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Flying Machines - Construction and Operation
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FLYING MACHINE: CONSTRUCTION AND OPERATION

By W.J. Jackman and Thos. H. Russell

A Practical Book Which Shows, in Illustrations, Working Plans and Text, How to Build and Navigate the Modern Airship.

W.J. JACKMAN, M.E., Author of "A B C of the Motorcycle," "Facts for Motorists," etc. etc.

and

THOS. H. RUSSELL, A.M., M.E., Charter Member of the Aero Club of Illinois, Author of "History of the Automobile," "Motor Boats: Construction and Operation," etc. etc.

With Introductory Chapter By Octave Chanute, C.E., President Aero Club of Illinois

1912



PREFACE.

This book is written for the guidance of the novice in aviation—the man who seeks practical information as to the theory, construction and operation of the modern flying machine. With this object in view the wording is intentionally plain and non-technical. It contains some propositions which, so far as satisfying the experts is concerned, might doubtless be better stated in technical terms, but this would defeat the main purpose of its preparation. Consequently, while fully aware of its shortcomings in this respect, the authors have no apologies to make.

In the stating of a technical proposition so it may be clearly understood by people not versed in technical matters it becomes absolutely necessary to use language much different from that which an expert would employ, and this has been done in this volume.

No man of ordinary intelligence can read this book without obtaining a clear, comprehensive knowledge of flying machine construction and operation. He will learn, not only how to build, equip, and manipulate an aeroplane in actual flight, but will also gain a thorough understanding of the principle upon which the suspension in the air of an object much heavier than the air is made possible.

This latter feature should make the book of interest even to those who have no intention of constructing or operating a flying machine. It will enable them to better understand and appreciate the performances of the daring men like the Wright brothers, Curtiss, Bleriot, Farman, Paulhan, Latham, and others, whose bold experiments have made aviation an actuality.

For those who wish to engage in the fascinating pastime of construction and operation it is intended as a reliable, practical guide.

It may be well to explain that the sub-headings in the articles by Mr. Chanute were inserted by the authors without his knowledge. The purpose of this was merely to preserve uniformity in the typography of the book. This explanation is made in justice to Mr. Chanute.

THE AUTHORS.



IN MEMORIAM.

Octave Chanute, "the father of the modern flying machine," died at his home in Chicago on November 23, 1910, at the age of 72 years. His last work in the interest of aviation was to furnish the introductory chapter to the first edition of this volume, and to render valuable assistance in the handling of the various subjects. He even made the trip from his home to the office of the publishers one inclement day last spring, to look over the proofs of the book and, at his suggestion, several important changes were made. All this was "a labor of love" on Mr. Chanute's part. He gave of his time and talents freely because he was enthusiastic in the cause of aviation, and because he knew the authors of this book and desired to give them material aid in the preparation of the work—a favor that was most sincerely appreciated.

The authors desire to make acknowledgment of many courtesies in the way of valuable advice, information, etc., extended by Mr. Octave Chanute, C. E., Mr. E. L. Jones, Editor of Aeronautics, and the publishers of, the New England Automobile Journal and Fly.



CONTENTS

Chapter

I. Evolution of the Two-Surface Flying Machine Introductory Chapter by Octave Chanute, C. E. II. Theory Development and Use Origin of the Aeroplane—Developments by Chanute and the Wrights—Practical Uses and Limits. III. Mechanical Bird Action What the Motor Does—Puzzle in Bird Soaring. IV. Various Forms of Flying Machines Helicopters, Ornithopters and Aeroplanes— Monoplanes, Biplanes and Triplanes. V. Constructing a Gliding Machine Plans and Materials Required—Estimate of Cost— Sizes and Preparation of Various Parts—Putting the Parts Together VI. Learning to Fly How to Use the Glider—Effect of Body Movements —Rules for Beginners—Safest Place to Glide. VII. Putting On the Rudder Its Construction, Application and Use. VIII. The Real Flying Machine Surface Area Required—Proper Size of Frame and Auxiliaries—Installation of Motor—Cost of Constructing Machine. IX. Selection of the Motor Essential Features—Multiplicity of Cylinders—Power Required—Kind and Action of Propellers—Placing of the Motor X. Proper Dimensions of Machines Figuring Out the Details—How to Estimate Load Capacity—Distribution of the Weight—Measurements of Leading Machines. XI. Plane and Rudder Control Various Methods in Use—Wheels and Hand and Foot Levers XII. How to Use the Machine Rules of Leading Aviators—Rising from the Ground —Reasonable Altitude—Preserving Equilibrium— Learning to Steer. XIII. Peculiarities of Aeroplane Power Pressure of the Wind—How to Determine Upon Power—Why Speed Is Required—Bird find Flying Machine Areas. XIV. About Wind Currents, Etc. Uncertainty of Direct Force—Trouble With Gusty Currents—Why Bird Action Is Imitated. XV. The Element of Danger Risk Small Under Proper Conditions—Two Fields of Safety—Lessons in Recent Accidents. XVI. Radical Changes Being Made Results of Recent Experiments—New Dimensions —Increased Speed—The One Governing Rule. XVII. Some of the New Designs Automatic Control of Plane Stability—Inventor Herring's Devices—Novel Ideas of Students. XVIII. Demand for Flying Machines Wonderful Results in a Year—Factories Over- crowded with Orders. XIX. Law of the Airship Rights of Property Owners—Some Legal Peculiarities—Danger of Trespass. XX. Soaring Flight XXI. Flying Machines vs. Balloons XXII. Problems of Aerial Flight XXIII. Amateurs May Use Wright Patents XXIV. Hints on Propeller Construction XXV. New Motors and Devices XXVI. Monoplanes, Triplanes, Multiplanes XXVII. Records of Various Kinds



FLYING MACHINES: CONSTRUCTION and OPERATION



CHAPTER I. EVOLUTION OF TWO-SURFACE FLYING MACHINE.

By Octave Chanute.

I am asked to set forth the development of the "two-surface" type of flying machine which is now used with modifications by Wright Brothers, Farman, [1] Delagrange, Herring and others.

This type originated with Mr. F. H. Wenham, who patented it in England in 1866 (No. 1571), taking out provisional papers only. In the abridgment of British patent Aeronautical Specifications (1893) it is described as follows:

"Two or more aeroplanes are arranged one above the other, and support a framework or car containing the motive power. The aeroplanes are made of silk or canvas stretched on a frame by wooden rods or steel ribs. When manual power is employed the body is placed horizontally, and oars or propellers are actuated by the arms or legs.

"A start may be obtained by lowering the legs and running down hill or the machine may be started from a moving carriage. One or more screw propellers may be applied for propelling when steam power is employed."

On June 27, 1866, Mr. Wenham read before the "Aeronautical Society of Great Britain," then recently organized, the ablest paper ever presented to that society, and thereby breathed into it a spirit which has continued to this day. In this paper he described his observations of birds, discussed the laws governing flight as to the surfaces and power required both with wings and screws, and he then gave an account of his own experiments with models and with aeroplanes of sufficient size to carry the weight of a man.

Second Wenham Aeroplane.

His second aeroplane was sixteen feet from tip to tip. A trussed spar at the bottom carried six superposed bands of thin holland fabric fifteen inches wide, connected with vertical webs of holland two feet apart, thus virtually giving a length of wing of ninety-six feet and one hundred and twenty square feet of supporting surface. The man was placed horizontally on a base board beneath the spar. This apparatus when tried in the wind was found to be unmanageable by reason of the fluttering motions of the fabric, which was insufficiently stiffened with crinoline steel, but Mr. Wenham pointed out that this in no way invalidated the principle of the apparatus, which was to obtain large supporting surfaces without increasing unduly the leverage and consequent weight of spar required, by simply superposing the surfaces.

This principle is entirely sound and it is surprising that it is, to this day, not realized by those aviators who are hankering for monoplanes.

Experiments by Stringfellow.

The next man to test an apparatus with superposed surfaces was Mr. Stringfellow, who, becoming much impressed with Mr. Wenham's proposal, produced a largish model at the exhibition of the Aeronautical Society in 1868. It consisted of three superposed surfaces aggregating 28 square feet and a tail of 8 square feet more. The weight was under 12 pounds and it was driven by a central propeller actuated by a steam engine overestimated at one-third of a horsepower. It ran suspended to a wire on its trials but failed of free flight, in consequence of defective equilibrium. This apparatus has since been rebuilt and is now in the National Museum of the Smithsonian Institution at Washington. Linfield's Unsuccessful Efforts.

In 1878 Mr. Linfield tested an apparatus in England consisting of a cigar-shaped car, to which was attached on each side frames five feet square, containing each twenty-five superposed planes of stretched and varnished linen eighteen inches wide, and only two inches apart, thus reminding one of a Spanish donkey with panniers. The whole weighed two hundred and forty pounds. This was tested by being mounted on a flat car behind a locomotive going 40 miles an hour. When towed by a line fifteen feet long the apparatus rose only a little from the car and exhibited such unstable equilibrium that the experiment was not renewed. The lift was only about one-third of what it would have been had the planes been properly spaced, say their full width apart, instead of one-ninth as erroneously devised.

Renard's "Dirigible Parachute."

In 1889 Commandant Renard, the eminent superintendent of the French Aeronautical Department, exhibited at the Paris Exposition of that year, an apparatus experimented with some years before, which he termed a "dirigible parachute." It consisted of an oviform body to which were pivoted two upright slats carrying above the body nine long superposed flat blades spaced about one-third of their width apart. When this apparatus was properly set at an angle to the longitudinal axis of the body and dropped from a balloon, it travelled back against the wind for a considerable distance before alighting. The course could be varied by a rudder. No practical application seems to have been made of this device by the French War Department, but Mr. J. P. Holland, the inventor of the submarine boat which bears his name, proposed in 1893 an arrangement of pivoted framework attached to the body of a flying machine which combines the principle of Commandant Renard with the curved blades experimented with by Mr. Phillips, now to be noticed, with the addition of lifting screws inserted among the blades.

