Navigating the air : a scientific statement of the progress of aeronautical science up to the present time

Front matter

PROVO, UTAH

E K L i iJ f s 5 WaCdirl •Jdckson]

I

Contents

PAGE

Preface ix

By Cortlandt Field Bishop

II The Relations Of Weight, Speed, And Power Of Flyers

By Wilbur and Orville Wright

HE flyer of 1903 carried a four-cylinder gasolene motor of four-inch bore and four-inch stroke. Complete with magneto, radiators, tanks, water, fuel, etc., the motor weighed a little over 200 lbs. ; and at 1200 revolutions per minute, developed 16 horse-power for the first 15 seconds after starting. After a minute or two the power did not exceed 13 to 14 horse-power. At 1020 revolutions per minute— the speed of the motor in the flights at Kitty Hawk on the 17th of December, 1903,— it developed about 12 horse-power.

The flyer of 1904 was equipped with a motor similar to the first, but of % inch larger bore. This engine at 1500 revolutions per minute developed 24 horse-power for the first 15 seconds, but only 16 to 17 horse-power after a few minutes’ run. Complete with water, fuel, and other accessories, it weighed 240 lbs.

The same engine, with a' few modifications in the oiling device and the carbureter, was used in all the flights of 1905. A test of its power made soon after the flights of October, 1905, revealed a gain of 3 horse-power over tests made just before mounting it on the flyer in 1904. This gain is attributed to the increased smoothness of the cylinders and pistons produced by wear. The small output of these engines was due to lack of experience in building gasolene motors.

During the past year further improvements have been made, and our latest engines of four-inch bore and four-inch stroke produce about 25 horse-power continuously. The improvement in the reliability of the motor has been even more marked, so that now flights of long distances can be attempted without danger of failure on account of the stopping of the motor.

A comparison of the flyers of 1903, 1904, and 1905 shows some interesting facts. The flyer of 1903 weighed, complete with operator, 745 lbs. Its longest flight was of 59 seconds’ duration with a speed of 30 miles an hour and an expenditure of 12 horse-power. The flyer of 1904 weighed about 900 lbs., including a load of 70 lbs. in iron bars. A speed of more than 34 miles an hour was maintained for a distance of 3 miles with an expenditure of 17 horse-power. The flyer of 1905 weighed, including load, 925 lbs. With an expenditure of 19 to 20 horse-power it traveled over 24 miles at a speed of more than 38 miles an hour. The flights of 1904 and 1905 would have been slightly faster had they been made in a straight line, as were those of 1903.

In 1903, 62 lbs. per horse-power were carried at a speed of 30 miles an hour; in 1904, 53 lbs. at 34 miles an hour; and in 1905, 46 lbs. at 38 miles an hour. It will be noticed that the weight carried per horse-power is almost exactly in inverse ratio to the speed, as theory demands— the higher the speed, the smaller the weight carried per horse-power.

Since flyers can be built with approximately the same dynamic efficiency for all speeds up to 6o miles an hour, a flyer designed to carry a total weight of 745 lbs. at 20 miles an hour would require only 8 horse-power, or two-thirds of the power necessary for 30 miles an hour. At 60 miles 24 horse-power would be necessary— twice that required to carry the same weight at 30 miles an hour. At 120 miles an hour 60 to 75 horse-power would pipbably be necessary, and the weight carried per horse-power would be only 10 or 12 lbs. At such high speed the resistance of the operator’s body and the engine is a formidable factor, consuming 64 times as much horse-power as at 30 miles an hour. At speeds below 60 miles an hour this resistance is almost negligible.

It is evident that the limits of speed have not as yet been closely approached in the flyers already built, and that in the matter of distance, the possibilities are even more encouraging. Even in the existing state of the art it is easy to design a practical and durable flyer that will carry an operator and supplies of fuel for a flight of over 500 miles at a speed of 50 miles an hour.

Dayton, Ohio, December 7, 1906.

