Aeroplanes.

by J. S. Zerbe.

INTRODUCTORY

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

The art of aviation is in a most primitive state.

So many curious theories have been brought out that, while they furnish food for thought, do not, in any way, advance or improve the structure of the machine itself, nor are they of any service in teaching the novice how to fly.

The author considers it of far more importance to teach right principles, and correct reasoning than to furnish complete diagrams of the details of a machine. The former teach the art, whereas the latter merely point out the mechanical arrangements, independently of the reasons for making the structures in that particular way.

Relating the history of an art, while it may be interesting reading, does not even lay the foundations of a knowledge of the subject, hence that field has been left to others.

The boy is naturally inquisitive, and he is interested in knowing WHY certain things are necessary, and the reasons for making structures in particular ways. That is the void into which these 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 this spirit of inquiry. Some boys were discussing the curved plane structure. One of them ventured the opinion that birds' wings were concaved on the lower side. "But," retorted another, "why are birds' wings hollowed?"

This was going back to first principles at one leap. It was not satisfying enough to know that man was copying nature. It was more important to know why nature originated that type of formation, because, it is obvious, that if such structures are universal in the kingdom of flying creatures, there must be some underlying principle which accounted for it.

It is not the aim of the book to teach the art of flying, but rather to show how and why the present machines fly. The making and the using are separate and independent functions, and of the two the more important is the knowledge how to make a correct machine.

Hundreds of workmen may contribute to the building of a locomotive, but one man, not a builder, knows better how to handle it. To manipulate a flying machine is more difficult to navigate than such a ponderous machine, because it requires peculiar talents, and the building is still more important and complicated, and requires the exercise of a kind of skill not necessary in the locomotive.

The art is still very young; so much is done which arises from speculation and theories; too much dependence is placed on the aviator; the desire in the present condition of the art is to exploit the man and not the machine; dare-devil exhibitions seem to be more important than perfecting the mechanism; and such useless attempts as flying upside down, looping the loop, and characteristic displays of that kind, are of no value to the art.

THE AUTHOR.

AEROPLANES

CHAPTER I

THEORIES AND FACTS ABOUT FLYING

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

We may be able to learn something by carefully examining the different views presented by those interested in the art, and then see how they conform to the facts as brought out by the actual experiments.

MACHINE TYPES.--There is really but one type of plane machine. While technically two forms are known, namely, the monoplane and the bi-plane, they are both dependent on outstretched wings, longer transversely than fore and aft, so far as the supporting surfaces are concerned, and with the main weight high in the structure, thus, in every particular, conforming to the form pointed out by nature as the apparently correct type of a flying structure.

SHAPE OR FORM NOT ESSENTIAL.--It may be stated with perfect confidence, that shape or form has nothing to do with the mere act of flying. It is simply a question of power. This is a broad a.s.sertion, and its meaning may be better understood by examining the question of flight in a broad sense.

A STONE AS A FLYING MACHINE.--When a stone is propelled through s.p.a.ce, shape is of no importance.

If it has rough and jagged sides its speed or its distance may be limited, as compared with a perfectly rounded form. It may be made in such a shape as will offer less resistance to the air in flight, but its actual propulsion through s.p.a.ce does not depend on how it is made, but on the power which propelled it, and such a missile is a true heavier-than-air machine.

A flying object of this kind may be so constructed that it will go a greater distance, or require less power, or maintain itself in s.p.a.ce at less speed; but it is a flying machine, nevertheless, in the sense that it moves horizontally through the air.

POWER THE GREAT ELEMENT.--Now, let us examine the question of this power which is able to set gravity at naught. The quality called energy resides in material itself. It is something within matter, and does not come from without. The power derived from the explosion of a charge of powder comes from within the substance; and so with falling water, or the expansive force of steam.

GRAVITY AS POWER.--Indeed, the very act of the ball gradually moving toward the earth, by the force of gravity, is an ill.u.s.tration of a power within the object itself. Long after Galileo firmly established the law of falling bodies it began to dawn on scientists that weight is force.

After Newton established the law of gravitation the old idea, that power was a property of each body, pa.s.sed away.

In its stead we now have the firmly established view, that power is something which must have at least two parts, or consist in pairs, or two elements acting together. Thus, a stone poised on a cliff, while it exerts no power which can be utilized, has, nevertheless, what is called potential energy. When it is pushed from its lodging place kinetic energy is developed. In both cases, gravity, acting in conjunction with the ma.s.s of the stone, produced power.

