The Problem of Mechanical Flight


The Problem of Mechanical Flight


The evolution of the flying machine has been slower than that of any other mechanical device of which we have record. The problem before the inventors is reduced to the question of devising an apparatus that will maintain its equilibrium and support a human being during the process of flight through the air. Just how far they have succeeded is explained in the following article.

THE theory of flying mechanically is an interesting and pretty study, but in practice it has experienced a gloomy record. Many of the theories advanced work out similar to the case of a needle floating upon the surface of a tumbler of water. For if the size of the needle were increased to that of a telegraph pole and the water body increased in proportion we would at once find the comparison theoretically inaccurate. So the flight of birds must not be too closely imitated in the machine, as there are several laws which do not apply in the same relations between an animate thing and a mechanical apparatus. It is remarkable how well poised a human being is and how easily walking is accomplished, yet how difficult it is to construct an automaton that will walk at all.

While the world is ready for the airship it is interesting to observe how nearly ready the bona fide airship is to serve the varied needs of mankind. Ever since the Montgolfier brothers made their spectacular discovery of the principles underlying the balloon the latter has been exploited more or less as a royal route to artificial flight, and those who advocate it point out that it is the only method we are acquainted with by which a body can be sustained in the air for an indefinite length of time, and which can be made dirigible within certain limits. Its inherent failings greatly offset these admirable qualities, however, and engineers who have studied the mechanics of the air are largely of the opinion that practical flight is not to be found in its employment.

The chief defect in the dirigible balloon will be obvious to the veriest tyro when it is stated that it requires fourteen cubic feet of the lightest gas known, namely, pure hydrogen, to lift a single pound; this being the case, by the time a balloon has been made large enough to lift any considerable load, it offers such an enormous surface to the resistance of the air that a very moderate breeze is sufficient to buffet it about and drive it out of its course, rendering it in consequence a useless means of intelligent aerial navigation.

The dirigible balloon is interesting, nevertheless, from a number of viewpoints, and to treat fairly the cause of aeronautics it cannot be ignored. A dirigible balloon is always an inspiring and an impressive sight as it sails smoothly and gracefully through the great aerial ocean, and the recent experiments of Roy Knabenshue will be remembered by thousands of New Yorkers. His exploits practically duplicated those of Santos Dumont, who manoeuvred his frail craft around the Eiffel Tower and back again to the point from which he started in Longchamp. Stanley Spencer a summer or two ago sailed in various directions over the city of London, his balloon seemingly under very excellent control, while the Lebandy brothers with a similar type of airship performed like evolutions over the suburbs of Paris, in one instance covering a distance of nearly eight miles in twenty-five minutes.

Prior to these essays in flight— that is to say, in 1885—Commandant Renard, of the French Balloon Corps, had designed and constructed an elongated gas bag which he fitted with an eight-horse-power motor, the total weight, including the auxiliary appliances, being approximately 220 pounds. This was the first instance where the propeller was placed in front instead of at the rear of the balloon; a plan that the later workers cited above found it expedient to adopt. Although in advance of Santos Dumont nearly fifteen years, Renard demonstrated it possible to sail against the wind if not too brisk; this he did by starting from Chalais-Mendo and, after traversing a predetermined course of a few miles, returning to the place where he ascended.

Only a year before, the Tissandier brothers had built a balloon that seems to have been utilized by Santos Dumont, but since the internal combustion engine was in its infancy it was deemed a more favorable plan to employ an electric battery and a motor to generate the power needed. The battery provided current for two and a half hours and the electric motor developed one and one-third horse power, turning the propellers at a rate sufficient to drive the airship along at a clip equivalent to about 780 feet per minute. When we have considered Dupuy de Lome’s cigar-shaped dirigible balloon, built in 1872, in which a two-bladed propeller twenty feet in diameter was operated by eight men equal to about one horse power, and Giffard’s sausage-like balloon, constructed in 1852, in which he placed a crude and cumbersome steam engine, we have resolved the art of aerial navigation, in so far as the elongated gas bag is concerned, down to its source.

Looking backward over the past fifty years, we find that the only improvements in dirigible balloons are those of propulsion; and since the action of propeller screws has been very carefully analyzed and internal combustion engines have been built weighing only five pounds to the horse power, it is clear that the limits of speed and of controlling the course of balloons of whatever size and shape have been practically reached.

Another method for the accomplishment of mechanical flight is that of impelling bodies heavier than the air with such rapidity that they will remain suspended until the impulse gives out. A leaf or a sheet of paper is an example of the above, but neither possesses stability. The boomerang is in reality a toy flying machine, and when thrown will speed through the air in long, graceful curves and return to the thrower before it strikes the ground, thus vividly demonstrating its stability, and its capability of being guided.

