birds. Wings not Motionless.

CHAPTER II. PRINCIPLES OF AEROPLANE FLIGHTSpeed as one of the Elements. Shape and Speed.What "Square of the Speed" Means. Action of a"Skipper." Angle of Incidence. Speed and Surface.Control of the Direction of Flight. Vertical Planes.

CHAPTER III. THE FORM OR SHAPE OF FLYING MACHINESThe Theory of Copying Nature. Hulls of Vessels.Man Does not Copy Nature. Principles Essential, notForms. Nature not the Guide as to Forms. The PropellerType. Why Specially-designed Forms ImproveNatural Structures. Mechanism Devoid of Intelligence.A Machine Must Have a Substitute for Intelligence.Study of Bird Flight Useless. Shape ofSupporting Surface. The Trouble Arising From OutstretchedWings. Density of the Atmosphere. Elasticityof the Air. "Air Holes." Responsibility forAccidents. The Turning Movement. Centrifugal Action:The Warping Planes.

CHAPTER IV. FORE AND AFT CONTROLThe Bird Type of Fore and Aft Control. Angle andDirection of Flight. Why Should the Angle of theBody Change. Changing Angle of Body not Safe. ANon-changing Body. Descending Positions by PowerControl. Cutting off the Power. The Starting Movement.The Suggested Type. The Low Center of Gravity.Fore and Aft Oscillations. Application of theNew Principle. Low Weight not Necessary with Synchronously-moving wings.

CHAPTEB V. DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICSThe Helicopter. Aeroplanes. The Monoplane. ItsAdvantages. Its Disadvantages. The Bi-plane. Stabilityin Bi-planes. The Orthopter. Nature's Typenot Uniform. Theories About Flight of Birds. Instinct.The Mode of Motion. The Wing Structure.The Wing Movement. The Helicopter Motion.

CHAPTER VI. THE LIFTING SURFACES OF AEROPLANESRelative Speed and Angle. Narrow Planes Most Effective.Stream Lines Along a Plane. The Center ofPressure. Air Lines on the Upper Side of a Plane.Rarefied Area. Rarefaction Produced by Motion. TheConcaved Plane. The Center of Pressure. Utilizingthe Rarefied Area. Changing Center of Pressure.Plane Monstrosities. The Bird Wing Structure.Torsion. The Bat's Wing. An Abnormal Shape. TheTail as a Monitor.

CHAPTER VII. ABNORMAL FLYING STUNTS AND SPEEDSLack of Improvements in Machines. Men Exploitedand not Machines. Abnormal Flying of no Value.The Art of Juggling. Practical Uses the Best Test.Concaved and Convex Planes. How Momentum is aFactor in Inverted Flying. The Turning Movement.When Concaved Planes are Desirable. The SpeedMania. Uses of Flying Machines. Perfection in MachinesMust Come Before Speed. The Range of itsUses. Commercial Utility.

CHAPTER VIII. KITES AND GLIDERSThe Dragon Kite. Its Construction. The MalayKite. Dihedral Angle. The Common Kite. The BowKite. The Box Kite. The Voison Bi-plane. LateralStability in Kites, not Conclusive as to Planes. TheSpear Kite. The Cellular Kite. Tetrahedral Kite.The Deltoid. The Dunne Flying Machine. RotatingKite. Kite Principles. Lateral Stability in Kites.Similarity of Fore and Aft Control. Gliding FlightOne of the Uses of Glider Experiments. Hints inGliding.

CHAPTER IX. AEROPLANE CONSTRUCTIONLateral and Fore and Aft. Transverse. Stabilityand Stabilization. The Wright System. Controllingthe Warping Ends. The Curtiss Wings. The FarmanAilerons. Features Well Developed. Depressing theRear End. Determining the Size. Rule for Placingthe Planes. Elevating Plane. Action in Alighting.The Monoplane. The Common Fly. Stream Lines.The Monoplane Form.

CHAPTER X. POWER AND ITS APPLICATIONFeatures in Power Application. Amount of PowerNecessary. The Pull of the Propeller. Foot PoundsSmall Amount of Power Available. High PropellerSpeed Important. Width and Pitch of Blades. Effectof Increasing Propeller Pull. Disposition of thePlanes. Different Speeds with Same Power. Increaseof Speed Adds to Resistance. How Power Decreaseswith Speed. How to Calculate the Power Applied.Pulling Against an Angle. The Horizontal and theVertical Pull. The Power Mounting. Securing thePropeller to the Shaft. Vibrations. Weaknesses inMounting. The Gasoline Tank. Where to Locate theTank. The Danger to the Pilot. The Closed-in Body.Starting the Machine. Propellers with Varying Pitch.

CHAPTER XI. FLYING MACHINE ACCESSORIESThe Anemometer. The Anemograph. The Anemometrograph.The Speed Indicator. Air Pressure Indicator.Determining the Pressure From the Speed.Calculating Pressure From Speed. How the Figuresare Determined. Converting Hours Into Minutes.Changing Speed Hours to Seconds. Pressure as theSquare of the Speed. Gyroscopic:Balance. The PrinciplesInvolved. The Application of the Gyroscope.Fore and Aft Gyroscopic Control. Angle Indicator.Pendulum Stabilizer. Steering and ControllingWheel. Automatic Stabilizing Wings. Barometers.Aneroid Barometer. Hydroplanes. Sustaining Weightof Pontoons. Shape of the Pontoon.

CHAPTER XII. EXPERIMENTAL WORK IN FLYINGCertain Conditions in Flying. Heat in Air. MotionWhen in Flight. Changing Atmosphere. "AscendingCurrents." "Aspirate Currents." Outstretched Wings.The Starting Point. The Vital Part of the Machine.Studying the Action of the Machine. Elevating theMachine. How to Practice. The First Stage. Patiencethe Most Difficult Thing. The Second Stage.The Third Stage. Observations While in Flight. Flyingin a Wind. First Trials in a Quiet Atmosphere.Making Turns. The Fourth Stage. The Figure 8.The Vol Plane. The Landing. Flying Altitudes.

CHAPTER XIII. THE PROPELLERPropeller Changes. Propeller Shape. The Diameter.Pitch. Laying Out the Pitch. Pitch Rule. LaminatedConstruction. Laying up a Propeller Form.Making Wide Blades. Propeller Outline. For HighSpeeds. Increasing Propeller Efficiency.

CHAPTER XIV. EXPERIMENTAL GLIDERS AND MODEL AEROPLANESThe Relation of Models to Flying Machines. LessonsFrom Models. Flying Model Aeroplanes. AnEfficient Glider. The Deltoid Formation. RacingModels. The Power for Model Aeroplanes. Makingthe Propeller. Material for the Propeller. Rubber.Propeller Shape and Size. Supporting Surfaces.

CHAPTER XV. THE AEROPLANE IN THE GREAT WARBalloon Observations. Changed Conditions in Warfare.The Effort to Conceal Combatants. SmokelessPowder. Inventions to Attack Aerial Craft. Functionsof the Aeroplane in War. Bomb-throwing Tests.Method for Determining the Movement of a Bomb.The Great Extent of Modern Battle Lines. The AeroplaneDetecting the Movements of Armies. The EffectiveHeight for Scouting. Sizes of Objects at GreatDistances. Some Daring Feats in War. The GermanTaube. How Aeroplanes Report Observations. SignalFlags. How Used. Casualties Due to BombsFrom Aeroplanes.

GLOSSARY

INTRODUCTORY

In preparing this volume on Flying Machinesthe aim has been to present the subject in such amanner as will appeal to boys, or beginners, inthis field of human activity.

The art of aviation is in a most primitive state.So many curious theories have been brought outthat, while they furnish food for thought, do not,in any way, advance or improve the structure ofthe machine itself, nor are they of any servicein teaching the novice how to fly.

The author considers it of far more importanceto teach right principles, and correct reasoningthan to furnish complete diagrams of the detailsof a machine. The former teach the art, whereasthe latter merely point out the mechanicalarrangements, independently of the reasons formaking the structures in that particular way.

Relating the history of an art, while it may beinteresting reading, does not even lay the foundationsof a knowledge of the subject, hence thatfield has been left to others.

The boy is naturally inquisitive, and he is interestedin knowing WHY certain things arenecessary, and the reasons for making structures inparticular ways. That is the void into whichthese pages are placed.

The author knows from practical experience,while experimenting with and building aeroplanes,how eagerly every boy inquires into details.They want the reasons for things.

One such instance is related to evidence thisspirit of inquiry. Some boys were discussing thecurved plane structure. One of them venturedthe opinion that birds' wings were concaved on thelower side. "But," retorted another, "why arebirds' wings hollowed?"

This was going back to first principles at oneleap. It was not satisfying enough to know thatman was copying nature. It was more importantto know why nature originated that type of formation,because, it is obvious, that if such structuresare universal in the kingdom of flying creatures,there must be some underlying principlewhich accounted for it.

It is not the aim of the book to teach the artof flying, but rather to show how and why thepresent machines fly. The making and the usingare separate and independent functions, and ofthe two the more important is the knowledge howto make a correct machine.

Hundreds of workmen may contribute to thebuilding of a locomotive, but one man, not abuilder, knows better how to handle it. Tomanipulate a flying machine is more difficult tonavigate than such a ponderous machine, becauseit requires peculiar talents, and the building isstill more important and complicated, and requiresthe exercise of a kind of skill not necessaryin the locomotive.

The art is still very young; so much is donewhich arises from speculation and theories; toomuch dependence is placed on the aviator; thedesire in the present condition of the art is to exploitthe man and not the machine; dare-devil exhibitionsseem to be more important than perfectingthe mechanism; and such useless attempts asflying upside down, looping the loop, and characteristicdisplays of that kind, are of no value tothe art. THE AUTHOR.

AEROPLANES

CHAPTER I

THEORIES AND FACTS ABOUT FLYING

THE "SCIENCE" OF AVIATION.—It may bedoubted whether there is such a thing as a "scienceof aviation." Since Langley, on May 6,1896, flew a motor-propelled tandem monoplanefor a minute and an half, without a pilot, and theWright Brothers in 1903 succeeded in flying abi-plane with a pilot aboard, the universal opinionhas been, that flying machines, to be successful,must follow the structural form of birds, andthat shape has everything to do with flying.

We may be able to learn something by carefullyexamining the different views presented bythose interested in the art, and then see how theyconform to the facts as brought out by the actualexperiments.

MACHINE TYPES.—There is really but one typeof plane machine. While technically two formsare known, namely, the monoplane and thebi-plane, they are both dependent on outstretchedwings, longer transversely than fore and aft, sofar as the supporting surfaces are concerned, andwith the main weight high in the structure, thus,in every particular, conforming to the formpointed out by nature as the apparently correcttype of a flying structure.

SHAPE OR FORM NOT ESSENTIAL.—It may bestated with perfect confidence, that shape or formhas nothing to do with the mere act of flying. Itis simply a question of power. This is a broadassertion, and its meaning may be better understoodby examining the question of flight in abroad sense.

A STONE AS A FLYING MACHINE.—When a stoneis propelled through space, shape is of no importance.If it has rough and jagged sides its speedor its distance may be limited, as compared witha perfectly rounded form. It may be made insuch a shape as will offer less resistance to the airin flight, but its actual propulsion through spacedoes not depend on how it is made, but on thepower which propelled it, and such a missile is atrue heavier-than-air machine.

A flying object of this kind may be so constructedthat it will go a greater distance, or requireless power, or maintain itself in space atless speed; but it is a flying machine, nevertheless,in the sense that it moves horizontally through theair.

POWER THE GREAT ELEMENT.—Now, let us examinethe question of this power which is able toset gravity at naught. The quality called energyresides in material itself. It is something withinmatter, and does not come from without. Thepower derived from the explosion of a charge ofpowder comes from within the substance; and sowith falling water, or the expansive force ofsteam.

GRAVITY AS POWER.—Indeed, the very act of theball gradually moving toward the earth, by theforce of gravity, is an illustration of a powerwithin the object itself. Long after Galileofirmly established the law of falling bodies it beganto dawn on scientists that weight is force.After Newton established the law of gravitationthe old idea, that power was a property of eachbody, passed away.

In its stead we now have the firmly establishedview, that power is something which must haveat least two parts, or consist in pairs, or two elementsacting together. Thus, a stone poised ona cliff, while it exerts no power which can beutilized, has, nevertheless, what is called potentialenergy. When it is pushed from its lodging placekinetic energy is developed. In both cases,gravity, acting in conjunction with the mass ofthe stone, produced power.

So in the case of gunpowder. It is the unity oftwo or more substances, that causes the expansioncalled power. The heat of the fuel convertingwater into steam, is another illustration of theunity of two or more elements, which are necessaryto produce energy.

MASS AN ELEMENT IN FLYING.—The boy whoreads this will smile, as he tells us that the powerwhich propelled the ball through the air camefrom the thrower and not from the ball itself.Let us examine this claim, which came from a realboy, and is another illustration how acute his mindis on subjects of this character.

We have two balls the same diameter, one ofiron weighing a half pound, and the other of cottonweighing a half ounce. The weight of oneis, therefore, sixteen times greater than the other.

Suppose these two balls are thrown with theexpenditure of the same power. What will be theresult! The iron ball will go much farther, or,if projected against a wall will strike a harderblow than the cotton ball.

MOMENTUM A FACTOR.—Each had transferredto it a motion. The initial speed was the same,and the power set up equal in the two. Why thisdifference, The answer is, that it is in thematerial itself. It was the mass or density which accountedfor the difference. It was mass multipliedby speed which gave it the power, called, inthis case, momentum.

The iron ball weighing eight ounces, multipliedby the assumed speed of 50 feet per second, equals400 units of work. The cotton ball, weighing 1/2ounce, with the same initial speed, represents 25units of work. The term "unit of work" meansa measurement, or a factor which may be used tomeasure force.

It will thus be seen that it was not the throwerwhich gave the power, but the article itself. Afeather ball thrown under the same conditions,would produce a half unit of work, and the ironball, therefore, produced 800 times more energy.

RESISTANCE.—Now, in the movement of any bodythrough space, it meets with an enemy at everystep, and that is air resistance. This is muchmore effective against the cotton than the ironball: or, it might be expressed in another way:The momentum, or the power, residing in themetal ball, is so much greater than that within thecotton ball that it travels farther, or strikes amore effective blow on impact with the wall.

HOW RESISTANCE AFFECTS THE SHAPE.—It is becauseof this counterforce, resistance, that shapebecomes important in a flying object. The metalball may be flattened out into a thin disk, and now,when the same force is applied, to project it forwardly,it will go as much farther as the differencein the air impact against the two forms.

MASS AND RESISTANCE.—Owing to the fact thatresistance acts with such a retarding force on anobject of small mass, and it is difficult to set up arapid motion in an object of great density, lightnessin flying machine structures has been considered,in the past, the principal thing necessary.

THE EARLY TENDENCY TO ELIMINATE MOMENTUM.—Builders of flying machines, for severalyears, sought to eliminate the very thingwhich gives energy to a horizontally-movablebody, namely, momentum.

Instead of momentum, something had to besubstituted. This was found in so arranging themachine that its weight, or a portion of it, wouldbe sustained in space by the very element whichseeks to retard its flight, namely, the atmosphere.

If there should be no material substance, likeair, then the only way in which a heavier-than-airmachine could ever fly, would be by propelling itthrough space, like the ball was thrown, or bysome sort of impulse or reaction mechanism onthe air-ship itself. It could get no support fromthe atmosphere.

LIGHT MACHINES UNSTABLE.—Gradually thequestion of weight is solving itself. Aviators arebeginning to realize that momentum is a wonderfulproperty, and a most important element inflying. The safest machines are those which haveweight. The light, willowy machines are subjectto every caprice of the wind. They are notoriouslyunstable in flight, and are dangerous evenin the hands of experts.

THE APPLICATION OF POWER.—The thing now toconsider is not form, or shape, or the distributionof the supporting surfaces, but HOW to applythe power so that it will rapidly transfer a machineat rest to one in motion, and thereby getthe proper support on the atmosphere to hold itin flight.

THE SUPPORTING SURFACES.—This brings us tothe consideration of one of the first great problemsin flying machines, namely, the supportingsurfaces,—not its form, shape or arrangement,(which will be taken up in their proper places), butthe area, the dimensions, and the angle necessaryfor flight.

AREA NOT THE ESSENTIAL THING.—The historyof flying machines, short as it is, furnishes manyexamples of one striking fact: That area hasbut little to do with sustaining an aeroplane whenonce in flight. The first Wright flyer weighed741 pounds, had about 400 square feet of planesurface, and was maintained in the air with a 12horse power engine.

True, that machine was shot into the air by acatapult. Motion having once been imparted to it,the only thing necessary for the motor was tomaintain the speed.

There are many instances to show that whenonce in flight, one horse power will sustain over100 pounds, and each square foot of supportingsurface will maintain 90 pounds in flight.

THE LAW OF GRAVITY.—As the effort to flymay be considered in the light of a struggle toavoid the laws of nature with respect to matter,it may be well to consider this great force as afitting prelude to the study of our subject.

Proper understanding, and use of terms is verydesirable, so that we must not confuse them.Thus, weight and mass are not the same. Weightvaries with the latitude, and it is different at variousaltitudes; but mass is always the same.

If projected through space, a certain masswould move so as to produce momentum, whichwould be equal at all places on the earth's surface,or at any altitude.

Gravity has been called weight, and weightgravity. The real difference is plain if gravityis considered as the attraction of mass for mass.Gravity is generally known and considered as aforce which seeks to draw things to the earth.This is too narrow.

Gravity acts in all directions. Two balls suspendedfrom strings and hung in close proximityto each other will mutually attract each other.If one has double the mass it will have twice theattractive power. If one is doubled and the othertripled, the attraction would be increased sixtimes. But if the distance should be doubled theattraction would be reduced to one-fourth; andif the distance should be tripled then the pullwould be only one-ninth.

The foregoing is the substance of the law,namely, that all bodies attract all other bodieswith a force directly in proportion to their mass,and inversely as the square of their distance fromone another.

To explain this we cite the following illustration:Two bodies, each having a mass of 4pounds, and one inch apart, are attracted towardeach other, so they touch. If one has twice themass of the other, the smaller will draw the largeronly one-quarter of an inch, and the large onewill draw the other three-quarters of an inch,thus confirming the law that two bodies will attracteach other in proportion to their mass.

Suppose, now, that these balls are placed twoinches apart,—that is, twice the distance. Aseach is, we shall say, four pounds in weight, thesquare of each would be 16. This does not meanthat there would be sixteen times the attraction,but, as the law says, inversely as the square ofthe distance, so that at two inches there is onlyone-sixteenth the attraction as at one inch.

If the cord of one of the balls should be cut, itwould fall to the earth, for the reason that theattractive force of the great mass of the earth isso much greater than the force of attraction inits companion ball.

INDESTRUCTIBILITY OF GRAVITATION.—Gravitycannot be produced or destroyed. It acts betweenall parts of bodies equally; the force beingproportioned to their mass. It is not affected byany intervening substance; and is transmittedinstantaneously, whatever the distance may be.

While, therefore, it is impossible to divest matterof this property, there are two conditionswhich neutralize its effect. The first of these isposition. Let us take two balls, one solid andthe other hollow, but of the same mass, or density.If the cavity of the one is large enough to receivethe other, it is obvious that while gravity is stillpresent the lines of attraction being equal atall points, and radially, there can be no pull whichmoves them together.

DISTANCE REDUCES GRAVITATIONAL PULL.—Orthe balls may be such distance apart that the attractiveforce ceases. At the center of the earthan object would not weigh anything. A poundof iron and an ounce of wood, one sixteen timesthe mass of the other, would be the same,—absolutelywithout weight.

If the object should be far away in space itwould not be influenced by the earth's gravity;so it will be understood that position plays animportant part in the attraction of mass for mass.

HOW MOTION ANTAGONIZES GRAVITY.—The secondway to neutralize gravity, is by motion. Aball thrown upwardly, antagonizes the force ofgravity during the period of its ascent. In likemanner, when an object is projected horizontally,while its mass is still the same, its weight is less.

Motion is that which is constantly combatingthe action of gravity. A body moving in a circlemust be acted upon by two forces, one which tendsto draw it inwardly, and the other which seeks tothrow it outwardly.

The former is called centripetal, and the lattercentrifugal motion. Gravity, therefore, representscentripetal, and motion centrifugal force.

If the rotative speed of the earth should be retarded,all objects on the earth would be increasedin weight, and if the motion should be acceleratedobjects would become lighter, and if sufficientspeed should be attained all matter would fly offthe surface, just as dirt dies off the rim of awheel at certain speeds.

A TANGENT.—When an object is thrown horizontallythe line of flight is tangential to the earth,or at right angles to the force of gravity. Sucha course in a flying machine finds less resistancethan if it should be projected upwardly, or directlyopposite the centripetal pull.

Fig 1. Tangential Flight

TANGENTIAL MOTION REPRESENTS CENTRIFUGALPULL.—A tangential motion, or a horizontalmovement, seeks to move matter away from thecenter of the earth, and any force which impartsa horizontal motion to an object exerts a centrifugalpull for that reason.

In Fig. 1, let A represent the surface of theearth, B the starting point of the flight of an object,and C the line of flight. That represents atangential line. For the purpose of explainingthe phenomena of tangential flight, we will assumethat the missile was projected with a sufficientforce to reach the vertical point D, whichis 4000 miles from the starting point B.

In such a case it would now be over 5500 milesfrom the center of the earth, and the centrifugalpull would be decreased to such an extent that theball would go on and on until it came within thesphere of influence from some other celestialbody.

EQUALIZING THE TWO MOTIONS.—But now let usassume that the line of flight is like that shownat E, in Fig. 2, where it travels along parallelwith the surface of the earth. In this case theforce of the ball equals the centripetal pull,—or,to put it differently, the centrifugal equals thegravitational pull.

The constant tendency of the ball to fly off ata tangent, and the equally powerful pull ofgravity acting against each other, produce amotion which is like that of the earth, revolvingaround the sun once every three hundred andsixty-five days.

It is a curious thing that neither Langley, norany of the scientists, in treating of the matter offlight, have taken into consideration this qualityof momentum, in their calculations of the elementsof flight.

Fig. 2 Horizontal Flight

All have treated the subject as though thewhole problem rested on the angle at which theplanes were placed. At 45 degrees the lift anddrift are assumed to be equal.

LIFT AND DRIFT.—The terms should be explained,in view of the frequent allusion whichwill be made to the terms hereinafter. Liftis the word employed to indicate the amountwhich a plane surface will support while in flight.Drift is the term used to indicate the resistancewhich is offered to a plane moving forwardlyagainst the atmosphere.

Fig. 3. Lift and Drift

In Fig. 3 the plane A is assumed to be movingforwardly in the direction of the arrow B. Thisindicates the resistance. The vertical arrow Cshows the direction of lift, which is the weightheld up by the plane.

NORMAL PRESSURE.—Now there is another termmuch used which needs explanation, and that isnormal pressure. A pressure of this kindagainst a plane is where the wind strikes it atright angles. This is illustrated in Fig. 4, inwhich the plane is shown with the wind strikingit squarely.

It is obvious that the wind will exert a greaterforce against a plane when at its normal. On theother hand, the least pressure against a plane iswhen it is in a horizontal position, because thenthe wind has no force against the surfaces, andthe only effect on the drift is that which takesplace when the wind strikes its forward edge.

Fig. 4. Normal Air Pressure

Fig. 5. Edge Resistance

HEAD RESISTANCE.—Fig. 5 shows such a plane,the only resistance being the thickness of theplane as at A. This is called head resistance,and on this subject there has been much controversy,and many theories, which will be consideredunder the proper headings.

If a plane is placed at an angle of 45 degreesthe lift and the drift are the same, assumedly, because,if we were to measure the power requiredto drive it forwardly, it would be found to equalthe weight necessary to lift it. That is, supposewe should hold a plane at that angle with a heavywind blowing against it, and attach two pairs ofscales to the plane, both would show the samepull.

Fig. 6. Measuring Lift and Drift

MEASURING LIFT AND DRIFT.—In Fig. 6, A is theplane, B the horizontal line which attaches theplane to a scale C, and D the line attaching it tothe scale E. When the wind is of sufficient forceto hold up the plane, the scales will show the samepull, neglecting, of course, the weight of theplane itself.

PRESSURE AT DIFFERENT ANGLES.—What everyone wants to know, and a subject on which agreat deal of experiment and time have been expended,is to determine what the pressures are atthe different angles between the horizontal, andlaws have been formulated which enable the pressuresto be calculated.

DIFFERENCE BETWEEN LIFT AND DRIFT IN MOTION.—Thefirst observation is directed to the differencesthat exist between the lift and drift,when the plane is placed at an angle of less than45 degrees. A machine weighing 1000 poundshas always the same lift. Its mass does notchange. Remember, now, we allude to its mass,or density.

We are not now referring to weight, becausethat must be taken into consideration, in theproblem. As heretofore stated, when an objectmoves horizontally, it has less weight than whenat rest. If it had the same weight it would notmove forwardly, but come to rest.

When in motion, therefore, while the lift, sofar as its mass is concerned, does not change, thedrift does decrease, or the forward pull is lessthan when at 45 degrees, and the decrease is lessand less until the plane assumes a horizontal position,where it is absolutely nil, if we do not considerhead resistance.

TABLES OF LIFT AND DRIFT.—All tables of Liftand Drift consider only the air pressures. Theydo not take into account the fact that momentumtakes an important part in the translation of anobject, like a flying machine.

A mass of material, weighing 1000 pounds whileat rest, sets up an enormous energy when movingthrough the air at fifty, seventy-five, or one hundredmiles an hour. At the latter speed the movementis about 160 feet per second, a motion whichis nearly sufficient to maintain it in horizontalflight, independently of any plane surface.

Such being the case, why take into account onlythe angle of the plane? It is no wonder thataviators have not been able to make the theoreticalconsiderations and the practical demonstrationsagree.

WHY TABLES OF LIFT AND DRIFT ARE WRONG.—A little reflection will show why such tables arewrong. They were prepared by using a planesurface at rest, and forcing a blast of air againstthe plane placed at different angles; and for determiningair pressures, this is, no doubt, correct.But it does not represent actual flying conditions.It does not show the conditions existingin an aeroplane while in flight.

To determine this, short of actual experimentswith a machine in horizontal translation, is impossible,unless it is done by taking into accountthe factor due to momentum and the elementattributable to the lift of the plane itself due to itsimpact against the atmosphere.

LANGLEY'S LAW.—The law enunciated byLangley is, that the greater the speed the less thepower required to propel it. Water as a propellingmedium has over seven hundred timesmore force than air. A vessel having, for instance,twenty horse power, and a speed of tenmiles per hour, would require four times thatpower to drive it through the water at double thespeed. The power is as the square of the speed.