Phillips Fails on Stability Problem.

In 1893 Mr. Horatio Phillips, of England, after some very interesting experiments with various wing sections, from which he deduced conclusions as to the shape of maximum lift, tested an apparatus resembling a Venetian blind which consisted of fifty wooden slats of peculiar shape, 22 feet long, one and a half inches wide, and two inches apart, set in ten vertical upright boards. All this was carried upon a body provided with three wheels. It weighed 420 pounds and was driven at 40 miles an hour on a wooden sidewalk by a steam engine of nine horsepower which actuated a two-bladed screw. The lift was satisfactory, being perhaps 70 pounds per horsepower, but the equilibrium was quite bad and the experiments were discontinued. They were taken up again in 1904 with a similar apparatus large enough to carry a passenger, but the longitudinal equilibrium was found to be defective. Then in 1907 a new machine was tested, in which four sets of frames, carrying similar sets of slat "sustainers" were inserted, and with this arrangement the longitudinal stability was found to be very satisfactory. The whole apparatus, with the operator, weighed 650 pounds. It flew about 200 yards when driven by a motor of 20 to 22 h.p. at 30 miles an hour, thus exhibiting a lift of about 32 pounds per h.p., while it will be remembered that the aeroplane of Wright Brothers exhibits a lifting capacity of 50 pounds to the h.p.

Hargrave's Kite Experiments.

After experimenting with very many models and building no less than eighteen monoplane flying model machines, actuated by rubber, by compressed air and by steam, Mr. Lawrence Hargrave, of Sydney, New South Wales, invented the cellular kite which bears his name and made it known in a paper contributed to the Chicago Conference on Aerial Navigation in 1893, describing several varieties. The modern construction is well known, and consists of two cells, each of superposed surfaces with vertical side fins, placed one behind the other and connected by a rod or frame. This flies with great steadiness without a tail. Mr. Hargrave's idea was to use a team of these kites, below which he proposed to suspend a motor and propeller from which a line would be carried to an anchor in the ground. Then by actuating the propeller the whole apparatus would move forward, pick up the anchor and fly away. He said: "The next step is clear enough, namely, that a flying machine with acres of surface can be safely got under way or anchored and hauled to the ground by means of the string of kites."

The first tentative experiments did not result well and emphasized the necessity for a light motor, so that Mr. Hargrave has since been engaged in developing one, not having convenient access to those which have been produced by the automobile designers and builders.

Experiments With Glider Model.

And here a curious reminiscence may be indulged in. In 1888 the present writer experimented with a two-cell gliding model, precisely similar to a Hargrave kite, as will be confirmed by Mr. Herring. It was frequently tested by launching from the top of a three-story house and glided downward very steadily in all sorts of breezes, but the angle of descent was much steeper than that of birds, and the weight sustained per square foot was less than with single cells, in consequence of the lesser support afforded by the rear cell, which operated upon air already set in motion downward by the front cell, so nothing more was done with it, for it never occurred to the writer to try it as a kite and he thus missed the distinction which attaches to Hargrave's name.

Sir Hiram Maxim also introduced fore and aft superposed surfaces in his wondrous flying machine of 1893, but he relied chiefly for the lift upon his main large surface and this necessitated so many guys, to prevent distortion, as greatly to increase the head resistance and this, together with the unstable equilibrium, made it evident that the design of the machine would have to be changed.

How Lilienthal Was Killed.

In 1895, Otto Lilienthal, the father of modern aviation, the man to whose method of experimenting almost all present successes are due, after making something like two thousand glides with monoplanes, added a superposed surface to his apparatus and found the control of it much improved. The two surfaces were kept apart by two struts or vertical posts with a few guy wires, but the connecting joints were weak and there was nothing like trussing. This eventually cost his most useful life. Two weeks before that distressing loss to science, Herr Wilhelm Kress, the distinguished and veteran aviator of Vienna, witnessed a number of glides by Lilienthal with his double-decked apparatus. He noticed that it was much wracked and wobbly and wrote to me after the accident: "The connection of the wings and the steering arrangement were very bad and unreliable. I warned Herr Lilienthal very seriously. He promised me that he would soon put it in order, but I fear that he did not attend to it immediately."

In point of fact, Lilienthal had built a new machine, upon a different principle, from which he expected great results, and intended to make but very few more flights with the old apparatus. He unwisely made one too many and, like Pilcher, was the victim of a distorted apparatus. Probably one of the joints of the struts gave way, the upper surface blew back and Lilienthal, who was well forward on the lower surface, was pitched headlong to destruction.

Experiments by the Writer.

In 1896, assisted by Mr. Herring and Mr. Avery, I experimented with several full sized gliding machines, carrying a man. The first was a Lilienthal monoplane which was deemed so cranky that it was discarded after making about one hundred glides, six weeks before Lilienthal's accident. The second was known as the multiple winged machine and finally developed into five pairs of pivoted wings, trussed together at the front and one pair in the rear. It glided at angles of descent of 10 or 11 degrees or of one in five, and this was deemed too steep. Then Mr. Herring and myself made computations to analyze the resistances. We attributed much of them to the five front spars of the wings and on a sheet of cross-barred paper I at once drew the design for a new three-decked machine to be built by Mr. Herring.

Being a builder of bridges, I trussed these surfaces together, in order to obtain strength and stiffness. When tested in gliding flight the lower surface was found too near the ground. It was taken off and the remaining apparatus now consisted of two surfaces connected together by a girder composed of vertical posts and diagonal ties, specifically known as a "Pratt truss." Then Mr. Herring and Mr. Avery together devised and put on an elastic attachment to the tail. This machine proved a success, it being safe and manageable. Over 700 glides were made with it at angles of descent of 8 to 10 degrees, or one in six to one in seven.

First Proposed by Wenham.

The elastic tail attachment and the trussing of the connecting frame of the superposed wings were the only novelties in this machine, for the superposing of the surfaces had first been proposed by Wenham, but in accordance with the popular perception, which bestows all the credit upon the man who adds the last touch making for success to the labors of his predecessors, the machine has since been known by many persons as the "Chanute type" of gliders, much to my personal gratification.

It has since been improved in many ways. Wright Brothers, disregarding the fashion which prevails among birds, have placed the tail in front of their apparatus and called it a front rudder, besides placing the operator in horizontal position instead of upright, as I did; and also providing a method of warping the wings to preserve equilibrium. Farman and Delagrange, under the very able guidance and constructive work of Voisin brothers, then substituted many details, including a box tail for the dart-like tail which I used. This may have increased the resistance, but it adds to the steadiness. Now the tendency in France seems to be to go back to the monoplane.

Monoplane Idea Wrong.

The advocates of the single supporting surface are probably mistaken. It is true that a single surface shows a greater lift per square foot than superposed surfaces for a given speed, but the increased weight due to leverage more than counterbalances this advantage by requiring heavy spars and some guys. I believe that the future aeroplane dynamic flier will consist of superposed surfaces, and, now that it has been found that by imbedding suitably shaped spars in the cloth the head resistance may be much diminished, I see few objections to superposing three, four or even five surfaces properly trussed, and thus obtaining a compact, handy, manageable and comparatively light apparatus. [2]



CHAPTER II. THEORY, DEVELOPMENT, AND USE.

While every craft that navigates the air is an airship, all airships are not flying machines. The balloon, for instance, is an airship, but it is not what is known among aviators as a flying machine. This latter term is properly used only in referring to heavier-than-air machines which have no gas-bag lifting devices, and are made to really fly by the application of engine propulsion.

Mechanical Birds.

All successful flying machines—and there are a number of them—are based on bird action. The various designers have studied bird flight and soaring, mastered its technique as devised by Nature, and the modern flying machine is the result. On an exaggerated, enlarged scale the machines which are now navigating the air are nothing more nor less than mechanical birds.

Origin of the Aeroplane.

Octave Chanute, of Chicago, may well be called "the developer of the flying machine." Leaving balloons and various forms of gas-bags out of consideration, other experimenters, notably Langley and Lilienthal, antedated him in attempting the navigation of the air on aeroplanes, or flying machines, but none of them were wholly successful, and it remained for Chanute to demonstrate the practicability of what was then called the gliding machine. This term was adopted because the apparatus was, as the name implies, simply a gliding machine, being without motor propulsion, and intended solely to solve the problem of the best form of construction. The biplane, used by Chanute in 1896, is still the basis of most successful flying machines, the only radical difference being that motors, rudders, etc., have been added.

Character of Chanute's Experiments.

It was the privilege of the author of this book to be Mr. Chanute's guest at Millers, Indiana, in 1896, when, in collaboration with Messrs. Herring and Avery, he was conducting the series of experiments which have since made possible the construction of the modern flying machine which such successful aviators as the Wright brothers and others are now using. It was a wild country, much frequented by eagles, hawks, and similar birds. The enthusiastic trio, Chanute, Herring and Avery, would watch for hours the evolutions of some big bird in the air, agreeing in the end on the verdict, "When we master the principle of that bird's soaring without wing action, we will have come close to solving the problem of the flying machine."

Aeroplanes of various forms were constructed by Mr. Chanute with the assistance of Messrs. Herring and Avery until, at the time of the writer's visit, they had settled upon the biplane, or two-surface machine. Mr. Herring later equipped this with a rudder, and made other additions, but the general idea is still the basis of the Wright, Curtiss, and other machines in which, by the aid of gasolene motors, long flights have been made.

Developments by the Wrights.