A boomerang and a kite may not appear to have anything in common, yet the laws governing them are identical. A kite usually comprises a plane surface, and it is therefore called an aeroplane, the principles involved forming the basis of the second type of flying machine. The names “kite” and “aerodrome” are usually employed to designate in the first instance planes made of paper or cloth attached to slender wooden frames which are flown in the air by means of a cord held by a boy or man, while in the last case the device is formed of similar surfaces, but is self-supporting when propelled through the air. That confusion may be avoided, it has been suggested that it would be well to designate kites as aeroplanes and flying machines built on this principle as aerodromes, and these definitions will be adhered to in the present text.

A bird’s wing is really a curved or, as it is more properly termed, an arcuated aeroplane, and those who are believers in flying machines having rigid plane surfaces point out that the movements of a bird’s wings do very little in the way of actual flight, but that the purpose a bird has in view in beating its wings is to get a good start; this being accomplished, it then makes its wings rigid and sails on the air like a kite.

In the same year that Giffard exhibited his dirigible balloon, namely, 1852, Stringfellow showed the model of an aerodrome in the Crystal Palace, London. Though the machine only occasionally left the wire track along which it was run to get its start, there were strong indications that the design was inherently correct, and it gave considerable encouragement to this form of flight.

Since then there have been many attempts to imitate the soaring action of birds, those of Lilienthal, Pilcher, and Chanute being the best known, though by no means the only ones. Lilienthal, the Prussian who lost his life in an effort to describe a circle, proved that it was possible to sail the air by using a pair of fixed wings, though it was necessary to start from an elevation. Under proper conditions the descent was about one foot in eight, depending upon the strength of the wind, and in several trials when the wind was blowing with sufficient velocity he was enabled to actually soar upward, though the wings had a surface of only seven square yards.

Pilcher, of England, like Lilienthal, lost his life by the overturning of his apparatus. Chanute, of Chicago, who was the next to vie with the soaring birds, having the tragic experiences of his predecessors before him, proceeded with the utmost caution, and finally did develop a kite-like apparatus in which he and his assistants sailed through the air without accident and apparently without danger. Chanute’s contrivance was built along the lines of Stringfellow’s, but not until Hiram Maxim, the inventor of the machine gun, built and tested out an aeroplane with motive power, in 1892, could it be said to have really had an adequate trial. Maxim performed a great number of experiments for the purpose of determining the most effective form of surface for the impinging air, for the form of screw that would give the greatest pull per unit of power, and for an engine which should be at once both powerful and light enough for the performance of its purpose.

The Maxim aerodrome consisted of a slight covered framework resting on a small flat car and extending outward and upward above it, while projecting before and after this central structure were horizontal surfaces that served as rudders, and these were movable at the will of the operator. The complete machine weighed 8,000 pounds, and the surfaces, which were both plane and arcuate, comprised some 5,000 feet. To get a start the machine was run down a track, when the resistance of the air became great enough to lift it from the car, or at least this was the intention of the designer. The aerodrome was driven by a 300 horse power steam engine, the lightest ever made up to that time, but in the tests which followed only forty horse power of the total amount was used, and this developed a lifting power that caused it to rise prematurely from the rails, when it toppled over, the sudden impact with the earth leaving it a wreck.

While the result of the experiment was a failure, it served to show, firstly, that an aero-surface can be made to lift itself by simply driving it forward with the requisite speed, provided it is fixed at a small angle of inclination relative to the direction of its flight; secondly, that the propeller screw is an eminently effective instrument for the propulsion of the aerial craft; and thirdly, that an engine at once light and powerful enough for driving a practical flying machine can now be made.

But there is an obvious mathematical law stating that the area in bodies in general increases as the square of their dimensions, while their weight increases with the cube; hence it is an apparently plain inference that the larger the creature or machine, the less the relative area of support—that is, if we consider the mathematical relationship without reference to the question whether this diminished support is actually physically sufficient or not —so that we soon reach a condition where we cannot imagine flight possible. Thus, if in a soaring bird, which let us suppose weighs two pounds, we should find that it had two square feet of surface, or a ratio of a foot to a pound, it would follow from the law just stated that in a soaring bird of twice the dimensions we should have a weight of sixteen pounds and an area of eight square feet, or only half a square foot of supporting area to the pound of weight, so that if flight is possible in the first case it would appear to be highly improbable in the second.

The difficulty grows greater as we increase the size, for when we have a creature of three times the dimensions we shall have twenty-seven times the weight and only nine times the sustaining surface, which is but one-third of a foot to a pound. This is a consequence of a mathematical law from which it would appear to follow that we cannot have a flying creature much greater than a limit of area like the condor, unless endowed with extraordinary strength of wing.

Some years ago Prof. Simon Newcomb concluded 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.” The process of reasoning by which this scientist arrived at this remarkable result was undoubtedly correct, but his deductions were very wide of the mark.