“Aero Club of America, - New York City, N. Y.

“My dear sir:

“In response to your request of November 21, I take pleasure in telling of my observance of the Wright Brothers’ aeroplane.

Early in October, 1905, it was my privilege to witness a very successful flight made by Mr. Wilbur Wright in the aeroplane of their own invention. When I arrived at the appointed place, the air-ship had already ascended and was flying at what seemed to me to be a distance of fifty feet from the ground, and in a rectangular course. That is, the operator was going first north, then west, then south, and then east, guiding and controlling his machine at will.

“A distance of twenty-four miles was covered on this occasion, in about thirty-eight minutes. The turns at the various corners of the field in which the flight was made, were made easily and gracefully, and it seemed to be as easy for Mr. Wright to operate it as for any one else to ride a bicycle. When the machine came to earth at the end of the flight it did so with a gliding motion, giving no perceptible jar or jolt to the operator. I believe that the aeroplane of the Wright Brothers has successfully solved the problem of aerial navigation.

‘Wery truly yours,

‘‘E. W. Ellis,

“Assistant City Auditor.”

Dayton, 0., December 5, 1906.

“Aero Club of America.

” Gentlemen:

“In reply to your inquiry of recent date, I would state that I witnessed a flight of the Wright Brothers’ aeroplane and there exists in my mind no doubt that, to the Wright Brothers is due the credit of the solution of aerial navigation without the aid of balloons or like contrivance.

lO

‘The day I witnessed their flight the aeroplane remained in the air at a height of between 50 to 100 feet for a period of about 23 minutes, and in that time covered a distance of about 15 miles, according to the meter attached to the aeroplane.

“The machine appeared at all times to be under perfect control, the operator elevating and lowering it at will. In his flight he described a circle of about a mile in circumference. Unfortunately, however, he was obliged to descend on account of a hot bearing.

“To an observer the machine resembles a huge bird in flight, and to me was the most inspiring sight that I have ever witnessed.

“Yours very truly,

“Howard M. Meyers.”

Dayton, Ohio, November 25, 1906.

“Aero Club of America,

New York City.

‘‘Dear Sir:

“The brothers, Wilbur and Orville Wright, have lived from childhood within a few squares of my home and have always had the fullest confidence of all their neighbors and acquaintance; but I must confess that when I read that they had solved the problem of human flight down on the coast of North Carolina I did not believe it. I thought that what they had accomplished was not real flight at all, but due to some peculiar condition of the atmosphere in that locality. I believed mechanical flight as impossible as perpetual motion.

“It was not until I saw one of their flights, near Dayton, with my own eyes that every doubt was removed.

“I was on the grounds and stood within a few feet of the machine while preparations were being made for the flight. I saw the machine start on the track upon

II which it acquired initial speed, and I watched it as it gradually rose higher and higher in the air.

“I simply cannot describe my feelings during the first few minutes. When it was well above the tree-tops it continued on a level course in easy circles about the field, for more than half an hour, as timed by several spectators present.

“The operator brought it to the ground, without any damage whatever, directly in front of the building in which it was housed. I had seen the eighth wonder of the world !

“Respectfully yours,

“Henry Webbers.”

Dayton, Ohio, November 24, 1906.

“Aero Club of America,

New York.

“Dear Sir:

“I take great pleasure in answering your letter of November 21, 1906.

“Along with some friends, I had the privilege of witnessing a flight of the Wright Brothers, in the autumn of 1905, a few miles east of Dayton. The machine started from a short track lying on the ground, and rose into the. air on an inclined path till it was well above the height of the tallest trees. It then kept on a horizontal path flying round and round the meadow in circles about a quarter of a mile in diameter.

“The flight lasted more than a half hour. At last Mr. Orville Wright shut off the power and landed as gracefully as a bird just in front of the building in which the machine was kept.