In 1900 the Wright brothers, William and Orville, who were then in the bicycle business in Dayton, Ohio, became interested in Chanute's experiments and communicated with him. The result was that the Wrights took up Chanute's ideas and developed them further, making many additions of their own, one of which was the placing of a rudder in front, and the location of the operator horizontally on the machine, thus diminishing by four-fifths the wind resistance of the man's body. For three years the Wrights experimented with the glider before venturing to add a motor, which was not done until they had thoroughly mastered the control of their movements in the air.

Limits of the Flying Machine.

In the opinion of competent experts it is idle to look for a commercial future for the flying machine. There is, and always will be, a limit to its carrying capacity which will prohibit its employment for passenger or freight purposes in a wholesale or general way. There are some, of course, who will argue that because a machine will carry two people another may be constructed that will carry a dozen, but those who make this contention do not understand the theory of weight sustentation in the air; or that the greater the load the greater must be the lifting power (motors and plane surface), and that there is a limit to these—as will be explained later on—beyond which the aviator cannot go.

Some Practical Uses.

At the same time there are fields in which the flying machine may be used to great advantage. These are:

Sports—Flying machine races or flights will always be popular by reason of the element of danger. It is a strange, but nevertheless a true proposition, that it is this element which adds zest to all sporting events.

Scientific—For exploration of otherwise inaccessible regions such as deserts, mountain tops, etc.

Reconnoitering—In time of war flying machines may be used to advantage to spy out an enemy's encampment, ascertain its defenses, etc.



CHAPTER III. MECHANICAL BIRD ACTION

In order to understand the theory of the modern flying machine one must also understand bird action and wind action. In this connection the following simple experiment will be of interest:

Take a circular-shaped bit of cardboard, like the lid of a hat box, and remove the bent-over portion so as to have a perfectly flat surface with a clean, sharp edge. Holding the cardboard at arm's length, withdraw your hand, leaving the cardboard without support. What is the result? The cardboard, being heavier than air, and having nothing to sustain it, will fall to the ground. Pick it up and throw it, with considerable force, against the wind edgewise. What happens? Instead of falling to the ground, the cardboard sails along on the wind, remaining afloat so long as it is in motion. It seeks the ground, by gravity, only as the motion ceases, and then by easy stages, instead of dropping abruptly as in the first instance.

Here we have a homely, but accurate illustration of the action of the flying machine. The motor does for the latter what the force of your arm does for the cardboard—imparts a motion which keeps it afloat. The only real difference is that the motion given by the motor is continuous and much more powerful than that given by your arm. The action of the latter is limited and the end of its propulsive force is reached within a second or two after it is exerted, while the action of the motor is prolonged.

Another Simple Illustration.

Another simple means of illustrating the principle of flying machine operation, so far as sustentation and the elevation and depression of the planes is concerned, is explained in the accompanying diagram.

A is a piece of cardboard about 2 by 3 inches in size. B is a piece of paper of the same size pasted to one edge of A. If you bend the paper to a curve, with convex side up and blow across it as shown in Figure C, the paper will rise instead of being depressed. The dotted lines show that the air is passing over the top of the curved paper and yet, no matter how hard you may blow, the effect will be to elevate the paper, despite the fact that the air is passing over, instead of under the curved surface.

In Figure D we have an opposite effect. Here the paper is in a curve exactly the reverse of that shown in Figure C, bringing the concave side up. Now if you will again blow across the surface of the card the action of the paper will be downward—it will be impossible to make it rise. The harder you blow the greater will be the downward movement.

Principle In General Use.

This principle is taken advantage of in the construction of all successful flying machines. Makers of monoplanes and biplanes alike adhere to curved bodies, with the concave surface facing downward. Straight planes were tried for a time, but found greatly lacking in the power of sustentation. By curving the planes, and placing the concave surface downward, a sort of inverted bowl is formed in which the air gathers and exerts a buoyant effect. Just what the ratio of the curve should be is a matter of contention. In some instances one inch to the foot is found to be satisfactory; in others this is doubled, and there are a few cases in which a curve of as much as 3 inches to the foot has been used.

Right here it might be well to explain that the word "plane" applied to flying machines of modern construction is in reality a misnomer. Plane indicates a flat, level surface. As most successful flying machines have curved supporting surfaces it is clearly wrong to speak of "planes," or "aeroplanes." Usage, however, has made the terms convenient and, as they are generally accepted and understood by the public, they are used in like manner in this volume.

Getting Under Headway.

A bird, on first rising from the ground, or beginning its flight from a tree, will flap its wings to get under headway. Here again we have another illustration of the manner in which a flying machine gets under headway—the motor imparts the force necessary to put the machine into the air, but right here the similarity ceases. If the machine is to be kept afloat the motor must be kept moving. A flying machine will not sustain itself; it will not remain suspended in the air unless it is under headway. This is because it is heavier than air, and gravity draws it to the ground.

Puzzle in Bird Soaring.

But a bird, which is also heavier than air, will remain suspended, in a calm, will even soar and move in a circle, without apparent movement of its wings. This is explained on the theory that there are generally vertical columns of air in circulation strong enough to sustain a bird, but much too weak to exert any lifting power on a flying machine, It is easy to understand how a bird can remain suspended when the wind is in action, but its suspension in a seeming dead calm was a puzzle to scientists until Mr. Chanute advanced the proposition of vertical columns of air.

Modeled Closely After Birds.

So far as possible, builders of flying machines have taken what may be called "the architecture" of birds as a model. This is readily noticeable in the form of construction. When a bird is in motion its wings (except when flapping) are extended in a straight line at right angles to its body. This brings a sharp, thin edge against the air, offering the least possible surface for resistance, while at the same time a broad surface for support is afforded by the flat, under side of the wings. Identically the same thing is done in the construction of the flying machine.

Note, for instance, the marked similarity in form as shown in the illustration in Chapter II. Here A is the bird, and B the general outline of the machine. The thin edge of the plane in the latter is almost a duplicate of that formed by the outstretched wings of the bird, while the rudder plane in the rear serves the same purpose as the bird's tail.



CHAPTER IV. VARIOUS FORMS OF FLYING MACHINES.

There are three distinct and radically different forms of flying machines. These are:

Aeroplanes, helicopters and ornithopers.

Of these the aeroplane takes precedence and is used almost exclusively by successful aviators, the helicopters and ornithopers having been tried and found lacking in some vital features, while at the same time in some respects the helicopter has advantages not found in the aeroplane.

What the Helicopter Is.

The helicopter gets its name from being fitted with vertical propellers or helices (see illustration) by the action of which the machine is raised directly from the ground into the air. This does away with the necessity for getting the machine under a gliding headway before it floats, as is the case with the aeroplane, and consequently the helicopter can be handled in a much smaller space than is required for an aeroplane. This, in many instances, is an important advantage, but it is the only one the helicopter possesses, and is more than overcome by its drawbacks. The most serious of these is that the helicopter is deficient in sustaining capacity, and requires too much motive power.

Form of the Ornithopter.

The ornithopter has hinged planes which work like the wings of a bird. At first thought this would seem to be the correct principle, and most of the early experimenters conducted their operations on this line. It is now generally understood, however, that the bird in soaring is in reality an aeroplane, its extended wings serving to sustain, as well as propel, the body. At any rate the ornithoper has not been successful in aviation, and has been interesting mainly as an ingenious toy. Attempts to construct it on a scale that would permit of its use by man in actual aerial flights have been far from encouraging.

Three Kinds of Aeroplanes.

There are three forms of aeroplanes, with all of which more or less success has been attained. These are:

The monoplane, a one-surfaced plane, like that used by Bleriot.

The biplane, a two-surfaced plane, now used by the Wrights, Curtiss, Farman, and others.

The triplane, a three-surfaced plane This form is but little used, its only prominent advocate at present being Elle Lavimer, a Danish experimenter, who has not thus far accomplished much.

Whatever of real success has been accomplished in aviation may be credited to the monoplane and biplane, with the balance in favor of the latter. The monoplane is the more simple in construction and, where weight-sustaining capacity is not a prime requisite, may probably be found the most convenient. This opinion is based on the fact that the smaller the surface of the plane the less will be the resistance offered to the air, and the greater will be the speed at which the machine may be moved. On the other hand, the biplane has a much greater plane surface (double that of a monoplane of the same size) and consequently much greater weight-carrying capacity.

Differences in Biplanes.

While all biplanes are of the same general construction so far as the main planes are concerned, each aviator has his own ideas as to the "rigging."

Wright, for instance, places a double horizontal rudder in front, with a vertical rudder in the rear. There are no partitions between the main planes, and the bicycle wheels used on other forms are replaced by skids.

Voisin, on the contrary, divides the main planes with vertical partitions to increase stability in turning; uses a single-plane horizontal rudder in front, and a big box-tail with vertical rudder at the rear; also the bicycle wheels.

Curtiss attaches horizontal stabilizing surfaces to the upper plane; has a double horizontal rudder in front, with a vertical rudder and horizontal stabilizing surfaces in rear. Also the bicycle wheel alighting gear.



CHAPTER V. CONSTRUCTING A GLIDING MACHINE.

First decide upon the kind of a machine you want—monoplane, biplane, or triplane. For a novice the biplane will, as a rule, be found the most satisfactory as it is more compact and therefore the more easily handled. This will be easily understood when we realize that the surface of a flying machine should be laid out in proportion to the amount of weight it will have to sustain. The generally accepted rule is that 152 square feet of surface will sustain the weight of an average-sized man, say 170 pounds. Now it follows that if these 152 square feet of surface are used in one plane, as in the monoplane, the length and width of this plane must be greater than if the same amount of surface is secured by using two planes—the biplane. This results in the biplane being more compact and therefore more readily manipulated than the monoplane, which is an important item for a novice.

Glider the Basis of Success.