With air the conditions are entirely different.The boat submergence in the water is practicallythe same, whether going ten or twenty miles anhour. The head resistance is the same, substantially,at all times in the case of the boat; with theflying machine the resistance of its sustainingsurfaces decreases.

Without going into a too technical descriptionof the reasoning which led to the discovery of thelaw of air pressures, let us try and understandit by examining the diagram, Fig. 7.

A represents a plane at an angle of 45 degrees,moving forwardly into the atmosphere in thedirection of the arrows B. The measurementacross the plane vertically, along the line B,which is called the sine of the angle, representsthe surface impact of air against the plane.

In Fig. 8 the plane is at an angle of 27 degrees,which makes the distance in height across the lineC just one-half the length of the line B of Fig. 7,hence the surface impact of the air is one-half thatof Fig. 7, and the drift is correspondingly decreased.

Fig. 7. Equal Lift and Drift in Flight.

Fig. 8. Unequal Lift and Drift.

MOVING PLANES VS. WINDS.—In this way Boisset,Duchemin, Langley, and others, determinedthe comparative drift, and those results have beenlargely relied upon by aviators, and assumed tobe correct when applied to flying machines.

That they are not correct has been proven bythe Wrights and others, the only explanation beingthat some errors had been made in the calculations,or that aviators were liable to commit errorsin observing the true angle of the planeswhile in flight.

MOMENTUM NOT CONSIDERED.—The great factorof momentum has been entirely ignored, and it isour desire to press the important point on thosewho begin to study the question of flying machines.

THE FLIGHT OF BIRDS.—Volumes have beenwritten concerning observations on the flight ofbirds. The marvel has been why do soaring birdsmaintain themselves in space without flappingtheir wings. In fact, it is a much more remarkablething to contemplate why birds which dependon flapping wings can fly.

THE DOWNWARD BEAT.—It is argued that thedownward beat of the wings is so much morerapid than the upward motion, that it gets an actionon the air so as to force the body upwardly.This is disposed of by the wing motion of manybirds, notoriously the crow, whose lazily-flappingwings can be readily followed by the eye, and thedifference in movement, if any, is not perceptible.

THE CONCAVED WING.—It is also urged that theconcave on the under side of the wing gives thequality of lift. Certain kinds of beetles, and particularlythe common house fly, disprove that theory,as their wings are perfectly flat.

FEATHER STRUCTURE CONSIDERED.—Then thefeather argument is advanced, which seeks toshow that as each wing is made up of a pluralityof feathers, overlapping each other, they form asort of a valved surface, opening so as to permitair to pass through them during the period oftheir upward movement, and closing up as thewing descends.

It is difficult to perform this experiment withwings, so as to show such an individual feathermovement. It is certain that there is nothing inthe structure of the wing bone and the featherconnection which points to any individual feathermovement, and our observation is, that eachfeather is entirely too rigid to permit of such anopening up between them.

It is obvious that the wing is built up in thatway for an entirely different reason. Soaringbirds, which do not depend on the flapping motion,have the same overlapping feather formation.

WEBBED WINGS.—Furthermore, there are numerousflying creatures which do not havefeathered wings, but web-like structures, or like thehouse fly, in one continuous and unbrokenplane.

That birds which fly with flapping wings derivetheir support from the air, is undoubtedly true,and that the lift produced is due, not to the form,or shape, or area of the wing, is also beyond question.The records show that every conceivabletype of outlined structure is used by nature; thematerial and texture of the wings themselves differto such a degree that there is absolutely nosimilarity; some have concaved under surfaces,and others have not; some fly with rapidly beatingwings, and others with slow and measuredmovements; many of them fly with equal facilitywithout flapping movements; and the proportionsof weight to wing surface vary to such an extentthat it is utterly impossible to use such data as aguide in calculating what the proper surfaceshould be for a correct flying machine.

THE ANGLE OF MOVEMENT.—How, then, it maybe asked, do they get their support? There mustbe something, in all this variety and diversity ofform, of motion, and of characteristics, whichsupplies the true answer. The answer lies in theangle of movement of every wing motion, whichis at the control of the bird, and if this is examinedit will be found that it supplies the correctanswer to every type of wing which nature hasmade.

AN INITIAL IMPULSE OR MOVEMENT NECESSARY.—Let A, Fig. 9, represent the section of a bird'swing. All birds, whether of the soaring or theflapping kind, must have an initial forward movementin order to attain flight. This impulse isacquired either by running along the ground, orby a leap, or in dropping from a perch. Soaringbirds cannot, by any possibility, begin flight,unless there is such a movement to change from aposition of rest to one of motion.

Fig. 9. Wing Movement in Flight.

In the diagram, therefore, the bird, in movingforwardly, while raising the wing upwardly, depressesthe rear edge of the wing, as in position1, and when the wing beats downwardly the rearmargin is raised, in relation to its front margin,as shown in position 2.

A WEDGING MOTION.—Thus the bird, by awedge-like motion, gives a forwardly-propellingaction, and as the rear margin has more or lessflexure, its action against the air is less during itsupward beat, and this also adds to the upward liftof the body of the bird.

NO MYSTERY IN THE WAVE MOTION.—There isno mystery in the effect of such a wave-like motion,and it must be obvious that the hummingbird, and like flyers, which poise at one spot, areable to do so because, instead of moving forwardly,or changing the position of its body horizontally,in performing the undulatory motion ofthe wing, it causes the body to rock, so that at thepoint where the wing joins the body, an ellipticalmotion is produced.

Fig. 10. Evolution of Humming-Bird's Wing.

HOW BIRDS POISE WITH FLAPPING WINGS.—Thisis shown in Fig. 10, in which eight successive positionsof the wing are shown, and wherein fourof the position, namely, 1, 2, 3, and 4, representthe downward movement, and 6, 7, 8, and 9, theupward beat.

All the wing angles are such that whether thesuspension point of each wing is moving downwardly,or upwardly, a support is found in somepart of the wing.

NARROW-WINGED BIRDS.—Birds with rapid flappingmotions have comparatively narrow wings,fore and aft. Those which flap slowly, and arenot swift flyers, have correspondingly broaderwings. The broad wing is also typical of thesoaring birds.

But how do the latter overcome gravitationwithout exercising some sort of wing movement?

INITIAL MOVEMENT OF SOARING BIRDS.—Acuteobservations show that during the early stagesof flight, before speed is acquired, they dependon the undulating movement of the wings, andsome of them acquire the initial motion by flapping.When speed is finally attained it is difficultfor the eye to note the motion of the wings.

SOARING BIRDS MOVE SWIFTLY.—Now, the firstobservation is, that soaring birds are swiftly-moving creatures. As they sail overheadmajestically they seem to be moving slowly. Butdistance is deceptive. The soaring bird travelsat great speeds, and this in itself should be sufficientto enable us to cease wondering, when it isremembered that swift translation decreasesweight, so that this factor does not, under thoseconditions, operate against flight.

MUSCULAR ENERGY EXERTED BY SOARING BIRDS.—It is not conceivable that the mere will of thebird would impel it forwardly, without it exertedsome muscular energy to keep up its speed. Thedistance at which the bird performs this wonderfulevolution is at such heights from the observerthat the eye cannot detect a movement.

WINGS NOT MOTIONLESS.—While the wings appearto be absolutely motionless, it is more reasonableto assume that a slight sinuous movement,or a rocking motion is constantly kept up, whichwedges forwardly with sufficient speed to compelmomentum to maintain it in flight. To do so requiresbut a small amount of energy. The headresistance of the bird formation is reduced to aminimum, and at such high speeds the angle ofincidence of the wings is very small, requiring butlittle aid to maintain it in horizontal flight.

CHAPTER II

PRINCIPLES OF AEROPLANE FLIGHT

FROM the foregoing chapter, while it may berightly inferred that power is the true secret ofaeroplane flight, it is desirable to point out certainother things which must be considered.

SPEED AS ONE OF THE ELEMENTS—Every boy,probably, has at some time or other thrown smallflat stones, called "skippers." He has noticedthat if they are particularly thin, and large indiameter, that there is a peculiar sailing motion,and that they move through the air in an undulatingor wave-like path.

Two things contribute to this motion; one is thesize of the skipper, relative to its weight, and theother is its speed. If the speed is slow it willquickly wend its way to the earth in a gradualcurve. This curved line is called its trajectory.If it is not very large diametrically, in proportionto its weight, it will also make a gradual curve indescending, without "skimming" up and downin its flight.

SHAPE AND SPEED.—It has been observed, also,that a round ball, or an object not flattened out,will make a regular curved path, whatever thespeed may be.

It may be assumed, therefore, that the shapealone does not account for this sinuous motion;but that speed is the element which accounts forit. Such being the case it may be well to inquireinto the peculiar action which causes a skipperto dart up and down, and why the path thusformed grows more and more accentuated as thespeed increases.

As will be more fully described in a later chapter,the impact of air against a moving body doesnot increase in proportion to its speed, but in theratio of the square of the speed.

WHAT SQUARE OF THE SPEED MEANS.—In mathematicsa figure is squared when it is multipliedby itself. Thus, 4 X 4= 16; 5 X 5 = 25; and soon, so that 16 is the square of 4, and 25 the squareof 5. It has been found that a wind moving at thespeed of 20 miles an hour has a striking or pushingforce of 2 pounds on every square foot of surface.

If the wind travels twice as fast, or 40 milesan hour, the pushing force is not 4 pounds, but8 pounds. If the speed is 60 miles an hour thepushing force increases to 18 pounds.

ACTION OF A SKIPPER.—When the skipper leavesthe hands of the thrower it goes through the airin such a way that its fiat surface is absolutelyon a line with the direction in which it is projected.

At first it moves through the air solely by forceof the power which impels it, and does not in anyway depend on the air to hold it up. See Fig.1, in which A represents the line of projection,and B the disk in its flight.

Fig. 11. A Skipper in Flight.

After it has traveled a certain distance, andthe force decreases, it begins to descend, thus describingthe line C, Fig. 1, the disk B, in this casedescending, without changing its position, whichmight be described by saying that it merely settlesdown to the earth without changing its plane.

The skipper still remains horizontal, so that asit moves toward the earth its flat surface, whichis now exposed to the action of the air, meetswith a resistance, and this changes the angle ofthe disk, so that it will not be horizontal. Insteadit assumes the position as indicated at D,and this impinging effect against the air causesthe skipper to move upwardly along the line E,and having reached a certain limit, as at, say E,it automatically again changes its angle and movesdownwardly along the path F, and thus continuesto undulate, more or less, dependent on the combinedaction of the power and weight, or momentum,until it reaches the earth.

It is, therefore, clear that the atmosphere hasan action on a plane surface, and that the extentof the action, to sustain it in flight, depends on twothings, surface and speed.

Furthermore, the greater the speed the less thenecessity for surface, and that for gliding purposesspeed may be sacrificed, in a large measure,where there is a large surface.

This very action of the skipper is utilized bythe aviator in volplaning,—that is, where thepower of the engine is cut off, either by accident,or designedly, and the machine descends to theearth, whether in a long straight glide, or in agreat circle.

As the machine nears the earth it is caused tochange the angle of flight by the control mechanismso that it will dart upwardly at an angle, or downwardly,and thus enable the pilot to sail to anotherpoint beyond where he may safely land.This changing the course of the machine so thatit will glide upwardly, means that the incidenceof the planes has been changed to a positiveangle.

ANGLE OF INCIDENCE.—In aviation this is a termgiven to the position of a plane, relative to theair against which it impinges. If, for instance,an aeroplane is moving through the air with thefront margin of the planes higher than their rearmargins, it is said to have the planes at a positiveangle of incidence. If the rear margins arehigher than the front, then the planes have a negativeangle of incidence.

The word incidence really means, a fallingupon, or against; and it will be seen, therefore,that the angle of incidence means the tilt of theplanes in relation to the air which strikes it.

Having in view, therefore, that the two qualities,namely, speed and surface, bear an intimaterelation with each other, it may be understoodwherein mechanical flight is supposed to be analogousto bird flight.

SPEED AND SURFACE.—Birds which poise in theair, like the humming bird, do so because theybeat their wings with great rapidity. Thosewhich soar, as stated, can do so only by movingthrough the atmosphere rapidly, or by having alarge wing spread relative to the weight. It willthus be seen that speed and surface become thecontrolling factors in flight, and that while thelatter may be entirely eliminated from the problem,speed is absolutely necessary under any andall conditions.

By speed in this connection is not meant highvelocity, but that a movement, produced by powerexpressed in some form, is the sole and most necessaryrequisite to movement through the air withall heavier-than-air machines.

If sufficient power can be applied to an aeroplane,surface is of no consequence; shape neednot be considered, and any sort of contrivancewill move through the air horizontally.

CONTROL OF THE DIRECTION OF FLIGHT.—But thecontrol of such a body, when propelled throughspace by force alone, is a different matter. Tochange the machine from a straight path to acurved one, means that it must be acted upon bysome external force.

We have explained that power is somethingwhich is inherent in the thing itself. Now, in orderthat there may be a change imparted to amoving mass, advantage must be taken of the mediumthrough which it moves,—the atmosphere.

VERTICAL CONTROL PLANES.—If vertically-arrangedplanes are provided, either fore or aft ofthe machine, or at both ends, the angles of incidencemay be such as to cause the machine toturn from its straight course.

In practice, therefore, since it is difficult to supplysufficient power to a machine to keep it in motionhorizontally, at all times, aeroplanes are providedwith supporting surfaces, and this aid inholding it up grows less and less as its speed increases.

But, however strong the power, or great thespeed, its control from side to side is not dependenton the power of the engine, or the speedat which it travels through the air.

Here the size of the vertical planes, and theirangles, are the only factors to be considered, andthese questions will be considered in their properplaces.

CHAPTER III

THE FORM OR SHAPE OF FLYING MACHINES

EVERY investigator, experimenter, and scientist,who has given the subject of flight study, proceedson the theory that in order to fly man mustcopy nature, and make the machine similar to thetype so provided.

THE THEORY OF COPYING NATURE.—If such is thecase then it is pertinent to inquire which bird isthe proper example to use for mechanical flight.We have shown that they differ so radically inevery essential, that what would be correct in onething would be entirely wrong in another.

The bi-plane is certainly not a true copy. Theonly thing in the Wright machine which in anyway resembles the bird's wing, is the rounded endof the planes, and judging from other machines,which have square ends, this slight similarity doesnot contribute to its stability or otherwise helpthe structure.

The monoplane, which is much nearer the birdtype, has also sounded wing ends, made not somuch for the purpose of imitating the wing of thebird, as for structural reasons.

HULLS OF VESSELS.—If some marine architectshould come forward and assert that he intendedto follow nature by making a boat with a hull ofthe shape or outline of a duck, or other swimmingfowl, he would be laughed at, and justly so, becausethe lines of vessels which are most efficientare not made like those of a duck or other swimmingcreatures.

MAN DOES NOT COPY NATURE.—Look about you,and see how many mechanical devices follow theforms laid down by nature, or in what respectman uses the types which nature provides in devisingthe many inventions which ingenuity hasbrought forth.

PRINCIPLES ESSENTIAL, NOT FORMS.—It is essentialthat man shall follow nature's laws. He cannotevade the principles on which the operationsof mechanism depend; but in doing so he has, innearly every instance, departed from the formwhich nature has suggested, and made the machineirrespective of nature's type.

Let us consider some of these striking differencesto illustrate this fact. Originally pins werestuck upon a paper web by hand, and placed inrows, equidistant from each other. This necessitatesthe cooperative function of the fingers andthe eye. An expert pin sticker could thus assemblefrom four to five thousand pins a day.

The first mechanical pinsticker placed over500,000 pins a day on the web, rejecting every bentor headless pin, and did the work with greateraccuracy than it was possible to do it by hand.There was not the suggestion of an eye, or a fingerin the entire machine, to show that nature furnishedthe type.

NATURE NOT THE GUIDE AS TO FORMS.—Naturedoes not furnish a wheel in any of its mechanicalexpressions. If man followed nature's formin the building of the locomotive, it would movealong on four legs like an elephant. Curiouslyenough, one of the first road wagons had "pushlegs,"—an instance where the mechanic tried tocopy nature,—and failed.

THE PROPELLER TYPE.—The well known propelleris a type of wheel which has no prototype innature. It is maintained that the tail of a fishin its movement suggested the propeller, but thelatter is a long departure from it.

The Venetian rower, who stands at the stern,and with a long-bladed oar, fulcrumed to theboat's extremity, in making his graceful lateraloscillations, simulates the propelling motion ofthe tail in an absolutely perfect manner, but it isnot a propeller, by any means comparable to thekind mounted on a shaft, and revoluble.

How much more efficient are the spirally-formedblades of the propeller than any wing or fin movement,in air or sea. There is no comparison betweenthe two forms in utility or value.

Again, the connecting points of the arms andlegs with the trunk of a human body afford themost perfect types of universal joints which naturehas produced. The man-made universaljoint has a wider range of movement, possessesgreater strength, and is more perfect mechanically.A universal joint is a piece of mechanismbetween two elements, which enables them to beturned, or moved, at any angle relative to eachother.

But why multiply these instances. Like sampleswill be found on every hand, and in all directions,and man, the greatest of all of nature'sproducts, while imperfect in himself, is improvingand adapting the things he sees about him.

WHY SPECIALLY-DESIGNED FORMS IMPROVE NATURALSTRUCTURES.—The reason for this is, primarily,that the inventor must design the articlefor its special work, and in doing so makes it betteradapted to do that particular thing. Thehands and fingers can do a multiplicity of things,but it cannot do any particular work with the facilityor the degree of perfection that is possiblewith the machine made for that purpose.

The hands and fingers will bind a sheaf ofwheat, but it cannot compete with the special machinemade for that purpose. On the other handthe binder has no capacity to do anything else thanwhat it was specially made for.

In applying the same sort of reasoning to thebuilding of flying machines we must be led to theconclusion that the inventor can, and will, eventually,bring out a form which is as far superior tothe form which nature has taught us to use asthe wonderful machines we see all about us aresuperior to carry out the special work they weredesigned to do.

On land, man has shown this superiority overmatter, and so on the sea. Singularly, the submarines,which go beneath the sea, are very farfrom that perfected state which have been attainedby vessels sailing on the surface; and whilethe means of transportation on land are arrivingat points where the developments are swift andremarkable, the space above the earth has not yetbeen conquered, but is going through that sameperiod of development which precedes the productionof the true form itself.

MECHANISM DEVOID OF INTELLIGENCE.—The greaterror, however, in seeking to copy nature's formin a flying machine is, that we cannot invest themechanism with that which the bird has, namely,a guiding intelligence to direct it instinctively, asthe flying creature does.

A MACHINE MUST HAVE A SUBSTITUTE FOR INTELLIGENCE.—Such being the case it must be endowedwith something which is a substitute. Abird is a supple, pliant organism; a machine is arigid structure. One is capable of being directedby a mind which is a part of the thing itself; whilethe other must depend on an intelligence which isseparate from it, and not responsive in feeling ormovement.

For the foregoing reasons success can neverbe attained until some structural form is devisedwhich will consider the flying machine independentlyof the prototypes pointed out as the correctthings to follow. It does not, necessarily, have tobe unlike the bird form, but we do know that thepresent structures have been made and insistedupon blindly, because of this wrong insistence onforms.

STUDY OF BIRD FLIGHT USELESS.—The study ofthe flight of birds has never been of any specialvalue to the art. Volumes have been written onthe subject. The Seventh Duke of Argyle, andlater, Pettigrew, an Englishman, contributed avast amount of written matter on the subject ofbird flight, in which it was sought to show thatsoaring birds did not exert any power in flying.

Writers and experimenters do not agree on thequestion of the propulsive power, or on the formor shape of the wing which is most effective, orin the matter of the relation of surface to weight,nor do they agree in any particular as to the effectand action of matter in the soaring principle.

Only a small percentage of flying creatures usemotionless wings as in soaring. By far, thegreater majority use beating wings, a method oftranslation in air which has not met with successin any attempts on the part of the inventor.

Nevertheless, experimenting has proceeded onlines which seek to recognize nature's form only,while avoiding the best known and most persistenttype.

SHAPE OF SUPPORTING SURFACES.—When we examinethe prevailing type of supporting surfaceswe cannot fail to be impressed with one feature,namely, the determination to insist on a broadspread of plane surface, in imitation of the birdwith outstretched wings.

THE TROUBLE ARISING FROM OUTSTRETCHEDWINGS.—This form of construction is what bringsall the troubles in its train. The literature onaviation is full of arguments on this subject, alldeclaring that a wide spread is essential, because,—birds fly that way.

These assertions are made notwithstanding thefact that only a few years ago, in the great exhibitof aeroplanes in Paris, many unique forms of machineswere shown, all of them capable of flying,as proven by numerous experiments, and amongthem were a half dozen types whose length foreand aft were much greater than transversely, andit was particularly noted that they had most wonderfulstability.

DENSITY OF THE ATMOSPHERE.—Experts declarethat the density of the atmosphere varies throughout,—that it has spots here and there which are,apparently, like holes, so that one side or theother of the machine will, unaccountably, tilt, andsometimes the entire machine will suddenly dropfor many feet, while in flight.

ELASTICITY OF THE AIR.—Air is the most elasticsubstance known. The particles constituting itare constantly in motion. When heat or cold penetratethe mass it does so, in a general way, so asto permeate the entire body, but the conductivityof the atmospheric gases is such that the heatdoes not reach all parts at the same time.

AIR HOLES.—The result is that varying strataof heat and cold seem to be superposed, and alsodistributed along the route taken by a machine,causing air currents which vary in direction andintensity. When, therefore, a rapidly-movingmachine passes through an atmosphere so disturbed,the surfaces of the planes strike a mass ofair moving, we may say, first toward the plane,and the next instant the current is reversed, andthe machine drops, because its support is temporarilygone, and the aviator experiences the sensationof going into a "hole."

RESPONSIBILITY FOR ACCIDENTS.—These so-called"holes" are responsible for many accidents. Theoutstretched wings, many of them over forty feetfrom tip to tip, offer opportunities for a tilt at oneend or the other, which has sent so many machinesto destruction.

The high center of gravity in all machines makesthe weight useless to counterbalance the risingend or to hold up the depressed wing.

All aviators agree that these unequal areas ofdensity extend over small spaces, and it is, therefore,obvious that a machine which is of such astructure that it moves through the air broadsideon, will be more liable to meet these inequalitiesthan one which is narrow and does not take in sucha wide path.

Why, therefore, persist in making a form which,by its very nature, invites danger? Because birdsfly that way!

THE TURNING MOVEMENT.—This structural arrangementaccentuates the difficulty when the machineturns. The air pressure against the wingsurface is dependent on the speed. The broadoutstretched surfaces compel the wing at the outerside of the circle to travel faster than the innerone. As a result, the outer end of the aeroplaneis elevated.

CENTRIFUGAL ACTION.—At the same time therunning gear, and the frame which carries it andsupports the machine while at rest, being belowthe planes, a centrifugal force is exerted, whenturning a circle, which tends to swing the wheelsand frame outwardly, and thereby still furtherelevating the outer end of the plane.

THE WARPING PLANES.—The only remedy tomeet this condition is expressed in the mechanismwhich wraps or twists the outer ends of the planes,as constructed in the Wright machine, or theailerons, or small wings at the rear margins of theplanes, as illustrated by the Farman machine.The object of this arrangement is to decrease theangle of incidence at the rising end, and increasethe angle at the depressed end, and thus, by manually-operated means keep the machine on an evenkeel.

CHAPTER IV

FORE AND AFT CONTROL

THERE is no phase of the art of flying more importantthan the fore and aft control of an airship.Lateral stability is secondary to this feature, forreasons which will appear as we develop thesubject.

THE BIRD TYPE OF FORE AND AFT CONTROL.—Every aeroplane follows the type set by naturein the particular that the body is caused to oscillateon a vertical fore and aft plane while inflight. The bird has one important advantage,however, in structure. Its wing has a flexure atthe joint, so that its body can so oscillate independentlyof the angle of the wings.

The aeroplane has the wing firmly fixed to thebody, hence the only way in which it is possibleto effect a change in the angle of the wing is bychanging the angle of the body. To be consistentthe aeroplane should be so constructed that theangle of the supporting surfaces should be movable,and not controllable by the body.

The bird, in initiating flight from a perch, dartsdownwardly, and changes the angle of the body tocorrespond with the direction of the flying start.When it alights the body is thrown so that itsbreast banks against the air, but in ordinary flightits wings only are used to change the angle offlight.

ANGLE AND DIRECTION OF FLIGHT.—In order tobecome familiar with terms which will be frequentlyused throughout the book, care should betaken to distinguish between the terms angle anddirection of flight. The former has reference tothe up and down movement of an aeroplane,whereas the latter is used to designate a turningmovement to the right or to the left.

WHY SHOULD THE ANGLE OF THE BODY CHANGE?—The first question that presents itself is, whyshould the angle of the aeroplane body change?Why should it be made to dart up and down andproduce a sinuous motion? Why should its nosetilt toward the earth, when it is descending, andraise the forward part of the structure while ascending?

The ready answer on the part of the bird-formadvocate is, that nature has so designed a flyingstructure. The argument is not consistent, becausein this respect, as in every other, it is notmade to conform to the structure which they seekto copy.

CHANGING ANGLE OF BODY NOT SAFE.—Furthermore,there is not a single argument which can beadvanced in behalf of that method of building,which proves it to be correct. Contrariwise, ananalysis of the flying movement will show that it isthe one feature which has militated against safety,and that machines will never be safe so long asthe angle of the body must be depended upon tocontrol the angle of flying.

Fig. 11a Monoplane in Flight.

In Fig. 11a three positions of a monoplane areshown, each in horizontal flight. Let us say thatthe first figure A is going at 40 miles per hour,the second, B, at 50, and the third, C, at 60 miles.The body in A is nearly horizontal, the angle ofthe plane D being such that, with the tail E alsohorizontal, an even flight is maintained.

When the speed increases to 50 miles an hour,the angle of incidence in the plane D must bedecreased, so that the rear end of the frame mustbe raised, which is done by giving the tail an angleof incidence, otherwise, as the upper side of thetail should meet the air it would drive the rearend of the frame down, and thus defeat the attemptto elevate that part.

Fig. 12. Angles of Flight.

As the speed increases ten miles more, the tailis swung down still further and the rear end ofthe frame is now actually above the plane of flight.In order, now, to change the angle of flight, withoutaltering the speed of the machine, the tail isused to effect the control.

Examine the first diagram in Fig. 12. Thisshows the tail E still further depressed, and theair striking its lower side, causes an upward movementof the frame at that end, which so much decreasesthe angle of incidence that the aeroplanedarts downwardly.

In order to ascend, the tail, as shown in the seconddiagram, is elevated so as to depress the rearend, and now the sustaining surface shoots upwardly.