“I can only say that it was the most wonderful sight of all my life. I was astonished to see farmers, driving home from the city, stop and watch the flight for ten or fifteen minutes, and then drive on again ; but I suppose they lived near-by and had seen the machine in flight many times before,

“Yours respectfully,

“Chas. Webbert/'

Ill

A FEW NOTES OF PROGRESS IN THE CON- STRUCTION OF AN AfiRODROMEi

By Dr. Alexander Graham Bell

For many years past the subject of aerial flight has had a great fascination for me; and in 1896, the sight of Langley’s steam aerodrome circling in the sky, convinced me that the age of the flying machine was at hand.

I therefore quietly worked away at the subject in my Nova Scotia laboratory in the hope that I, too, might be able to contribute something of value to the world’s knowledge on this important subject.

Warned by the experiences of others, I have sought for a safe method of approach— a method that should risk human life as little as possible during the earlier stages of experiment.

Experiments with aerodromes must necessarily be fraught with danger, until man, by practical experience of the conditions to be met with in the air, and of the means of overcoming them, shall have attained skill in the control of aerial apparatus.

*An extract from an address upon “Aerial Locomotion,” delivered before the Washington Academy of Sciences, December 13, 1906.

. 14

A man cannot even ride a bicycle without practice; and the birds themselves have to learn to fly.

Man, not having any inherited instincts to help him in this matter, must first control his flight consciously, guided by knowledge gained through experiment.

Skill can only be obtained by actual experience in the air; and this experience will involve accidents and disasters of various sorts before skill can be obtained.

If these disasters should, as so often in the past, prove fatal to the experimenter, skill cannot be gained. The knowledge obtained by the would-be aviator will then be lost to the world; and others must begin all over again instead of pursuing the subject where he left off, with the benefit of his knowledge and his experience.

It is, therefore, of the utmost consequence to progress in the art of aviation, that the first attempts to gain experience in the air, should be made under such conditions of safety as to reduce to a minimum the liability to fatal results.

The Wright Brothers’ successful flying-machine travels at the rate of about 37 miles an hour; and judging from its great flying weight (nearly 2 lbs. per square foot of supporting surface), it is unlikely that it could be maintained in the air if it had a very much less velocity. But should an accident happen to a body propelled through the air with the velocity of a railroad train, how about the -safety of the occupants ? Accidents will happen, sooner or later, and the chances are largely in favor of the first accident being the last experiment.

While, therefore, we may look forward with confidence to the ultimate possession of flying-machines exceeding in speed the fastest railroad trains, it might be the part of wisdom to begin our first experiments at gaining experience in the air, with machines traveling at such moderate velocities, and at such moderate elevations, as to reduce the chances of a fatal catastrophe to a minimum. This means that they should be light flying-machines ; that is, the ratio of weight to supporting surface should be small.

While theory indicates that the greater the weight in proportion to supporting surface consistent with flight the more independent of the wind will the machine be, yet it might be advisable to begin, if possible, with such a moderate flying weight as to permit of the machine being flown as a kite. There would be little difficulty then in raising it into the air; and, should an accident occur to the propelling apparatus, the machine would descend gently to the ground ; or the aviator could cast anchor, and his machine would continue flying as a kite.

One of the chief causes that have led to disasters in the past has been- a lack of stability in the air. Automatic stability under varying conditions is of the very first consequence to safety; for what would it profit a man were he to gain the whole world and lose his own equilibrium in the air?

It occurred to me that the question of equilibrium could most safely be studied by constructing an aerial vehicle that could be flown as a kite: it would follow as a matter of course that, if propelled through calm air with the velocity of the wind that supported it as a kite, the machine would also be supported in the air as a free flying-machine.

On two previous occasions I have presented communications to the National Academy of Sciences relating to experiments with kites. The first was on ‘‘Kites with Radial Wings” presented April, 1899; and reviewed with illustrations, in the “Monthly Weather Review” for April, 1899 (Vol. XXVI, pp. 154- 155, Plate XI).