Flying machines without motors are called gliders. In making a flying machine you first construct the glider. If you use it in this form it remains a glider. If you install a motor it becomes a flying machine. You must have a good glider as the basis of a successful flying machine.

It will be well for the novice, the man who has never had any experience as an aviator, to begin with a glider and master its construction and operation before he essays the more pretentious task of handling a fully-equipped flying machine. In fact, it is essential that he should do so.

Plans for Handy Glider.

A glider with a spread (advancing edge) of 20 feet, and a breadth or depth of 4 feet, will be about right to begin with. Two planes of this size will give the 152 square yards of surface necessary to sustain a man's weight. Remember that in referring to flying machine measurements "spread" takes the place of what would ordinarily be called "length," and invariably applies to the long or advancing edge of the machine which cuts into the air. Thus, a glider is spoken of as being 20 feet spread, and 4 feet in depth. So far as mastering the control of the machine is concerned, learning to balance one's self in the air, guiding the machine in any desired direction by changing the position of the body, etc., all this may be learned just as readily, and perhaps more so, with a 20-foot glider than with a larger apparatus.

Kind of Material Required.

There are three all-important features in flying machine construction, viz.: lightness, strength and extreme rigidity. Spruce is the wood generally used for glider frames. Oak, ash and hickory are all stronger, but they are also considerably heavier, and where the saving of weight is essential, the difference is largely in favor of spruce. This will be seen in the following table:

Weight Tensile Compressive per cubic ft. Strength Strength Wood in lbs. lbs. per sq. in. lbs. per sq in. Hickory 53 12,000 8,500 Oak 50 12,000 9,000 Ash 38 12,000 6,000 Walnut 38 8,000 6,000 Spruce 25 8,000 5,000 Pine 25 5,000 4,500

Considering the marked saving in weight spruce has a greater percentage of tensile strength than any of the other woods. It is also easier to find in long, straight-grained pieces free from knots, and it is this kind only that should be used in flying machine construction.

You will next need some spools or hanks of No. 6 linen shoe thread, metal sockets, a supply of strong piano wire, a quantity of closely-woven silk or cotton cloth, glue, turnbuckles, varnish, etc.

Names of the Various Parts.

The long strips, four in number, which form the front and rear edges of the upper and lower frames, are called the horizontal beams. These are each 20 feet in length. These horizontal beams are connected by upright strips, 4 feet long, called stanchions. There are usually 12 of these, six on the front edge, and six on the rear. They serve to hold the upper plane away from the lower one. Next comes the ribs. These are 4 feet in length (projecting for a foot over the rear beam), and while intended principally as a support to the cloth covering of the planes, also tend to hold the frame together in a horizontal position just as the stanchions do in the vertical. There are forty-one of these ribs, twenty-one on the upper and twenty on the lower plane. Then come the struts, the main pieces which join the horizontal beams. All of these parts are shown in the illustrations, reference to which will make the meaning of the various names clear.

Quantity and Cost of Material.

For the horizontal beams four pieces of spruce, 20 feet long, 1 1/2 inches wide and 3/4 inch thick are necessary. These pieces must be straight-grain, and absolutely free from knots. If it is impossible to obtain clear pieces of this length, shorter ones may be spliced, but this is not advised as it adds materially to the weight. The twelve stanchions should be 4 feet long and 7/8 inch in diameter and rounded in form so as to offer as little resistance as possible to the wind. The struts, there are twelve of them, are 3 feet long by 11/4 x 1/2 inch. For a 20-foot biplane about 20 yards of stout silk or unbleached muslin, of standard one yard width, will be needed. The forty-one ribs are each 4 feet long, and 1/2 inch square. A roll of No. 12 piano wire, twenty-four sockets, a package of small copper tacks, a pot of glue, and similar accessories will be required. The entire cost of this material should not exceed $20. The wood and cloth will be the two largest items, and these should not cost more than $10. This leaves $10 for the varnish, wire, tacks, glue, and other incidentals. This estimate is made for cost of materials only, it being taken for granted that the experimenter will construct his own glider. Should the services of a carpenter be required the total cost will probably approximate $60 or $70.

Application of the Rudders.

The figures given also include the expense of rudders, but the details of these have not been included as the glider is really complete without them. Some of the best flights the writer ever saw were made by Mr. A. M. Herring in a glider without a rudder, and yet there can be no doubt that a rudder, properly proportioned and placed, especially a rear rudder, is of great value to the aviator as it keeps the machine with its head to the wind, which is the only safe position for a novice. For initial educational purposes, however, a rudder is not essential as the glides will, or should, be made on level ground, in moderate, steady wind currents, and at a modest elevation. The addition of a rudder, therefore, may well be left until the aviator has become reasonably expert in the management of his machine.

Putting the Machine Together.

Having obtained the necessary material, the first move is to have the rib pieces steamed and curved. This curve may be slight, about 2 inches for the 4 feet. While this is being done the other parts should be carefully rounded so the square edges will be taken off. This may be done with sand paper. Next apply a coat of shellac, and when dry rub it down thoroughly with fine sand paper. When the ribs are curved treat them in the same way.

Lay two of the long horizontal frame pieces on the floor 3 feet apart. Between these place six of the strut pieces. Put one at each end, and each 4 1/2 feet put another, leaving a 2-foot space in the center. This will give you four struts 4 1/2 feet apart, and two in the center 2 feet apart, as shown in the illustration. This makes five rectangles. Be sure that the points of contact are perfect, and that the struts are exactly at right angles with the horizontal frames. This is a most important feature because if your frame "skews" or twists you cannot keep it straight in the air. Now glue the ends of the struts to the frame pieces, using plenty of glue, and nail on strips that will hold the frame in place while the glue is drying. The next day lash the joints together firmly with the shoe thread, winding it as you would to mend a broken gun stock, and over each layer put a coating of glue. This done, the other frame pieces and struts may be treated in the same way, and you will thus get the foundations for the two planes.

Another Way of Placing Struts.

In the machines built for professional use a stronger and more certain form of construction is desired. This is secured by the placing the struts for the lower plane under the frame piece, and those for the upper plane over it, allowing them in each instance to come out flush with the outer edges of the frame pieces. They are then securely fastened with a tie plate or clamp which passes over the end of the strut and is bound firmly against the surface of the frame piece by the eye bolts of the stanchion sockets.

Placing the Rib Pieces.

Take one of the frames and place on it the ribs, with the arched side up, letting one end of the ribs come flush with the front edge of the forward frame, and the other end projecting about a foot beyond the rear frame. The manner of fastening the ribs to the frame pieces is optional. In some cases they are lashed with shoe thread, and in others clamped with a metal clamp fastened with 1/2-inch wood screws. Where clamps and screws are used care should be taken to make slight holes in the wood with an awl before starting the screws so as to lessen any tendency to split the wood. On the top frame, twenty-one ribs placed one foot apart will be required. On the lower frame, because of the opening left for the operator's body, you will need only twenty.

Joining the Two Frames.

The two frames must now be joined together. For this you will need twenty-four aluminum or iron sockets which may be purchased at a foundry or hardware shop. These sockets, as the name implies, provide a receptacle in which the end of a stanchion is firmly held, and have flanges with holes for eye-bolts which hold them firmly to the frame pieces, and also serve to hold the guy wires. In addition to these eye-bolt holes there are two others through which screws are fastened into the frame pieces. On the front frame piece of the bottom plane place six sockets, beginning at the end of the frame, and locating them exactly opposite the struts. Screw the sockets into position with wood screws, and then put the eye-bolts in place. Repeat the operation on the rear frame. Next put the sockets for the upper plane frame in place.

You are now ready to bring the two planes together. Begin by inserting the stanchions in the sockets in the lower plane. The ends may need a little rubbing with sandpaper to get them into the sockets, but care must be taken to have them fit snugly. When all the stanchions are in place on the lower plane, lift the upper plane into position, and fit the sockets over the upper ends of the stanchions.

Trussing with Guy Wires.

The next move is to "tie" the frame together rigidly by the aid of guy wires. This is where the No. 12 piano wire comes in. Each rectangle formed by the struts and stanchions with the exception of the small center one, is to be wired separately as shown in the illustration. At each of the eight corners forming the rectangle the ring of one of the eye-bolts will be found. There are two ways of doing this "tieing," or trussing. One is to run the wires diagonally from eye-bolt to eye-bolt, depending upon main strength to pull them taut enough, and then twist the ends so as to hold. The other is to first make a loop of wire at each eye-bolt, and connect these loops to the main wires with turn-buckles. This latter method is the best, as it admits of the tension being regulated by simply turning the buckle so as to draw the ends of the wire closer together. A glance at the illustration will make this plain, and also show how the wires are to be placed. The proper degree of tension may be determined in the following manner:

After the frame is wired place each end on a saw-horse so as to lift the entire frame clear of the work-shop floor. Get under it, in the center rectangle and, grasping the center struts, one in each hand, put your entire weight on the structure. If it is properly put together it will remain rigid and unyielding. Should it sag ever so slightly the tension of the wires must be increased until any tendency to sag, no matter how slight it may be, is overcome.

Putting on the Cloth.

We are now ready to put on the cloth covering which holds the air and makes the machine buoyant. The kind of material employed is of small account so long as it is light, strong, and wind-proof, or nearly so. Some aviators use what is called rubberized silk, others prefer balloon cloth. Ordinary muslin of good quality, treated with a coat of light varnish after it is in place, will answer all the purposes of the amateur.

Cut the cloth into strips a little over 4 feet in length. As you have 20 feet in width to cover, and the cloth is one yard wide, you will need seven strips for each plane, so as to allow for laps, etc. This will give you fourteen strips. Glue the end of each strip around the front horizontal beams of the planes, and draw each strip back, over the ribs, tacking the edges to the ribs as you go along, with small copper or brass tacks. In doing this keep the cloth smooth and stretched tight. Tacks should also be used in addition to the glue, to hold the cloth to the horizontal beams.