Suppose that in either of the positions 1 or 2,thus described, the aviator should lose control ofthe mechanism, or it should become deranged or"stick," conditions which have existed in the historyof the art, what is there to prevent an accident?

In the first case, if there is room, the machinewill loop the loop, and in the second case the machinewill move upwardly until it is vertical, andthen, in all probability, as its propelling power isnot sufficient to hold it in that position, like ahelicopter, and having absolutely no wing supportingsurface when in that position, it will dartdown tail foremost.

A NON-CHANGING BODY.—We may contrast theforegoing instances of flight with a machine havingthe sustaining planes hinged to the body insuch a manner as to make the disposition of itsangles synchronous with the tail. In other words,see how a machine acts that has the angle of flightcontrollable by both planes,—that is, the sustainingplanes, as well as the tail.

Fig. 13. Planes on Non-changing Body.

In Fig. 13 let the body of the aeroplane be horizontal,and the sustaining planes B disposed atthe same angle, which we will assume to be 15degrees, this being the imaginary angle for illustrativepurposes, with the power of the machineto drive it along horizontally, as shown in position1.

In position 2 the angles of both planes are nowat 10 degrees, and the speed 60 miles an hour,which still drives the machine forward horizontally.

In position 3 the angle is still less, being nowonly 5 degrees but the speed is increased to 80miles per hour, but in each instance the body ofthe machine is horizontal.

Now it is obvious that in order to ascend, ineither case, the changing of the planes to a greaterangle would raise the machine, but at the sametime keep the body on an even keel.

Fig. 14. Descent with Non-changing Body.

DESCENDING POSITIONS BY POWER CONTROL.—InFig. 14 the planes are the same angles in the threepositions respectively, as in Fig. 13, but now thepower has been reduced, and the speeds are 30,25, and 20 miles per hour, in positions A, B and C.

Suppose that in either position the power shouldcease, and the control broken, so that it would beimpossible to move the planes. When the machinebegins to lose its momentum it will descend on acurve shown, for instance, in Fig. 15, where position1 of Fig. 14 is taken as the speed and anglesof the plane when the power ceased.

Fig. 15. Utilizing Momentum.

CUTTING OFF THE POWER.—This curve, A, mayreach that point where momentum has ceased asa forwardly-propelling factor, and the machinenow begins to travel rearwardly. (Fig. 16.) Ithas still the entire supporting surfaces of theplanes. It cannot loop-the-loop, as in the instancewhere the planes are fixed immovably to the body.

Carefully study the foregoing arrangement, andit will be seen that it is more nearly in accord withthe true flying principle as given by nature thanthe vaunted theories and practices now indulgedin and so persistently adhered to.

The body of a flying machine should not be oscillatedlike a lever. The support of the aeroplaneshould never be taken from it. While it may beimpossible to prevent a machine from comingdown, it can be prevented from overturning, andthis can be done without in the least detractingfrom it structurally.

Fig. 16. Reversing Motion.

The plan suggested has one great fault, however.It will be impossible with such a structureto cause it to fly upside down. It does not presentany means whereby dare-devil stunts can be performedto edify the grandstand. In this respectit is not in the same class with the present types.

THE STARTING MOVEMENT.—Examine this planfrom the position of starting, and see the advantagesit possesses. In these illustrations wehave used, for convenience only, the monoplanetype, and it is obvious that the same remarks applyto the bi-plane.

Fig. 17 shows the starting position of the stockmonoplane, in position 1, while it is being initiallyrun over the ground, preparatory to launching.Position 2 represents the negative angle at whichthe tail is thrown, which movement depresses therear end of the frame and thus gives the supportingplanes the proper angle to raise the machine,through a positive angle of incidence, of the plane.

Fig. 17. Showing changing angle of body.

THE SUGGESTED TYPE.—In Fig. 18 the suggestedtype is shown with the body normally in a horizontalposition, and the planes in a neutral position,as represented in position 1. When sufficientspeed had been attained both planes areturned to the same angle, as in position 2, andflight is initiated without the abnormal oscillatingmotion of the body.

But now let us see what takes place the momentthe present type is launched. If, by any error onthe part of the aviator, he should fail to readjustthe tail to a neutral or to a proper angle of incidence,after leaving the ground, the machine wouldtry to perform an over-head loop.

The suggested plan does not require this caution.The machine may rise too rapidly, or itsplanes may be at too great an angle for the poweror the speed, or the planes may be at too small anangle, but in either case, neglect would not turnthe machine to a dangerous position.

These suggestions are offered to the novice, becausethey go to the very foundation of a correctunderstanding of the principles involved in thebuilding and in the manipulation of flying machinesand while they are counter to the beliefs ofaviators, as is shown by the persistency in adheringto the old methods, are believed to be mechanicallycorrect, and worthy of consideration.

THE LOW CENTER OF GRAVITY.—But we have stillto examine another feature which shows the wrongprinciple in the fixed planes. The question isoften asked, why do the builders of aeroplanesplace most of the weight up close to the planes?It must be obvious to the novice that the lowerthe weight the less liability of overturning.

FORE AND AFT OSCILLATIONS.—The answer is,that when the weight is placed below the planes itacts like a pendulum. When the machine is travelingforward, and the propeller ceases its motion,as it usually does instantaneously, the weight, beingbelow, and having a certain momentum, continuesto move on, and the plane surface meetingthe resistance just the same, and having no meansto push it forward, a greater angle of resistance isformed.

In Fig. 19 this action of the two forces is illustrated. Theplane at the speed of 30 miles is atan angle of 15 degrees, the body B of the machinebeing horizontal, and the weight C suspended directlybelow the supporting surfaces.

The moment the power ceases the weight continuesmoving forwardly, and it swings the forwardend of the frame upwardly, Fig. 20, and we nowhave, as in the second figure, a new angle of incidence,which is 30 degrees, instead of 12. It willbe understood that in order to effect a change inthe position of the machine, the forward end ascends,as shown by the dotted line A.

Fig. 20. Action when Propeller ceases to pull.

The weight a having now ascended as far aspossible forward in its swing, and its motionchecked by the banking action of the plan it willagain swing back, and again carry with it theframe, thus setting up an oscillation, which is extremelydangerous.

The tail E, with its unchanged angle, does not,in any degree, aid in maintaining the frame onan even keel. Being nearly horizontal while inflight, if not at a negative angle, it actually assiststhe forward end of the frame to ascend.

APPLICATION OF THE NEW PRINCIPLE.—Extendingthe application of the suggested form, let us seewherein it will prevent this pendulous motion atthe moment the power ceases to exert a forwardly-propelling force.

Fig. 21. Synchronously moving Planes.

In Fig. 21 the body A is shown to be equippedwith the supporting plane B and the tail a, sothey are adjustable simultaneously at the sameangle, and the weight D is placed below, similar tothe other structure.

At every moment during the forward movementof this type of structure, the rear end ofthe machine has a tendency to move upwardly,the same as the forward end, hence, when theweight seeks, in this case to go on, it acts on therear plane, or tail, and causes that end to raise,and thus by mutual action, prevents any pendulousswing.

LOW WEIGHT NOT NECESSARY WITH SYNCHRONOUSLY-MOVING WINGS.—A little reflection will convinceany one that if the two wings move in harmony,the weight does not have to be placed low,and thus still further aid in making a compactmachine. By increasing the area of the tail, andmaking that a true supporting surface, instead ofa mere idler, the weight can be moved furtherback, the distance transversely across the planesmay be shortened, and in that way still furtherincrease the lateral stability.

CHAPTER V

DIFFERENT MACHINE TYPES AND THEIR CHARACTERISTICS

THERE are three distinct types of heavier-than-air machines, which are widely separated in alltheir characteristics, so that there is scarcely asingle feature in common.

Two of them, the aeroplane, and the orthopter,have prototypes in nature, and are distinguishedby their respective similarities to the soaringbirds, and those with flapping wings.

The Helicopter, on the other hand, has no antecedenttype, but is dependent for its raisingpowers on the pull of a propeller, or a pluralityof them, constructed, as will be pointed out hereinafter.

AEROPLANES.—The only form which has metwith any success is the aeroplane, which, inpractice, is made in two distinct forms, one witha single set of supporting planes, in imitation ofbirds, and called a monoplane; and the other havingtwo wings, one above the other, and calledthe bi-plane, or two-planes.

All machines now on the market which do notdepend on wing oscillations come under thosetypes.

THE MONOPLANE.—The single plane type hassome strong claims for support. First of theseis the comparatively small head resistance, dueto the entire absence of vertical supporting posts,which latter are necessary with the biplane type.The bracing supports which hold the outer endsof the planes are composed of wires, which offerbut little resistance, comparatively, in flight.

ITS ADVANTAGES.—Then the vertical height ofthe machine is much less than in the biplane. Asa result the weight, which is farther below thesupporting surface than in the biplane, aids inmaintaining the lateral stability, particularlysince the supporting frame is higher.

Usually, for the same wing spread, the monoplaneis narrower, laterally, which is a furtheraid to prevent tilting.

ITS DISADVANTAGES.—But it also has disadvantageswhich must be apparent from its structure.As all the supporting surface is concentratedin half the number of planes, they mustbe made of greater width fore and aft, and this,as we shall see, later on, proves to be a disadvantage.

It is also doubted whether the monoplane canbe made as strong structurally as the other form,owing to the lack of the truss formation which isthe strong point with the superposed frame. Atruss is a form of construction where braces canbe used from one member to the next, so as tobrace and stiffen the whole.

THE BIPLANE.—Nature does not furnish a typeof creature which has superposed wings. In thisparticular the inventor surely did not follow nature.The reasons which led man to employ thistype may be summarized as follows:

In experimenting with planes it is found thata broad fore and aft surface will not lift as muchas a narrow plane. This subject is fully explainedin the chapter on The Lifting Surfaces ofPlanes. In view of that the technical descriptionsof the operation will not be touched uponat this place, except so far as it may be necessaryto set forth the present subject.

This peculiarity is due to the accumulation ofa mass of moving air at the rear end of the plane,which detracts from its lifting power. As itwould be a point of structural weakness to makethe wings narrow and very long, Wenham manyyears ago suggested the idea of placing one planeabove the other, and later on Chanute, anengineer, used that form almost exclusively, inexperimenting with his gliders.

It was due to his influence that the Wrightsadopted that form in their gliding experiments,and later on constructed their successful flyersin that manner. Originally the monoplane wasthe type generally employed by experimenters,such as Lilienthal, and others.

STABILITY IN BIPLANES.—Biplanes are not naturallyas stable laterally as the monoplane.The reason is, that a downward tilt has the benefitof only a narrow surface, comparable with themonoplane, which has broadness of wing.

To illustrate this, let us assume that we havea biplane with planes five feet from front to rear,and thirty-six feet in length. This would givetwo planes with a sustaining surface of 360 squarefeet. The monoplane would, probably, dividethis area into one plane eight and a half feet fromfront to rear, and 42 feet in length.

In the monoplane each wing would project outabout three feet more on each side, but it wouldhave eight and a half feet fore and aft spreadto the biplane's five feet, and thus act as a greatersupport.

THE ORTHOPTER.—The term orthopter, or ornithopter,meaning bird wing, is applied to suchflying machines as depend on wing motion to supportthem in the air.

Unquestionably, a support can be obtained bybeating on the air but to do so it is necessary toadopt the principle employed by nature to securean upward propulsion. As pointed out elsewhere,it cannot be the concaved type of wing,or its shape, or relative size to the weight it mustcarry.

As nature has furnished such a variety of dataon these points, all varying to such a remarkabledegree, we must look elsewhere to find the secret.Only one other direction offers any opportunity,and that is in the individual wing movement.

NATURE'S TYPE NOT UNIFORM.—When this isexamined, the same obscurity surrounds the issue.Even the speeds vary to such an extent that whenit is tried to differentiate them, in comparisonwith form, shape, and construction, the experimenterfinds himself wrapt in doubt and perplexity.

But birds do fly, notwithstanding this wonderfularray of contradictory exhibitions. Observationhas not enabled us to learn why these thingsare so. High authorities, and men who are expertaviators, tell us that the bird flies becauseit is able to pick out ascending air currents.

THEORIES ABOUT FLIGHT OF BIRDS.—Then weare offered the theory that the bird has an instinctwhich tells it just how to balance in theair when its wings are once set in motion.Frequently, what is taken for instinct, is somethingentirely different.

It has been assumed, for instance, that a cyclistmaking a turn at a rapid speed, and a bird flyingaround a circle will throw the upper part of thebody inwardly to counteract the centrifugal forcewhich tends to throw it outwardly.

Experiments with the monorail car, which isequipped with a gyroscope to hold it in a verticalposition, show that when the car approaches acurve the car will lean inwardly, exactly the sameas a bird, or a cyclist, and when a straight stretchis reached, it will again straighten up.

INSTINCT.—Now, either the car, so equippedpossesses instinct, or there must be a principlein the laws of nature which produces the similarityof action.

In like manner there must be some principlethat is entirely independent of the form of matter,or its arrangement, which enables the birdto perform its evolutions. We are led to believefrom all the foregoing considerations that it isthe manner or the form of the motion.

MODE OF MOTION.—In this respect it seems tobe comparable in every respect to the great anduniversal law of the motions in the universe.Thus, light, heat and electricity are the same, themanifestations being unlike only because theyhave different modes of motion.

Everything in nature manifests itself by motion.It is the only way in which nature acts.Every transformation from one thing to another,is by way of a movement which is characteristicin itself.

Why, then, should this great mystery of nature,act unlike the other portions of which it isa part?

THE WING STRUCTURE.—The wing structure ofevery flying creature that man has examined, hasone universal point of similarity, and that is themanner of its connection with the body. It is asort of universal joint, which permits the wingto swing up and down, perform a gyratory movementwhile doing so, and folds to the rear whenat rest.

Some have these movements in a greater orless degree, or capable of a greater range; butthe joint is the same, with scarcely an exception.When the stroke of the wing is downwardly therear margin is higher than the front edge, sothat the downward beat not only raises the bodyupwardly, but also propels it forwardly.

THE WING MOVEMENT.—The moment the wingstarts to swing upwardly the rear end isdepressed, and now, as the bird is moving forwardly,the wing surface has a positive angle ofincidence, and as the wing rises while the forwardmotion is taking place, there is no resistancewhich is effective enough to counteract themomentum which has been set up.

The great problem is to put this motion into amechanical form. The trouble is not ascribableto the inability of the mechanic to describe thismovement. It is an exceedingly simple one.The first difficulty is in the material that mustbe used. Lightness and strength for the wingitself are the first requirements. Then rigidityin the joint and in the main rib of the wing, arethe next considerations.

In these respects the ability of man is limited.The wing ligatures of flying creatures is exceedinglystrong, and flexible; the hollow bone formationand the feathers are extremely light, comparedwith their sustaining powers.

THE HELICOPTER MOTION.—The helicopter, orhelix-wing, is a form of flying machine which dependson revolving screws to maintain it in theair. Many propellers are now made, six feet inlength, which have a pull of from 400 to 500pounds. If these are placed on vertically-disposedshafts they would exert a like power toraise a machine from the earth.

Obviously, it is difficult to equip such a machinewith planes for sustaining it in flight, after it isonce in the air, and unless such means are providedthe propellers themselves must be themechanism to propel it horizontally.

This means a change of direction of the shaftswhich support the propellers, and the constructionis necessarily more complicated than if theywere held within non-changeable bearings.

This principle, however, affords a safer meansof navigating than the orthopter type, becausethe blades of such an instrument can be forcedthrough the air with infinitely greater speed thanbeating wings, and it devolves on the inventor todevise some form of apparatus which will permitthe change of pull from a vertical to a horizontaldirection while in flight.

CHAPTER VI

THE LIFTING SURFACES OF AEROPLANES

THIS subject includes the form, shape and angleof planes, used in flight. It is the direction inwhich most of the energy has been expended indeveloping machines, and the true form is stillinvolved in doubt and uncertainty.

RELATIVE SPEED AND ANGLE.—The relativespeed and angle, and the camber, or the curvedformation of the plane, have been considered inall their aspects, so that the art in this respect hasadvanced with rapid strides.

NARROW PLATES MOST EFFECTIVE.—It waslearned, in the early stages of the developmentby practical experiments, that a narrow plane,fore and aft, produces a greater lift than a wideone, so that, assuming the plane has 100 squarefeet of sustaining surface, it is far better to makethe shape five feet by twenty than ten by ten.

However, it must be observed, that to use thenarrow blade effectively, it must be projectedthrough the air with the long margin forwardly.Its sustaining power per square foot of surfaceis much less if forced through the air lengthwise.

Experiments have shown why a narrow bladehas proportionally a greater lift, and this maybe more clearly understood by examining theillustrations which show the movement of planesthrough the air at appropriate angles.

Fig. 22. Stream lines along a plane.

STREAM LINES ALONG A PLANE.—In Fig. 22, Ais a flat plane, which we will assume is 10 feetfrom the front to the rear margin. For convenienceseven stream lines of air are shown,which contact with this inclined surface. The firstline 1, after the contact at the forward end, isdriven downwardly along the surface, so that itforms what we might term a moving film.

The second air stream 2, strikes the first stream,followed successively by the other streams, 3, 4,and so on, each succeeding stream being compelledto ride over, or along on the preceding mass ofcushioned air, the last lines, near the lower end,being, therefore, at such angles, and contactingwith such a rapidly-moving column, that it producesbut little lift in comparison with the 1st,2d and 3d stream lines. These stream lines aretaken by imagining that the air approaches andcontacts with the plane only along the lines indicatedin the sketch, although they also in practiceare active against every part of the plane.

THE CENTER OF PRESSURE.—In such a plane thecenter of pressure is near its upper end, probablynear the line 3, so that the greater portion of thelift is exerted by that part of the plane aboveline 3.

AIR LINES ON THE UPPER SIDE OF THE PLANE.—Now, another factor must be considered, namely,the effect produced on the upper side of the plane,over which a rarefied area is formed at certainpoints, and, in practice, this also produces, orshould be utilized to effect a lift.

RAREFIED AREA.—What is called a rarefied area,has reference to a state or condition of the atmospherewhich has less than the normal pressure orquantity of air. Thus, the pressure at sea level,is about 14 3/4 per square inch

As we ascend the pressure grows less, and theair is thus rarer, or, there is less of it. This is acondition which is normally found in the atmosphere.Several things tend to make a rarefiedcondition. One is altitude, to which we have justreferred.

Then heat will expand air, making it less dense,or lighter, so that it will move upwardly, to bereplaced by a colder body of air. In aeronauticsneither of these conditions is of any importancein considering the lifting power of aeroplane surfaces.

RAREFACTION PRODUCED BY MOTION.—The thirdrarefied condition is produced by motion, and generallythe area is very limited when brought aboutby this means. If, for instance, a plane is heldhorizontally and allowed to fall toward the earth,it will be retarded by two forces, namely, compressionand rarefaction, the former acting on theunder side of the plane, and the latter on the upperside.

Of the two rarefaction is the most effectual,and produces a greater effect than compression.This may be proven by compressing air in a longpipe, and noting the difference in gauge pressurebetween the ends, and then using a suction pumpon the same pipe.

When a plane is forced through the air at anyangle, a rarefied area is formed on the side whichis opposite the one having the positive angle ofincidence.

If the plane can be so formed as to make a largeand effective area it will add greatly to the valueof the sustaining surface.

Unfortunately, the long fiat plane does not lendany aid in this particular, as the stream line flowsdown along the top, as shown in Fig. 23, withoutbeing of any service.

Fig. 23. Air lines on the upper side of a Plane.

THE CONCAVED PLANE.—These considerationsled to the adoption of the concaved plane formation,and for purposes of comparison the diagram,Fig. 24, shows the plane B of the same length andangle as the straight planes.

In examining the successive stream lines it willbe found that while the 1st, 2d and 3d lines havea little less angle of impact than the correspondinglines in the straight plane, the last lines, 5, 6and 7, have much greater angles, so that only line4 strikes the plane at the same angle.

Such a plane structure would, therefore, haveits center of pressure somewhere between thelines 3 and 4, and the lift being thus, practically,uniform over the surface, would be more effective.

THE CENTER OF PRESSURE.—This is a term usedto indicate the place on the plane where the airacts with the greatest force. It has reference toa point between the front and rear margins onlyof the plane.

Fig. 24. Air lines below a concaved Plane.

UTILIZING THE RAREFIED AREA.—This structure,however, has another important advantage, as itutilizes the rarefied area which is produced, andwhich may be understood by reference to Fig. 25.

The plane B, with its upward curve, and at thesame angle as the straight plane, has its lowerend so curved, with relation to the forward movement,that the air, in rushing past the upper end,cannot follow the curve rapidly enough to maintainthe same density along C, hence this exerts

an upward pull, due to the rarefied area, whichserves as a lifting force, as well as the compressedmass beneath the plane.

CHANGING CENTER OF PRESSURE.—The center ofpressure is not constant. It changes with theangle of the plane, but the range is considerablyless on a concave surface than on a flat plane.

Fig. 25. Air lines above a convex Plane.

In a plane disposed at a small angle, A, as inFig. 26, the center of pressure is nearer the forwardend of the plane than with a greater positiveangle of incidence, as in Fig. 27, and whenthe plane is in a normal flying angle, it is at thecenter, or at a point midway between the margins.

PLANE MONSTROSITIES.—Growing out of the ideathat the wing in nature must be faithfully copied,it is believed by many that a plane with apronounced thickness at its forward margin is oneof the secrets of bird flight.

Accordingly certain inventors have designedtypes of wings which are shown in Figs. 28 and29.

Fig. 28 Changing centers of Pressures.

Fig 29. Bird-wing structures.

Both of these types have pronounced bulges,designed to "split" the air, forgetting, apparently,that in other parts of the machine every effort ismade to prevent head resistance.

THE BIRD WING STRUCTURE.—The advocates ofsuch construction maintain that the forward edgeof the plane must forcibly drive the air columnapart, because the bird wing is so made, and thatwhile it may not appear exactly logical, still thereis something about it which seems to do the work,and for that reason it is largely adopted.

WHY THE BIRD'S WING HAS A PRONOUNCEDBULGE.—Let us examine this claim. The bonewhich supports the entire wing surface, called the(pectoral), has a heavy duty to perform. It is soconstructed that it must withstand an extraordinarytorsional strain, being located at the forwardportion of the wing surface. Torsion hasreference to a twisting motion.

In some cases, as in the bat, this primary bonehas an attachment to the rear of the main joint,where the rear margin of the wing is attached tothe leg of the animal, thus giving it a supportand the main bone is, therefore, relieved of thistorsional stress.

THE BAT'S WING.—An examination of the bat'swing shows that the pectoral bone is very smalland thin, thus proving that when the entire wingsupport is thrown upon the primary bone it mustbe large enough to enable it to carry out its functions.It is certainly not so made because it is anecessary shape which best adapts it for flying.

If such were the case then nature erred in thecase of the bat, and it made a mistake in thehousefly's wing which has no such anterior enlargementto assist (?) it in flying.

AN ABNORMAL SHAPE.—Another illustration isshown in Fig. 30, which has a deep concave directlybehind the forward margin, as at A, sothat when the plane is at an angle of about 22degrees, a horizontal line, as B, passing back fromthe nose, touches the incurved surface of the planeat a point about one-third of its measurementback across the plane.

Fig. 30. One of the Monstrosities

This form is an exact copy of the wing of anactual bird, but it belongs, not to the soaring,but to the class which depends on flapping wings,and as such it cannot be understood why it shouldbe used for soaring machines, as all aeroplanesare.

The foregoing instances of construction arecited to show how wildly the imagination willroam when it follows wrong ideals.

THE TAIL AS A MONITOR.—The tendency of thecenter of pressure to change necessitates a correctionalmeans, which is supplied in the tail ofthe machine, just as the tail of a kite serves tohold it at a correct angle with respect to the windand the pull of the supporting string.

CHAPTER VII

ABNORMAL FLYING STUNTS AND SPEEDS

"PEQUOD, a Frenchman, yesterday repeatedlyperformed the remarkable feat of flying with themachine upside down. This exhibition showsthat the age of perfection has arrived in flyingmachines, and that stability is an accomplishedfact."—News item.

This is quoted to show how little the generalpublic knows of the subject of aviation. It correctlyrepresents the achievement of the aviator,and it probably voiced the sentiment of manyscientific men, as well as of the great majority ofaviators.

A few days afterwards, the same newspaperpublished the following:

"Lieutenant ——, while experimenting yesterdaymorning, met his death by the overturningof his machine at an altitude of 300 meters.Death was instantaneous, and the machine wascompletely destroyed."

The machines used by the two men were of thesame manufacture, as Pequod used a stock machinewhich was strongly braced to support theinverted weight, but otherwise it was not unlikethe well known type of monoplane.

Beachy has since repeated the experiment witha bi-plane, and it is a feat which has many imitators,and while those remarkable exhibitionsare going on, one catastrophe follows the otherwith the same regularity as in the past.

Let us consider this phase of flying. Are theyof any value, and wherein do they teach anythingthat may be utilized,

LACK OF IMPROVEMENTS IN MACHINES.—It is remarkablethat not one single forward step hasbeen taken to improve the type of flying machinesfor the past five years. They possess the sameshape, their stabilizing qualities and mechanismfor assuring stability are still the same.

MEN EXPEDITED, AND NOT THE MACHINE.—Thefact is, that during this period the man has beenexploited and not the machine. Men have learned,some few of them, to perform peculiar stunts,such as looping the loop, the side glide, the drop,and other features, which look, and are, hazardous,all of which pander to the sentiments of the spectators.

ABNORMAL FLYING OF NO VALUE.—It would betoo broad an assertion to say that it has absolutelyno value, because everything has its usein a certain sense, but if we are to judge fromthe progress of inventions in other directions,such exhibitions will not improve the art of buildingthe device, or make a fool-proof machine.

Indeed, it is the very thing which serves as adeterrent, rather than an incentive. If machinescan be handled in such a remarkable manner, theymust be, indeed, perfect! Nothing more isneeded! They must represent the highest structuraltype of mechanism!

That is the idea sought to be conveyed in thefirst paragraph quoted. It is pernicious, insteadof praiseworthy, because it gives a false impression,and it is remarkable that even certain scientificjournals have gravely discussed the perfected(?) type of flying machine as demonstratedby the experiments alluded to.

THE ART OF JUGGLING.—We may, occasionally,see a cyclist who understands the art of balancingso well that he can, with ease, ride a machinewhich has only a single wheel; or he can, with astock bicycle, ride it in every conceivable attitude,and make it perform all sorts of feats.

It merely shows that man has become anexpert at juggling with a machine, the same as hemanipulates balls, and wheels, and other artifices,by his dexterity.

PRACTICAL USES THE BEST TEST.—The bicycledid not require such displays to bring it to perfection.It has been the history of every inventionthat improvements were brought about, notby abnormal experiments, but by practical usesand by normal developments.

