A study of the trend of development in aeroplane construction renders it possible to predict with some degree of certainty the leading characteristics of the aeroplane of the future, and especially of that type which will be built purely for racing purposes. The following is an attempted study along these lines. The writer has no wish to assume the role of prophet, and the accompanying drawings and description are based mainly upon a survey of the work which has been done during the present year of phenomenal development by the designer, the constructor, and the airman. The keynote of this development is to be found in the fact that the speed of the aeroplane in straight-away flight has risen during the past year from fifty to seventy-five miles an hour, and that the "blue ribbon" of the air (if we may borrow a nautical phrase) has passed from the biplane to the monoplane, the type which, at the present writing, is so far in the lead, as to speed, lightness, and stability, that it stands in a class by itself.
The racer of the future, then, will be a monoplane; and in narrowing down to this type, man is but treading in the footsteps of Nature, the master builder, who, working through a process of evolution that has stretched out over millions of years, has produced, .in that wonderful bird, the albatross, the perfect flying machine. The future high-speed flyer, then, will possess the same tapering, rounded body and the widespread wings of narrow width which characterize the swiftest of the birds. Langley, in his classic researches, showed that it was the leading portion of a plane which was the most efficient, and this for the reason that it was continually moving on to fresh bodies of undisturbed air. He showed that as the after portion of the plane had to do its work upon air which had already received from the forward portion a downward velocity, this air was unable to provide the effective reaction which was exerted by air absolutely inert. Hence it follows that a plane 5 feet in width by 10 feet in length would be rendered more efficient if it were divided longitudinally, and the same area were presented in a plane 2-1/2 feet wide and 20 feet in length. The wings of the racer will be long and narrow; and when they come to be built of metal instead of the present wood and fabric, it will be possible to give them those sweeping, rounded forms which prevent eddy-making, and also, from a constructional point of view, add not a little to the strength. The body will be of a generally circular or oval section; and to allow of a long and gradual taper, for ease in traversing the air, the body will have considerable length. The greater length also will add greatly to the fore-and-aft stability in flight.
The present wood-canvas-and-wire construction will have to go. It is makeshift work at the best, and was adopted because, in the early days of experiment, it offered a cheap and light combination of material, and one which, in the event of the inevitable breakages, incidental to experimental work, could be cheaply and quickly repaired, Its place will be taken by some one of the many remarkable alloys of steel which are now available-metals of enormous strength and toughness in proportion to their weight. The use of these, coupled with careful designing by the skilled engineer, will make it possible to produce an aeroplane of much greater strength, that will weigh no more than the present machine, and will present far less resistance.
The principal resistances encountered by an aeroplane when in flight are those due to the lift and the head surface. The resistance due to the lift is fairly constant; for as the speed increases the angle of incidence decreases, and there is always an adjustment between the two which provides sufficient vertical reaction at all times to lift the weight of 500 to 1,000 pounds, as the case may be. The head resistance, however, increases approximately as the square of the speed; and if it is 100 pounds, say, at 40 miles per hour, it will rise to 400 pounds at 80 miles per hour. Hence the great importance, in a racing machine, of reducing the head surface to the least possible limit consistent with structural requirements.
It is this consideration of head resistance which has doomed the biplane as a purely racing type. When Octave Chanute built the first biplane glider, with its light, but very rigid Pratt trussing of vertical wooden struts and diagonal wire ties, he produced an excellent piece of engineering construction, which has proved to be ideally adapted to the early experimental stage which is now drawing to its close; but for high-speed results, because of the large amount of head surface presented, the Pratt truss was doomed to ultimate extinction. Unquestionably, the higher speeds which have been attained by the monoplane are due largely to the fact that its trussing is simpler, and the head surface, particularly of the wire stays, is relatively much less.
Now a word as to the resistance offered by a mass of tightly-strung wires, Prof. Langley showed in his whirling-table experiments that the resistance of a wire is much greater than that which would be due to its projected area. As the speed increased, the resistance would rise rather quickly until, at a certain critical point, at which the wire would sing with a peculiar note, there was a sudden and very large jump in the resistance. This is explained by the fact that the rate of vibration of the wire under the rush of air is so great that it practically presents a solid surface, whose width is equal to the amplitude of vibration. Hence a tightly-strung wire presents a resistance to the air which is seemingly out of all proportion' to its actual surface.
It follows, then, that even the simple king-pin trussing of the Blériot and Antoinette types must go if we are to achieve the high speeds which are predicted for the future racing machine. Now this will be possible only if some high-grade sheet metal is substituted for the canvas of the wing surface, and the necessary transverse bending strength. is secured by means of plate-steel members inclosed within the wing surfaces and strongly riveted to the structure of the main body of the machine.