Next, give the cloth a coat of varnish on the clear, or upper side, and when this is dry your glider will be ready for use.

Reinforcing the Cloth.

While not absolutely necessary for amateur purposes, reinforcement of the cloth, so as to avoid any tendency to split or tear out from wind-pressure, is desirable. One way of doing this is to tack narrow strips of some heavier material, like felt, over the cloth where it laps on the ribs. Another is to sew slips or pockets in the cloth itself and let the ribs run through them. Still another method is to sew 2-inch strips (of the same material as the cover) on the cloth, placing them about one yard apart, but having them come in the center of each piece of covering, and not on the laps where the various pieces are joined.

Use of Armpieces.

Should armpieces be desired, aside from those afforded by the center struts, take two pieces of spruce, 3 feet long, by 1 x 1 3/4 inches, and bolt them to the front and rear beams of the lower plane about 14 inches apart. These will be more comfortable than using the struts, as the operator will not have to spread his arms so much. In using the struts the operator, as a rule, takes hold of them with his hands, while with the armpieces, as the name implies, he places his arms over them, one of the strips coming under each armpit.

Frequently somebody asks why the ribs should be curved. The answer is easy. The curvature tends to direct the air downward toward the rear and, as the air is thus forced downward, there is more or less of an impact which assists in propelling the aeroplane upwards.



CHAPTER VI. LEARNING TO FLY.

Don't be too ambitious at the start. Go slow, and avoid unnecessary risks. At its best there is an element of danger in aviation which cannot be entirely eliminated, but it may be greatly reduced and minimized by the use of common sense.

Theoretically, the proper way to begin a glide is from the top of an incline, facing against the wind, so that the machine will soar until the attraction of gravitation draws it gradually to the ground. This is the manner in which experienced aviators operate, but it must be kept in mind that these men are experts. They understand air currents, know how to control the action and direction of their machines by shifting the position of their bodies, and by so doing avoid accidents which would be unavoidable by a novice.

Begin on Level Ground.

Make your first flights on level ground, having a couple of men to assist you in getting the apparatus under headway. Take your position in the center rectangle, back far enough to give the forward edges of the glider an inclination to tilt upward very slightly. Now start and run forward at a moderately rapid gait, one man at each end of the glider assisting you. As the glider cuts into the air the wind will catch under the uplifted edges of the curved planes, and buoy it up so that it will rise in the air and take you with it. This rise will not be great, just enough to keep you well clear of the ground. Now project your legs a little to the front so as to shift the center of gravity a trifle and bring the edges of the glider on an exact level with the atmosphere. This, with the momentum acquired in the start, will keep the machine moving forward for some distance.

Effect of Body Movements.

When the weight of the body is slightly back of the center of gravity the edges of the advancing planes are tilted slightly upward. The glider in this position acts as a scoop, taking in the air which, in turn, lifts it off the ground. When a certain altitude is reached—this varies with the force of the wind—the tendency to a forward movement is lost and the glider comes to the ground. It is to prolong the forward movement as much as possible that the operator shifts the center of gravity slightly, bringing the apparatus on an even keel as it were by lowering the advancing edges. This done, so long as there is momentum enough to keep the glider moving, it will remain afloat.

If you shift your body well forward it will bring the front edges of the glider down, and elevate the rear ones. In this way the air will be "spilled" out at the rear, and, having lost the air support or buoyancy, the glider comes down to the ground. A few flights will make any ordinary man proficient in the control of his apparatus by his body movements, not only as concerns the elevating and depressing of the advancing edges, but also actual steering. You will quickly learn, for instance, that, as the shifting of the bodily weight backwards and forwards affects the upward and downward trend of the planes, so a movement sideways—to the left or the right—affects the direction in which the glider travels.

Ascends at an Angle.

In ascending, the glider and flying machine, like the bird, makes an angular, not a vertical flight. Just what this angle of ascension may be is difficult to determine. It is probable and in fact altogether likely, that it varies with the force of the wind, weight of the rising body, power of propulsion, etc. This, in the language of physicists, is the angle of inclination, and, as a general thing, under normal conditions (still air) should be put down as about one in ten, or 5 3/4 degrees. This would be an ideal condition, but it has not, as vet been reached. The force of the wind affects the angle considerably, as does also the weight and velocity of the apparatus. In general practice the angle varies from 23 to 45 degrees. At more than 45 degrees the supporting effort is overcome by the resistance to forward motion.

Increasing the speed or propulsive force, tends to lessen the angle at which the machine may be successfully operated because it reduces the wind pressure. Most of the modern flying machines are operated at an angle of 23 degrees, or less.

Maintaining an Equilibrium.

Stable equilibrium is one of the main essentials to successful flight, and this cannot be preserved in an uncertain, gusty wind, especially by an amateur. The novice should not attempt a glide unless the conditions are just right. These conditions are: A clear, level space, without obstructions, such as trees, etc., and a steady wind of not exceeding twelve miles an hour. Always fly against the wind.

When a reasonable amount of proficiency in the handling of the machine on level ground has been acquired the field of practice may be changed to some gentle slope. In starting from a slope it will be found easier to keep the machine afloat, but the experience at first is likely to be very disconcerting to a man of less than iron nerve. As the glider sails away from the top of the slope the distance between him and the ground increases rapidly until the aviator thinks he is up a hundred miles in the air. If he will keep cool, manipulate his apparatus so as to preserve its equilibrium, and "let nature take its course," he will come down gradually and safely to the ground at a considerable distance from the starting place. This is one advantage of starting from an elevation—your machine will go further.

But, if the aviator becomes "rattled"; if he loses control of his machine, serious results, including a bad fall with risk of death, are almost certain. And yet this practice is just as necessary as the initial lessons on level ground. When judgment is used, and "haste made slowly," there is very little real danger. While experimenting with gliders the Wrights made flights innumerable under all sorts of conditions and never had an accident of any kind.

Effects of Wind Currents.

The larger the machine the more difficult it will be to control its movements in the air, and yet enlargement is absolutely necessary as weight, in the form of motor, rudder, etc., is added.

Air currents near the surface of the ground are diverted by every obstruction unless the wind is blowing hard enough to remove the obstruction entirely. Take, for instance, the case of a tree or shrub, in a moderate wind of from ten to twelve miles an hour. As the wind strikes the tree it divides, part going to one side and part going to the other, while still another part is directed upward and goes over the top of the obstruction. This makes the handling of a glider on an obstructed field difficult and uncertain. To handle a glider successfully the place of operation should be clear and the wind moderate and steady. If it is gusty postpone your flight. In this connection it will be well to understand the velocity of the wind, and what it means as shown in the following table:

Miles per hour Feet per second Pressure per sq. foot 10 14.7 .492 25 36.7 3.075 50 73.3 12.300 100 146.6 49.200

Pressure of wind increases in proportion to the square of the velocity. Thus wind at 10 miles an hour has four times the pressure of wind at 5 miles an hour. The greater this pressure the large and heavier the object which can be raised. Any boy who has had experience in flying kites can testify to this, High winds, however, are almost invariably gusty and uncertain as to direction, and this makes them dangerous for aviators. It is also a self-evident fact that, beyond a certain stage, the harder the wind blows the more difficult it is to make headway against it.

Launching Device for Gliders.

On page 195 will be found a diagram of the various parts of a launcher for gliders, designed and patented by Mr. Octave Chanute. In describing this invention in Aeronautics, Mr. Chanute says:

"In practicing, the track, preferably portable, is generally laid in the direction of the existing wind and the car, preferably a light platform-car, is placed on the track. The truck carrying the winding-drum and its motor is placed to windward a suitable distance—say from two hundred to one thousand feet—and is firmly blocked or anchored in line with the portable track, which is preferably 80 or 100 feet in length. The flying or gliding machine to be launched with its operator is placed on the platform-car at the leeward end of the portable track. The line, which is preferably a flexible combination wire-and-cord cable, is stretched between the winding-drum on the track and detachably secured to the flying or gliding machine, preferably by means of a trip-hoop, or else held in the hand of the operator, so that the operator may readily detach the same from the flying-machine when the desired height is attained."

How Glider Is Started.

"Then upon a signal given by the operator the engineer at the motor puts it into operation, gradually increasing the speed until the line is wound upon the drum at a maximum speed of, say, thirty miles an hour. The operator of the flying-machine, whether he stands upright and carries it on his shoulders, or whether he sits or lies down prone upon it, adjusts the aeroplane or carrying surfaces so that the wind shall strike them on the top and press downward instead of upward until the platform-car under action of the winding-drum and line attains the required speed.

"When the operator judges that his speed is sufficient, and this depends upon the velocity of the wind as well as that of the car moving against the wind, he quickly causes the front of the flying-machine to tip upward, so that the relative wind striking on the under side of the planes or carrying surfaces shall lift the flying machine into the air. It then ascends like a kite to such height as may be desired by the operator, who then trips the hook and releases the line from the machine."

What the Operator Does.

"The operator being now free in the air has a certain initial velocity imparted by the winding-drum and line and also a potential energy corresponding to his height above the ground. If the flying or gliding machine is provided with a motor, he can utilize that in his further flight, and if it is a simple gliding machine without motor he can make a descending flight through the air to such distance as corresponds to the velocity acquired and the height gained, steering meanwhile by the devices provided for that purpose.

"The simplest operation or maneuver is to continue the flight straight ahead against the wind; but it is possible to vary this course to the right or left, or even to return in downward flight with the wind to the vicinity of the starting-point. Upon nearing the ground the operator tips upward his carrying-surfaces and stops his headway upon the cushion of increased air resistance so caused. The operator is in no way permanently fastened to his machine, and the machine and the operator simply rest upon the light platform-car, so that the operator is free to rise with the machine from the car whenever the required initial velocity is attained.

