Popular Science Monthly/Volume 46/March 1895/Wellner's Sail-Wheel Flying Machine
|WELLNER'S SAIL-WHEEL FLYING MACHINE.|
ONE of the latest and most ingenious schemes for solving the problem of aërial navigation is that devised by Prof. G. Wellner, of Brunn, Moravia, who has sought to bring in the application of a new principle. He calls his apparatus the "sail-wheel flying machine" (Segelrad-Flugmaschine), and regards the mechanism of it as a kind of cross between those of the screw-propeller and of the kite, combining the advantages and avoiding the inconveniences of both. His system has won approval and confidence from eminent engineers and experts in aërial navigation to such an extent that the Vienna Association of Engineers and Architects is having experiments and observations made which will show very soon the degree of practicability and value possessed by his invention.
In his paper on the subject, Prof. Wellner describes his line of thought and the result of his researches, prefacing them with a summary of the experiments and investigations of his co-workers. Fig. 1.—Air-ship La France. The oblong form of balloons chosen by Giffard in Paris in 1852, by Dupuy de Lôme in Vincennes in 1872, by Tissandier in 1883, and by Renard and Krebs at Chalais in 1885 for their balloon "La France," conquered to a considerable degree the resistance of the air and thus increased the velocity (Fig. 1). They contained electro-dynamic motors with a galvanic column so admirably suited to the apparatus as to secure the greatest possible power with the least weight. Various improvements made obviated the danger of pitching. The "La France" almost completely fulfilled the condition that the balloon must return to its point of departure; in seven ascents a return was five times made to the starting point, showing that five times a complete control of direction had been gained. A speed of 6·5 metres per second (about fourteen miles per hour) was reached. Efforts have been made by the French military department to double this velocity, making it thirteen metres per second. This would be important, as in aërial navigation direction can be controlled only by velocity. But the weight of the motor required for such great power must constitute a serious embarrassment. Moreover, the pressure of air currents and the resistance of the wind endanger the balloon constructed of light material.
These circumstances lead to the conviction that the aëronautic problem will most probably admit of a satisfactory solution only by means of dynamic flying machines. Prof. Wellner is of the opinion that, manifold as are the difficulties besetting the road to this end, it is likely to be attained before the close of our century. The inventor's starting point is the observation and analysis of the flight of insects and birds, which have of late been made possible by the graphic methods of chronometric observation and photography. It would, of course, be a mistake to attempt a close imitation of the organs of motion observed in birds or insects, as these would lose their utility through the unavoidable clumsiness of man's appliances. What must be aimed at is the most advantageous shape and construction of wings, productive of the greatest propelling power with the expenditure of the smallest possible sum of energy; the application of a light but powerful motor; a contrivance for easy and efficient steering, available alike at the time of the ascent, while flying, and in alighting; and arrangements for the prevention of accidents.
It may be regarded as an established fact that gently curved or arched surfaces, pointed toward their ends, make the fittest wings for flying machines; they must be carried against the atmosphere at small angles. The lifting power of the wings arises from the carrying quality of the air compressed and forming, we might say, an air-cushion under the aëroplanes. The air pressure increases in a duplicate ratio to the velocity of the latter; consequently very small wings are capable of great lifting power when vigorously and swiftly plied. In order to advance the airship, a power imparting horizontal motion is needed; this has to be secured by a retrograde movement, thrusting the air backward and thus causing it to propel the air-ship. The shape, position, and direction of the aëroplanes will have to be such as to combine the vertical lifting with the horizontal propulsion. The two great distinct groups of air-ships attempting to secure this end are those propelled by screws and those working on the principle of a kite.
The models constructed by Ponton d'Amécourt, Achenbach, Dieuaide, Forlanini, Philipps Popper, Jarolimik, and some others are based on the screw principle. They employ propeller screws moving horizontally on vertical axes and connected with aëroplane surfaces which are capable of inclination between the horizontal and vertical positions like those of a windmill. These aëroplanes pressing down the air act very much like the propeller screw in a ship, which drives the water backward so as to make it move the ship forward. The difficulty inherent to this construction arises from a considerable loss of motive power, caused by the difference in revolving speed of the screw at various points nearer to or remoter from the axis. This difference of speed in the turning of the screw combined with the inevitably small angles at which its slanting surfaces are presented to the wind make it incapable of developing, by the help of any of the dynamo machines now in use, a power adequate to the weight of the machine itself, its accessories, and the aëronauts.