Dr. Alexander Graham Bell finally hit upon a means by which he was enabled to circumvent this law of mathematics which eminent authorities have long looked upon as standing forever ready to defeat the hopes of human beings to navigate the air. The scheme is simple enough after it has once been discovered. Take three straws and join their ends together so as to form a triangle. Then at each angle or corner of the figure so formed place another straw of the same length as those first used and bring their free ends together at the top. This forms the framework of one of Bell’s famous tetrahedral cells; that is, a frame having four bases or sides. By covering any two sides, since they all are of the same form and area, a one-cell Bell kite is produced. By joining cell to cell, the largest structures may be built up, which absolutely defeats the law that the weight must increase faster than the spread of surface, for his largest kites, having hundreds of square feet of surface, remain in every particular, weight, surface, and strength, proportioned to those of the smallest size.

Mr. Langley’s aerodrome of 1896, the most successful model of a flying machine that ever flew, weighed only thirty pounds, equal in weight to the pterodactyl, but had a supporting area twice as great in square feet and four times the horse power. The sustaining planes were oppositely disposed and formed rigid wings, two on a side, like the wings of the insect known as the devil’s darning needle. These measured fourteen feet from tip to tip, were fastened at an angle upward and outward from the body, which was eighteen feet long, and they were concave on their under sides. The centre of gravity was not nearly so low as in the Maxim make, and the propellers, which were screws thirty-six inches in diameter and placed amidships, were so swung as to take a part of their air from above and a part from below the machine. The motive power was furnished by one of the lightest and most efficient steam engines and boilers ever built, developing one and a half horse power with a total weight of about seven pounds.

This machine flew repeatedly over a distance of a mile and only ceased when its steam was exhausted, and then it gently alighted on the water of the Potomac River over which it was flown. These interesting and successful tests led Langley to build a machine on a much larger scale, capable of carrying a man. This he completed in 1903; the new aerodrome weighed, together with its aeronaut, 830 pounds; its sustaining surface measured 1,040 square feet, while the engine, of the internal-combustion type, developed fifty-two horse power and weighed considerably less than five pounds to the horse power. This machine has not yet been given a fair trial, and in each of the two preceding tests the launching device failed in the performance of its part and precipitated the machine into the water below. The difficulty in all the precursory experiments with aerodromes is that encountered in launching, and in every instance this has proven more troublesome and discouraging than the construction of the original apparatus.

This brings us vividly to the realization of yet another and a third method for solving the flight problem, and this is the beating wing. It is the opinion of Dr. T. Bayard Collins, of New York, and others of the younger class of investigators that in this lies the way to success. These students point out that there is not a bird, great or small, but that depends upon the flapping of its wings when it arises from a state of test, when it hastens its flight, when it carries a load, when it alights, and especially in the maintenance of its equilibrium —the very points wherein the aeroplane fails. The beating wing would supply the requirements of a successful flying machine in precisely those respects where the rigid aeroplane fails. It would enable the machine to rise without the aid of apparatus especially designed for the purpose ; it would insure stability, and finally it would settle the question of poising and remaining stationary in the air, and a machine so built could alight at any time and place.

Lawrence Hargrave, of New South Wales, made some beautiful flying models that were propelled by the operation of beating wings, while the lamented Lilienthal constructed a machine having these wings on either side of a central structure, and these he kept in motion by pedals similar to those of a bicycle. By his own efforts, with this clumsy device, he was enabled to raise one-half his own weight and that of the machine, and had he utilized a gas engine, the machine must have ascended. It is not necessary that the complicated movement of the natural wing should be imitated —indeed it would not be desirable to do this, even though it were possible; but what would amount to the same thing—that is, beating the air on the down stroke and avoiding it on the up stroke—is easily attainable by proper mechanism. Such a mechanical movement need not be jerky, but as smooth and continuous as the operation of the engine running it.

It is interesting to mention that such men as Peter Cooper Hewitt, Alexander Graham Bell, John P. Holland, and S. P. Langley are now engaged in devising improved constructions in flying machines, though none of the above will give out any information as to their latest discoveries at the present time. Israel Ludlow has conducted some very interesting experiments during the past summer along the Hudson River with an improved construction of kite. On several trips Ludlow ’s kite carried a human aeronaut, who manipulated the steering apparatus at an altitude of nearly one-quarter of a mile.

With these considerations of the difficulties and the advantages of these different methods in view, the writer sees in the first practical flying machine a composite structure, comprising an elongated balloon of very small dimensions serving to sustain to a limited extent a series of movable arcuate wings which will also act as aeroplanes; these will be used for arising, poising, and alighting, while propeller screws will drive the machine forward. Such an arrangement will not be swift-flying by any means, but it will obviate the awkward features found in the other individual types and will serve as a working basis for improvement. As the art unfolds the balloon will gradually be made smaller and beautifully less until it disappears altogether, and then the flying machine will begin to grow in dimensions, in stability, in speed, and in answering the problem when aerial navigation will become a concrete fact instead of an abstract fancy.

Keep the faculty of effort alive in you by a little gratuitous exercise every day. That is, be systematically ascetic or heroic in little, unnecessary points; do every day or two something for no other reason than that you would rather not do it: so that, when the hour of dire need draws nigh it may find you not unnerved and untrained to stand the test.—Professor William James.