The form of wing shown in our drawings will afford a sufficiently strong construction in metal. The wings should widen considerably as they approach the body; for this would provide increasing space between the upper and under surfaces, and allow the depth of the channels to be increased proportionately to the bending stresses. These channels. would be carried into the main body and riveted to transverse diaphragms, which should be so cut that the metal of the diaphragm would extend unbroken for some distance into the wings. We are convinced that by careful designing, the selection of the highest grades of steel, and by first-class workmanship, it will be possible to provide wings of ample strength without exceeding the limit of weight imposed by aeroplane requirements. Buckling in the fore and aft direction will be provided against by rolling the metal of the wing surfaces with shallow corrugations, as shown in the drawings. The main body of the aeroplane will be built also of thin sheet metal, and will be generally elliptical in cross section; two very light trusses, one horizontal; the other vertical, extending from the operator to near the tail. The chords of these trusses will be formed of light T-iron.
To provide for the heavy loads and stresses that are concentrated at the wings and motor, the T-irons of the trusses will be increased in depth and run entirely around the forward end of the body, forming, at their intersection in the nose, a strong construction for carrying the motor. Additional strength will be provided by transverse diaphragms. It is understood, of course, that all of this metal work will be specially rolled in extremely light sections, and that the material will be some alloy, such as vanadium steel, which in experimental specimens, as noted on our editorial page, has shown elastic limits running up to over 200,000 pounds to the square inch. The motor, of from 75 to 150 horse-power, according to the size of the aeroplane, will probably be of the revolving type; the Gnome motor having shown itself to be the ideal aeroplane drive.
Turning to nature for guidance again, we find that the fast-flying birds fold their legs snugly beneath them when in flight. The racing aeroplane must do the same. We show a suggested arrangement for a folding chassis, hinged just below the body, and provided with a yoke which leads from the axle up to the crosshead of a piston rod, which with the guides and cylinder is carried by the T-iron that forms the bottom member of the vertical truss. The cylinder is provided with a two-way valve and connections, by which compressed air can be introduced to the forward or after end of the cylinder. When the chassis is down and in operation, the compressed air acts as a cushion to provide a certain amount of fore and aft movement to the wheels. As soon as the machine rises, a throw of the valve introduces compressed air at the forward end of the cylinder, and the chassis is drawn up snugly against the body. A small tank of compressed air, which supplies the folding mechanism, also supplies a small cylinder of similar construction placed transversely to the car, which operates the movable wing tips. The two-way valve of this cylinder is controlled by a small gyroscope, which may be thrown out of gear when the airman wishes to make a turn, or perform other evolutions.
In answer to the question as to what speed may be expected from a machine of this general design, we think it will be agreed that, in view of its sweetness of form, the complete absence of wires, struts and other energy-consuming surfaces, and the fact that because of the smoothness of the steel surface, skin friction will be reduced to a minimum-it is conservative to expect from such a machine, after it has been developed by experimental work, speeds of from 100 to 125 miles an hour.
It would be interesting to see what Mr. Nat Herreshoff could accomplish, if he applied to the steel aeroplane the same constructive genius which enabled him to produce such fine results with steel racing yachts.
Aircraft in War the Possibilities of Aeroplanes and Dirigibles
No sooner had the Wright brothers demonstrated that human flight in a controllable motor-driven machine was possible, than the important bearing of this new device upon the art of war became evident. Up to that time, the movement of naval and military forces, and the reconnoitering to determine the strength and movements of the enemy, had been carried out entirely upon the surface of the earth. Movements, whether of the ,individual scout, or of the army one hundred thousand strong, had hitherto been confined to the two dimensions of length and breadth. To these had now been added a third dimension, and this enormous enlargement of the field of operations was recognized as complicating to an inconceivable degree the already difficult art of war.
More important than the clash of armies upon the field of battle are those preliminary investigations and movements by which the generals of the contending forces endeavor to ascertain the numbers and disposition of the enemy. An accurate knowledge of the position and movements of the opposing army, and of the characteristics of the country in which he is operating, has frequently enabled a general to dispose his troops in such advantageous positions relative to the enemy, that the battle has been won before a single shot was fired. Hitherto, successful strategy has depended largely upon the possession of accurate maps of the country, upon the activity and intelligence of the individual scout, or upon armed reconnaissances by a comparatively small body of troops sent forward to draw the enemy's fire and obtain some knowledge of his position and strength. Of late years, the advent of smokeless powder and the high-velocity, long-range rifle have rendered the present methods of scouting extremely difficult and precarious, particularly when the opposing general has taken every precaution to preserve the secrecy and invisibility which are the very essence of successful strategy.
The advent of the aeroplane and the dirigible, however, has rendered secrecy impossible. The aerial scout must, of necessity, exercise an enormous influence upon the conduct of future campaigns, rendering the already difficult art of war perplexing to a degree that only the military man can fully appreciate.
Whatever the future may have in store, it is certain that, at present, both the dirigible and the aeroplane, and particularly the latter, will find their field of usefulness confined almost entirely to the work of scouting.