The ability of an aviator to fly with the machinein an inverted position is no test of the machine'sstability, nor does it in any manner prove thatit is correctly built. It is simply and solely ajuggling feat—something in the capacity of a certainman to perform, and attract attention becausethey are out of the ordinary.

CONCAVED AND COXVEX PLANES:—They were performedas exhibition features, and intended assuch, and none of the exponents of that kind offlying have the effrontery to claim that they proveanything of value in the machine itself, exceptthat it incidentally has destroyed the largelyvaunted claim that concaved wings for supportingsurfaces are necessary.

HOW MOMENTUM IS A FACTOR IN INVERTED FLYING.—When flying "upside down," the convexside of the plane takes the pressure of the air,and maintains, so it is asserted, the weight of themachine. This is true during that period whenthe loop is being made. The evolution is madeby first darting down, as shown in Fig. 31, fromthe horizontal position, 1, to the position 2, wherethe turn begins.

Fig. 31. Flying upside down.

TURNING MOVEMENT.—Now note the characteristicangles of the tail, which is the controllingfactor. In position 1 the tail is practicallyhorizontal. In fact, in all machines, athigh flight, the tail is elevated so as to give littlepositive angle of incidence to the supportingplanes.

In position No. 2, the tail is turned to an angleof incidence to make the downward plunge, andwhen the machine has assumed the vertical, as inposition 3, the tail is again reversed to assumethe angle, as in 1, when flying horizontally.

At the lower turn, position 4, the tail is turnedsimilar to the angle of position 2, which throwsthe rear end of the machine down, and as thehorizontal line of flight is resumed, in an invertedposition, as in position 4, the tail has the sameangle, with relation to the frame, as the supportingplanes.

During this evolution the engine is running, andthe downward plunge develops a tremendousspeed, and the great momentum thus acquired,together with the pulling power of the propellerwhile thus in flight, is sufficient to propel it alonghorizontally, whatever the plane surface curve, orformation may be.

It is the momentum which sustains it in space,not the air pressure beneath the wings, forreasons which we have heretofore explained.Flights of sufficient duration have thus been madeto prove that convex, as well as concave surfacesare efficient; nevertheless, in its proper place wehave given an exposition of the reasoning whichled to the adoption of the concaved supportingsurfaces.

WHEN CONCAVED PLANES ARE DESIRABLE.—Unquestionably, for slow speeds the concaved wingis desirable, as will be explained, but for highspeeds, surface formation has no value. That isshown by Pequod's feat.

THE SPEED MANIA.—This is a type of maniawhich pervades every field of activity in the buildingof aeroplanes. Speed contests are of moreimportance to the spectators on exhibitiongrounds than stability or durability. Builderspander to this, hence machines are built on lineswhich disregard every consideration of safetywhile at normal flight.

USES OF FLYING MACHINES.—The machine asnow constructed is of little use commercially.Within certain limitations it is valuable for scoutingpurposes, and attempts have been made touse it commercially. But the unreliable characterof its performances, due to the many elementswhich are necessary to its proper working, haveoperated against it.

PERFECTION IN MACHINES MUST COME BEFORESPEED.—Contrary to every precept in the buildingof a new article, the attempt is made to makea machine with high speed, which, in the verynature of things, operates against its improvement.The opposite lack of speed—is of fargreater utility at this stage of its development.

THE RANGE OF ITS USE.—The subject might beillustrated by assuming that we have a line runningfrom A to Z, which indicates the range ofspeeds in aeroplanes. The limits of speeds arefairly stated as being within thirty and eighty-five miles per hour. Less than thirty miles areimpossible with any type of plane, and while somehave made higher speeds than eighty-five miles itmay be safe to assume that such flights took placeunder conditions where the wind contributed tothe movement.

Fig. 32. Chart showing Range of Uses

COMMERCIAL UTILITY.—Before machines can beused successfully they must be able to attainslower speeds. Alighting is the danger factor.Speed machines are dangerous, not in flight orat high speeds, but when attempting to land. Alarge plane surface is incompatible with speed,which is another illustration that at high velocitiessupporting surfaces are not necessary.

Commercial uses require safety as the first element,and reliability as the next essential. Forpassenger service there must be an assurance thatit will not overturn, or that in landing danger isnot ever-present. For the carrying of freight interruptedservice will militate against it.

How few are the attempts to solve the problemof decreased speed, and what an eager, restlesscampaign is being waged to go faster and faster,and the addition of every mile above the recordis hailed as another illustration of the perfection(?) of the flying machine.

To be able to navigate a machine at ten, or fifteenmiles an hour, would scarcely be interestingenough to merit a paragraph; but such an accomplishmentwould be of far more value than all ofPequod's feats, and be more far-reaching in itseffects than a flight of two hundred miles per hour.

CHAPTER VIII

KITES AND GLIDERS

KITES are of very ancient origin, and in China,Japan, and the Malayan Peninsula, they have beenused for many years as toys, and for the purposesof exhibiting forms of men, animals, and particularlydragons, in their periodical displays.

THE DRAGON KITE.—The most noted of all arethe dragon kites, many of them over a hundredfeet in length, are adapted to sail along majestically,their sinuous or snake-like motions lendingan idea of reality to their gorgeously-colored appearancein flight.

ITS CONSTRUCTION.—It is very curiouslywrought, and as it must be extremely light, bambooand rattan are almost wholly used, togetherwith rice paper, in its construction.

Fig. 33 shows one form of the arrangement, inwhich the bamboo rib, A, in which only two sectionsare shown, as B, B, form the backbone, andthese sections are secured together with pivotpins C. Each section has attached thereto ahoop, or circularly-formed rib, D, the rib passingthrough the section B, and these ribs areconnected together loosely by cords E, which runfrom one to the other, as shown.

These circular ribs, D, are designed to carry aplurality of light paper disks, F, which are attachedat intervals, and they are placed at suchangles that they serve as small wing surfaces oraeroplanes to hold the structure in flight.

Fig. 33. Ribs of Dragon Kite

THE MALAY KITE.—The Malay kite, of whichFig. 34 shows the structure, is merely made up oftwo cross sticks, A, B, the vertical strip, A, beingbent and rigid, whereas the cross stick, B, is lightand yielding, so that when in flight it will bend,as shown, and as a result it has wonderful stabilitydue to the dihedral angles of the two surfaces. This kiterequires no tail to give it stability.

Fig. 34. The Malay Kite.

DIHEDRAL ANGLES.—This is a term to designatea form of disposing of the wings which has beenfound of great service in the single plane machines.A plane which is disposed at a risingangle, as A, A, Fig. 35, above the horizontal line,is called dihedral, or diedral.

Fig. 35. Dihedral Angle.

This arrangement in monoplanes does awaywith the necessity of warping the planes, orchanging them while in flight. If, however, the angleis too great, the wind from either quarter is liableto raise the side that is exposed.

THE COMMON KITE.—While the Malay kite hasonly two points of cord attachment, both alongthe vertical rib, the common kite, as shown inFig. 36, has a four-point connection, to which theflying cord is attached. Since this form has nodihedral angle, it is necessary to supply a tail,which thus serves to keep it in equilibrium, whilein flight.

Fig. 36. Common Kite.

Various modifications have grown out of theMalay kite. One of these forms, designed byEddy, is exactly like the Malay structure, but insteadof having a light flexible cross piece, it isbent to resemble a bow, so that it is rigidly heldin a bent position, instead of permitting the windto give it the dihedral angle.

THE BOW KITE.—Among the different types arethe bow kite, Fig. 37, and the sexagonal structure,Fig. 38, the latter form affording an especiallylarge surface.

_Fig. 37. Bow Kite.-

Fig. 38. Hexagonal Kite.

THE BOX KITE.—The most marked improvementin the form of kites was made by Hargreaves,in 1885, and called the box kite. It has wonderfulstability, and its use, with certain modifications,in Weather Bureau experiments, have proven itsvalue.

It is made in the form of two boxes, A, B, openat the ends, which are secured together by meansof longitudinal bars, C, that extends from one tothe other, so that they are held apart a distance,approximately, equal to the length of one of theboxes.

Fig. 39. Hargreave Kite.

Their fore and aft stability is so perfect thatthe flying cord D is attached at one point only,and the sides of the boxes provide lateral stabilityto a marked degree.

THE VOISON BIPLANE.—This kind of kite furnishedthe suggestion for the Voison biplane,which was one of the earlier productions in flyingmachines.

Fig. 40 shows a perspective of the Voison plane,which has vertical planes A, A, at the ends, andalso intermediate curtains B, B. This was foundto be remarkably stable, but during its turningmovements, or in high winds, was not satisfactory,and for that reason was finally abandoned.

LATERAL STABILITY IN KITES NOT CONCLUSIVE ASTO PLANES.—This is instanced to show that whilesuch a form is admirably adapted for kite purposes,where vertical curtains are always in linewith the wind movement, and the structure is heldtaut by a cord, the lateral effect, when used on amachine which does not at all times move in linewith the moving air current. A condition is thusset up which destroys the usefulness of the boxkite formation.

Fig. 40. Voison Biplane.

THE SPEAR KITE.—This is a novel kite, withremarkable steadiness and is usually made withthe wings on the rear end larger than those onthe forward end (Fig. 41), as thereby the cordA can be attached to the spear midway betweenthe two sets of wings.

Fig. 41. Spear Kite.

THE CELLULAR KITE.—Following out the suggestionof the Hargreaves kite, numerous formsembodying the principle of the box structure weremade and put on the market before the aeroplanebecame a reality.

Fig. 42. Cellular Kite.

A structure of this form is illustrated in Fig.42. Each box, as A, B, has therein a plurality ofvertical and horizontal partitions, so that a numberof cells are provided, the two cell-like boxesbeing held apart by a bar C, axially arranged.

This type is remarkably stable, due to the smallcells, and kites of this kind are largely used formaking scientific experiments.

THE TETRAHEDRAL KITE.—Prof. Bell, inventorof the telephone, gave a great deal of study tokites, which resulted in the tetrahedral formation,as shown in Fig. 43.

Fig. 43. Tetrahedral Kite.

The structure, apparently, is somewhat complicated,but an examination of a single pair ofblades, as shown at A, shows that it is built up oftriangularly-formed pieces, and that the openingsbetween the pieces are equal to the latter, therebyproviding a form of kite which possesses equilibriumto a great degree.

It has never been tried with power, and it isdoubtful whether it would be successful as a sustainingsurface for flying machines, for the samereasons that caused failure with the box-like formationof the Voison Machine.

THE DELTOID.—The deltoid is the simplest, andthe most easily constructed of all the kites. It isusually made from stiff cardboard, A-shaped inoutline, as shown in Figs. 44 and 45, and bent alonga central line, as at A, forming two wings, eachof which is a right-angled triangle.

Fig. 44. and 45. Deltoid Formation.

The peculiarity of this formation is, that it hasremarkable stability when used as a kite, witheither end foremost. If a small weight is placedat the pointed end, and it is projected through theair, it will fly straight, and is but little affectedby cross currents.

THE DUNNE FLYING MACHINE.—A top view ofthis biplane is shown in Fig. 46. The A-shapeddisposition of the planes, gives it good lateralstability, but it has the disadvantage under whichall aeroplanes labor, that the entire body of themachine must move on a fore and aft verticalplan in order to ascend or descend.

Fig. 46. The Dunne Bi-plane.

This is a true deltoid formation, as the angle ofincidence of the planes is so disposed that whenthe planes are horizontal from end to end, the inclinationis such as to make it similar to the deltoidkite referred to.

ROTATING KITE.—A type of kite unlike theothers illustrated is a rotating structure, whichgives great stability, due to the gyroscopic actionon the supporting surfaces.

Fig. 47 shows a side view with the top in section.The supporting surface is umbrella-shaped.In fact, the ordinary umbrella will answer if notdished too much. An angularly-bent piece of wireA, provided with loops B, B, at the ends, serve asbearings for the handle of the umbrella.

At the bend of the wire loop C, the cord D isattached. The lower side of the umbrella top hascup-shaped pockets E, near the margin, so arrangedthat their open ends project in the samedirection, and the wind catching them rotates thecircular plane.

Fig. 47. Rotable Umbrella Kite.

KITE PRINCIPLES.—A careful study of the exampleshere given, will impress the novice withone important fact, which, in its effect has a moreimportant bearing on successful flight, than allthe bird study and speculations concerning itsmysteries.

This fact, in essence, is, that the angle of thekite is the great factor in flight next to the powernecessary to hold it. Aside from this, thecomparison between kites and aeroplanes is of nopractical value.

Disregarding the element of momentum, thedrift of a machine against a wind, is the same,dynamically, as a plane at rest with the windmoving past it. But there is this pronounceddifference: The cord which supports the kiteholds it so that the power is in one direction only.

When a side gust of wind strikes the kite itis moved laterally, in sympathy with the kite,hence the problem of lateral displacement is notthe same as with the aeroplane.

LATERAL STABILITY IN KITES.—In the latter thepower is definitely fixed with relation to the machineitself, and if we should assume that a planewith a power on it sufficient to maintain a flightof 40 miles an hour, should meet a wind movingat the same speed, the machine would be stationaryin space.

Such a condition would be the same, so far asthe angles of the planes are concerned, with akite held by a string, but there all similarity inaction ends.

The stabilizing quality of the kite may be perfect,as the wind varies from side to side, but theaeroplane, being free, moves to the right or tothe left, and does not adjust itself by means of afixed point, but by a movable one.

SIMILARITY OF FORE AND AFT CONTROL.—Foreand aft, however, the kite and aeroplane act thesame. Fig. 48 shows a diagram which illustratesthe forces which act on the kite, and by meansof which it adjusts its angle automatically.

Let us assume that the kite A is flown froma cord B, so that its angle is 22 1/2 degrees, thewind being 15 miles per hour to maintain thecord B at that angle. When the wind increasesto 20 miles an hour there is a correspondinglygreater lift against the kite.

Fig. 48. Action of Wind forces on Kite.

As its angle is fixed by means of the loop C,it cannot change its angle with reference to thecord, or independently of it, and its only courseis to move up higher and assume the positionshown by the figure at D, and the angle of incidenceof the kite is therefore changed to 15 degrees,or even to 10 degrees.

In the case of the aeroplane the effect is similarfrom the standpoint of power and dispositionof the planes. If it has sufficient power, and theangle of the planes is not changed, it will ascend;if the planes are changed to 15 degrees to correspondwith the kite angle it will remain stationary.

GLIDING FLIGHT.—The earliest attempt to flyby gliding is attributed to Oliver, a Monk ofMalmesbury who, in 1065 prepared artificialwings, and with them jumped from a tower, beinginjured in the experiment.

Nearly 700 years later, in 1801, Resnier, a
Frenchman, conducted experiments with varying
results, followed by Berblinger, in 1842, and
LeBris, a French sailor, in 1856.

In 1884, J. J. Montgomery, of California, designeda successful glider, and in 1889 Otto andGustav Lilienthal made the most extended tests,in Germany, and became experts in handlinggliders.

Pilcher, in England, was the next to take up thesubject, and in 1893 made many successful glides,all of the foregoing machines being single planesurfaces, similar to the monoplane.

Long prior to 1896 Octave Chanute, anengineer, gave the subject much study, and in thatyear made many remarkable flights, developingthe double plane, now known as the biplane.

He was an ardent believer in the ability of manto fly by soaring means, and without using powerfor the purpose.

It is doubtful whether gliders contributed muchto the art in the direction of laterally stabilizingaeroplanes. They taught useful lessons with respectto area and fore and aft control.

The kite gave the first impulse to seek out ameans for giving equilibrium to planes, andMontgomery made a kite with warping wings asearly as 1884.

Penaud, a Frenchman, in 1872, made a modelaeroplane which had the stabilizing means in thetail. All these grew out of kite experiments; andall gliders followed the kite construction, or theprinciples involved in them, so that, really, thereis but one intervening step between the kite andthe flying machine, as we know it, the latter beingmerely kites with power attached, as substitutesfor the cords.

ONE OF THE USES OF GLIDER EXPERIMENTS.—There is one direction in which gliders are valuableto the boy and to the novice who are interestedin aviation. He may spend a lifetime ingliding and not advance in the art. It isquestionable whether in a scientific way it will be ofany service to him; but experiments of this charactergive confidence, the ability to quickly graspa situation, and it will thus teach self reliance inemergencies.

When in a glider quick thinking is necessary.The ability to shift from one position to another;to apply the weight where required instantaneously;to be able during the brief exciting momentof flight to know just what to do, requires alertness.

Some are so wedded to the earth that slightelevation disturbs them. The sensation in aglider while in flight is unlike any other experience.It is like riding a lot of tense springs, and theexhilaration in gliding down the side of a hill,with the feet free and body suspended, is quitedifferent from riding in an aeroplane with powerattached.

HINTS IN GLIDING.—It seems to be a difficultmatter to give any advice in the art of gliding. Itis a feat which seems to necessitate experimentfrom first to last. During the hundreds of testspersonally made, and after witnessing thousandsof attempts, there seems to be only a few suggestionsor possible directions in which caution mightbe offered.

First, in respect to the position of the body atthe moment of launching. The glider is usuallyso made that in carrying it, preparatory to makingthe run and the leap required to glide, it is heldso that it balances in the hands.

Now the center of air pressure in gliding maynot be at the same point as its sustaining weightwhen held by the hand, and furthermore, as thearm-pits, by which the body of the experimenterare held while gliding, are not at the same point,but to the rear of the hands, the moment the glideris launched too great a weight is brought to therear margin of the planes, hence its forward endlifts up.

This condition will soon manifest itself, and becorrected by the experimenter; but there is anotherdifficulty which is not so easy to discoverand so quick to remedy, and that is the swing ofthe legs the moment the operator leaves theground.

The experimenter learns, after many attempts,that gliding is a matter of a few feet only, and heanticipates landing too soon, and the moment heleaps from the ground the legs are swung forwardlyready to alight.

This is done unconsciously, just as a jumperswings his legs forwardly in the act of alighting.Such a motion naturally disturbs the fore and aftstability of the gliding machine, by tilting up theforward margin, and it banks against the air,instead of gliding.

The constant fear of all gliders is, that themachine will point downwardly, and his motion,as well as the position of the body, tend to shootit upwardly, instead.

CHAPTER IX

AEROPLANE CONSTRUCTION

As may be inferred from the foregoing statements,there are no definite rules for the constructionof either type of flying machine, as theflying models vary to such an extent that it isdifficult to take either of them as a model to representthe preferred type of construction.

LATERAL, AND FORE AND AFT.—The term lateralshould be understood, as applied to aeroplanes.It is always used to designate the direction atright angles to the movement of the machine.Fore and aft is a marine term meaning lengthwise,or from front to rear, hence is always at rightangles to the lateral direction.

The term transverse is equivalent to lateral,in flying machine parlance, but there is thisdistinction: Transverse has reference to a machineor object which, like the main planes of an aeroplane,are broader, (that is,—from end to end)than their length, (from front to rear).

On the other hand, lateral has reference to sidebranches, as, for instance, the monoplane wings,which branch out from the sides of the fore andaft body.

STABILITY AND STABILIZATION.—These terms constantlyappear in describing machines and theiroperations. If the flying structure, whatever itmay be, has means whereby it is kept from rockingfrom side to side, it has stability, which is usuallydesignated as lateral stability. The mechanismfor doing this is called a stabilizer.

THE WRIGHT SYSTEM.—The Wright machine hasreference solely to the matter of laterally controllingthe flying structure, and does not pertainto the form or shape of the planes.

In Fig. 49 A designates the upper and lowerplanes of a Wright machine, with the peculiarrounded ends. The ends of the planes are soarranged that the rear margins may be raised orlowered, independently of the other portions ofthe planes, which are rigid. This movement isindicated in sketch 1, where the movable part Bis, as we might say, hinged along the line C.

The dotted line D on the right hand end, showshow the section is depressed, while the dottedlines E at the left hand end shows the sectionraised. It is obvious that the downturned ends,as at D, will give a positive angle at one end of theplanes, and the upturned wings E at the other endwill give a negative angle, and thus cause the righthand end to raise, and the other end to movedownwardly, as the machine moves forwardlythrough the air.

CONTROLLING THE WARPING ENDS.—Originallythe Wrights controlled these warping sections bymeans of a cradle occupied by the aviator, so thatthe cradle would move or rock, dependent on thetilt of the machine. This was what was termedautomatic control. This was found to be unsatisfactory,and the control has now been placed sothat it connects with a lever and is operated bythe aviator, and is called Manually-operated control.

In all forms of control the wings on one side aredepressed on one side and correspondingly elevatedon the other.

THE CURTIS WINGS.—Curtis has small wings,or ailerons, intermediate the supporting surfaces,and at their extremities, as shown in sketch 2.These are controlled by a shoulder rack or swingingframe operated by the driver, so that the bodyin swinging laterally will change the two wingsat the same time, but with angles in differentdirections.

THE FARMAN AILERONS.—Farman's dispositionis somewhat different, as shown in sketch 3. Thewings are hinged to the upper planes at their rearedges, and near the extremities of the planes.Operating wires lead to a lever within reach of theaviator, and, by this means, the wings are held atany desired angle, or changed at will.

The difficulty of using any particular model, istrue, also, of the arrangement of the fore and aftcontrol, as well as the means for laterally stabilizingit. In view of this we shall submit a generalform, which may be departed from at will.

FEATURES WELL DEVELOPED.—Certain featuresare fairly well developed, however. One is theangle of the supporting plane, with reference tothe frame itself; and the other is the height atwhich the tail and rudder should be placed abovethe surface of the ground when the machine is atrest.

DEPRESSING THE REAR END.—This latter is amatter which must be taken into consideration,because in initiating flight the rear end of theframe is depressed in order to give a sufficientangle to the supporting planes so as to be able toinaugurate flight.

In order to commence building we should havesome definite idea with respect to the power, asthis will, in a measure, determine the area of thesupporting surfaces, as a whole, and from thisthe sizes of the different planes may be determined.

DETERMINING THE SIZE.—Suppose we decide on300 square feet of sustaining surface. This mayrequire a 30, a 40 or a 50 horse power motor,dependent on the speed required, and much higherpower has been used on that area.

However, let us assume that a forty horse powermotor is available, our 300 square feet of surfacemay be put into two planes, each having 150 squarefeet of surface, which would make each 5' by 30'in size; or, it may be decided to make the planesnarrower, and proportionally longer. This is immaterial.The shorter the planes transversely,the greater will be the stability, and the wider theplanes the less will be the lift, comparatively.

RULE FOR PLACING THE PLANES.—The rule forplacing the planes is to place them apart a distanceequal to the width of the planes themselves,so that if we decide on making them five feet wide,they should be placed at least five feet apart.This rule, while it is an admirable one for slowmovements or when starting flight, is not of anyadvantage while in rapid flight.

If the machine is made with front and rearhorizontally-disposed rudders, or elevators, theyalso serve as sustaining surfaces, which, for thepresent will be disregarded.

Lay off a square A, Fig. 49a, in which the verticallines B, B, and the horizontal lines C, C, are5' long, and draw a cross D within this, the linesrunning diagonally from the corners.

Now step off from the center cross line D, threespaces, each five feet long, to a point E, and jointhis point by means of upper and lower bars F,G, with the upper and lower planes, so as to formthe tail frame.

Fig. 49a. Rule for spacing Planes.

As shown in Fig. 50, the planes should now beindicated, and placed at an angle of about 8 degreesangle, which are illustrated, H being theupper and I the lower plane. Midway between theforward edges of the two planes, is a horizontalline J, extending forwardly, and by stepping offthe width of two planes, a point K is made, whichforms the apex of a frame L, the rear ends of thebars being attached to the respective planes H, I,at their forward edges.

Fig. 50. Frame of Control Planes.

Fig. 51. and Fig. 52.

ELEVATING PLANES.—We must now have the generalside elevation of the frame, the planes, theirangles, the tail and the rudder support, and theframe for the forward elevator.

To this may be added the forward elevatingplane L, the rear elevator, or tail M, and the verticalsteering rudder N.

The frame which supports the structure thusdescribed, may be made in a variety of ways, theobject being to provide a resilient connection forthe rear wheel O.

Fig. 52 shows a frame which is simple in constructionand easily attached. The lower foreand aft side bars P have the single front wheelaxle at the forward end, and the aft double wheelsat the rear end, a flexible bar Q, running from therear wheel axle to the forward end of the lowerplane.

A compression spring R is also mounted betweenthe bar and rear end of the lower plane totake the shock of landing. The forward end ofthe bar P has a brace S extending up to the frontedge of the lower plane, and another brace T connectsthe bars P, S, with the end of the forwardly-projecting frame.

Fig. 53. Plan view.

The full page view, Fig. 53, represents a planview, with one of the wings cut away, showing thegeneral arrangement of the frame, and the threewheels required for support, together with thebrace bars referred to.

The necessity of the rear end elevation willnow be referred to. The tail need not, necessarily,be located at a point on a horizontal linebetween the planes. It may be higher, or lowerthan the planes, but it should not be in a positionto touch the ground when the machine is aboutto ascend.

Fig. 54. Alighting.

The angle of ascension in the planes need notexceed 25 degrees so the frame does not requirean angle of more than 17 degrees. This is shownin Fig. 54, where the machine is in a positionready to take the air at that angle, leaving ampleroom for the steering rudder.

ACTION IN ALIGHTING.—Also, in alighting, themachine is banked, practically in the sameposition thus shown, so that it alights on the rearwheels O.

The motor U is usually mounted so its shaft ismidway between the planes, the propeller V beingconnected directly with the shaft, and being behindthe planes, is on a medial line with themachine.

The control planes L, M, N, are all connected upby means of flexible wires with the aviator at theset W, the attachments being of such a characterthat their arrangement will readily suggest themselvesto the novice.

THE MONOPLANE.—From a spectacular standpointa monoplane is the ideal flying machine. Itis graceful in outline, and from the fact that itclosely approaches the form of the natural flyer,seems to be best adapted as a type, compared withthe biplane.

THE COMMON FLY.—So many birds have beencited in support of the various flying theories thatthe house fly, as an example has been disregarded.We are prone to overlook the small insect, but itis, nevertheless, a sample which is just as potentto show the efficiency of wing surface as the condoror the vulture.

The fly has greater mobility than any other flyingcreature. By the combined action of its legsand wings it can spring eighteen inches in thetenth of a second; and when in flight can changeits course instantaneously.

If a sparrow had the same dexterity, proportionally,it could make a flight of 800 feet in thesame time. The posterior legs of the fly are thesame length as its body, which enable it to springfrom its perch with amazing facility.

Fig. 55. Common Fly. Outstretched Wings.

The wing surface, proportioned to its body andweight, is no less a matter for wonder and consideration.

In Fig. 55 is shown the outlines of the fly withoutstretched wings. Fig. 56 represents it withthe wing folded, and Fig. 57 is a view of a wingwith the relative size of the top of the body shownin dotted lines.