The laws that come into play in the flying of a kite are involved in the flight of birds independent of the movement of their wings. In calm weather the kite is moved forward by the boy, who runs along, drawing the string with him. This movement, creating a wind under the kite, causes the air to gather under its slanting surface, and thus calls into play the lifting power of the atmosphere. The flying machines propelled from the rear by a motor with sufficient velocity, on rising into the air are enabled to soar on the same principle. The stronger the wind, the better the kite will rise; the quicker the horizontal motion of the flying machine, the better its aëroplanes will develop the supporting
power of the air. The exertion made by a bird on traveling a long distance is smaller, and its sailing power greater, the faster it flies.
The fastest fliers have the smallest wing surface. Some birds even reduce the area of their supporting surfaces when they increase their speed by drawing in their wings and closing their tails. Consequently, in order to keep the aëroplanes of the flying machine within a moderate size, considerable velocity has to be developed. This at the same time serves to overcome the resistance of the wind and of air currents. The air-ship is not capable of maintaining the direction pursued unless its velocity is so much greater than that of the strongest wind that it can overcome the latter and yet have velocity to spare.
While the construction of the kite machines seems to insure success through the high velocity of movement that must be attained, a new obstacle arises from the difficulty of ascent. The speed of motion being the condition of their rising power, they can not be made to ascend slowly. Once progressing on their road with the tremendous speed adequate to their weight and wing surface, the kite machines can not be stopped or propelled at a lesser rate without at once descending from the level attained. Fig. 3.—Lilienthal's Flying Apparatus. The landing. The contrivances applied to counteract these disadvantages have not proved efficient to overcome them. Nevertheless, the experiments and constructions made by Stringfellow, Moy, Tatin, by Kress in Vienna, Lilienthal in Berlin, Koch in Munich, Philipps, Langley, Edison in America, Maxim in England, and by Hargrave in Australia, all represent so many stages of constant progress. Mr. O. Lilienthal has just succeeded in floating down at a moderate rate from a height of two hundred metres; his personal skill in the handling of the apparatus adds considerably to the advantages derived from its judicious construction (Figs. 2, 3, and 4). Some of the most remarkable experiments in the field of aërodynamics are those devised and carried out by Prof. Langley.
The essence of Prof. Wellner's innovation is his invention of the sail-wheel (Fig. 5). It consists of a horizontally placed axis with spokes and arched aëroplanes attached to them in a cylindrical form. While revolving round the axis the latter take a slightly slanting position, which causes the forward edges of these surfaces to be inclined, and consequently to compress the air in the way of a sail or a kite, calling into play the vertical force. Three ribs running across each lifting surface and made in the form of Fig. 4.—Lillienthal's Flying Apparatus. In flight. a screw at the same time serve to strengthen the aëroplanes and to add to the horizontal force.
These sail-wheels set in pairs can be placed, according to the size of airship aimed at, in one or more groups of two wheels, revolving in opposite directions, behind or beside each other. The cigar-shaped car, furnished with a motor and carrying the aëronauts, is attached horizontally under the center of the wheels, so that the whole construction will resemble a colossal bird, propelled, instead of by wings, by revolving wheels, the lifting surfaces of which are consecutively and constantly developing vertical and horizontal power. The bird's movements in flying and the speedy headway motion necessary to the kite- flying machines for their support in the air are in Prof. Wellner's invention changed to a rotary motion. This construction, while permitting of an easy, slow ascent, assures the horizontal position and constant stability of the air-ship, at the same time permitting of a high velocity. The more the latter is increased, the stronger is the lifting power developed. The direction is given by a rudder at the end of the ship or by increasing the velocity of the sail-wheels on one side only. It is the peculiar quality of these wheels that they do not, as might be supposed, disperse the air around them; they rather attract it toward their rapidly moving surfaces, condensing it to a powerful stream, which passes down obliquely through their cylinders. Their velocity can be made to surpass by far that of railway trains, thus enabling them to conquer contrary winds and air currents. This flying machine
will hardly be called upon to rise above the cloud region; it will be most efficient to reach its goal on the shortest air line at a moderate height above the earth.