Motor For the Launcher.

"The motor may be of any suitable kind or construction, but is preferably an electric or gasolene motor. The winding-drum is furnished with any suitable or customary reversing-guide to cause the line to wind smoothly and evenly upon the drum. The line is preferably a cable composed of flexible wire and having a cotton or other cord core to increase its flexibility. The line extends from the drum to the flying or gliding machine. Its free end may, if desired, be grasped and held by the operator until the flying-machine ascends to the desired height, when by simply letting go of the line the operator may continue his flight free. The line, however, is preferably connected to the flying or gliding machine directly by a trip-hook having a handle or trip lever within reach of the operator, so that when he ascends to the required height he may readily detach the line from the flying or gliding machine."



CHAPTER VII. PUTTING ON THE RUDDER.

Gliders as a rule have only one rudder, and this is in the rear. It tends to keep the apparatus with its head to the wind. Unlike the rudder on a boat it is fixed and immovable. The real motor-propelled flying machine, generally has both front and rear rudders manipulated by wire cables at the will of the operator.

Allowing that the amateur has become reasonably expert in the manipulation of the glider he should, before constructing an actual flying machine, equip his glider with a rudder.

Cross Pieces for Rudder Beam.

To do this he should begin by putting in a cross piece, 2 feet long by 1/4 x 3/4 inches between the center struts, in the lower plane. This may be fastened to the struts with bolts or braces. The former method is preferable. On this cross piece, and on the rear frame of the plane itself, the rudder beam is clamped and bolted. This rudder beam is 8 feet 11 inches long. Having put these in place duplicate them in exactly the same manner and dimensions from the upper frame The cross pieces on which the ends of the rudder beams are clamped should be placed about one foot in advance of the rear frame beam.

The Rudder Itself.

The next step is to construct the rudder itself. This consists of two sections, one horizontal, the other vertical. The latter keeps the aeroplane headed into the wind, while the former keeps it steady—preserves the equilibrium.

The rudder beams form the top and bottom frames of the vertical rudder. To these are bolted and clamped two upright pieces, 3 feet, 10 inches in length, and 3/4 inch in cross section. These latter pieces are placed about two feet apart. This completes the framework of the vertical rudder. See next page (59).

For the horizontal rudder you will require two strips 6 feet long, and four 2 feet long. Find the exact center of the upright pieces on the vertical rudder, and at this spot fasten with bolts the long pieces of the horizontal, placing them on the outside of the vertical strips. Next join the ends of the horizontal strips with the 2-foot pieces, using small screws and corner braces. This done you will have two of the 2-foot pieces left. These go in the center of the horizontal frame, "straddling" the vertical strips, as shown in the illustration.

The framework is to be covered with cloth in the same manner as the planes. For this about ten yards will be needed.

Strengthening the Rudder.

To ensure rigidity the rudder must be stayed with guy wires. For this purpose the No. 12 piano wire is the best. Begin by running two of these wires from the top eye-bolts of stanchions 3 and 4, page 37, to rudder beam where it joins the rudder planes, fastening them at the bottom. Then run two wires from the top of the rudder beam at the same point, to the bottom eye-bolts of the same stanchions. This will give you four diagonal wires reaching from the rudder beam to the top and bottom planes of the glider. Now, from the outer ends of the rudder frame run four similar diagonal wires to the end of the rudder beam where it rests on the cross piece. You will then have eight truss wires strengthening the connection of the rudder to the main body of the glider.

The framework of the rudder planes is then to be braced in the same way, which will take eight more wires, four for each rudder plane. All the wires are to be connected at one end with turn-buckles so the tension may be regulated as desired.

In forming the rudder frame it will be well to mortise the corners, tack them together with small nails, and then put in a corner brace in the inside of each joint. In doing this bear in mind that the material to be thus fastened is light, and consequently the lightest of nails, screws, bolts and corner pieces, etc., is necessary.



CHAPTER VIII. THE REAL FLYING MACHINE.

We will now assume that you have become proficient enough to warrant an attempt at the construction of a real flying machine—one that will not only remain suspended in the air at the will of the operator, but make respectable progress in whatever direction he may desire to go. The glider, it must be remembered, is not steerable, except to a limited extent, and moves only in one direction—against the wind. Besides this its power of flotation—suspension in the air—is circumscribed.

Larger Surface Area Required.

The real flying machine is the glider enlarged, and equipped with motor and propeller. The first thing to do is to decide upon the size required. While a glider of 20 foot spread is large enough to sustain a man it could not under any possible conditions, be made to rise with the weight of the motor, propeller and similar equipment added. As the load is increased so must the surface area of the planes be increased. Just what this increase in surface area should be is problematical as experienced aviators disagree, but as a general proposition it may be placed at from three to four times the area of a 20-foot glider. [3]

Some Practical Examples.

The Wrights used a biplane 41 feet in spread, and 6 1/2 ft. deep. This, for the two planes, gives a total surface area of 538 square feet, inclusive of auxiliary planes. This sustains the engine equipment, operator, etc., a total weight officially announced at 1,070 pounds. It shows a lifting capacity of about two pounds to the square foot of plane surface, as against a lifting capacity of about 1/2 pound per square foot of plane surface for the 20-foot glider. This same Wright machine is also reported to have made a successful flight, carrying a total load of 1,100 pounds, which would be over two pounds for each square foot of surface area, which, with auxiliary planes, is 538 square feet.

To attain the same results in a monoplane, the single surface would have to be 60 feet in spread and 9 feet deep. But, while this is the mathematical rule, Bleriot has demonstrated that it does not always hold good. On his record-breaking trip across the English channel, July 25th, 1909, the Frenchman was carried in a monoplane 24 1/2 feet in spread, and with a total sustaining surface of 150 1/2 square feet. The total weight of the outfit, including machine, operator and fuel sufficient for a three-hour run, was only 660 pounds. With an engine of (nominally) 25 horsepower the distance of 21 miles was covered in 37 minutes.

Which is the Best?

Right here an established mathematical quantity is involved. A small plane surface offers less resistance to the air than a large one and consequently can attain a higher rate of speed. As explained further on in this chapter speed is an important factor in the matter of weight-sustaining capacity. A machine that travels one-third faster than another can get along with one-half the surface area of the latter without affecting the load. See the closing paragraph of this chapter on this point. In theory the construction is also the simplest, but this is not always found to be so in practice. The designing and carrying into execution of plans for an extensive area like that of a monoplane involves great skill and cleverness in getting a framework that will be strong enough to furnish the requisite support without an undue excess of weight. This proposition is greatly simplified in the biplane and, while the speed attained by the latter may not be quite so great as that of the monoplane, it has much larger weight-carrying capacity.

Proper Sizes For Frame.

Allowing that the biplane form is selected the construction may be practically identical with that of the 20-foot glider described in Chapter V., except as to size and elimination of the armpieces. In size the surface planes should be about twice as large as those of the 20-foot glider, viz: 40 feet spread instead of 20, and 6 feet deep instead of 3. The horizontal beams, struts, stanchions, ribs, etc., should also be increased in size proportionately.

While care in the selection of clear, straight-grained timber is important in the glider, it is still more important in the construction of a motor-equipped flying machine as the strain on the various parts will be much greater.

How to Splice Timbers.

It is practically certain that you will have to resort to splicing the horizontal beams as it will be difficult, if not impossible, to find 40-foot pieces of timber totally free from knots and worm holes, and of straight grain.

If splicing is necessary select two good 20-foot pieces, 3 inches wide and 1 1/2 inches thick, and one 10-foot long, of the same thickness and width. Plane off the bottom sides of the 10-foot strip, beginning about two feet back from each end, and taper them so the strip will be about 3/4 inch thick at the extreme ends. Lay the two 20-foot beams end to end, and under the joint thus made place the 10-foot strip, with the planed-off ends downward. The joint of the 20-foot pieces should be directly in the center of the 10-foot piece. Bore ten holes (with a 1/4-inch augur) equi-distant apart through the 20-foot strips and the 10-foot strip under them. Through these holes run 1/4-inch stove bolts with round, beveled heads. In placing these bolts use washers top and bottom, one between the head and the top beam, and the other between the bottom beam and the screw nut which holds the bolt. Screw the nuts down hard so as to bring the two beams tightly together, and you will have a rigid 40-foot beam.

Splicing with Metal Sleeves.

An even better way of making a splice is by tonguing and grooving the ends of the frame pieces and enclosing them in a metal sleeve, but it requires more mechanical skill than the method first named. The operation of tonguing and grooving is especially delicate and calls for extreme nicety of touch in the handling of tools, but if this dexterity is possessed the job will be much more satisfactory than one done with a third timber.

As the frame pieces are generally about 1 1/2 inch in diameter, the tongue and the groove into which the tongue fits must be correspondingly small. Begin by sawing into one side of one of the frame pieces about 4 inches back from the end. Make the cut about 1/2 inch deep. Then turn the piece over and duplicate the cut. Next saw down from the end to these cuts. When the sawed-out parts are removed you will have a "tongue" in the end of the frame timber 4 inches long and 1/2 inch thick. The next move is to saw out a 5/8-inch groove in the end of the frame piece which is to be joined. You will have to use a small chisel to remove the 5/8-inch bit. This will leave a groove into which the tongue will fit easily.

Joining the Two Pieces.

Take a thin metal sleeve—this is merely a hollow tube of aluminum or brass open at each end—8 inches long, and slip it over either the tongued or grooved end of one of the frame timbers. It is well to have the sleeve fit snugly, and this may necessitate a sand-papering of the frame pieces so the sleeve will slip on.