Fig. 56. Common Fly. Folded Wings.

The first thing that must attract attention, aftera careful study is the relative size of the bodyand wing surface. Each wing is slightly smallerthan the upper surface of the body, and the thicknessof the body is equal to each wing spread.

Fig. 57. Relative size of wing and body.

The weight, compared with sustaining surface,if expressed in understandable terms, would beequal to sixty pounds for every square foot of surface.

STREAM LINES.—The next observation is, thatwhat are called stream lines do not exist in the fly.Its head is as large in cross section as its body,with the slightest suggestion only, of a pointedend. Its wings are perfectly flat, forming a trueplane, not dished, or provided with a cambre, even,that upward curve, or bulge on the top of the aeroplanesurface, which seems to possess such a fascinationfor many bird flight advocates.

It will also be observed that the wing connectionwith the body is forward of the line A, whichrepresents the point at which the body will balanceitself, and this line passes through the wingsso that there is an equal amount of supportingsurface fore and aft of the line.

Again, the wing attachment is at the upper sideof the body, and the vertical dimension of thebody, or its thickness, is equal to four-fifths of thelength of he wing.

The wing socket permits a motion similar to auniversal joint, Fig. 55 showing how the innerend of the wing has a downward bend where itjoins the back, as at B.

THE MONOPLANE FORM.—For the purpose ofmaking comparisons the illustrations of the monoplaneshow a machine of 300 square feet of surface,which necessitates a wing spread of fortyfeet from tip to tip, so that the general dimensionsof each should be 18 1/2 feet by 8 1/2 feet at itswidest point.

First draw a square forty feet each way, as inFig. 58, and through this make a horizontal line1, and four intermediate vertical lines are thendrawn, as 2, 3, 4, 5, thus providing five divisions,each eight feet wide. In the first division theplanes A, B, are placed, and the tail, or elevatorC, is one-half the width of the last division.

Fig. 58. Plan of Monoplane.

The frame is 3 1/2 feet wide at its forward end,and tapers down to a point at its rear end, wherethe vertical control plane D is hinged, and thecross struts E, E, are placed at the division lines3, 4, 5.

The angles of the planes, with relation to theframe, are usually greater than in the biplane,for the reason that the long tail plane requiresa greater angle to be given to the planes whenarising; or, instead of this, the planes A, B, aremounted high enough to permit of sufficient anglefor initiating flight without injuring the tail D.

Some monoplanes are built so they have a supporton wheels placed fore and aft. In othersthe tail is supported by curved skids, as shownat A, Fig. 59, in which case the forwardsupporting wheels are located directly beneath the planes.As the planes are at about eighteen degreesangle, relative to the frame, and the tail planeB is at a slight negative angle of incidence, asshown at the time when the engine is started, theair rushing back from the propeller, elevates thetail, and as the machine moves forwardly overthe ground, the tail raises still higher, so as togive a less angle of incidence to the planes whileskimming along the surface of the ground.

Fig. 59. Side Elevation, Monoplane.

In order to mount, the tail is suddenly turnedto assume a sharp negative angle, thus swingingthe tail downwardly, and this increases the angleof planes to such an extent that the machine leavesthe ground, after which the tail is brought to theproper angle to assure horizontal flight.

The drawing shows a skid at the forward end,attached to the frame which carries the wheels.The wheels are mounted beneath springs so thatwhen the machine alights the springs yield sufficientlyto permit the skids to strike the ground,and they, therefore, act as brakes, to prevent themachine from traveling too far.

CHAPTER X

POWER AND ITS APPLICATION

THIS is a phase of the flying machine which hasthe greatest interest to the boy. He instinctivelysees the direction in which the machine has itslife,—its moving principle. Planes have theirfascination, and propellers their mysterious elements,but power is the great and absorbing questionwith him.

We shall try to make its application plain inthe following pages. We have nothing to do herewith the construction and operation of the motoritself, as, to do that justice, would require pages.

FEATURES IN POWER APPLICATION.—It will bemore directly to the point to consider the followingfeatures of the power and its application:

1. The amount of power necessary.

2. How to calculate the power applied.

3. Its mounting.

WHAT AMOUNT OF POWER IS NECESSARY.—In theconsideration of any power plant certain calculationsmust be made to determine what is required.A horse power means the lifting of a certainweight, a definite distance, within a specifiedtime.

If the weight of the vehicle, with its load, areknown, and its resistance, or the character of theroadway is understood, it is a comparatively easymatter to calculate just how much power must beexerted to overcome that resistance, and move thevehicle a certain speed.

In a flying machine the same thing is true, butwhile these problems may be known in a generalway, the aviator has several unknown elementsever present, which make estimates difficult tosolve.

THE PULL OF THE PROPELLER.—Two such factorsare ever present. The first is the propellerpull. The energy of a motor, when put into apropeller, gives a pull of less than eight poundsfor every horse power exerted.

FOOT POUNDS.—The work produced by a motoris calculated in Foot Pounds. If 550 poundsshould be lifted, or pulled, one foot in one secondof time, it would be equal to one horse power.

But here we have a case where one horse powerpulls only eight pounds, a distance of one footwithin one second of time, and we have utilizedless than one sixty-fifth of the actual energy produced.

SMALL AMOUNT OF POWER AVAILABLE.—This isdue to two things: First, the exceeding lightnessof the air, and its great elasticity; and, second,the difficulty of making a surface which, when itstrikes the air, will get a sufficient grip to effecta proper pull.

Now it must be obvious, that where only sucha small amount of energy can be made available,in a medium as elusive as air, the least change, orform, of the propeller, must have an importantbearing in the general results.

HIGH PROPELLER SPEED IMPORTANT.—Furthermore,all things considered, high speed is importantin the rotation of the propeller, up to a certainpoint, beyond which the pull decreases inproportion to the speed. High speed makes avacuum behind the blade and thus decreases theeffective pull of the succeeding blade.

WIDTH AND PITCH OF BLADES.—If the blade istoo wide the speed of the engine is cut down to apoint where it cannot exert the proper energy; ifthe pitch is very small then it must turn further toget the same thrust, so that the relation of diameter,pitch and speed, are three problems far frombeing solved.

It may be a question whether the propeller form,as we now know it, is anything like the true orultimate shape, which will some day be discovered.

EFFECT OF INCREASING PROPELLER PULL.—If thepresent pull could be doubled what a wonderfulrevolution would take place in aerial navigation,and if it were possible to get only a quarter ofthe effective pull of an engine, the results wouldbe so stupendous that the present method of flyingwould seem like child's play in comparison.

It is in this very matter,—the application ofthe power, that the bird, and other flying creaturesso far excel what man has done. Calculationsmade with birds as samples, show that manyof them are able to fly with such a small amountof power that, if the same energy should be appliedto a flying machine, it would scarcely driveit along the ground.

DISPOSITION OF THE PLANES.—The second factoris the disposition or arrangement of the planeswith relation to the weight. Let us illustrate thiswith a concrete example:

We have an aeroplane with a sustaining surfaceof 300 square feet which weighs 900 pounds,or 30 pounds per square foot of surface.

DIFFERENT SPEEDS WITH SAME POWER.—Now, wemay be able to do two things with an airship underthose conditions. It may be propelled throughthe air thirty miles an hour, or sixty miles, withthe expenditure of the same power.

An automobile, if propelled at sixty, instead ofthirty miles an hour, would require an additionalpower in doing so, but an airship acts differently,within certain limitations.

When it is first set in motion its effective pullmay not be equal to four pounds for each horsepower, due to the slow speed of the propeller, andalso owing to the great angle of incidence whichresists the forward movement of the ship.

INCREASE OF SPEED ADDS TO RESISTANCE.—Finally,as speed increases, the angle of the planesdecrease, resistance is less, and up to a certainpoint the pull of the propeller increases; but beyondthat the vacuum behind the blades becomesso great as to bring down the pull, and there isthus a balance,—a sort of mutual governing motionwhich, together, determine the ultimate speedof the aeroplane.

HOW POWER DECREASES WITH SPEED.—If now,with the same propeller, the speed should bedoubled, the ship would go no faster, because thebite of the propeller on the air would be ineffective,hence it will be seen that it is not the amountof power in itself, that determines the speed, butthe shape of the propeller, which must be so madethat it will be most effective at the speed requiredfor the ship.

While that is true when speed is the matter ofgreatest importance, it is not the case where it isdesired to effect a launching. In that case thepropeller must be made so that its greatest pullwill be at a slow speed. This means a widerblade, and a greater pitch, and a comparativelygreater pull at a slow speed.

No such consideration need be given to an automobile.The constant accretion of power addsto its speed. In flying machines the aviator mustalways consider some companion factor whichmust be consulted.

HOW TO CALCULATE THE POWER APPLIED.—In aprevious chapter reference was made to a planeat an angle of forty-five degrees, to which twoscales were attached, one to get its horizontal pull,or drift, and the other its vertical pull, or lift.

PULLING AGAINST AN ANGLE.—Let us take thesame example in our aeroplane. Assuming thatit weighs 900 pounds, and that the angle of theplanes is forty-five degrees. If we suppose thatthe air beneath the plane is a solid, and frictionless,and a pair of scales should draw it up the incline,the pull in doing so would be one-half of itsweight, or 450 pounds.

It must be obvious, therefore, that its force, inmoving downwardly, along the surface A, Fig. 60,would be 450 pounds.

The incline thus shown has thereon a weight B,mounted on wheels a, and the forwardly-projectingcord represents the power, or propeller pull,which must, therefore, exert a force of 450 poundsto keep it in a stationary position against the surfaceA.

In such a case the thrust along the diagonalline E would be 900 pounds, being the compositionof the two forces pulling along the lines D, F.

THE HORIZONTAL AND VERTICAL PULL.—Now itmust be obvious, that if the incline takes half ofthe weight while it is being drawn forwardly, inthe line of D, if we had a propeller drawing alongthat line, which has a pull of 450 pounds, it wouldmaintain the plane in flight, or, at any rate holdit in space, assuming that the air should be movingpast the plane.

Fig. 60. Horizontal and Vertical pull.

The table of lift and drift gives a fairly accuratemethod of determining this factor, and we refer tothe chapter on that subject which will show themanner of making the calculations.

THE POWER MOUNTING.—More time and laborhas been wasted, in airship experiments, in poormotor mounting, than in any other direction.This is especially true where two propellers areused, or where the construction is such that thepropeller is mounted some distance from the motor.

SECURING THE PROPELLER TO THE SHAFT.—Buteven where the propeller is mounted on the engineshaft, too little care is exercised to fix it securely.The vibratory character of the mountingmakes this a matter of first importance. If thereis a solid base a poorly fixed propeller will holdmuch longer, but it is the extreme vibration thatcauses the propeller fastening to give way.

VIBRATIONS.—If experimenters realized that aninsecure, shaking, or weaving bed would cause aloss of from ten to fifteen per cent. in the pull ofthe propeller, more care and attention would begiven to this part of the structure.

WEAKNESSES IN MOUNTING.—The general weaknessesto which attention should be directed are,first, the insecure attachment of the propeller tothe shaft; second, the liability of the base toweave; or permit of a torsional movement; third,improper bracing of the base to the main body ofthe aeroplane.

If the power is transferred from the cylinderto the engine shaft where it could deliver its outputwithout the use of a propeller, it would notbe so important to consider the matter of vibration;but the propeller, if permitted to vibrate,or dance about, absorbs a vast amount of energy,while at the same time cutting down its effectivepull.

Aside from this it is dangerous to permit theslightest displacement while the engine is running.Any looseness is sure to grow worse, insteadof better, and many accidents have beenregistered by bolts which have come loose fromexcessive vibration. It is well, therefore, to haveeach individual nut secured, or properly locked,which is a matter easily done, and when so securedthere is but little trouble in going over the machineto notice just how much more the nut mustbe taken up to again make it secure.

THE GASOLINE TANK.—What horrid details havebeen told of the pilots who have been burned todeath with the escaping gasoline after an accident,before help arrived. There is no excuse forsuch dangers. Most of such accidents were dueto the old practice of making the tanks of exceedinglylight or thin material, so that the leastundue jar would tear a hole at the fasteningpoints, and thus permit the gasoline to escape.

A thick copper tank is by far the safest, as thismetal will not readily rupture by the wrench whichis likely in landing.

WHERE TO LOCATE THE TANK.—There has beenconsiderable discussion as to the proper place tolocate the tank. Those who advocate its placementoverhead argue that in case of an accidentthe aeroplane is likely to overturn, and the tankwill, therefore, be below the pilot. Those whobelieve it should be placed below, claim that incase of overturning it is safer to have the tankafire above than below.

DANGER TO THE PILOT.—The great danger to thepilot, in all cases of accidents, lies in theoverturning of the machine. Many have had accidentswhere the machine landed right side up, evenwhere the fall was from a great height, and theonly damage to the aviator was bruises. Few, ifany, pilots have escaped where the machine hasoverturned.

It is far better, in case the tank is light, to haveit detached from its position, when the ship strikesthe earth, because in doing so, it will not be solikely to burn the imprisoned aviator.

In all cases the tank should be kept as far awayfrom the engine as possible. There is no reasonwhy it cannot be placed toward the tail end ofthe machine, a place of safety for two reasons:First, it is out of the reach of any possibledanger from fire; and, second, the accidents in thepast show that the tail frame is the least likely tobe injured.

In looking over the illustrations taken from theaccidents, notice how few of the tails are evendisarranged, and in many of them, while the entirefore body and planes were crushed to atoms,the tail still remained as a relic, to show itscomparative freedom from the accident.

In all monoplanes the tail really forms part ofthe supporting surface of the machine, and theadding of the weight of the gasoline would beplacing but little additional duty on the tail, andit could be readily provided for by a larger tailsurface, if required.

THE CLOSED-IN BODY.—The closed-in body is avast improvement, which has had the effect ofgiving greater security to the pilot, but even thisis useless in case of overturning.

STARTING THE MACHINE.—The direction in whichimprovements have been slow is in the startingof the machine. The power is usually so mountedthat the pilot has no control over the starting,as he is not in a position to crank it.

The propeller being mounted directly on theshaft, without the intervention of a clutch, makesit necessary, while on the ground, for the propellerto be started by some one outside, whileothers hold the machine until it attains the properspeed.

This could be readily remedied by using aclutch, but in the past this has been regarded asone of the weight luxuries that all have been tryingto avoid. Self starters are readily provided,and this with the provision that the propeller canbe thrown in or out at will, would be a vast improvementin all machines.

PROPELLERS WITH VARYING PITCH.—It is growingmore apparent each day, that a new type ofpropeller must be devised which will enable thepilot to change the pitch, as the speed increases,and to give a greater pitch, when alighting, soas to make the power output conform to the conditions.

Such propellers, while they may be dangerous,and much heavier than the rigid type, will, nodoubt, appear in time, and the real improvementwould be in the direction of having the bladescapable of automatic adjustment, dependent onthe wind pressure, or the turning speed, and thusnot impose this additional duty on the pilot.

CHAPTER XI

FLYING MACHINE ACCESSORIES

THE ANEMOMETER.—It requires an expert tojudge the force or the speed of a wind, and eventhey will go astray in their calculations. It isan easy matter to make a little apparatus whichwill accurately indicate the speed. A device ofthis kind is called an Anemometer.

Two other instruments have grown out of this,one to indicate the pressure, and the other thedirection of the moving air current.

THE ANEMOGRAPH.—While these instruments indicate,they are also made so they will record thespeed, the pressure and the direction, and the devicefor recording the speed and pressure is calleda Anemograph.

All these instruments may be attached to thesame case, and thus make a handy little device,which will give all the information at a glance.

THE ANEMOMETROGRAPH.—This device for recording,as well as indicating the speed, pressureand direction, is called an Anemometrograph,The two important parts of the combinedapparatus, for the speed and pressure, are illustrated,to show the principle involved. While the speedwill give the pressure, it is necessary to make acalculation to get the result while the machine doesthis for you.

Fig. 61. Speed Indicator.

THE SPEED INDICATOR.—Four hemisphericalcups A are mounted on four radiating arms B,which are secured to a vertical stem C, andadapted to rotate in suitable bearings in acase, which, for convenience in explaining, is notshown.

On the lower end of the stem C, is a small bevelpinion, which meshes with a smaller bevel pinionwithin the base. This latter is on a shaft whichcarries a small gear on its other end, to meshwith a larger gear on a shaft which carries apointer D that thus turns at a greatly reducedspeed, so that it can be easily timed.

Fig. 62. Air Pressure Indicator.

AIR PRESSURE INDICATOR.—This little apparatusis readily made of a base A which is providedwith two uprights B, C, through the upper ends ofwhich are holes to receive a horizontally-disposedbar D. One end of the bar is a flat planesurface E, which is disposed at right angles to thebar, and firmly fixed thereto.

The other end of the bar has a lateral pin toserve as a pivot for the end of a link F, its otherend being hinged to the upper end of a lever G,which is pivoted to the post C, a short distancebelow the hinged attachment of the link F, sothat the long end of the pointer which is constitutedby the lever G is below its pivot, and has,therefore, a long range of movement.

A spring I between the upper end of the pointerG and the other post B, serves to hold the pointerat a zero position. A graduated scale plate J,within range of the pointer will show at a glancethe pressure in pounds of the moving wind, andfor this purpose it would be convenient to makethe plane E exactly one foot square.

DETERMINING THE PRESSURE FROM THE SPEED.—These two instruments can be made to check eachother and thus pretty accurately enable you todetermine the proper places to mark the pressureindicator, as well as to make the wheels in theanemometer the proper size to turn the pointerin seconds when the wind is blowing at a certainspeed, say ten miles per hour.

Suppose the air pressure indicator has the scaledivided into quarter pound marks. This willmake it accurate enough for all purposes.

CALCULATING PRESSURES FROM SPEED.—The followingtable will give the pressures from 5 to 100miles per hour:

Velocity of wind in Pressure Velocity of wind in Pressure
miles per hour per sq. ft. miles per hour per sq ft
     5 .112 55 15.125
     10 .500 60 18.000
     15 1.125 65 21.125
     20 2.000 70 22.500
     25 3.125 75 28.125
     30 4.600 80 32.000
     35 6.126 86 36.126
     40 8.000 90 40.500
     45 10.125 95 45.125
     50 12.5 100 50.000

HOW THE FIGURES ARE DETERMINED.—The foregoingfigures are determined in the following manner:As an example let us assume that the velocityof the wind is forty-five miles per hour. Ifthis is squared, or 45 multiplied by 45, the productis 2025. In many calculations the mathematicianemploys what is called a constant, a figure thatnever varies, and which is used to multiply ordivide certain factors.

In this case the constant is 5/1000, or, as usuallywritten, .005. This is the same as one two hundredthsof the squared figure. That would makethe problem as follows:

45 X 45 = 2025 / 200 = 10.125; or, 45 X 45 - 2025 X .005 = 10.125.

Again, twenty-five miles per hour would be25 X 25 = 625; and this multiplied by .005 equals2 pounds pressure.

CONVERTING HOURS INTO MINUTES.—It is sometimesconfusing to think of miles per hour, whenyou wish to express it in minutes or seconds. Asimple rule, which is not absolutely accurate, butis correct within a few feet, in order to expressthe speed in feet per minute, is to multiply thefigure indicating the miles per hour, by 8 3/4.

To illustrate: If the wind is moving at therate of twenty miles an hour, it will travel in thattime 105,600 feet (5280 X 20). As there are sixtyminutes in an hour, 105,600 divided by 60, equals1760 feet per minute. Instead of going throughall this process of calculating the speed per minute,remember to multiply the speed in miles perhour by 90, which will give 1800 feet.

This is a little more then two per cent. abovethe correct figure. Again; 40 X 90 equals 3600.As the correct figure is 3520, a little mental calculationwill enable you to correct the figures soas to get it within a few feet.

CHANGING SPEED HOURS TO SECONDS.—As one-sixtieth of the speed per minute will represent therate of movement per second, it is a comparativelyeasy matter to convert the time from speed inmiles per hour to fraction of a mile traveled ina second, by merely taking one-half of the speedin miles, and adding it, which will very nearly expressthe true number of feet.

As examples, take the following: If the windis traveling 20 miles an hour, it is easy to takeone-half of 20, which is 10, and add it to 20, making30, as the number of feet per second. If thewind travels 50 miles per hour, add 25, making75, as the speed per second.

The correct speed per second of a wind traveling20 miles an hour is a little over 29 feet. At50 miles per hour, the correct figure is 73 1/3 feet,which show that the figures under this rule arewithin about one per cent. of being correct.

With the table before you it will be an easymatter, by observing the air pressure indicator,to determine the proper speed for the anemometer.Suppose it shows a pressure of two pounds,which will indicate a speed of twenty miles anhour. You have thus a fixed point to start from.

PRESSURE AS THE SQUARE OF THE SPEED.—Nowit must not be assumed that if the pressure attwenty miles an hour is two pounds, that fortymiles an hour it is four pounds. The pressureis as the square of the speed. This may be explainedas follows: As the speed of the windincreases, it has a more effective push against anobject than its rate of speed indicates, and thisis most simply expressed by saying that each timethe speed is doubled the pressure is four timesgreater.

As an example of this, let us take a speed of tenmiles an hour, which means a pressure of one-half pound. Double this speed, and we have 20miles. Multiplying one-half pound by 4, the resultis 2 pounds. Again, double 20, which means40 miles, and multiplying 2 by 4, the result is 8.Doubling forty is eighty miles an hour, and againmultiplying 8 by 4, we have 32 as the pounds pressureat a speed of 80 miles an hour.

The anemometer, however, is constant in itsspeed. If the pointer should turn once a secondat 10 miles an hour, it would turn twice at 20 milesan hour, and four times a second at 40 miles anhour.

GYROSCOPIC BALANCE.—Some advance has beenmade in the use of the gyroscope for the purposeof giving lateral stability to an aeroplane. Whilethe best of such devices is at best a makeshift,it is well to understand the principle on which theyoperate, and to get an understanding how they areapplied.

THE PRINCIPLE INVOLVED.—The only thingknown about the gyroscope is, that it objects tochanging the plane of its rotation. This statementmust be taken with some allowance, however,as, when left free to move, it will change inone direction.

To explain this without being too technical, examineFig. 63, which shows a gyroscopic top, oneend of the rim A, which supports the rotatingwheel B, having a projecting finger C, that ismounted on a pin-point on the upper end of thepedestal D.

Fig. 63. The Gyroscope.

When the wheel B is set in rotation it will maintainitself so that its axis E is horizontal, or atany other angle that the top is placed in when thewheel is spun. If it is set so the axis is horizontalthe wheel B will rotate on a vertical plane,and it forcibly objects to any attempt to make itturn except in the direction indicated by thecurved arrows F.

The wheel B will cause the axis E to swingaround on a horizontal plane, and this turningmovement is always in a certain direction in relationto the turn of the wheel B, and it is obvious,therefore, that to make a gyroscope thatwill not move, or swing around an axis, the placingof two such wheels side by side, and rotatedin opposite directions, will maintain them in afixed position; this can also be accomplished byso mounting the two that one rotates on a planeat right angles to the other.

Fig. 64. Application of the Gyroscope.

THE APPLICATION OF THE GYROSCOPE.—Withoutin any manner showing the structural details ofthe device, in its application to a flying machine,except in so far as it may be necessary to explainits operation, we refer to Fig. 64, whichassumes that A represents the frame of the aeroplane,and B a frame for holding the gyroscopicwheel C, the latter being mounted so it rotates ona horizontal plane, and the frame B being hingedfore and aft, so that it is free to swing to the rightor to the left.

For convenience in explaining the action, theplanes E are placed at right angles to their regularpositions, F being the forward margin of theplane, and G the rear edge. Wires H connectthe ends of the frame B with the respectiveplanes, or ailerons, E, and another wire I joinsthe downwardly-projecting arms of the twoailerons, so that motion is transmitted to both atthe same time, and by a positive motion in eitherdirection.

Fig. 65. Action of the Gyroscope.

In the second figure, 65, the frame of the aeroplaneis shown tilted at an angle, so that its rightside is elevated. As the gyroscopic wheel remainslevel it causes the aileron on the right side tochange to a negative angle, while at the sametime giving a positive angle to the aileron on theleft side, which would, as a result, depress theright side, and bring the frame of the machineback to a horizontal position.

FORE AND AFT GYROSCOPIC CONTROL.—It isobvious that the same application of this force maybe applied to control the ship fore and aft, althoughit is doubtful whether such a plan wouldhave any advantages, since this should be whollywithin the control of the pilot.

Laterally the ship should not be out of balance;fore and aft this is a necessity, and as the greattrouble with all aeroplanes is to control themlaterally, it may well be doubted whether it wouldadd anything of value to the machine by havingan automatic fore and aft control, which might,in emergencies, counteract the personal control ofthe operator.

ANGLE INDICATOR.—In flight it is an exceedinglydifficult matter for the pilot to give an accurateidea of the angle of the planes. If the air iscalm and he is moving over a certain course, andknows, from experience, what his speed is, he maybe able to judge of this factor, but he cannot tellwhat changes take place under certain conditionsduring the flight.

For this purpose a simple little indicator maybe provided, shown in Fig. 66, which is merely avertical board A, with a pendulum B, swingingfore and aft from a pin a which projects outfrom the board a short distance above its center.

The upper end of the pendulum has a heart-shaped wire structure D, that carries a slidingweight E. Normally, when the aeroplane is onan even keel, or is even at an angle, the weightE rests within the bottom of the loop D, butshould there be a sudden downward lurch or aquick upward inclination, which would cause thependulum below to rapidly swing in eitherdirection, the sliding weight E would at once moveforward in the same direction that the pendulumhad moved, and thus counteract, for the instantonly, the swing, when it would again drop backinto its central position.

Fig. 66. Angle Indicator.

With such an arrangement, the pendulum wouldhang vertically at all times, and the pointer below,being in range of a circle with degreesindicated thereon, and the base attached to theframe of the machine, can always be observed,and the conditions noted at the time the changestake place.

PENDULUM STABILIZER.—In many respects theuse of a pendulum has advantages over the gyroscope.The latter requires power to keep it inmotion. The pendulum is always in conditionfor service. While it may be more difficult toadjust the pendulum, so that it does not affectthe planes by too rapid a swing, or an oscillationwhich is beyond the true angle desired, still, theseare matters which, in time, will make the penduluma strong factor in lateral stability.

Fig. 67. Simple Pendulum Stabilizer.

It is an exceedingly simple matter to attach thelead wires from an aileron to the pendulum. InFig. 67 one plan is illustrated. The pendulumA swings from the frame B of the machine, theailerons a being in this case also shown at rightangles to their true positions.