Fig. 5 shows a small sail-wheel air-ship for two aëronauts. Each of the two wheels has a diameter of 4·77 metres and six planes five metres wide. Two steam engines of twenty horse power each are said to produce during one hundred and eighty rotations per minute a velocity of forty-five metres, a soaring speed of fifteen metres per second, and a carrying power of fifteen hundred kilogrammes.
A larger machine (Fig. 6), comprising six sail-wheels of 6·4 metres diameter and a steam motor representing eighty horse power, will, at one hundred and thirty-five rotations, carry sixty-four hundred kilogrammes and accommodate eight persons.
The latest experiments with Prof. Wellner's flying machine do not seem to favor the construction of those air-ships which are intended to rise by the strength of their lifting power only, this power sufficiently outbalancing their weight. Some eminent European aëronauts—Profs. Pistio, Miller, Hauenfels, and Wellner himself—now favor the principle of partial disburdening by the application of some gas or other, which will add to the lifting power of the machine.
Important and very animated discussions of the present aspect of aëronautics have recently taken place in London and in Vienna. In the Aëronautic Section of the British Association Prof. H. Maxim laid before his colleagues a detailed report of the
experiments made with the model which he has had constructed for the purpose, and which, though it has met with an accident and has not led to a definite result so far, has certainly brought the vital question nearer to its solution. Prof. Maxim's apparatus is a wonder of ingenuity. It carries its provision of fuel in the form of naphtha in a small, exceedingly light boiler, so constructed as to cause a constant, unvarying pressure. The machine proved able to rise and fly for thirteen hours at a velocity of more than fifty English miles per hour. Its two large screw-propellers are set in motion by two compound engines, the strongest in proportion to their size that have ever been made. Their construction allows of the power being raised within one minute from two hundred to three hundred and twenty-five pounds per square inch. The screws are capable of more than five hundred rotations per minute. The entire weight of this flying machine and crew is eight thousand pounds and its lifting power ten thousand. Unfortunately, the surplus power of two thousand pounds during the experiment lifted the machine off the rails on which it was running, and broke the rear axletrees that were holding it down, thus wrecking the apparatus. The prominent English physicists. Lord Kelvin, Lord Rayleigh, etc., speak of Maxim's air-ship with the greatest enthusiasm; they expect him actually to solve the problem in a near future. The German scientists, however, at the Sixty-sixth Congress of German Naturalists, which was held in Vienna in September, stated that while Maxim's experiment has certainly brought the problem nearer its solution, it has cost one hundred and fifty thousand dollars, and left the question of steering the air-ship, which is at present the greatest impediment to ultimate success, altogether unimproved. They expressed their hope of seeing the real invention made by a German, after all, although their nation does not command pecuniary means which permit of such costly experimenting as that done by Mr. Maxim, whose apparatus, they say, is in its main traits merely the application of Mr. Kress the German inventor's model, executed in colossal dimensions. Mr. Kress demonstrated before the assembly the capacities of his model, which he constructed some years ago, and was loudly applauded as his machine rose with great speed and landed at the appointed place on one of the galleries. Prof. Ludwig Boltzmann, of the Vienna University, gave a general survey of the latest inventions. He considered as a very important step the work done by the engineer, Mr. Otto Lilienthal, in Berlin. This gentleman, while using a flying machine of the smallest possible dimensions, has made great progress in the art of steering it, partly by the application of a rudder that takes the place of a bird's tail, partly by well-calculated motion of his own body and feet. An extensive practice is likely to produce absolute mastery of this part of the problem. "The aëronaut," said Prof. Maxim in his report before the British Association, "has to excel not as an expert in technique only, but also as an acrobat." This implies the same conception of the task to which Prof. Boltzmann gave utterance when speaking of Mr. Lilienthal's work and its prospects. He added that Mr. Kress has recently constructed an apparatus for steering which is based on new principles and gives fair promise of good results.