The second was upon “The Tetrahedral Principle in Kite Structure” presented April 23, 1903; and published, with ninety-one illustrations and an Appendix, in the “National Geographic Magazine” for June, 1903 (Vol. XIV, pp. 220-251).

The experiments referred to, which were undertaken at first for my own pleasure and amusement, have gradually assumed a serious character from their bearing upon the flying-machine problem.

The word “kite,” unfortunately, is suggestive to most minds of a toy — just as the telephone at first was thought to be a toy— so that the word does not at all adequately express the nature of the enormous flying structures employed in some of my experiments. These structures were really aerial vehicles rather than kites, for they were capable of lifting men and heavy weights into the air. They were flown after the manner of kites, but their flying-cords were stout manila ropes. They could not be held by hand in a heavy breeze, but had to be anchored to the ground by several turns of the ropes around stout cleats like those employed on steamships and men-of-war.

One of the great difficulties in making a large structure light enough to be flown as a kite, has been pointed out by Prof. Simon Newcomb in an article in “Mc- Clure’s Magazine” published in September, 1901, entitled “Is the Air-ship Coming?”; and this difficulty had so much weight with him at that time, as to lead him to the general conclusion that “the construction of an aerial vehicle which could carry even a single man from place to place at pleasure, requires the discovery of some new metal, or some new force.”

This conclusion, the Wright Brothers, and now Santos-Dumont, have demonstrated to be incorrect; but Prof. Newcomb’s objections undoubtedly have great force; and reveal the cause of the failures of attempts to construct large-sized flying-machines upon the basis of smaller models that actually flew.

Prof. Newcomb shows that where two aerial vehicles are made exactly alike, only differing in the scale of their dimensions, the ratio of weight to supporting surface is greater in the larger one than in the smaller,— the weight increasing as the cube of the dimensions, whereas the supporting surfaces only increase as the squares.

From this the conclusion is obvious that if we make our structure large enough, it will be too heavy to fly —even by itself— far less be the means of supporting an additional load like a man, and an engine for motive power. This conclusion is undoubtedly correct in the case of structures that are “exactly alike, excepting in their dimensions” ; but it is not true as a general proposition.

A small bird could not sustain a heavy load in the i8 air; and while it is true that a similar bird of double the dimensions would be able to carry a less proportionate weight because it is itself heavier in proportion to its wing surface than the smaller bird— eight times as heavy in fact, with only four times the wing surface-still it is conceivable that a flock of small birds could sustain a heavy load divided equally among them, and it is obvious that in this case the ratio of weight to wing surface would be the same for the whole flock as for the individual bird.

If, then, we build our large structure by combining together a number of small structures each light enough to fly; instead of simply copying the small structure upon a larger scale, we arrive at a compound or cellular structure in which the ratio of weight to supporting surface is the same as that of the individual units of which it is composed, thus overcoming entirely the really valid objections of Prof. Newcomb to the construction of large flying machines.

In my paper upon the tetrahedral principle in kite structure, I have shown that a framework having the form of a tetrahedron possesses in a remarkable degree the properties of strength and lightness. This is especially the case when we adopt as our unit structure the form of the regular tetrahedron, in which the skeleton frame is composed of six. rods of equal length, as this form seems to give the maximum of strength with the minimum of material. When these tetrahedral frames or cells are connected together by their corners they compose a structure of remarkable rigidity, even when made of light and fragile material— the

Professor Alexander Graham Bell and his tetrahedral designs at the first annual exhibition of the Aero Club of

America whole structure possessing the same properties of strength and lightness inherent in the individual cells themselves.

The unit tetrahedral cell yields the skeleton form of a solid, and it is bounded by four equal triangular faces. By covering two adjoining faces with silk, or other material suitable for use in kites, we arrive at the unit “Winged Cell’^ of the compound kite; the two triangular surfaces, in their flying position, resembling a pair of wings raised with their points upward— the surfaces forming a dihedral angle.