The other, Fig. 68, assumes that the machine isexactly horizontal, and as the pendulum is in avertical position, the forward edges of both aileronsare elevated, but when the pendulum swingsboth ailerons will be swung with their forwardmargins up or down in unison, and thus the properangles are made to right the machine.

STEERING AND CONTROLLING WHEEL.—For thepurpose of concentrating the control in a singlewheel, which has not alone a turning motion, butis also mounted in such a manner that it will oscillateto and fro, is very desirable, and is adaptedfor any kind of machine.

Fig. 68. Pendulum Stabilizers.

Fig. 69 shows such a structure, in which Arepresents the frame of the machine, and B asegment for the stem of the wheel, the segmentbeing made of two parts, so as to form a guidewayfor the stem a to travel between, and the segmentis placed so that the stem will travel in afore and aft direction.

The lower end of the stem is mounted in asocket, at D, so that while it may be turned, itwill also permit this oscillating motion. Near itslower end is a cross bar E from which the wiresrun to the vertical control plane, and also to theailerons, if the machine is equipped with them, orto the warping ends of the planes.

Fig. 69. Steering and Control Wheel.

Above the cross arms is a loose collar F towhich the fore and aft cords are attached that goto the elevators, or horizontal planes. The upperend of the stem has a wheel G, which may also beequipped with the throttle and spark levers.

AUTOMATIC STABILIZING WINGS.—Unquestionably,the best stabilizer is one which will act onits own initiative. The difficulty with automaticdevices is, that they act too late, as a generalthing, to be effective. The device represented inFig. 70 is very simple, and in practice is found tobe most efficient.

In this Fig. 70 A and B represent the upperand the lower planes, respectively. Near the endvertical standards a, D, are narrow wings E E,F F, hinged on a fore and aft line close beloweach of the planes, the wings being at such distancesfrom the standards C D that when theyswing outwardly they will touch the standards,and when in that position will be at an angle ofabout 35 degrees from the planes A B.

Fig. 70. Automatic Stabilizing Wings.

Fig. 71. Action of Stabilizing Wings.

Inwardly they are permitted to swing up andlie parallel with the planes, as shown in Fig. 71where the planes are at an angle. In turning, allmachines skid,—that is they travel obliquelyacross the field, and this is also true when theship is sailing at right angles to the course of thewind.

This will be made clear by reference to Fig.72, in which the dart A represents the directionof the movement of the aeroplane, and B thedirection of the wind, the vertical rudder a beingalmost at right angles to the course of the wind.

Fig. 72. Into the Wind at an Angle.

In turning a circle the same thing takes placeas shown in Fig. 73, with the tail at a differentangle, so as to give a turning movement to theplane. It will be seen that in the circling movementthe tendency of the aeroplane is to fly outat a tangent, shown by the line D, so that theplanes of the machine are not radially-disposedwith reference to the center of the circle, the lineE showing the true radial line.

Referring now to Fig. 71, it will be seen thatthis skidding motion of the machine swings thewings E F inwardly, so that they offer no resistanceto the oblique movement, but the wings EE, at the other end of the planes are swung outwardly,to provide an angle, which tends to raiseup the inner end of the planes, and thereby seekto keep the planes horizontal.

Fig. 73. Turning a Circle.

BAROMETERS.—These instruments are used forregistering heights. A barometer is a device formeasuring the weight or pressure of the air.The air is supposed to extend to a height of 40miles from the surface of the sea. A column ofair one inch square, and forty miles high, weighsthe same as a column of mercury one inch squareand 30 inches high.

Such a column of air, or of mercury, weighs14 3/4 pounds. If the air column should beweighed at the top of the mountain, that partabove would weigh less than if measured at thesea level, hence, as we ascend or descend the pressurebecomes less or more, dependent on the altitude.

Mercury is also used to indicate temperature,but this is brought about by the expansive qualityof the mercury, and not by its weight.

Fig. 74. Aneroid Barometer.

ANEROID BAROMETER.—The term Aneroid barometeris frequently used in connection with air-ship experiments. The word aneroid means notwet, or not a fluid, like mercury, so that, whileaneroid barometers are being made which do usemercury, they are generally made without.

One such form is illustrated in Fig. 74, whichrepresents a cylindrical shell A, which has at eachend a head of concentrically formed corrugations.These heads are securely fixed to the ends of theshell A. Within, one of the disk heads has ashort stem C, which is attached to the short endof a lever D, this lever being pivoted at E. Theouter end of this lever is hinged to the short endof another lever F, and so by compounding thelevers, it will be seen that a very slight movementof the head B will cause a considerable movementin the long end of the lever F.

This end of the lever F connects with one limbof a bell-crank lever G, and its other limb has atoothed rack connection with a gear H, whichturns the shaft to which the pointer I is attached.

Air is withdrawn from the interior of the shell,so that any change in the pressure, or weight ofthe atmosphere, is at once felt by the disk heads,and the finger turns to indicate the amount ofpressure.

HYDROPLANES.—Hydro means water, hence theterm hydroplane has been given to machineswhich have suitable pontoons or boats, so theymay alight or initiate flight from water.

There is no particular form which has beenadopted to attach to aeroplanes, the object generallybeing to so make them that they will sustainthe greatest amount of weight with the leastsubmergence, and also offer the least resistancewhile the motor is drawing the machine along thesurface of the water, preparatory to launching it.

SUSTAINING WEIGHT OF PONTOONS.—A pontoonhaving within nothing but air, is merely a measuringdevice which determines the difference betweenthe weight of water and the amount placedon the pontoon. Water weighs 62 1/2 pounds percubic foot. Ordinary wood, an average of 32pounds, and steel 500 pounds.

It is, therefore, an easy matter to determinehow much of solid matter will be sustained by apontoon of a given size, or what the dimensionsof a pontoon should be to hold up an aeroplanewhich weighs, with the pilot, say, 1100 pounds.

As we must calculate for a sufficient excess toprevent the pontoons from being too much immersed,and also allow a sufficient difference inweight so that they will keep on the surface whenthe aeroplane strikes the surface in alighting, wewill take the figure of 1500 pounds to make thecalculations from.

If this figure is divided by 62 1/2 we shall findthe cubical contents of the pontoons, not considering,of course, the weight of the material of whichthey are composed. This calculation shows thatwe must have 24 cubic feet in the pontoons.

As there should be two main pontoons, and asmaller one for the rear, each of the main onesmight have ten cubic feet, and the smaller onefour cubic feet.

SHAPES OF THE PONTOONS.—We are now readyto design the shapes. Fig. 75 shows three generaltypes, A being made rectangular in form,with a tapering forward end, so constructed as toride up on the water.

The type B has a rounded under body, the forwardend being also skiff-shaped to decrease asmuch as possible the resistance of the water impact.

Fig. 75. Hydroplane Floats.

The third type C is made in the form of aclosed boat, with both ends pointed, and the bottomrounded, or provided with a keel. Or, as insome cases the body may be made triangular incross section so that as it is submerged its sustainingweight will increase at a greater degreeas it is pressed down than its vertical measurementindicates.

All this, however, is a matter left to the judgmentof the designer, and is, in a great degree,dependent on the character of the craft to whichit is to be applied.

CHAPTER XII

EXPERIMENTAL WORK IN FLYING

THE novice about to take his first trial trip inan automobile will soon learn that the great taskin his mind is to properly start the machine. Heis conscious of one thing, that it will be an easymatter to stop it by cutting off the fuel supplyand applying the brakes.

CERTAIN CONDITIONS IN FLYING.—In an aeroplaneconditions are reversed. Shutting off thefuel supply and applying the brakes only bringon the main difficulty. He must learn to stop themachine after all this is done, and this is thegreat test of flying. It is not the launching,—the ability to get into the air, but the landing, thatgives the pupil his first shock.

Man is so accustomed to the little swirls of airall about him, that he does not appreciate whatthey mean to a machine which is once free toglide along in the little currents which are so unnoticeableto him as a pedestrian.

The contour of the earth, the fences, trees, littleelevations and other natural surroundings, allhave their effect on a slight moving air current,and these inequalities affect the air and disturbit to a still greater extent as the wind increases.Even in a still air, with the sun shining, there areair eddies, caused by the uneven heating of theair in space.

HEAT IN AIR.—Heat is transmitted through theair by what is called convection, that is, the particlesof the air transmit it from one point to thenext. If a room is closed up tight, and a littleaperture provided so as to let in a streak of sunlight,it will give some idea of the unrest of theatmosphere. This may be exhibited by smokealong the line of the sun's rays, which indicatesthat the particles of air are constantly in motion,although there may be absolutely nothing in theroom to disturb it.

MOTION WHEN IN FLIGHT.—If you can imaginea small airship floating in that space, you canreadily conceive that it will be hurled hither andthither by the motion which is thus apparent tothe eye.

This motion is greatly accentuated by the surfaceof the earth, independently of its uneven contour.If a ball is thrown through the air, itsdynamic force is measured by its impact. Sowith light, and heat. In the space between theplanets it is very cold. The sunlight, or the raysfrom the sun are there, just the same as on theearth.

Unless the rays come into contact with something,they produce no effect. When the beamsfrom the sun come into contact with the atmospherea dynamic force is exerted, just the sameas when the ball struck an object. When the raysreach the earth, reflection takes place, and thesereflected beams act on the air under different conditions.

CHANGING ATMOSPHERE.—If the air is full ofmoisture, as it may be at some places, whilecomparatively dry at other points, the reflectionthroughout the moist area is much greater than inthe dry places, hence evaporation will take placeand whenever a liquid vaporizes it means heat.

On the other hand, when the vapor is turningto a liquid, condensation takes place, and thatmeans cooling. If the air should be of the samedegree of saturation throughout,—that is, havethe same amount of moisture everywhere, therewould be few winds. These remarks apply toconditions which exist over low altitudes all overthe earth.

But at high altitudes the conditions are entirelydifferent. As we ascend the air becomes rarer.It has less moisture, because a wet atmosphere,being heavier, lies nearer the surface of the earth.Being rarer the action of sunlight on the particlesis less intense. Reflection and refraction of therays acting on the light atmosphere do not producesuch a powerful effect as on the air near theground.

All these conditions—the contour of the earth;the uneven character of the moisture in the air;the inequalities of the convection currents; andthe unstable, tenuous, elastic nature of the atmosphere,make the trials of the aviator a hazardousone, and it has brought out numerous theoriesconnected with bird flight. One of these assumesthat the bird, by means of its finely organizedsense, is able to detect rising air currents, and itselects them in its flight, and by that means is enabledto continue in flight indefinitely, by soaring,or by flapping its wings.

ASCENDING CURRENTS.—It has not been explainedhow it happens that these particular "ascendingcurrents" always appear directly in the line ofthe bird flight; or why it is that when, for instance,a flock of wild geese which always fly throughspace in an A-shaped formation, are able to getascending air currents over the wide scope of spacethey cover.

ASPIRATE CURRENTS.—Some years ago, in makingexperiments with the outstretched wings ofone of the large soaring birds, a French sailorwas surprised to experience a peculiar pulling motion,when the bird's wings were held at a certainangle, so that the air actually seemed to draw itinto the teeth of the current.

It is known that if a ball is suspended by astring, and a jet of air is directed against it, ina particular way, the ball will move toward thejet, instead of being driven away from it. A wellknown spraying device, called the "ball nozzle,"is simply a ball on the end of a nozzle, and thestream of water issuing is not effectual to drivethe ball away.

From the bird incident alluded to, a new theorywas propounded, namely, that birds flew becauseof the aspirated action of the air, and the wingsand body were so made as to cause the moving aircurrent to act on it, and draw it forwardly.

OUTSTRETCHED WINGS.—This only added to the"bird wing" theory a new argument that all flyingthings must have outstretched wings, in orderto fly, forgetting that the ball, which has nooutstretched wings, has also the same "aspirate"movement attributed to the wings of the bird.

The foregoing remarks are made in order to impresson the novice that theories do not makeflying machines, and that speculations, or analogiesof what we see all about us, will not make anaviator. A flying machine is a question ofdynamics, just as surely as the action of the sun onthe air, and the movements of the currents, andthe knowledge of applying those forces in the flyingmachine makes the aviator.

THE STARTING POINT.—Before the uninitiatedshould attempt to even mount a machine he shouldknow what it is composed of, and how it is made.His investigation should take in every part of themechanism; he should understand about the planesurface, what the stresses are upon its surface,what is the duty of each strut, or brace or wireand be able to make the proper repairs.

THE VITAL PART OF THE MACHINE.—The motor,the life of the machine itself, should be like abook to him. It is not required that he shouldknow all the theories which is necessary in thebuilding, as to the many features which go tomake up a scientifically-designed motor; but hemust know how and why it works. He should understandthe cam action, whereby the valves arelifted at the proper time; what the effect of thespark advance means; the throttling of the engine;air admission and supply; the regulationof the carbureter; its mechanism and construction;the propeller should be studied, and its actionat various speeds.

STUDYING THE ACTION OF THE MACHINE.—Thencomes the study on the seat of the machine itself.It will be a novel sensation. Before him is thesteering wheel, if it should be so equipped. Turningit to the right, swings the vertical tail planeso the machine will turn to the right. Certainly,he knows that; but how far must he turn thewheel to give it a certain angle.

It is not enough to know that a lever or a wheelwhen moved a certain way will move a plane adefinite direction. He should learn to knowinstinctively, how FAR a movement to make to geta certain result in the plane itself, and under runningconditions, as well.

Suppose we have an automobile, running at therate of ten miles an hour, and the chauffeur turnsthe steering wheel ten degrees. He can do so withperfect safety; but let the machine be going fortymiles an hour, and turn the wheel ten degrees,and it may mean an accident. In one case themachine is moving 14 1/2 feet a second, and in theother instance 58 feet.

If the airship has a lever for controlling theangle of flight, he must study its arrangement,and note how far it must be moved to assumethe proper elevating angle. Then come the meansfor controlling the lateral stability of the machine.All these features should be considered and studiedover and over, until you have made them yourfriends.

While thus engaged, you are perfectly sure thatyou can remember and act on a set of complicatedmovements. You imagine that you are skimmingover the ground, and your sense tells you that youhave sufficient speed to effect a launching. Inyour mind the critical time has come.

ELEVATING THE MACHINE.—Simply give the elevatorlever the proper angle, sharp and quick andup you go. As the machine responds, and you canfeel the cushioning motion, which follows, as it beginsto ride the air, you are aware of a sensationas though the machine were about to turn overto one side; you think of the lateral control atonce, but in doing so forget that the elevator mustbe changed, or you will go too high.

You forget about the earth; you are too busythinking about several things which seem to needyour attention. Yes, there are a variety of matterswhich will crowd upon you, each of which requiretwo things; the first being to get the properlever, and the second, to move it just so far.

In the early days of aeroplaning, when accidentscame thick and fast, the most usual explanationwhich came from the pilot, when he recovered,was: "I pushed the lever too far."

Hundreds of trial machines were built, whenman learned that he could fly, and in every instance,it is safe to say, the experimenter made themost strenuous exertion to get up in the air thefirst time the machine was put on the trial ground.

It is a wonder that accidents were not recordedby the hundreds, instead of by the comparativelyfew that were heard from. It was very discouraging,no doubt, that the machines would not fly,but that all of them, if they had sufficient power,would fly, there can be no doubt.

HOW TO PRACTICE.—Absolute familiarity withevery part of the machine and conditions is thefirst thing. The machine is brought out, and theengine tested, the machine being held in leashwhile this is done. It is then throttled down sothat the power of the engine will be less than isnecessary to raise the machine from the ground.

THE FIRST STAGE.—Usually it will require over25 miles an hour to raise the machine. The engineis set in motion, and now, for the first time a newsensation takes possession of you, for the reasonthat you are cut off from communication withthose around you as absolutely as though theywere a hundred miles away.

This new dependence on yourself is, in itself,one of the best teachers you could have, becauseit begins to instill confidence and control. As themachine darts forward, going ten or fifteen milesan hour, with the din of the engine behind you,and feeling the rumbling motion of the wheelsover the uneven surface of the earth, you have thesensation of going forty miles an hour.

The newness of the first sensation, which isalways under those conditions very much augmentedin the mind, wears away as the machinegoes back and forth. There is only one controlthat requires your care, namely, to keep it on astraight course. This is easy work, but you arelearning to make your control a reflex action,—todo it without exercising a distinct will power.

PATIENCE THE MOST DIFFICULT THING.—If youhave the patience, as you should, to continue thisrunning practice, until you absolutely eliminatethe right and left control, as a matter of thought,occasionally, if the air is still turning the machine,and eventually, bringing it back, by turningit completely around, while skimming the ground,you will be ready for the second stage in thetrials.

THE SECOND STAGE.—The engine is now arrangedso that it will barely lift, when runningat its best. After the engine is at full speed, andyou are sure the machine is going fast enough,the elevator control is turned to point the machinein the air. It is a tense moment. You are on thealert.

The elevator is turned, and the forward endchanges its relation with the ground before you.There was a slight lift, but your caution inducesyou to return the planes to their normal runningangle. You try it again. You are now certainthat the machine made a leap and left the ground.This is the exhilarating moment.

With a calm air the machine is turned whilerunning, by means of the vertical rudders. Thisis an easy matter, because while going at twentymiles an hour, the weight of the machine on thesurface of the ground is less than one-tenth of itsweight when at rest.

Thus the trial spins, half the time in the air,in little glides of fifty to a hundred feet, increasingin length, give practice, practice, PRACTICE,each turn of the field making the sport less excitingand fixing the controls more perfectly in themind.

THE THIRD STAGE.—Thus far you have beenturning on the ground. You want to turn in theair. Only the tail control was required while onthe ground. Now two things are required afteryou leave the ground in trying to make a turn:namely, putting the tail at the proper angle, andtaking charge of the stabilizers, because in makingthe turn in the air, the first thing which willarrest the attention will be the tendency of themachine to turn over in the direction that you areturning.

After going back and forth in straight-awayglides, until you have perfect confidence and fullcontrol, comes the period when the turns shouldbe practiced on. These should be long, and triedonly on that portion of the field where you haveplenty of room.

OBSERVATIONS WHILE IN FLIGHT.—If there areany bad spots, or trees, or dangerous places, theyshould be spotted out, and mentally noted beforeattempting to make any flight. When in the airduring these trials you will have enough to occupyyour mind without looking out for the hazardousregions at the same time.

Make the first turns in a still air. If you shouldattempt to make the first attempts with a windblowing you will find a compound motion that willvery likely give you a surprise. In making thefirst turn you will get the sensation of trying tofly against a wind. Assuming that you are turningto the left, it will have the sensation of a windcoming to you from the right.

FLYING IN A WIND.—Suppose you are flying directlyin the face of a wind, the moment you beginto turn the action, or bite of the wind, will causethe ends of the planes to the right to be undulyelevated, much more so than if the air should becalm. This raising action will be liable to startleyou, because up to this time you have been accustomedto flying along in a straight line.

While flying around at the part of the circlewhere the wind strikes you directly on the rightside the machine has a tendency to climb, and youtry to depress the forward end, but as soon as youreach that part of the circle where the winds beginto strike on your back, an entirely new thingoccurs.

As the machine is now traveling with the wind,its grip on the air is less, and since the planes wereset to lower the machine, at the first part of theturn, the descent will be pretty rapid unless theangle is corrected.

FIRST TRIALS IN QUIET ATMOSPHERE.—All thiswould be avoided if the first trials were made ina quiet atmosphere. Furthermore, you will betold that in making a turn the machine should bepointed downwardly, as though about to make aglide. This can be done with safety, in a stillair, although you may be flying low, but it wouldbe exceedingly dangerous with a wind blowing.

MAKING TURNS.—When making a turn, under nocircumstances try to make a landing. Thisshould never be done except when flying straight,and then safety demands that the landing shouldbe made against the wind and not with it. Thereare two reasons for this: First, when flying withthe wind the speed must be greater than when flyingagainst it.

By greater speed is meant relative to the earth.If the machine has a speed of thirty miles an hour,in still air, the speed would be forty miles an hourgoing with the wind, but only twenty miles againstthe wind. Second, the banking of the planesagainst the air is more effective when going intothe wind than when traveling with it, and, therefore,the speed at which you contact with the earthis lessened to such an extent that a comparativelyeasy landing is effected.

THE FOURTH STAGE.—After sufficient time hasbeen devoted to the long turns shorter turns maybe made, and these also require the same care,and will give an opportunity to use the lateralcontrols to a greater extent. Begin the turns, notby an abrupt throw of the turning rudder, butbring it around gently, correcting the turningmovement to a straight course, if you find themachine inclined to tilt too much, until you get usedto the sensation of keeling over. Constant practiceat this will soon give confidence, and assureyou that you have full control of the machine.

THE FIGURE 8.—You are now to increase theheight of flying, and this involves also the abilityto turn in the opposite direction, so that you maybe able to experience the sensation of using thestabilizers in the opposite direction. You willfind in this practice that the senses must take inthe course of the wind from two quarters now, asyou attempt to describe the figure 8.

This is a test which is required in order to obtaina pilot's license. It means that you shallbe able to show the ability to turn in either directionwith equal facility. To keep an even flyingaltitude while describing this figure in a wind, isthe severest test that can be exacted.

THE VOLPLANE.—This is the technical term fora glide. Many accidents have been recorded owingto the stopping of the motor, which in thepast might have been avoided if the character ofthe glide had been understood. The only thingthat now troubles the pilot when the engine "goesdead," is to select a landing place.

The proper course in such a case is to urgethe machine to descend as rapidly as possible, inorder to get a headway, for the time being. Asthere is now no propelling force the glide is dependedupon to act as a substitute. The experiencedpilot will not make a straight-away glide,but like the vulture, or the condor, and birds ofthat class, soar in a circle, and thus, by passingover and over the same surfaces of the earth, enablehim to select a proper landing place.

THE LANDING.—The pilot who can make a goodlanding is generally a good flyer. It requiresnicety of judgment to come down properly. Onething which will appear novel after the first altitudeflights are attempted is the peculiar sensationof the apparently increased speed as the earthcomes close up to the machine.

At a height of one hundred feet, flying thirtymiles an hour, does not seem fast, because the surfaceof the earth is such a distance away that particularobjects remain in view for some moments;but when within ten feet of the surface the sameobject is in the eye for an instant only.

This lends a sort of terror to the novice. Heimagines a great many things, but forgets somethings which are very important to do at thistime. One is, that the front of the machine mustbe thrown up so as to bank the planes against thewind. The next is to shut off the power, whichis to be done the moment the wheels strike theground, or a little before.

Upon his judgment of the time of first touchingthe earth depends the success of safely alighting.He may bank too high, and come down on the tailwith disastrous results. If there is plenty of fieldroom it is better to come down at a less angle, oreven keep the machine at an even keel, and theelevator can then depress the tail while runningover the ground, and thus bring the machine torest.

Frequently, when about to land the machinewill rock from side to side. In such a case it isfar safer to go up into the air than to make theland, because, unless the utmost care is exercised,one of the wing tips will strike the earth andwreck the machine.

Another danger point is losing headway, as theearth is neared, due to flying at too flat an angle,or against a wind that happens to be blowing particularlyhard at the landing place. If the motoris still going this does not make so much difference,but in a volplane it means that the descentmust be so steep, at the last moment of flight, thatthe chassis is liable to be crushed by the impact.

FLYING ALTITUDE.—It is doubtful whether thedisturbed condition of the atmosphere, due tothe contour of the earth's surface, reaches higherthan 500 feet. Over a level area it is certain thatit is much less, but in some sections of the country,where the hill ranges extend for many miles,at altitudes of three and four hundred feet, theupper atmosphere may be affected for a thousandfeet above.

Prof. Lowe, in making a flight with a balloon,from Cincinnati to North Carolina, which lasteda day and all of one night, found that during theearly morning the balloon, for some reason, beganto ascend, and climbed nearly five thousandfeet in a few hours, and as unaccountablybegan to descend several hours before he landed.

Before it began to ascend, he was on the westernside of the great mountain range which extendssouth from Pennsylvania and terminates inGeorgia. He was actually climbing the mountainin a drift of air which was moving eastwardly,and at no time was he within four thousand feetof the earth during that period, which shows thatair movements are of such a character as to exerttheir influence vertically to great heights.

For cross country flying the safest altitude is1000 feet, a distance which gives ample opportunityto volplane, if necessary, and it is a heightwhich enables the pilot to make observations of thesurface so as to be able to judge of its character.

But explanations and statements, and the experiencesof pilots might be detailed in pages, andstill it would be ineffectual to teach the art of flying.The only sure course is to do the work onan actual machine.

Many of the experiences are valuable to thelearner, some are merely in the nature of cautions,and it is advisable for the beginner to learn whatthe experiences of others have been, although theymay never be called upon to duplicate them.

All agree that at great elevations the flyingconditions are entirely different from those metwith near the surface of the ground, and the historyof accidents show that in every case wherea mishap was had at high altitude it came aboutthrough defect in the machine, and not from gustsor bad air condition.

On the other hand, the uptilting of machines,the accidents due to the so-called "Holes in theair," which have dotted the historic pages withaccidents, were brought about at low altitudes.

At from two to five thousand feet the air may bemoving at speeds of from twenty to forty milesan hour,—great masses of winds, like the tradestream, which are uniform over vast areas. Tothe aviator flying in such a field, with the earthhidden from him, there would be no wind to indicatethat he was moving in any particular direction.

He would fly in that medium, in any direction,without the slightest sense that he was in a gale.It would not affect the control of the machine,because the air, though moving as a mass, wouldbe the same as flying in still air. It is only whenhe sees fixed objects that he is conscious of themovement of the wind.

CHAPTER XIII

THE PROPELLER

BY far the most difficult problem connectedwith aviation is the propeller. It is the one greatvital element in the science and art pertaining tothis subject which has not advanced in the slightestdegree since the first machine was launched.

The engine has come in for a far greater shareof expert experimental work, and has advancedmost rapidly during the past ten years. But,strange to say, the propeller is, essentially, thesame with the exception of a few small changes.

PROPELLER CHANGES.—The changes which havebeen made pertaining to the form of structure,principally, and in the use of new materials. Thekind of wood most suitable has been discovered,but the lines are the same, and nothing has beendone to fill the requirement which grows out ofthe difference in speed when a machine is in theact of launching and when it is in full flight.

PROPELLER SHAPE.—It cannot be possible thatthe present shape of the propeller will be its ultimateform. It is inconceivable that the propelleris so inefficient that only one sixty-fifth of thepower of the engine is available. The improvementin propeller efficiency is a direction whichcalls for experimental work on the part of inventorseverywhere.

The making of a propeller, although it appearsa difficult task, is not as complicated as would appear,and with the object in view of making thesubject readily understood, an explanation will begiven of the terms "Diameter," and "Pitch," asused in the art.

The Diameter has reference to the length ofthe propeller, from end to end. In calculatingpropeller pull, the diameter is that which indicatesthe speed of travel, and for this reason isa necessary element.