For such work the light, small, and swift aeroplane will prove to be simply invaluable. The military scout of the future will probably be a monoplane, capable of carrying two people, an operator and an observer, and it will be provided with a motor or motors capable of driving it, at a maximum speed of 75 miles an hour or even more, this high speed being necessary to carry it with all possible dispatch to the particular field of observation. When it has reached its destination, such high speed will be no longer desirable. The machine must be slowed down, and must proceed leisurely over the country that is to be surveyed. For this purpose the machine will be provided with reefing surfaces which, folded or drawn in during the faster flight, will now be extended to afford the large supporting surface necessary to the slower speed. The observer will be provided with camera, sketching pad, field glasses, and instruments of triangulation. While he is making his sketches, notes, etc., the aeroplane will be flying slowly in wide circles at an altitude of several thousand feet above the earth, where, by virtue of its great elevation 'and constant change of position, it will be practically safe, even against bursting shrapnel from the larger field guns. It is not unlikely that a practicable system of wireless telegraphy may be worked out, of a character suitable for transmitting messages up to distances of say fifty to seventy-five miles, between the aeroplane scout and the headquarters of the commander-in-chief. If so, the machine will carry a third man who will continuously transmit such information regarding the enemy as may be gathered.
The enormous influence of the aeroplane scout upon field operations must be evident to the veriest novice. Had Gen. Kuropatkin been possessed of half a dozen such machines, the task of the Japanese in throwing around Mukden their huge battle lines, over a hundred miles in length, would have been enormously complicated, if not rendered impossible. Certainly the great flanking movement to the westward, in which Gen. Nogi, with 50,000 Port Arthur veterans, was able to pass entirely around the right flank of the Russian army and break in upon its rear, would have been discovered and possibly frustrated. Sheridan's famous ride would have been made through the air, and twenty minutes of time would have placed him at the desired spot. The launching of a monoplane from the forward deck of Admiral Sampson's flagship "New York" would have been followed within the hour by the discovery of Cervera's ships in Santiago harbor; and the Schley-Sampson controversy would never have left its ugly smear across the pages of our naval history.
Just how great a modification the aeroplane scout will produce in naval and military strategy it is impossible to predict; but it is certain that the opposing commanders of the future will be somewhat in the position of two chess players, each of whom has a pretty clear knowledge of what his opponent's next move must be.
Outside of its scouting duties, we are inclined to think that the field of usefulness of the aeroplane will be rather limited. Because of its small 'carrying capacity, and the necessity for its operating at great altitude, if it is to escape hostile fire, the amount of damage that it will do by dropping high explosives upon cities, forts, hostile camps, or bodies of troops in the field, to say nothing of battleships at sea, will be so limited as to have no material effects on the issues of a campaign. It is one thing to drop oranges upon an imaginary battleship at an aviation meet from a few hundred feet up in the air, and quite another to drop high explosives from an elevation of several thousand feet upon a warship moving swiftly upon the high seas. Certain it is that the letting go of the very limited amount of high explosives that a few aeroplanes could carry upon a city or fortification would have an effect which might amount to something in a moral sense, but would amount to very little indeed in its material effect. Military men have come to realize that the mere bombardment of cities, whether by siege guns or those of an attacking fleet, while it may be irritating and the cause of some loss to the enemy, will very rarely, if ever, prove to be a serious factor in determining the issues of a campaign.
How comparatively small would be the damage done by aeroplane high-explosive attack is suggested, if not proved, by the results of the bombardment of the Russian fleet in Port Arthur by the 11-inch siege guns of the investing Japanese army. The fire of these guns was directed by a Japanese observer on a high hill which had been captured from the Russians; and the shells, each of which weighed a quarter of a ton and carried a charge of high explosive, rained down pitilessly, with great accuracy, and almost vertically, upon the Russian ships. It is known that the whole of the Russian fleet was sunk, and it was presumed that the Japanese shells had done the work. When these vessels came to be raised, after the capitulation of Port Arthur, it was found, to everyone's amazement, that the ships had been sunk by the Russians themselves, and that the damage done by the falling shells was astonishingly small. If then the falling of a 500-pound shell from a height of two miles did such little damage, small indeed would be the havoc wrought by the Lilliputian pellets to which, because of its small carrying capacity, the aeroplane will have to be restricted.
There are, however, certain other offensive operations for which the aeroplane would be admirably adapted; such, for instance, as making raids into the enemy's country for the purpose of attacking his lines of communication, cutting telegraph wires, blowing up bridges, and making sudden descent upon commissary depots with the object of setting fire to or otherwise destroying military stores. The swiftness, silence, and unforeseen character of such attacks would necessarily render them extremely annoying to the enemy, and, now and then, a blow might be struck that would seriously affect the outcome of important military movements. A swift aeroplane would form an ideal means of transport for the aides-de-camp in carrying dispatches to various parts of the field. Furthermore, crises may frequently arise in a great battle when there is a demand for the sudden presence of the commander-in-chief, or other high ranking officer, at certain distant points of the field. The presence of two or three swift aeroplanes at headquarters might prove of inestimable advantage in 'critical phases of a conflict that was strung out over a far-flung battle line.