Four of these unit cells, connected together at their corners, form a four-celled structure having itself the form of a tetrahedron, containing in the middle an empty space of octahedral form, equal in volume to the four tetrahedral cells themselves. In my paper, I showed that four of these four-celled structures connected at their corners resulted in a sixteen-celled structure of tetrahedral form, containing, in addition to the octahedral spaces between the unit cells, a large central space equivalent in volume to four of the four-celled structures.

In a similar manner four of the sixteen-celled structures connected together at their corners form a sixty-four-celled structure ; four of the sixty-four-celled structures form a two-hundred-and-fifty-six-celled structure, etc., etc. ; and in each of these cases an empty space exists in the center, equivalent to half of the cubical contents of the whole structure, in addition to spaces between the individual cells, and minor groups of cells.

Kites so formed, exhibit remarkable stability in the air under varying conditions of wind, and I stated in my paper that the kites which had the largest central spaces seemed to be the most stable in the air. Of course these were the structures that were composed of the largest number of unit cells, and I now have reason to believe that the automatic stability of these kites depends more upon the number of unit cells than upon the presence of large empty spaces in the kites ; for I have found, upon filling in these empty spaces with unit cells, that the flying qualities of a large kite have been greatly improved.

The structure, so modified, seems to fly in as light a breeze as before, but with greatly increased lifting power; while the gain in structural strength is enormous. I had hitherto supposed that if cells were placed directly behind one another, without providing large spaces between them, comparable to the space between the two cells of a Hargrave box-kite, the front cells would shield the others from the action of the wind, and thus cause them to lose their efficiency ; but no very marked effect of this kind has been observed in practice. Whatever theoretical interferences there may be, the detrimental effect upon the flying qualities of a kite are not, practically, obvious; while the gain in structural strength and in lifting power outweighs any disadvantages that may exist. I presume that there must be some limit to the number of cells that can be placed in close proximity to one another without detrimental effect, but so far my experiments have not revealed it.

To test the matter, I put together into one structure all the available cells I had in the laboratory — 1300 in number. These were closely attached together without any other empty spaces in the structure than those existing between the individual cells themselves when in contact at their corners. The resulting kite, known as the Frost King^ consisted of successive layers, or strata of cells, closely superposed upon one another. The lowest layer, or floor of the structure, consisted of 12 rows of 13 cells each. The cells forming each row were placed side by side attached to one another by their upper corners; and the 12 rows were placed one behind the other, the rear corners of one row being attached to the front corners of the row immediately behind. The next stratum above the floor had ii rows of 14 cells; the next, 10 rows of 15 cells, etc. ; each successive layer increasing in lateral dimensions and diminishing in the fore and aft direction; so that the top layer, or roof, consisted of a single row of 24 cells placed side by side.

One would imagine that a closely-packed mass of cells of this kind — 1300 in number— would have developed some difficulty in flying in a moderate breeze if the cells interfered with one another to any material extent ; but this kite not only flew well in a breeze estimated at not more than about 10 miles an hour because it did not raise white caps, but carried up a rope-ladder, several dangling ropes 10 or 12 meters long, and more than 200 meters of Manila rope used as flying lines, and, in addition to all this, supported a man in the air.

The whole kite, impedimenta and all, including the man, weighed about 13 1 kilograms (288 lbs.) ; and its greatest length from side to side was 6 meters at the top and 3 meters at the bottom. The sloping sides measured 3 meters, and the length from fore to aft at the square bottom was 3 meters.

It is obvious that this kite might be extended laterally at the top to twice its length without forming an immoderately large structure. It would then be 12 meters on the top (39 ft.), and 9 meters on the bottom from side to side, without changing the fore and aft dimensions, or the height. It would then contain more than double the number of cells, and so should be able to sustain in the air more than double the load ; so that such a structure would be quite capable of sustaining both a man, and an engine of the weight of a man, and yet be able to fly as a kite in a breeze no stronger than that which supported the Frost King.