Thus, for instance, a propeller three feet indiameter, rotating 500 times a minute, has a tipspeed of 1500 feet, whereas a six foot propeller,rotating at the same speed, moves 3000 feet at thetips.

PITCH.—This is the term which is most confusing,and is that which causes the most frequenttrouble in the mind of the novice. The term willbe made clear by carefully examining the accompanyingillustration and the following description:

In Fig. 76 is shown a side view of a propellerA, mounted on a shaft B, which is free to movelongitudinally. Suppose we turn the shaft so thetip will move along on the line indicated by thearrow C.

Now the pitch of the blade at D is such that itwill be exactly in line with the spirally-formedcourse E, for one complete turn. As the propellershaft has now advanced, along the line E, andstopped after one turn, at F, the measure betweenthe points F and G represents the pitch of the propeller.Another way to express it would be tocall the angle of the blade a five, or six, or a sevenfoot pitch, as the pitches are measured in feet.

Fig. 76. Describing the Pitch Line.

In the illustration thus given the propeller shaft,having advanced six feet, we have what is calleda six foot pitch.

Now, to lay out such a pitch is an easy matter.Assume, as in Fig. 77, that A represents the endof the blank from which the propeller is to be cut,and that the diameter of this blank, or its lengthfrom end to end is seven feet. The problem nowis to cut the blades at such an angle that we shallhave a six foot pitch.

Fig. 77. Laying out the Pitch.

LAYING OUT THE PITCH.—First, we must get thecircumference of the propeller, that is, the distancethe tip of the propeller will travel in makingone complete turn. This is done by multiplying7 by 3.1416. This equals 21.99, or, practically, 22feet.

A line B is drawn, extending out horizontallyalong one side of the blank A, this line being madeon a scale, to represent 22 feet. Secondly, at theend of this line drawn a perpendicular line C, 6feet long. A perpendicular line is always onewhich is at right angles to a base line. In thiscase B is the base line.

Line C is made 6 feet long, because we are tryingto find the angle of a 6 foot pitch. If, now, aline D is drawn from the ends of the two lines B,C, it will represent the pitch which, marked acrossthe end of the blank A, will indicate the line to cutthe blade.

PITCH RULE.—The rule may, therefore, bestated as follows: Multiply the diameter (infeet) of the propeller by 3.1416, and draw a linethe length indicated by the product. At one endof this line draw a perpendicular line the lengthof the pitch requirement (in feet), and join theends of the two lines by a diagonal line, and thisline will represent the pitch angle.

Propellers may be made of wood or metal, theformer being preferred for the reason that thismaterial makes a lighter article, and is stronger,in some respects, than any metal yet suggested.

LAMINATED CONSTRUCTION.—All propellersshould be laminated,—that is, built up of layersof wood, glued together and thoroughly dried,from which the propeller is cut.

A product thus made is much more serviceablethan if made of one piece, even though the laminatedparts are of the same wood, because thedifferent strips used will have their fibers overlappingeach other, and thus greatly augment thestrength of the whole.

Generally the alternate strips are of differentmaterials, black walnut, mahogany, birch, spruce,and maple being the most largely used, but mahoganyand birch seem to be mostly favored.

LAYING UP A PROPELLER FORM.—The first stepnecessary is to prepare thin strips, each, say,seven feet long, and five inches wide, and three-eighths of an inch thick. If seven such pieces areput together, as in Fig. 78, it will make an assemblageof two and five-eighth inches high.

Fig. 78. A Laminated Blank.

Bore a hole centrally through the assemblage,and place therein a pin B. The contact faces ofthese strips should be previously well paintedover with hot glue liberally applied. When theyare then placed in position and the pin is in place,the ends of the separate pieces are offset, one beyondthe other, a half inch, as shown, for instance,in Fig. 79.

This will provide ends which are eight and ahalf inches broad, and thus furnish sufficientmaterial for the blades. The mass is then subjectedto heavy pressure, and allowed to dry before theblades are pared down.

Fig. 79. Arranging the Strips.

MAKING WIDE BLADES.—If a wider blade is desired,a greater number of steps may be made byadding the requisite number of strips; or, thestrips may be made thicker. In many propellers,not to exceed four different strips are thus gluedtogether. The number is optional with themaker.

An end view of such an assemblage of stripsis illustrated in Fig. 80. The next step is to layoff the pitch, the method of obtaining which hasbeen explained.

Fig. 80. End view of Blank.

Before starting work the sides, as well as theends, should be marked, and care observed toplace a distinctive mark on the front side of thepropeller.

Around the pin B, Fig. 81, make S-shapedmarks C, to indicate where the cuts on the facesof the blades are to begin. Then on the ends ofthe block; scribe the pitch angle, which is indicatedby the diagonal line D, Fig. 80.

Fig. 81. Marking the Side.

This line is on the rear side of the propeller,and is perfectly straight. Along the front of thisline is a bowline E, which indicates the front surfaceof the propeller blade.

PROPELLER OUTLINE.—While the marks thusgiven show the angles, and are designed to indicatethe two faces of the blades, there is still anotherimportant element to be considered, andthat is the final outline of the blades.

Fig. 82. Outlining.

It is obvious that the outline may be variedso that the entire width at 1, Fig. 82, may be used,or it may have an outline, as represented by theline 2, in this figure, so that the widest part willbe at or near the dotted line 3, say two-thirds ofthe distance from the center of the blade.

This is the practice with most of the manufacturersat the present time, and some of themclaim that this form produces the best results.

FOR HIGHER SPEEDS.—Fig. 83 shows a propellercut from a blank, 4" x 6" in cross section, notlaminated.

Fig. 83. Cut from a 4" x 6" Single Blank.

It should be borne in mind that for high speedsthe blades must be narrow. A propeller sevenfeet in diameter with a six foot pitch, turning950 revolutions per minute, will produce a pull of350 pounds, if properly made.

Such a propeller can be readily handled by aforty horse power motor, such as are speciallyconstructed for flying machine purposes.

INCREASING PROPELLER EFFICIENCY.—Some experimentshave been made lately, which, it isclaimed, largely increase the efficiency of propellers.The improvement is directed to the outlineshape of the blade.

The typical propeller, such as we have illustrated,is one with the wide part of the blade atthe extremity. The new type, as suggested, reversesthis, and makes the wide part of the bladenear the hub, so that it gradually tapers down toa narrow tip.

Such a form of construction is shown in Fig.84. This outline has some advantages from onestandpoint, namely, that it utilizes that part ofthe blade near the hub, to produce a pull, anddoes not relegate all the duty to the extreme endsor tips.

Fig. 84. A Suggested Form.

To understand this more fully, let us take apropeller six feet in diameter, and measure thepull or thrust at the tips, and also at a point halfway between the tip and the hub.

In such a propeller, if the blade is the samewidth and pitch at the two points named, the pullat the tips will be four times greater than at theintermediate point.

CHAPTER XIV

EXPERIMENTAL GLIDERS AND MODEL AEROPLANES

AN amusing and very instructive pastime isafforded by constructing and flying gliding machines,and operating model aeroplanes, the latterbeing equipped with their own power.

Abroad this work has been very successful asa means of interesting boys, and, indeed, menwho have taken up the science of aviation aregiving this sport serious thought and study.

When a machine of small dimensions is madethe boy wonders why a large machine does notbear the same relation in weight as a small machine.This is one of the first lessons to learn.

THE RELATION OF MODELS TO FLYING MACHINES.—A model aeroplane, say two feet in length, whichhas, we will assume, 50 square inches of supportingsurface, seems to be a very rigid structure,in proportion to its weight. It may be droppedfrom a considerable height without injuring it,since the weight is only between two and threeounces.

An aeroplane twenty times the length of thismodel, however strongly it may be made, ifdropped the same distance, would be crushed, andprobably broken into fragments.

If the large machine is twenty times the dimensionsof the small one, it would be forty feet inlength, and, proportionally, would have onlyseven square feet of sustaining surface. But anoperative machine of that size, to be at all rigid,would require more than twenty times the materialin weight to be equal in strength.

It would weigh about 800 pounds, that is, 4800times the weight of the model, and instead ofhaving twenty times the plane surface would requireone thousand times the spread.

It is this peculiarity between models and theactual flyers that for years made the question offlying a problem which, on the basis of pure calculationalone, seemed to offer a negative; andmany scientific men declared that practical flyingwas an impossibility.

LESSONS FROM MODELS.—Men, and boys, too,can learn a useful lesson from the model aeroplanesin other directions, however, and the principalthing is the one of stability.

When everything is considered the form orshape of a flying model will serve to make a largeflyer. The manner of balancing one will be agood criterion for the other in practice, andexperimenting with these small devices is, therefore,most instructive.

The difference between gliders and model aeroplanesis, that gliders must be made much lighterbecause they are designed to be projected throughthe air by a kick of some kind.

FLYING MODEL AEROPLANES.—Model aeroplanescontain their own power and propellers which,while they may run for a few seconds only, servethe purpose of indicating how the propeller willact, and in what respect the sustaining surfacesare efficient and properly arranged.

It is not our purpose to give a treatise on thissubject but to confine this chapter to an expositionof a few of the gliders and model forms whichare found to be most efficient for experimentalwork.

AN EFFICIENT GLIDER.—Probably the simplestand most efficient glider, and one which can bemade in a few moments, is to make a copy of thedeltoid kite, previously referred to.

This is merely a triangularly-shaped piece ofpaper, or stiff cardboard A, Fig. 84, creased inthe middle, along the dotted line B, the side wingsC, C, being bent up so as to form, what are calleddiedral angles. This may be shot through theair by a flick of the finger, with the pointed endforemost, when used as a glider.

Fig. 85. Deltoid Glider.

THE DELTOID FORMATION.—This same form maybe advantageously used as a model aeroplane, butin that case the broad end should be foremost.

Fig. 86. The Deltoid Racer.

Fig. 86 shows the deltoid glider, or aeroplane,with three cross braces, A, B, C, in the two forwardbraces of which are journaled the propellershaft D, so that the propeller E is at the broadend of the glider.

A short stem F through the rear brace C, providedwith a crank, has its inner end connectedwith the rear end of the shaft D by a rubber bandG, by which the propeller is driven.

A tail may be attached to the rear end, or atthe apex of the planes, so it can be set for thepurpose of directing the angle of flight, but it willbe found that this form has remarkable stabilityin flight, and will move forwardly in a straightline, always making a graceful downward movementwhen the power is exhausted.

It seems to be a form which has equal stabilizingpowers whether at slow or at high speeds,thus differing essentially from many forms whichrequire a certain speed in order to get the bestresults.

RACING MODELS.—Here and in England manyracing models have been made, generally of theA-shaped type, which will be explained hereinafter.Such models are also strong, and able towithstand the torsional strain required by therubber which is used for exerting the power.

It is unfortunate that there is not some type ofcheap motor which is light, and adapted to runfor several minutes, which would be of great valuein work of this kind, but in the absence of suchmechanism rubber bands are found to be mostserviceable, giving better results than springs orbows, since the latter are both too heavy to beavailable, in proportion to the amount of powerdeveloped.

Unlike the large aeroplanes, the supportingsurfaces, in the models, are at the rear end ofthe frames, the pointed ends being in front.

Fig. 87. A-Shaped Racing Glider.

Fig. 87 shows the general design of the A-shaped gliding plane or aeroplane. This is composedof main frame pieces A, A, running foreand aft, joined at their rear ends by a cross barB, the ends of which project out slightly beyondtheir juncture with the side bars A, A. Theseprojecting ends have holes drilled therein to receivethe shafts a, a, of the propeller D, D.

A main plane E is mounted transversely acrossthis frame at its rear end, while at its forwardend is a small plane, called the elevator. Thepointed end of the frame has on each side a turnbuckleG, for the purpose of winding up the shaft,and thus twisting the propeller, although this isusually dispensed with, and the propeller itselfis turned to give sufficient twist to the rubber forthis purpose.

THE POWER FOR MODEL AEROPLANES.—One end
of the rubber is attached to the hook of the shaft
C, and the other end to the hook or to the turnbuckle
G, if it should be so equipped.

The rubbers are twisted in opposite directions,to correspond with the twist of the propellerblades, and when the propellers are permitted toturn, their grip on the air will cause the model toshoot forwardly, until the rubbers are untwisted,when the machine will gradually glide to theground.

MAKING THE PROPELLER.—These should havethe pitch uniform on both ends, and a simplelittle device can be made to hold the twisted bladeafter it has been steamed and bent. Birch andholly are good woods for the blades. The stripsshould be made thin and then boiled, or, what isbetter still, should be placed in a deep pan, andheld on a grid above the water, so they will bethoroughly steamed.

They are then taken out and bent by hand, orsecured between a form specially prepared forthe purpose. The device shown in Fig. 88 showsa base board which has in the center a pair ofparallel pins A, A, slightly separated from eachother.

Fig. 88. Making the Propeller.

At each end of the base board is a pair of holesC, D, drilled in at an angle, the angles being thepitch desired for the ends of the propeller. Inone of these holes a pin E is placed, so the pinsat the opposite ends project in different directions,and the tips of the propeller are heldagainst the ends of these pins, while the middleof the propeller is held between the parallel pinsA, A.

The two holes, at the two angles at the ends ofthe board, are for the purpose of making rightand left hand propellers, as it is desirable to usetwo propellers with the A-shaped model. Twopropellers with the deltoid model are not so necessary.

After the twist is made and the blade properlysecured in position it should be allowed to thoroughlydry, and afterwards, if it is coated withshellac, will not untwist, as it is the changingcharacter of the atmosphere which usually causesthe twisted strips to change their positions.Shellac prevents the moist atmosphere from affectingthem.

MATERIAL FOR PROPELLERS.—Very light propellerscan also be made of thin, annealed aluminumsheets, and the pins in that case will serve asguides to enable you to get the desired pitch.Fiber board may also be used, but this is moredifficult to handle.

Another good material is celluloid sheets,which, when cut into proper strips, is dipped inhot water, for bending purposes, and it readilyretains its shape when cooled.

RUBBER—Suitable rubber for the strips arereadily obtainable in the market. Experimentwill soon show what size and lengths are bestadapted for the particular type of propellerswhich you succeed in making.

PROPELLER SHAPE AND SIZE.—A good proportionof propeller is shown in Fig. 89. This alsoshows the form and manner of connecting theshaft. The latter A has a hook B on one end towhich the rubber may be attached, and its otherend is flattened, as at C, and secured to the bladeby two-pointed brads D, clinched on the otherside.

Fig. 89. Shape and Size.

The collar E is soldered on the shaft, and inpractice the shaft is placed through the bearinghole at the end of the frame before the hook isbent.

SUPPORTING SURFACES.—The supporting surfacesmay be made perfectly flat, although in thisparticular it would be well to observe the ruleswith respect to the camber of large machines.

CHAPTER XV

THE AEROPLANE IN THE GREAT WAR

DURING the civil war the Federal forces usedcaptive balloons for the purpose of discoveringthe positions of the enemy. They were of greatservice at that time, although they were stationedfar within the lines to prevent hostile guns fromreaching them.

BALLOON OBSERVATIONS.—Necessarily, observationsfrom balloons were and are imperfect. Itwas found to be very unsatisfactory during theRussian-Japanese war, because the angle of visionis very low, and, furthermore, at such distances themovements, or even the location of troops is notobservable, except under the most favorable conditions.

Balloon observation during the progress of abattle is absolutely useless, because the smokefrom the firing line is, necessarily, between theballoon and the enemy, so that the aerial scouthas no opportunity to make any observations, evenin detached portions of the fighting zone, whichare of any value to the commanders.

CHANGED CONDITIONS OF WARFARE.—Since ourgreat war, conditions pertaining to guns have beenrevolutionized. Now the ranges are so great thatcaptive balloons would have to be located far inthe rear, and at such a great distance from thefiring line that even the best field glasses wouldbe useless.

The science of war has also evolved anothercondition. Soldiers are no longer exposed duringartillery attacks. Uniforms are made to imitatenatural objects. The khaki suits were designedto imitate the yellow veldts of South Africa;the gray-green garments of the Germanforces are designed to simulate the green fieldsof the north.

THE EFFORT TO CONCEAL COMBATANTS.—TheFrench have discarded the historic red trousers,and the elimination of lace, white gloves, andother telltale insignias of the officers, have beendispensed with by special orders.

In the great European war armies have burrowedin the earth along battle lines hundreds ofmiles in length; made covered trenches; preparedartificial groves to conceal batteries, and in manyingenious ways endeavored to make the battlefieldan imitation field of nature.

SMOKELESS POWDER.—While smokeless powderhas been utilized to still further hide a fightingforce, it has, in a measure, uncovered itself, asthe battlefield is not now, as in olden times, overspreadwith masses of rolling smoke.

Nevertheless, over every battlefield there is ahaze which can be penetrated only from above,hence the possibilities of utilizing the aeroplanein war became the most important study with allnations, as soon as flying became an accomplishedfact.

INVENTIONS TO ATTACK AERIAL CRAFT.—Beforeany nation had the opportunity to make an actualtest on the battlefield, inventors were at work todevise a means whereby an aerial foe could bemet. In a measure the aerial gun has been successful,but months of war has shown that theaeroplane is one of the strongest arms of theservice in actual warfare.

It was assumed prior to the European war thatthe chief function of the aeroplane would be thedropping of bombs,—that is for service in attackinga foe. Actual practice has not justifiedthis theory. In some places the appearance ofthe aeroplane has caused terror, but it has beenfound the great value is its scouting advantages.

FUNCTION OF THE AEROPLANE IN WAR.—Whilebomb throwing may in the future be perfected,it is not at all an easy problem for an aviator todo work which is commensurate with the riskinvolved. The range is generally too great; thenecessity of swift movement in the machine toospeedy to assure accuracy, and to attack a foe athaphazard points can never be effectual. Eventhe slowly-moving gas fields, like the Zeppelin,cannot deliver bombs with any degree of precisionor accuracy.

BOMB-THROWING TESTS.—It is interesting, however,to understand how an aviator knows whereor when to drop the bomb from a swiftly-movingmachine. Several things must be taken into consideration,such as the height of the machine fromthe earth; its speed, and the parabolic curve thatthe bomb will take on its flight to the earth.

When an object is released from a moving machineit will follow the machine from which it isdropped, gradually receding from it, as it descends,so that the machine is actually beyondthe place where the bomb strikes the earth, dueto the retarding motion of the atmosphere againstthe missile.

The diagram Fig. 90 will aid the boy in graspingthe situation. A is the airship; B the pathof its flight; a the course of the bomb after itleaves the airship; and D the earth. The questionis how to determine the proper movementwhen to release the bomb.

METHOD FOR DETERMINING MOVEMENT OF ABOMB.—Lieut. Scott, U. S. A., of the Coast SurveyArtillery, suggested a method for determiningthese questions. It was necessary to ascertain,first, the altitude and speed. While the barometeris used to determine altitudes, it isobvious that speed is a matter much more difficultto ascertain, owing to the wind movements,which in all cases make it difficult for a flier todetermine, even with instruments which havebeen devised for the purpose.

Fig. 90. Course of a Bomb.

Instead, therefore, of relying on the barometer,the ship is equipped with a telescope which maybe instantly set at an angle of 45 degrees, or vertically.

Thus, Fig 91 shows a ship A, on which ismounted a telescope B, at an angle of 45 degrees.The observer first notes the object along the lineof 45 degrees, and starts the time of this observationby a stop watch.

The telescope is then turned so it is vertical,as at C, and the observer watches through thetelescope until the machine passes directly overthe object, when the watch is stopped, to indicatethe time between the two observations.

Fig. 91. Determining Altitude and Speed.

The height of the machine along the line D isthus equal to the line E from B to C, and the timeof the flight from B to a being thus known, aswell as the height of the machine, the observerconsults specially-prepared tables which showjust what kind of a curve the bomb will make atthat height and speed.

All that is necessary now is to set the sighterof the telescope at the angle given in the tables,and when the object to be hit appears at the sight,the bomb is dropped.

THE GREAT EXTENT OF MODERN BATTLE LINES.—The great war brought into the field such stupendousmasses of men that the battle lines haveextended over an unbroken front of over 200miles.

In the battle of Waterloo, about 140,000 menwere engaged on both sides, and the battle frontwas less than six miles. There were, thus massed,along the front, over 20,000 men every mile ofthe way, or 10,000 on each side.

In the conflict between the Allies and the Germansit is estimated that there were less than7500 along each mile. It was predicted in theearlier stages of the war that it would be an easymatter for either side to suddenly mass such anoverwhelming force at one point as to enable theattacking party to go through the opposing forcelike a wedge.

Such tactics were often employed by Napoleonand other great masters of war; but in every effortwhere it has been attempted in the presentconflict, it was foiled.

The opposing force was ready to meet the attackwith equal or superior numbers. The eyeof the army, the aeroplane, detected the movementsin every instance.

THE AEROPLANE DETECTING THE MOVEMENTS OFARMIES.—In the early stages of the war, whenthe Germans drove the left of the French armytowards Paris, the world expected an investmentof that city. Suddenly, and for no apparentreason, the German right was forced back andcommenced to retreat.

It was not known until weeks afterwards thatthe French had assembled a large army to thewest and northwest of Paris, ready to take theGermans in flank the moment an attempt shouldbe made to encircle the Paris forts.

The German aviators, flying over Paris, discoveredthe hidden army, and it is well they didso, for it is certain if they had surrounded theoutlying forts, it would have been an easy matterfor the concealed forces to destroy their communications,and probably have forced the surrenderof a large part of the besiegers.

The aeroplane in warfare, therefore, has constantlynoted every disposition of troops, locatedthe positions and judged the destination of convoys;the battery emplacements; and the directionin which large forces have been moved fromone part of the line to the other, thus keeping thecommanders so well informed that few surpriseswere possible.

THE EFFECTIVE HEIGHT FOR SCOUTING.—It hasbeen shown that aeroplane scouting is not effectiveat high altitudes. It is not difficult for aviatorsto reach and maintain altitudes of five thousandfeet and over, but at that elevation it is impossibleto distinguish anything but the movementof large forces.

SIZES OF OBJECTS AT GREAT DISTANCES.—At adistance of one mile an automobile, twenty feetin length, is about as large as a piece of pencilone inch long, viewed at a distance of thirty-fivefeet. A company of one hundred men, which inmarching order, say four abreast, occupies a spaceof eight by one hundred feet, looks to the aviatorabout as large as an object one inch in length, fourand a half feet from the eye.

The march of such a body of men, viewed atthat distance, is so small as almost to be imperceptibleto the eye of an observer at rest. Howmuch more difficult it is to distinguish a movementif the observer is in a rapidly-moving machine.

For these reasons observations must be madeat altitudes of less than a mile, and the hazardof these enterprises is, therefore, very great,since the successful scout must bring himselfwithin range of specially designed guns, whichare effective at a range of 3000 yards or more,knowing that his only hope of safety lies in thechance that the rapidly-moving machine will avoidthe rain of bullets that try to seek him out.

SOME DARING FEATS IN WAR.—It would be impossibleto recount the many remarkable aerialfights which have taken place in the great war.Some of them seem to be unreal, so startling arethe tales that have been told. We may well imaginethe bravery that will nerve men to fightthousands of feet above the earth.

One of the most thrilling combats took placebetween a Russian aeroplane and a Zeppelin, overRussian Poland, at the time of the first Germaninvasion. The Zeppelin was soaring over theRussian position, at an altitude of about a mile.A Russian aviator ascended and after circlingabout, so as to gain a position higher than theairship, darted down, and crashed into the greatgas field.

The aviator knew that it meant death to him,but his devotion led him to make the sacrifice.The Zeppelin, broken in two, and robbed of itsgas, slowly moved toward the earth, then graduallyincreased the speed of its descent, as theaeroplane clung to its shattered hulk, and by thetime it neared the earth its velocity was greatenough to assure the destruction of all on board,while the ship itself was crushed to atoms.

One of the most spectacular fights of the waroccurred outside Paris, when one of the GermanTaubes attempted to make its periodical tourof observation. One of the French aeroplanes,which had the advantage of greater speed,mounted to a greater altitude, and circled aboutthe Taube.

The latter with its machine gun made a furiousattack, during these maneuvers, but the Frenchship did not reply until it was at such an elevationthat it could deliver the attack from above.Then its machine gun was brought into play. Aswas afterwards discovered, the wings and bodyof the Taube were completely riddled, and it wasa marvel how it was possible for the German aviatorto remain afloat as long as he did.

Soon the Taube was noticed to lurch from sideto side, and then dart downwardly. The monoplane,in the pursuit, gradually descended, but itwas not able to follow the destroyed Taube to theearth, as the latter finally turned over, and wentswirling to destruction.

The observer, as well as the aviator, had bothbeen killed by the fire from the monoplane.

In the trenches on the Marne, to the northeastof Paris, where the most stubborn conflict ragedfor over a week, the air was never clear of aeroplanes.They could be seen in all directions, andalmost all types of machines were represented.The principal ones, however, were monoplanes.

THE GERMAN TAUBE.—The German Taube is amonoplane, its main supporting surfaces, as wellas the tail planes, are so constructed that theyrepresent a bird. Taube means dove. It wouldhave been more appropriate to call it a hawk.

On the other hand, the French monoplane, ofwhich the Bleriot is the best known example, haswings with well rounded extremities, and flaringtail, so that the two can be readily distinguished.

On one occasion, during the lull in the battle,two of the Taubes approached the area above theFrench lines, and after ascending to a greatheight, began the volplane toward their own lines.Such a maneuver was found to be the most advantageous,as it gave the scouting aeroplane theadvantage of being able to discover the positionsand movements with greater ease, and at the sametime, in case of accident to the machine, the impetusof the flight would be to their own lines.

Three of the French aeroplanes at once begantheir circling flight, mounting higher and higher,but without attempting to go near the Taubes.When the French ships had gained the properaltitude, they closed in toward the German ships,before the latter could reach their own lines intheir volplaning act.

This meant that they must retreat or fight, andthe crack of the guns showed that it meant astruggle. The monoplanes circled about withincredible skill, pouring forth shot after shot.Soon one of the Taubes was seen to flutter.This was the signal for a more concentrated attackon her.

The army in the trenches, and on the fields below,witnessed the novel combat. The flyingships were now approaching the earth, but thegunners below dared not use their guns, becausein the maneuvers they would be as likely to strikefriend as foe.

The wounded Taube was now shooting to theearth, and the two monoplanes began to give theirattention to the other ship, which was attemptingto escape to the north. The flash of the guns ofall the fliers could be plainly seen, but the soundswere drowned by the roar of the great conflict allabout them.

The Taube could not escape the net around her.She, too, was doomed. A shot seemed to strikethe gasoline tank, and the framework was soonenveloped in flames. Then she turned sidewise,as the material on one side burned away, andskidding to the left she darted to the earth,a shapeless mass.

