Steam Flight

The flying-machine differs from the balloon in the fact that it is not only propelled but is also supported by its own actively exerted energy. The attempts of inventors to imitate this method of self-support and of flight by human power have been numerous but unsuccessful, and, as indicated by Borelli long ago, are not likely to prove successful. The skeleton and muscular system of man are not adapted to use in flight; nor has he the endurance needed for prolonged exertion of such intensity. The inventor is now seeking ways of making heat-engines or other motor machines serve his purpose in this direction. As the writer has elsewhere remarked, "The researches of Langley have shown the power demanded for flight to be about 2 per cent of the amount once supposed a minimum; we know that nature's energy can be directly converted into useful power through the production of electricity, as in the gymnotus, and possibly in all animal mechanisms; we know that the modern storage batteries are of ten times the weight that science indicates to be the limit of perfect efficiency; both steam-engines and electric accumulators have been made light enough and powerful enough to raise their own weight, with something to spare; the flying lemur, the flying squirrel, the rude sustaining-membranes that inventors have constructed, have sustained their heavy weights in drifting many yards." Man has thus every reason to assume at least the possibility of solving this problem, the last and most tantalizing of all presented to the inventor in the field of transportation. In this study the researches of Langley lend great encouragement. It is also true that encouragement may be found in other directions.

The operation of the animal machine teaches many lessons, some of which should prove profitable to the engineer in his endeavor to solve this problem. It illustrates a combustion without high temperature, and yet with very high efficiency-quite in opposition to the accepted ideas of thermodynamic transformations. This may mean some as yet unknown system of modification of heat energy; or it may indicate a production of electricity, rather than heat, from the chemical union of foods with oxygen; or it may lead to discoveries of methods of transformation of energy and of their useful application as yet undreamed of by our philosophers. This animal energy, however developed, is applied with great effectiveness to these as yet unsolved problems of the engineer. The great secret which our own most original inventors and physicists are endeavoring to penetrate lies there for study and test. It is to-day easy to predict the power required to give to any well-shaped body any stated velocity in the air; it remains to ascertain how that power may be produced as economically, and as concentrated in volume and weight of mechanism, as nature produces it.

The fact that man has surpassed nature in transportation on land and on the sea may be fairly taken as giving reason to assume the possibility of his similarly succeeding, once he has entered upon this new path, in aerial navigation. Although the animal machine is, as shown by Hirn and by Ruhlman, more efficient as a dynamic motor than any heat-engine, rising to 0'29, it is not to be expected that artificial flight, by use of wings and man's own muscular power, will ever prove successful. In seeking to construct flying-machines, capable of transportation of merchandise and passengers on some comparatively large and effective commercial scale, the machine consists of some equivalent for the wing of the bird, as the aeroplane tested by Langley and others, and a car or vessel, carrying machinery and load, the resistance of which must be allowed for at a rate approximating, if well-formed, by Pole's formula: R= 0.000195*d^2*v^2, in pounds, feet and seconds being the units. This corresponds to the comparatively slight density of air: 1/800 that of water. The size of wing, x, required for a given load, y, will bear some close relation to that observed in the birds, in which, by Hannel's formula, x = y log. 500, nearly, in which x is in kilogrammes and y is the width of wing in meters.

Langley's experiments confirm for normal pressures the formula of Duchemin or Bossut, making the magnitude of that pressure a simple function of the normal pressure when moving transversely to its own plane; but he shows that, although the form and aspect of the plane have little effect when moving normally, they become important when the plane is inclined to its path. Chanute's investigations confirm the conclusions of Langley, and numerous experiments with an immense variety of flying-machines have thrown some light upon the subject, but have thus far revealed but little real progress in application.

These machines are variously constructed to secure support and propulsion by means of wings, by screws, and by screws combined with aeroplanes. The most successful have recently been impelled by the energy stored in twisted threads of rubber. Pichaneourt has made such "birds" capable of flying 50 to 100 feet; and many experimenters have employed the last-named combination. Of these, the most successful has been M. Penaud, or possibly M. Dandrieux, who makes a remarkably perfect imitation of the butterfly. None of these are more than toys, however, and usually support themselves but a few seconds. Mr. Lawrence Hargreaves has presented to the Royal Society of New South Wales accounts of more than a dozen self-propelling machines of his own construction, some of which have flown considerable distances, the driving-power being, in the best of them, compressed air operating a Brotherhood engine. His Nos. 13 and 14 flew at the rate of 10 to 12 miles an hour, and covered distances of 125 to 312 feet in 8 to 20 seconds. The inventor estimates that 400 lb. of tin tubing, silk, and steel wire would serve to carry one man 500 yards at 17 miles an hour." The motor constitutes one of the most difficult problems.

Marine steam-engines, with their boilers, weigh several hundred pounds per horse-power, while it is estimated that a successful aerial motor must weigh less than 50, and that it is desirable that it should even be much lighter than that. The lightest machinery yet built for continuous operation is that of the modern torpedo-boats, weighing sometimes less than 60 lb. per horse-power, and in occasional instances below 50. Stringfellow built an engine for aeronautic experiments weighing 13 lb. per horse-power, and Mr. H. S. Maxim has described one weighing less than 5,000 lb. to develop 300 horse-power.

Gas and inflammable vapor engines have been proposed for use in aeronautics; but they are as yet even heavier than the lightest steam-engines, and offer no promise of value. The best work thus far has given, as its product, gas-engines employing the vapor of petroleum and weighing between 80 and 100 lb. per horse-power. Electric power gives better results, and M. Trouve has constructed such of moderate size, weighing about 20 lb. per horse-power, and in one case, in which aluminium was freely used in construction, about 8 lb. Commandant Renard employed a dynamo in his balloon which weighed 26'4 lb. per horse-power. The primary battery used with it weighed 66 lb. per horse-power, and the whole thus weighed 130 lb., a weight still much too great to be suitable for any self-supporting and self-impelling machine.

The most elaborate and instructive experiments with solid bodies driven through the air at high speeds were made by Mr. Maxim, whose work on aeroplanes corroborates that of Langley completely. He found the resistance due to friction of the surfaces of the body thus driven was imperceptible, and might be neglected as unimportant. He concludes that a motor weighing less, as a total, than 100 lb. per horse-power would, so far as that goes, make aerial navigation possible. His own steam engine with a pressure of 250 lb., weighing with its accessories about 4,500 lb., is rated at 300 horsepower, or 15 lb. per horsepower. The machine is mainly of steel, this metal being found, as used, much lighter and stronger than similar parts made of aluminium.
Present indications seem to be, in the opinion of many aeronauts, that the use of the dirigible balloon will lead to the perfecting of the motor, and that ultimately the flying-machine, without supporting gas-bag, may come into use for speeds which can not be approached by the former. The dirigible balloon is so far perfected as today to constitute an important part of the equipment of every great army organization. French inventors have, as has been seen, constructed such machines capable of attaining about 15 miles an hour in calm weather, and it is supposed that they have, in later and unpublished plans, secured a much higher degree of efficiency. The German army is said to have similar machines in use in reconnaissance; and other nations now, and all must in time apparently, make use of this new method of transportation for such purpose.