So in the case of gunpowder. It is the unity of two or more substances, that causes the expansion called power. The heat of the fuel converting water into steam, is another ill.u.s.tration of the unity of two or more elements, which are necessary to produce energy.

Ma.s.s AN ELEMENT IN FLYING.--The boy who reads this will smile, as he tells us that the power which propelled the ball through the air came from the thrower and not from the ball itself.

Let us examine this claim, which came from a real boy, and is another ill.u.s.tration how acute his mind is on subjects of this character.

We have two b.a.l.l.s the same diameter, one of iron weighing a half pound, and the other of cotton weighing a half ounce. The weight of one is, therefore, sixteen times greater than the other.

Suppose these two b.a.l.l.s are thrown with the expenditure of the same power. What will be the result! The iron ball will go much farther, or, if projected against a wall will strike a harder blow than the cotton ball.

MOMENTUM A FACTOR.--Each had transferred to it a motion. The initial speed was the same, and the power set up equal in the two. Why this difference, The answer is, that it is in the material itself. It was the ma.s.s or density which accounted for the difference. It was ma.s.s multiplied by speed which gave it the power, called, in this case, momentum.

The iron ball weighing eight ounces, multiplied by the a.s.sumed speed of 50 feet per second, equals 400 units of work. The cotton ball, weighing 1/2 ounce, with the same initial speed, represents 25 units of work. The term "unit of work" means a measurement, or a factor which may be used to measure force.

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

RESISTANCE.--Now, in the movement of any body through s.p.a.ce, it meets with an enemy at every step, and that is air resistance. This is much more effective against the cotton than the iron ball: or, it might be expressed in another way: The momentum, or the power, residing in the metal ball, is so much greater than that within the cotton ball that it travels farther, or strikes a more effective blow on impact with the wall.

HOW RESISTANCE AFFECTS THE SHAPE.--It is because of this counterforce, resistance, that shape becomes important in a flying object. The metal ball 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 difference in the air impact against the two forms.

Ma.s.s AND RESISTANCE.--Owing to the fact that resistance acts with such a r.e.t.a.r.ding force on an object of small ma.s.s, and it is difficult to set up a rapid motion in an object of great density, lightness in flying machine structures has been considered, in the past, the princ.i.p.al thing necessary.

THE EARLY TENDENCY TO ELIMINATE MOMENTUM.-- Builders of flying machines, for several years, sought to eliminate the very thing which gives energy to a horizontally-movable body, namely, momentum.

Instead of momentum, something had to be subst.i.tuted. This was found in so arranging the machine that its weight, or a portion of it, would be sustained in s.p.a.ce by the very element which seeks to r.e.t.a.r.d its flight, namely, the atmosphere.

If there should be no material substance, like air, then the only way in which a heavier-than-air machine could ever fly, would be by propelling it through s.p.a.ce, like the ball was thrown, or by some sort of impulse or reaction mechanism on the air-ship itself. It could get no support from the atmosphere.

LIGHT MACHINES UNSTABLE.--Gradually the question of weight is solving itself. Aviators are beginning to realize that momentum is a wonderful property, and a most important element in flying. The safest machines are those which have weight. The light, willowy machines are subject to every caprice of the wind. They are notoriously unstable in flight, and are dangerous even in the hands of experts.

THE APPLICATION OF POWER.--The thing now to consider is not form, or shape, or the distribution of the supporting surfaces, but HOW to apply the power so that it will rapidly transfer a machine at rest to one in motion, and thereby get the proper support on the atmosphere to hold it in flight.

THE SUPPORTING SURFACES.--This brings us to the consideration of one of the first great problems in flying machines, namely, the supporting surfaces,--not its form, shape or arrangement, (which will be taken up in their proper places), but the area, the dimensions, and the angle necessary for flight.

AREA NOT THE ESSENTIAL THING.--The history of flying machines, short as it is, furnishes many examples of one striking fact: That area has but little to do with sustaining an aeroplane when once in flight. The first Wright flyer weighed 741 pounds, had about 400 square feet of plane surface, and was maintained in the air with a 12 horse power engine.

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

There are many instances to show that when once in flight, one horse power will sustain over 100 pounds, and each square foot of supporting surface will maintain 90 pounds in flight.