Push the sleeve well back out of the way. Cover the tongue thoroughly with glue, and also put some on the inside of the groove. Use plenty of glue. Now press the tongue into the groove, and keep the ends firmly together until the glue is thoroughly dried. Rub off the joint lightly with sand-paper to remove any of the glue which may have oozed out, and slip the sleeve into place over the joint. Tack the sleeve in position with small copper tacks, and you will have an ideal splice.

The same operation is to be repeated on each of the four frame pieces. Two 20-foot pieces joined in this way will give a substantial frame, but when suitable timber of this kind can not be had, three pieces, each 6 feet 11 inches long, may be used. This would give 20 feet 9 inches, of which 8 inches will be taken up in the two joints, leaving the frame 20 feet 1 inch long.

Installation of Motor.

Next comes the installation of the motor. The kinds and efficiency of the various types are described in the following chapter (IX). All we are interested in at this point is the manner of installation. This varies according to the personal ideas of the aviator. Thus one man puts his motor in the front of his machine, another places it in the center, and still another finds the rear of the frame the best. All get good results, the comparative advantages of which it is difficult to estimate. Where one man, as already explained, flies faster than another, the one beaten from the speed standpoint has an advantage in the matter of carrying weight, etc.

The ideas of various well-known aviators as to the correct placing of motors may be had from the following:

Wrights—In rear of machine and to one side.

Curtiss—Well to rear, about midway between upper and lower planes.

Raich—In rear, above the center.

Brauner-Smith—In exact center of machine.

Van Anden—In center.

Herring-Burgess—Directly behind operator.

Voisin—In rear, and on lower plane.

Bleriot—In front.

R. E. P.—In front.

The One Chief Object.

An even distribution of the load so as to assist in maintaining the equilibrium of the machine, should be the one chief object in deciding upon the location of the motor. It matters little what particular spot is selected so long as the weight does not tend to overbalance the machine, or to "throw it off an even keel." It is just like loading a vessel, an operation in which the expert seeks to so distribute the weight of the cargo as to keep the vessel in a perfectly upright position, and prevent a "list" or leaning to one side. The more evenly the cargo is distributed the more perfect will be the equilibrium of the vessel and the better it can be handled. Sometimes, when not properly stowed, the cargo shifts, and this at once affects the position of the craft. When a ship "lists" to starboard or port a preponderating weight of the cargo has shifted sideways; if bow or stern is unduly depressed it is a sure indication that the cargo has shifted accordingly. In either event the handling of the craft becomes not only difficult, but extremely hazardous. Exactly the same conditions prevail in the handling of a flying machine.

Shape of Machine a Factor.

In placing the motor you must be governed largely by the shape and construction of the flying machine frame. If the bulk of the weight of the machine and auxiliaries is toward the rear, then the natural location for the motor will be well to the front so as to counterbalance the excess in rear weight. In the same way if the preponderance of the weight is forward, then the motor should be placed back of the center.

As the propeller blade is really an integral part of the motor, the latter being useless without it, its placing naturally depends upon the location selected for the motor.

Rudders and Auxiliary Planes.

Here again there is great diversity of opinion among aviators as to size, location and form. The striking difference of ideas in this respect is well illustrated in the choice made by prominent makers as follows:

Voisin—horizontal rudder, with two wing-like planes, in front; box-like longitudinal stability plane in rear, inside of which is a vertical rudder.

Wright—large biplane horizontal rudder in front at considerable distance—about 10 feet—from the main planes; vertical biplane rudder in rear; ends of upper and lower main planes made flexible so they may be moved.

Curtiss—horizontal biplane rudder, with vertical damping plane between the rudder planes about 10 feet in front of main planes; vertical rudder in rear; stabilizing planes at each end of upper main plane.

Bleriot—V-shaped stabilizing fin, projecting from rear of plane, with broad end outward; to the broad end of this fin is hinged a vertical rudder; horizontal biplane rudder, also in rear, under the fin.

These instances show forcefully the wide diversity of opinion existing among experienced aviators as to the best manner of placing the rudders and stabilizing, or auxiliary planes, and make manifest how hopeless would be the task of attempting to select any one form and advise its exclusive use.

Rudder and Auxiliary Construction.

The material used in the construction of the rudders and auxiliary planes is the same as that used in the main planes—spruce for the framework and some kind of rubberized or varnished cloth for the covering. The frames are joined and wired in exactly the same manner as the frames of the main planes, the purpose being to secure the same strength and rigidity. Dimensions of the various parts depend upon the plan adopted and the size of the main plane.

No details as to exact dimensions of these rudders and auxiliary planes are obtainable. The various builders, while willing enough to supply data as to the general measurements, weight, power, etc., of their machines, appear to have overlooked the details of the auxiliary parts, thinking, perhaps, that these were of no particular import to the general public. In the Wright machine, the rear horizontal and front vertical rudders may be set down as being about one-quarter (probably a little less) the size of the main supporting planes.

Arrangement of Alighting Gear.

Most modern machines are equipped with an alighting gear, which not only serves to protect the machine and aviator from shock or injury in touching the ground, but also aids in getting under headway. All the leading makes, with the exception of the Wright, are furnished with a frame carrying from two to five pneumatic rubber-tired bicycle wheels. In the Curtiss and Voisin machines one wheel is placed in front and two in the rear. In the Bleriot and other prominent machines the reverse is the rule—two wheels in front and one in the rear. Farman makes use of five wheels, one in the extreme rear, and four, arranged in pairs, a little to the front of the center of the main lower plane.

In place of wheels the Wright machine is equipped with a skid-like device consisting of two long beams attached to the lower plane by stanchions and curving up far in front, so as to act as supports to the horizontal rudder.

Why Wood Is Favored.

A frequently asked question is: "Why is not aluminum, or some similar metal, substituted for wood." Wood, particularly spruce, is preferred because, weight considered, it is much stronger than aluminum, and this is the lightest of all metals. In this connection the following table will be of interest:

Compressive Weight Tensile Strength Strength per cubic foot per sq. inch per sq. inch Material in lbs. in lbs. in lbs. Spruce.... 25 8,000 5,000 Aluminum 162 16,000 ...... Brass (sheet) 510 23,000 12,000 Steel (tool) 490 100,000 40,000 Copper (sheet) 548 30,000 40,000

As extreme lightness, combined with strength, especially tensile strength, is the great essential in flying-machine construction, it can be readily seen that the use of metal, even aluminum, for the framework, is prohibited by its weight. While aluminum has double the strength of spruce wood it is vastly heavier, and thus the advantage it has in strength is overbalanced many times by its weight. The specific gravity of aluminum is 2.50; that of spruce is only 0.403.

Things to Be Considered.

In laying out plans for a flying machine there are five important points which should be settled upon before the actual work of construction is started. These are:

First—Approximate weight of the machine when finished and equipped.

Second—Area of the supporting surface required.

Third—Amount of power that will be necessary to secure the desired speed and lifting capacity.

Fourth—Exact dimensions of the main framework and of the auxiliary parts.

Fifth—Size, speed and character of the propeller.

In deciding upon these it will be well to take into consideration the experience of expert aviators regarding these features as given elsewhere. (See Chapter X.)

Estimating the Weights Involved.

In fixing upon the probable approximate weight in advance of construction much, of course, must be assumed. This means that it will be a matter of advance estimating. If a two-passenger machine is to be built we will start by assuming the maximum combined weight of the two people to be 350 pounds. Most of the professional aviators are lighter than this. Taking the medium between the weights of the Curtiss and Wright machines we have a net average of 850 pounds for the framework, motor, propeller, etc. This, with the two passengers, amounts to 1,190 pounds. As the machines quoted are in successful operation it will be reasonable to assume that this will be a safe basis to operate on.

What the Novice Must Avoid.

This does not mean, however, that it will be safe to follow these weights exactly in construction, but that they will serve merely as a basis to start from. Because an expert can turn out a machine, thoroughly equipped, of 850 pounds weight, it does not follow that a novice can do the same thing. The expert's work is the result of years of experience, and he has learned how to construct frames and motor plants of the utmost lightness and strength.

It will be safer for the novice to assume that he can not duplicate the work of such men as Wright and Curtiss without adding materially to the gross weight of the framework and equipment minus passengers.

How to Distribute the Weight.

Let us take 1,030 pounds as the net weight of the machine as against the same average in the Wright and Curtiss machines. Now comes the question of distributing this weight between the framework, motor, and other equipment. As a general proposition the framework should weigh about twice as much as the complete power plant (this is for amateur work).

The word "framework" indicates not only the wooden frames of the main planes, auxiliary planes, rudders, etc., but the cloth coverings as well—everything in fact except the engine and propeller.

On the basis named the framework would weigh 686 pounds, and the power plant 344. These figures are liberal, and the results desired may be obtained well within them as the novice will learn as he makes progress in the work.

Figuring on Surface Area.

It was Prof. Langley who first brought into prominence in connection with flying machine construction the mathematical principle that the larger the object the smaller may be the relative area of support. As explained in Chapter XIII, there are mechanical limits as to size which it is not practical to exceed, but the main principle remains in effect.

Take two aeroplanes of marked difference in area of surface. The larger will, as a rule, sustain a greater weight in relative proportion to its area than the smaller one, and do the work with less relative horsepower. As a general thing well-constructed machines will average a supporting capacity of one pound for every one-half square foot of surface area. Accepting this as a working rule we find that to sustain a weight of 1,200 pounds—machine and two passengers—we should have 600 square feet of surface.

Distributing the Surface Area.

The largest surfaces now in use are those of the Wright, Voisin and Antoinette machines—538 square feet in each. The actual sustaining power of these machines, so far as known, has never been tested to the limit; it is probable that the maximum is considerably in excess of what they have been called upon to show. In actual practice the average is a little over one pound for each one-half square foot of surface area.