. An engine of the weight of a man could certainly impart to the structure a velocity of 10 miles an hour, the estimated velocity of the supporting wind, and thus convert the kite into a free flying-machine.

The low speed at which I have been aiming— for safety’s sake— is therefore practicable.

In the Frost King and other kites composed exclusively of tetrahedral winged cells, there are no horizontal surfaces (or rather surfaces substantially horizontal as in ordinary kites), but the framework is admirably adapted for*the support of such surfaces. Horizontal aeroplanes have much greater lifting power than similar surfaces obliquely arranged, as in the tetrahedral construction, and I have made many experiments to combine horizontal surfaces with winged

NAVIGATING THE AlR cells with greatly improved results so far as lifting power is concerned. But there is always an element of instability in a horizontal aeroplane, especially if it is of large size; whereas kites composed exclusively of winged cells are wonderfully steady in the air under varying conditions, though deficient in lifting power ; and the kites composed of the largest number of winged cells seem to be most stable in the air.

In the case of an aeroplane of any kind the center of air pressure rarely coincides with the geometrical center of surface, but is usually nearer the front edge than the middle. It is liable to shift its position at the most unexpected times on account of some change in the inclination of the surface or the direction of the wind. The change is usually small in steady winds; but in unsteady winds great and sudden changes often occur. The extreme possible range of fluctuation is, of course, from the extreme front of the aeroplane to the rear, or vice versa; and the possible amount of change, therefore, depends upon the dimensions of the aeroplane— especially in the fore and aft direction. With a large aeroplane the center of pressure may suddenly change to such an extent as to endanger the equilibrium of the whole machine. Whereas, with smaller aeroplanes, especially those having slight extension in the fore and aft direction, the change, though proportionately as great, is small in absolute amount. Where we have a multitude of small surfaces well separated from one another, as in the tetrahedral construction, it is probable that the resultant center of pressure for the whole kite can shift to no greater extent than the centers of pressure of the individual surfaces themselves. It is, therefore, extremely unlikely that the equilibrium of a large kite could be endangered by the shifting of the centers of pressure in small surfaces within the kite. This may be the cause of the automatic stability of large structures built of small tetrahedral cells. If so, one principle of stability would be ; small surfaces, well separated, and many of them.

The converse proposition woula then hold true if we desired to produce instability and a tendency to upset in a squall, viz. : large surfaces, continuous, and few of them.

Another source of danger with large continuous surfaces is the fact that a sudden squall may strike the kite on one side, lifting it up at that side and tending to upset it. But the compound tetrahedral structure is so porous that a squall passes right through and lifts the other side as well as the side first struck ; so that the kite has not time to be upset before the blow on one side is counterbalanced by a blow on the other. I have flown a Hargrave box-kite simultaneously with a large kite of many tetrahedral cells in squally weather for the purpose of comparing them under similar circumstances. The tetrahedral structure often seemed to shiver when struck by a sudden squall, whereas the box-kite seemed to be liable to a swaying or tipping motion that would be exceedingly dangerous in a structure of large size forming part of a flying-machine.

Another element of stability in the tetrahedral structure lies in the fact that the winged surfaces are elevated at a greater angle above the horizon than 45°.

Supposing the wings of a cell to be opened out until they are nearly flat— or at least until they each make a comparatively small angle with the horizon — say 20° — then if, from any cause, the cell should tip so as to elevate one wing ( say to 25°) and depress the other (say to 15°}— then the lifting power of the wind will be increased upon the elevated wing and diminished on the depressed wing, so that there would be no tendency to a recovery of position, but the very reverse, the pressure of the wind would tend to increase the tipping action, and favor the production of oscillation and a tendency to upset ; for the lifting action of the wind upon a surface inclined at 10° would be less than at 20°, and greater at 25° than 20°. The more the wings are opened out and the flatter they become, the more essentially unstable is the arrangement in the air.