It was found that the aviator was not hurt bythe shot, but was, undoubtedly, killed by the impactwith the earth. The observer was riddledwith bullets, and was likely dead before the shipreached the earth.

In the western confines of Belgium, near Ypres,the British employed numerous aircraft, many ofthem biplanes, and at all times they were in theair, reporting observations. Many of the flyingfights have been recorded, and the reports whenpublished will be most thrilling reading.

HOW AEROPLANES REPORT OBSERVATIONS.—Itmay be of some interest to know how aeroplanesare able to report observations to the commandersin the field, from the airship itself. Manyingenious devices have been devised for this purpose.

SIGNAL FLAGS.—The best known and most universallyused method is by the use of signalingflags. Suppose the commander of a force is desirousof getting the range of a hidden battery,or a massed force in his front. The observer inthe aeroplane will sail over the area at an understoodaltitude, say one mile in height.

The officer in charge of the battery, knowingthe height of the airship, is able, by means ofthe angle thus given him, to get the distance betweenhis battery and the concealed point beneaththe airship. The observer in the airship, ofcourse, signals the engineer officer, the exact pointor time when the airship is directly above, andthis gives him the correct angle.

The guns of the battery are then directed andfired so as to reach the concealed point. It isnow important to be able to send intelligible signalsto the officer in charge of the battery. If theshot goes beyond the mark, the observer in theairship raises the flag above his head, which indicatesthat it was too high.

HOW USED.—If the shot fell short he wouldlower the flag. If the shot landed too far to theright, this would be indicated by the flag, and iftoo far to the left, the signal would, in like manner,be sufficient to enable the gunners to correctthe guns.

When the exact range is obtained the observerin the ship waves the flag about his head, intoken of approval. All this work of noting theeffect of the shots must be taken while the airshipis under fire, and while circling about withinvisual range of the concealed object below.

The officer in charge of the battery, as well asthe observer on the flying craft, must be equippedwith powerful glasses, so the effect of the shotsmay be noted on the one hand, and the signalsproperly read by the officer on the other hand.

It may be said, however, that air battles havenot been frequent and that they have been merelyincidents of the conditions under which they wereoperated. The mission of the aeroplane is nowconceded to be purely one of observation, such aswe have described.

Both French and German reports are full ofincidents showing the value of observations, andalso concerning the effects of bombs. Extractsfrom the diaries of prisoners gave many interestingfeatures of the results of aeroplane work.

CASUALTIES DUE TO AEROPLANES.—In the diaryof one was found the remark: "I was lucky toescape the bomb thrown by a French aviator atConrobet, which killed eight of my companions."

Another says: "The Seventh Company of theThird Regiment of the Guard had eight killed andtwenty-two wounded by bomb from a French aeroplane."

Another: "An officer showed us a torn coattaken from one of sixty soldiers wounded by abomb from an aeroplane."

A prisoner says: "Near Neuville an aeroplanebomb dropped on a supply train, killed four men,wounded six, and killed a considerable number ofhorses."

The Belgians, after their defeat and the captureof Antwerp, were forced to the west alongthe coast. In some way they learned that theKaiser was about to occupy a chateau near Dixmunde.Several aviators flew above the positionand dropped a number of bombs on the building,completely wrecking it, and it was fortunate thatthe Emperor left the building only twenty minutesbefore, as several of his aides and soldierson duty were killed.

On numerous occasions the headquarters of thedifferent commanders have been discovered andhad to be moved to safer places.

During all these wonderful exploits which willlive in history because men had the opportunityduring the war to use them for the first time inactual conflict, the official reports have notmentioned the aviators by name. The deaths of thebrave men have brought forth the acknowledgmentsof their services. During the first threemonths of the war it is estimated that over sixtyaviators and aides had lost their lives in the conflicton the two great battle lines. This does nottake into account those who met death on theZeppelins, of which five had been destroyed duringthat time.

THE END

GLOSSARY OF WORDS USED IN TEXT OF THIS VOLUME

Where a word has various meanings, that definition is givenwhich will express the terms used by the author in explainingthe mechanism or subject to which it refers.

Aviation. The art of flying.

Altitude. Height; a vertical distance above any point.

Attraction. The art or process of drawing towards.

Allusion. Referring to a certain thing.

Assume. Taking it for granted.

Accentuated. To lay great stress upon a thing.

Angle of Movement. Any direction which is upwardly or downwardly,as distinguished from the direction of movement which is eitherto the right or to the left.

Acquire. To obtain; to recover; to procure.

Analogous. Corresponding to or resembling some other thing orobject.

Air Hole. A term used to express a condition in flying where themachine while in horizontal flight takes a sudden drop, due tocounter currents.

Ailerons. Literally, small planes. Used to designate the smallplanes which are designed to stabilize a machine.

Angle. A figure, or two straight lines which start at the samepoint. The sides of these lines are termed the angle.

Analysis. To separate; to take apart and examine the variousparts or elements of a thing.

Aeroplane. Any form of machine which has planes, and is heavierthan air. Usually a flying structure which is propelled by somemotive power.

Accumulation. Adding to; bringing together the same or unlikearticles.

Ascribable. A reference to some antecedent source.

Aeronautics. The science of flying.

Anterior. Meaning the front or forward margin or portion of abody.

Artifices. Any artificial product, or workmanship.

Axially. Through the central portion. Thus, the shaft which goesthrough a cylinder is axially arranged.

Automatic. A thing which operates by its own mechanism; acontrivance which is made in such a manner that it will runwithout manual operation or care.

Alertness. Quick; being active.

Apex. The point at which two lines meet; also the extreme pointedend of a conical figure.

Ascension. Moving upwardly.

Accessories. The parts of a machine, or artielee which may haused in connection therewith.

Anemometer. An instrument for measuring the force or the velocityof wind.

Anemograph. An instrument that usually traces a curved line OHpaper to make a record of the force or direction, or velocity ofthe wind.

Anemometrograph. A device which determines the force, velocityand direction of the wind.

Accretion. Adding to little by little.

Accelerated. Quiekening; hurrying the process.

Abridged. Partly taken away from; shortened.

Abrogate. To dispense with; to set aside.

Abnormal Not in the usual manner; not in a regular way.

Alternate. First one and then another; going from one side to theother.

Ancient Lights. An old English law which prevents a neighbor fromshutting off sunlight.

Angularly. A line which runs out from another so that the two arenot parallel.

Aneroid. Not wet. Applied to the type of barometer where themedium for determ,ining the pressure is not made of mercury.

Aspirate. A term given by the French to that peculiar action ofwing, or other body, which, when placed in certain positions,relative to a current of air, will cause it to be drawn into thecurrent.

Assemblage. The bringing together of the parts or elements of amachine.

Augment. To aid; to add to or increase.

Banked. The term used in aviation which indicates that themachine is turned up so that its supporting surfacesrest against the air, as in alighting.

Barometer. An instrument for determining the air pressure, andthereby indicating altitudes.

Bevel Pinion. A toothed wheel driven by a larger wheel.

Bi-Plane. Two planes. In aviation that type which has two planes,similar in size, usually, and generally placed one above theother so they are separated the same distance from each other, asthe width of each of the planes.

Bulge. A hump; an enlargement beyond the normal at any point.

Camber, also Cambre. The upward curve in a plane.

Catapult. A piece of mechanism for projecting or throwing amissile.

Carbureter. The device which breaks up the fuel oil, and mixesthe proper quantity of air with it before it is drawn into theengine.

Catastrophe. A calamity; a sad ending; loss of life or ofproperty.

Cellular. Made up of small hollows, or compartments; filled withholes.

Celestial. Pertaining to the heavens.

Centrifugal. That force which throws outwardly from a rotatingbody.

Centripetal. That force, like the attraction of gravity, whichdraws a body to the center.

Characteristic. Striking; that which is peculiar to some thing orobject.

Commensurate. Sufficient; in proper proportion; sufficient forthe occasion.

Commercially. Pertaining to the nature of trade; the making ofmoney.

Complicated. Not easily explainable; not easy to separate.

Comparatively. Judged by something else; taken with reference toanother object or thing.

Compression. The drawing together; forcing into a smallercompass, or space.

Composition. Made up of different elements, or things.

Conceivable. Made up from the imagination.

Concaved. Hollowed: In aviation it has reference to the undersideof the plane, which is usually provided, structurally, with ahollow or trough formation.

Conforming. To make alike in form; to bring into harmony.

Conjunction. In eonneetion with; joining together.

Convex. A rounded surface; a bulging out.

Conclusion. The end; a finding in law; a reasoning from a certaincondition.

Conductivity. The property of materials whereby they willtransmit heat along from one part to another, also electricity.

Concentrated. Brought together; assembled in a smaller space.

Conclusive. A positive ending; decisive of the matter at issue.

Concentrically. A line which is at all points at the samedistance from one point.

Condensation. The act or process of making denser, or beingbrought together.

Contemplate. To consider; to judge.

Convoys. A protecting force which aeeompanies the transfer ofproperty.

Convection. The diffusion of heat through a liquid or gas.

Consistent. A state of harmony; the same at &11 times.

Constant. In mathematics, a figure which never changes; or afigure used as a fixed valuation in a problem.

Controllable. Held within bounds; that which can be within thepower to accomplish.

Correctional. The means whereby a fault may be made right.

Consequence. The result; that which flows from a precedingaction.

Counterforce. An action contrary or opposite to the main force.

Counter-balance. Any power equally opposing another.

Counteract. A force acting in opposition to another.

Countercurrent. An air current which sets up in an oppositedirection in the path of a moving aeroplane.

Cushioned. An action which takes place against a movingaeroplane, by a sudden gust of air or countercurrent.

Dedicated. To set apart for some special purpose.

Degree. An interval; a grade; a stage; a certain proportion.

Deltoid. Shaped like the Greek letter delta.

Density. Closeness of parts.

Demonstration. Making clear; showing up; an exhibition orexpression.

Deceptive. The power or tendency to give a false impression.

Deterrent. To hold back; to prevent action.

Detracting. The tendency to take away; to belittle.

Depressed. To move downwardly.

Destination. The place set for the end of the journey.

Despoiling. To take away from; robbing or taking from another by force or by stealth.

Dependant. Hanging below; projecting from the lower side.

Dexterity. Agility; smartness in action.

Deranged. Put out of order; wrongly arranged.

Develop. Brought out; to put into a correct shape or form.

Deferred. Put over to another time.

Designedly. With a direct purpose.

Diagonal. Across an object at an angle to one or more aides.

Diametrically. Across an object through or near the centerthereof.

Diagram. A mechanical plan or outline of an object.

Dimension. The distance across an object. The measurement, forinstance, of a propeller from tip to tip.

Dynamically. Pertaining to motion as a result of force.

Dispossessed. A term used to indicate the act which removes aperson from the possession of property.

Diameter. The measurement across an object.

Divest. Taken away from; removed out of.

Disregard. Deliberate lack of attention.

Diversity. The state wherein one is unlike another;dissimilarity.

Drift. The term used to indicate the horizontal motion, or thepull of an aeroplane.

Dragon. A fabulous monster, usually in the form of a serpent.

Duplicate. Two; made in exact imitation of an original.

Easement. A legal phrase to designate that right which manpossesses, irrespective of any law, to gain access to hisproperty.

Effrontery. Boldness with insolence; rashness without propriety.

Effective. To be efficient.

Element. One part of a whole.

Elasticity. Material which will go back to its original formafter being distorted, is said to be elastic.

Eliminate. To take away from; to remove a part, or the whole.

Elliptical. Oblong with rounded ends.

Elusive. Capable of escaping from; hard to hold.

Elevator. The horizontal planes in front or rear, or in bothfront and rear of the supporting surfaces of an aeroplane.

Emergency. A sudden occurrence calling for immediate action.

Emplacement. A spot designed to hold heavy field pieces inintrenchments.

Enactment. The formulation of a law; the doing of a specialthing.

Enunciated. Announced; setting forth of an act or a condition.

Energy. That quality by reason of which anything tends to move oract.

Equidistant. Two points or objects at equal distance from acommon point.

Equilibrinm. A balance produced by the action of two or moreforces.

Equalizing, One made equal to the other; one side the same as theother.

Equipped. Armed; provided with the proper material, or in thesame condition.

Essential. The important part or element.

Essence The real charaeter or element of the thing itself.

External. The outermost portion.

Evolution. A gradual change or building up; from a lower to ahigher order.

Evolved. Brought out from a crude condition to a better form.

Expression. The art of explaining or setting forth.

Expansion. Growing larger; to occupy a greater space.

Exerted. To work to the utmost; to put forth in action.

Exhilaratiorn. A lively, pleasing or happy sensation.

Exploited. To fully examine and consider, as well as carry out.

Extremity. The end; as far as ean be considered.

Facility. Ease of management; to do things without difficulty.

Factor. One of the elements in a problem, or in mechanicalaction.

Fascination, Attraetiveness that is pleasing.

Flexure. The capacity to bend and yield, and return to itsoriginal position.

Flexible, That which will yield; springy.

Fore and Aft. Lengthwise, as from stem to stern of a ship.

Formation. The shape or arrangement of an article or thing.

Formulated. Put into some eonerete form, or so arranged that itmay be understood.

Frictionless. Being without a grinding or retarding aotion.

Fulcrumed. A resting place for a lever.

Function. The duty or sphere of action in a person, or object.

Glider. An aeroplane, without power, adapted to be operatedby an aviator.

Governing. An element which is designed to control a machine in aregular manner.

Graduated. A marked portion, which is regularly laid off toindicate measurements or quantities.

Gravity. The attraction of mass for mass. The tendency of bodiesto move toward the earth.

Gravitatior The force with which all bodies attract each other.

Gyratory. Having a circular and wheeling as well as a rotarymotion.

Gyroscope. A wheel, designed to illustrate the laws of motion,which freely revolves in gimbals within a ring, and when set intomotion, objects to change its plane of rotation.

Hemispherical. The half of a sphere. The half of an apple wouldbe hemispherical.

Hazardous. That which is doubtful; accompanied by danger.

Helicopter. A type of flying machine which has a large propeller,or more than one, revolubly fixed on vertical shafts, by means ofwhich the machine is launched and projected through the air.

Horizontal. Level, like water.

Hydroplane. A term used to designate an aeroplane which isprovided with pontoons, whereby it may alight on the water, andbe launched from the surface. The term hydroaeroplane is mostgenerally used to indicate this type of machine.

Impact. The striking against; the striking force of one bodyagainst another.

Immersed. Placed under water below the surface.

Impinge. To strike against; usually applied where air strikesa plane or a surface at an angle.

Imitation. Similarity; the same in appearance.

Incompatible. Without harmony; incapable of existing together.

Incurved. Applied to a surface formation where there is adepression, or hollow.

Inequalities. Not smooth, or regular; uneven.

Infinitely, Boundless; in great number, or quality; withoutmeasure.

Initial. The first; that which is at the beginning.

Indestructibility. Not capable of being injured or destroyed.

Influenced. Swayed; to be induced to change.

Inherent. That which is in or belongs to itself.

Initiating. To teach; to instill; to give an insight.

Indicator. A term applied to mechanism which shows the results ofcertain operations and enables the user to read the measure,quantity, or quality shown.

Inconceivable. Not capable of understanding; that which cannot beunderstood by the human mind.

Institute. To start; to bring into operation.

Insignias. Things which are significant of any particular callingor profession.

Instinct. That quality in man or animals which prompts the doingof things independently of any direct knowledge or understanding.

Intermediate. Between; that which may be within or inside thescope of the mind, or of certain areas.

Intervening. The time between; also applied to the action of aperson who may take part in an affair between two or morepersons.

Interval. A time between.

Investigator. One who undertakes to find out certain things.

Incidence. In physics this is a term to indicate the line whichfalls upon or strikes another at an angle.

Inverted. Upside down.

Invest. To give to another thing something that it lacked before.

Kinetic. Consisting in or depending upon motion.

Laminated. Made up of a plurality of parts. When wooden strips,of different or of the same kinds are glued and then laidtogether and put under heavy pressureuntil thoroughly dried, the mass makes a far more rigid structurethan if cut out of a single piece.

Launchiug. The term applied to the raising, or starting of aboat, or of a flying object.

Lateral. In mining this is a term to indicate the drifts ortunnels which branch out from the main tunnel. Generally it hasreference to a transverse position or direction,—that is, atright angles to a fore and aft direction.

Lift. The vertical motion, or direction in an airship; thus thelift may be the load, or the term used to designatewhat the ship is capable of raising up.

Ligament. The exceedingly strong tendons or muscles of birds andanimals, usually of firm, compact tissues.

Limitations. Within certain bounds; in a prescribed scope.

Longitudinally. Usually that direction across the longest part.

Majestically. Grand; exalted dignity; the quality which inspiresreverence or fear.

Manipulate. To handle; to conduct so that it will result in acertain way.

Maneuver. A methodical movement or change in troops.

Manually. To perform by hand.

Manifestations. The act of making plain to the eye or to theunderstanding.

Manually-operated. With the hands; a term applied to suchmachines as have the control planes operated by hand.

Maintained. Kept up; to provide for; to sustain.

Material. The substance, or the matter from which an article ismade; also the important thing, or element.

Mass. In physics it is that which in an article is always thesame. It differs from weight in the particular that the mass ofan article is the same, however far it may be from the center ofthe earth, whereas weight changes, and becomes less and less asit recedes from the center of the earth.

Margin. The edge; the principal differecee between this word andedge, is, that margin has reference also to a border, or narrowstrip along the edge, as, for instance, the blank spaces at theedges of a printed page.

Medievral. Belonging to the Middle Ages.

Mercury. A silver-white liquid metal, usually called quicksilver,and rather heavy. It dissolves most metals, and this process iscalled amalgamation.

Militate. In determining a question, to have weight, or toinfluence a decision.

Mobility. Being freely movable; capable of quick change.

Modifieation. A change; making a difference.

Monitor. Advising or reproving. Advising or approving by way ofcaution.

Monstrosities. Anything which is huge, or distorted, or wrong instructure.

Monorail. A railway with a single track, designed to be used by abicycle form of carriage, with two wheels, fore and aft of eachother, and depending for its stability upon gyroscopes, mountedon the carriage.

Momentum. That which makes a moving body difficult to stop. It isthe weight of a moving body, multiplied by its speed.

Monoplane. The literal meaning is one plane. As monoplanemachines are all provided with a fore and aft body, and each hasa wing or plane projecting out from each side of this body, it isobvious that it has two planes instead of one. The term, however,has reference to the fact that it has only one supporting surfaceon the same plane. Biplanes have two supporting surfaces, oneabove the other.

Multiplicity. Frequently confounded with plurality. The lattermeans more than one, whereas multiplicity has reference to agreat number, or to a great variety.

Muscular. Being strong; well developed.

Negative. The opposite of positive; not decisive.

Neutralize. From the word neuter, which means neither, hence theterm may be defined as one which is not a part of either, or doesnot take up with either side.

Normal Pressure. Normal means the natural or usual, and whenapplied to air it would have reference to the condition of theatmosphere at that particular place. If the pressure could changefrom its usual condition, it would be an abnormal pressure.

Notoriously. Generally known, but not favorably so; the subjectof general remark; or unfavorably known.

Obscurity. Not well known; in the background; without clearvision; hidden from view.

Obliquely. That which differs from a right angle; neither obtuse nor acute; deviating from a line by any angle except aright angle.

Obvious. That which is readily observed and understood.

Orthopter. That type of flying machine which depends on flappingwings to hold it in space, and to transport it, in imitation ofthe motion of the wings of birds in flying.

Oscillate. Moving to and fro; the piston of a steam engine has anoscillating motion.

Outline. Describing a marginal line on a drawing; setting forththe principal features of an argument, or the details of a story,or the like.

Overlapping. One placed over the other.

Parabolic. A form of curve somewhat similar to an ellipse.

Pedestal. A standard or support; an upright to hold machinery.

Pertinent. Appropriate; pertaining to the subject.

Pectoral. The bone which forms the main rib or support at theforward edge of a bird's wing.

Persistent. Keeping at it; determination to proceed.

Perpendicular. At right angles to a surface. This term issometimes wrongly applied in referring to an object, particularlyto an object which is vertical, meaning up and down. The blade ofa square is perpendieular to the handle at all times, but theblade is vertical only when it points to the center of the earth.

Pernicious. Bad; not having good features or possessing wrongattributes.

Pendulum. A bar or body suspended at a point and adapted to swingto and fro.

Perpetual. For all time; unending or unlimited time.

Phenomena. Some peculiar happening, or event, or object.

Pitch. In aviation this applies to the angle at which the bladesof a propeller are cut. If a propeller is turned, and it movesforwardly in the exact path made by the angle, for one completeturn, the distance traveled by the propeller axially indicatesthe pitch in feet.

Placement. When an object is located at any particular point, sothat it is operative the location is called the placement.

Plane. A flat surface for supporting a flying machine in the air.Plane of movement pertains to the imaginary surface described bya moving body. A bicycle wheel, for instance, when movingforwardly in a straight line, has a plane of movement which isvertical; but when the machine turns in a circle the upper end ofthe wheel is turned inwardly, and the plane of rhovement is at anangle.

Pliant. Easily yielding; capable of being bent; liable to beput out of shape.

Plurality. See multiplicity. More than one.

Poise. Held in suspension; disposed in a particular way.

Pontoon. Applied to a series of boats ranged side by side tosupport a walk laid thereon. In aviation it has reference to afloat for supporting an aeroplane.

Ponderous. Large; heavy; difficult to handle.

Posterior. The rear end; the opposite of anterior.

Principles. The very nature or essence of a thing; the source orcause from which a thing springs.

Proportion. The relation that exists between different parts orthings.

Propounded. Questioned; stated; to state formally forconsideration

Proprietary. A right; the ownership of certain property.

Primitive. The beginning or early times; long ago.

Prelude. A statement or action which precedes the main featureto be presented.

Proximity. Close to; near at hand.

Prototype. That which is used as the sample from, which somethingis made or judged.

Propeller. The piece of meebanism, with screw shaped blade,designed to be rapidly rotated in order to drive a vesselforwardly. It is claimed by some that the word Impeller would bethe more proper term.

Primarily. At the first; the commencement.

Precedes. Goes ahead; forward of all.

Propulsive. The force which gives motion to an object.

Projected. Thrown forward; caused to fly through the air.

Radially. Out from the center; projecting like the spokes of awheel.

Ratio. The relation of degree, number, amount; one with another.

Reaction. A counterforce; acting against.

Recognize. To know; seeing, hearing, or feeling, and havingknowledge therefrom.

Reflection. Considering; judging one thing by the examination ofanother. A beam of light, or an object, leaving a surface.

Refraction. That peculiarity in a beam of light, which, inpassing through water at an angle, bends out of its course andagain assumes a direct line after passing through.

Reflex. Turned back on itself, or in the direction from which itcame.

Requisite. Enough; suffieient for all purposes.

Relegate. To put back or away.

Rectangular. Having one or more right angles.

Reservations. Land which is held by the Government for variouspurposes.

Resistance. That which holds back; preventing movement.

Retarding. Preventing a free movement.

Revoluble. The turning or swinging motion of a body like theearth in its movement around the sun. See Rotative. To cause tomove as in an orbit or circle.

Resilient. Springy; having the quality of elasticity.

Reversed. Changed about; turned front side to the rear.

Rotative. That which turns, like a shaft. The movement of theearth on its axis is rotative.

Saturation. Putting one substance into another until it will holdno more. For instance, adding salt to water until the watercannot take up any more.

Security. Safety, assuredness that there will be no danger.

Segment. A part eut off from a circle. Distinguished from asector, which might be likened to the form of one of the sectionsof an orange.

Sexagonal. Six-sided.

Sine of the Angle. The line dropped from the highest point of an
 angle to the line which runs out horizontally.

Sinuous. Wavelike; moving up and down like the waves of theocean.

Simulates. To pattern or copy after; the making of the like.

Skipper. A thin flat stone.

Spirally-formed. Made like an auger; twisted.

Stability. In airships that quality which holds the ship on aneven and unswerving course, and prevents plunging and sidemotions.

Structural. Belonging to the features of eonstruetion.

Strata. Two or more layers; one over or below the other.

Stream line. In expressing the action of moving air, or anaeroplane transported through air, every part is acted upon bythe air. Stream lines are imaginary lines which act upon theplanes at all points, and all in the same direction, or angle.

Stupendous. Great; important; above the ordinary.

Substitute. One taken for another; replacing one thing bysomething else.

Supporting. Giving aid; helping another.

Synchronous. Acting at the same time, and to the same extent.Thus if two wheels, separated from each other at great distances,are so arranged that they turn at exactly the same speed, theyare said to turn synchronously.

Tactics. The art of handling troops in the presence of an enemy.It differs from strategy in the particular that the latter wordis used to explain the movements or arrangement of forces beforethey arrive at the battle line.

Tandem. One before the other; one after the other.

Tangent. A line drawn from a circle at an angle, instead ofradially.

Technically. Pertaining to some particular trade, science or art.

Tenuous. Thin, slender, willowy, slight.

Tetrahedral. This has reference to a form which is made up of amultiplicity of triangularly shaped thin blades, so as to formnumerous cells, and thus make a large number of supportingsurfaces. Used as a kite.

Theories. Views based upon certain consideration.

Theoretical. Where opinions are founded on certain information,and expressed, not from the standpoint of actual knowledge, butupon conclusions derived from such examinations.

Torsion. A twist; a circular motion around a body.

Transmitted. Sent out; conveyed from one point to another.

Transformed. Changed; entirely made over from one thing toanother.

Transverse. When a body is shorter from front to rear than fromside to side its longest dimension is transversely.Distinguish from lateral, which has reference only to thedistance at right angles from the main body.

Translation. The transportation of a body through the air.

Trajectory. The path made by a body projected through the air.

Triangular. A form or body having three sides and three angles.

Typical. In the form of; a likeness to.

Ultimate. The end; the finality; the last that can be said.

Uninitiated. Not having full knowledge; withont information.

Unique. Peculiar; something that on account of its peculiarconstruction or arrangements stands out beyond the others.

Universal. Everywhere; all over the world.

Undulate. To move up and down; a wave-like motion.

Utility. Of use; to take advantageous use of.

Unstable. Not having anything permanent; in a ship in flight onethat will not ride on an even keel, and is liable to pitch about.

Vacuum. Where air is partly taken away, or rendered rarer.

Valved. A surface which has a multiplicity of openings withvalves therein, or, through which air can move in one direction.

Vaunted. To boast concerning; to give a high opinion.

Velocity. Speed; the rate at which an object can move from placeto place.

Vertical. A line running directly to the center of the earth; aline at right angles to the surface of water.

Vibratory. Moving from side to side; a regular motion.

Volplane. The glide of a machine without the use of power.

Warping. The twist given to certain portions of planes, so as tocause the air to aet against the warped portions.

Weight. The measure of the force which gravity exerts on allobjects.

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