Allowing that 600 square feet of surface will be used, the next question is how to distribute it to the best advantage. This is another important matter in which individual preference must rule. We have seen how the professionals disagree on this point, some using auxiliary planes of large size, and others depending upon smaller auxiliaries with an increase in number so as to secure on a different plan virtually the same amount of surface.

In deciding upon this feature the best thing to do is to follow the plans of some successful aviator, increasing the area of the auxiliaries in proportion to the increase in the area of the main planes. Thus, if you use 600 square feet of surface where the man whose plans you are following uses 500, it is simply a matter of making your planes one-fifth larger all around.

The Cost of Production.

Cost of production will be of interest to the amateur who essays to construct a flying machine. Assuming that the size decided upon is double that of the glider the material for the framework, timber, cloth, wire, etc., will cost a little more than double. This is because it must be heavier in proportion to the increased size of the framework, and heavy material brings a larger price than the lighter goods. If we allow $20 as the cost of the glider material it will be safe to put down the cost of that required for a real flying machine framework at $60, provided the owner builds it himself.

As regards the cost of motor and similar equipment it can only be said that this depends upon the selection made. There are some reliable aviation motors which may be had as low as $500, and there are others which cost as much as $2,000.

Services of Expert Necessary.

No matter what kind of a motor may be selected the services of an expert will be necessary in its proper installation unless the amateur has considerable genius in this line himself. As a general thing $25 should be a liberal allowance for this work. No matter how carefully the engine may be placed and connected it will be largely a matter of luck if it is installed in exactly the proper manner at the first attempt. The chances are that several alterations, prompted by the results of trials, will have to be made. If this is the case the expert's bill may readily run up to $50. If the amateur is competent to do this part of the work the entire item of $50 may, of course, be cut out.

As a general proposition a fairly satisfactory flying machine, one that will actually fly and carry the operator with it, may be constructed for $750, but it will lack the better qualities which mark the higher priced machines. This computation is made on the basis of $60 for material, $50 for services of expert, $600 for motor, etc., and an allowance of $40 for extras.

No man who has the flying machine germ in his system will be long satisfied with his first moderate price machine, no matter how well it may work. It's the old story of the automobile "bug" over again. The man who starts in with a modest $1,000 automobile invariably progresses by easy stages to the $4,000 or $5,000 class. The natural tendency is to want the biggest and best attainable within the financial reach of the owner.

It's exactly the same way with the flying machine convert. The more proficient he becomes in the manipulation of his car, the stronger becomes the desire to fly further and stay in the air longer than the rest of his brethren. This necessitates larger, more powerful, and more expensive machines as the work of the germ progresses.

Speed Affects Weight Capacity.

Don't overlook the fact that the greater speed you can attain the smaller will be the surface area you can get along with. If a machine with 500 square feet of sustaining surface, traveling at a speed of 40 miles an hour, will carry a weight of 1,200 pounds, we can cut the sustaining surface in half and get along with 250 square feet, provided a speed of 60 miles an hour can be obtained. At 100 miles an hour only 80 square feet of surface area would be required. In both instances the weight sustaining capacity will remain the same as with the 500 square feet of surface area—1,200 pounds.

One of these days some mathematical genius will figure out this problem with exactitude and we will have a dependable table giving the maximum carrying capacity of various surface areas at various stated speeds, based on the dimensions of the advancing edges. At present it is largely a matter of guesswork so far as making accurate computation goes. Much depends upon the shape of the machine, and the amount of surface offering resistance to the wind, etc.



CHAPTER IX. SELECTION OF THE MOTOR.

Motors for flying machines must be light in weight, of great strength, productive of extreme speed, and positively dependable in action. It matters little as to the particular form, or whether air or water cooled, so long as the four features named are secured. There are at least a dozen such motors or engines now in use. All are of the gasolene type, and all possess in greater or lesser degree the desired qualities. Some of these motors are:

Renault—8-cylinder, air-cooled; 50 horse power; weight 374 pounds.

Fiat—8-cylinder, air-cooled; 50 horse power; weight 150 pounds.

Farcot—8-cylinder, air-cooled; from 30 to 100 horse power, according to bore of cylinders; weight of smallest, 84 pounds.

R. E. P.—10-cylinder, air-cooled; 150 horse power; weight 215 pounds.

Gnome—7 and 14 cylinders, revolving type, air-cooled; 50 and 100 horse power; weight 150 and 300 pounds.

Darracq—2 to 14 cylinders, water cooled; 30 to 200 horse power; weight of smallest 100 pounds.

Wright—4-cylinder, water-cooled; 25 horse power; weight 200 pounds.

Antoinette—8 and 16-cylinder, water-cooled; 50 and 100 horse power; weight 250 and 500 pounds.

E. N. V.—8-cylinder, water-cooled; from 30 to 80 horse power, according to bore of cylinder; weight 150 to 400 pounds.

Curtiss—8-cylinder, water-cooled; 60 horse power; weight 300 pounds.

Average Weight Per Horse Power.

It will be noticed that the Gnome motor is unusually light, being about three pounds to the horse power produced, as opposed to an average of 4 1/2 pounds per horse power in other makes. This result is secured by the elimination of the fly-wheel, the engine itself revolving, thus obtaining the same effect that would be produced by a fly-wheel. The Farcot is even lighter, being considerably less than three pounds per horse power, which is the nearest approach to the long-sought engine equipment that will make possible a complete flying machine the total weight of which will not exceed one pound per square foot of area.

How Lightness Is Secured.

Thus far foreign manufacturers are ahead of Americans in the production of light-weight aerial motors, as is evidenced by the Gnome and Farcot engines, both of which are of French make. Extreme lightness is made possible by the use of fine, specially prepared steel for the cylinders, thus permitting them to be much thinner than if ordinary forms of steel were used. Another big saving in weight is made by substituting what are known as "auto lubricating" alloys for bearings. These alloys are made of a combination of aluminum and magnesium.

Still further gains are made in the use of alloy steel tubing instead of solid rods, and also by the paring away of material wherever it can be done without sacrificing strength. This plan, with the exclusive use of the best grades of steel, regardless of cost, makes possible a marked reduction in weight.

Multiplicity of Cylinders.

Strange as it may seem, multiplicity of cylinders does not always add proportionate weight. Because a 4-cylinder motor weighs say 100 pounds, it does not necessarily follow that an 8-cylinder equipment will weigh 200 pounds. The reason of this will be plain when it is understood that many of the parts essential to a 4-cylinder motor will fill the requirements of an 8-cylinder motor without enlargement or addition.

Neither does multiplying the cylinders always increase the horsepower proportionately. If a 4-cylinder motor is rated at 25 horsepower it is not safe to take it for granted that double the number of cylinders will give 50 horsepower. Generally speaking, eight cylinders, the bore, stroke and speed being the same, will give double the power that can be obtained from four, but this does not always hold good. Just why this exception should occur is not explainable by any accepted rule.

Horse Power and Speed.

Speed is an important requisite in a flying-machine motor, as the velocity of the aeroplane is a vital factor in flotation. At first thought, the propeller and similar adjuncts being equal, the inexperienced mind would naturally argue that a 50-horsepower engine should produce just double the speed of one of 25-horsepower. That this is a fallacy is shown by actual performances. The Wrights, using a 25-horsepower motor, have made 44 miles an hour, while Bleriot, with a 50-horsepower motor, has a record of a short-distance flight at the rate of 52 miles an hour. The fact is that, so far as speed is concerned, much depends upon the velocity of the wind, the size and shape of the aeroplane itself, and the size, shape and gearing of the propeller. The stronger the wind is blowing the easier it will be for the aeroplane to ascend, but at the same time the more difficult it will be to make headway against the wind in a horizontal direction. With a strong head wind, and proper engine force, your machine will progress to a certain extent, but it will be at an angle. If the aviator desired to keep on going upward this would be all right, but there is a limit to the altitude which it is desirable to reach—from 100 to 500 feet for experts—and after that it becomes a question of going straight ahead.

Great Waste of Power.

One thing is certain—even in the most efficient of modern aerial motors there is a great loss of power between the two points of production and effect. The Wright outfit, which is admittedly one of the most effective in use, takes one horsepower of force for the raising and propulsion of each 50 pounds of weight. This, for a 25-horsepower engine, would give a maximum lifting capacity of 1250 pounds. It is doubtful if any of the higher rated motors have greater efficiency. As an 8-cylinder motor requires more fuel to operate than a 4-cylinder, it naturally follows that it is more expensive to run than the smaller motor, and a normal increase in capacity, taking actual performances as a criterion, is lacking. In other words, what is the sense of using an 8-cylinder motor when one of 4 cylinders is sufficient?

What the Propeller Does.

Much of the efficiency of the motor is due to the form and gearing of the propeller. Here again, as in other vital parts of flying-machine mechanism, we have a wide divergence of opinion as to the best form. A fish makes progress through the water by using its fins and tail; a bird makes its way through the air in a similar manner by the use of its wings and tail. In both instances the motive power comes from the body of the fish or bird.

In place of fins or wings the flying machine is equipped with a propeller, the action of which is furnished by the engine. Fins and wings have been tried, but they don't work.

While operating on the same general principle, aerial propellers are much larger than those used on boats. This is because the boat propeller has a denser, more substantial medium to work in (water), and consequently can get a better "hold," and produce more propulsive force than one of the same size revolving in the air. This necessitates the aerial propellers being much larger than those employed for marine purposes. Up to this point all aviators agree, but as to the best form most of them differ.

Kinds of Propellers Used.

One of the most simple is that used by Curtiss. It consists of two pear-shaped blades of laminated wood, each blade being 5 inches wide at its extreme point, tapering slightly to the shaft connection. These blades are joined at the engine shaft, in a direct line. The propeller has a pitch of 5 feet, and weighs, complete, less than 10 pounds. The length from end to end of the two blades is 6 1/2 feet.

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