In describing the various proposals and experiments which have been made to compass artificial flight by means of rotating screws, the latter will chiefly be considered as instruments from which to obtain support of a given weight in the air. There is no question that they can serve as propellers if the support be otherwise obtained, nor that if a screw can lift and sustain its own prime motor, it can also be made to progress horizontally, either by inclining it at the proper angle or by adding a vertical screw.
It was to be expected that when inventors found how difficult it is to obtain a lifting effect from flapping wings, they should turn to aerial screws to sustain them in the air. Man has succeeded in out-traveling both land and marine animals by substituting rotary motion for the reciprocating action of their limbs: the locomotive far outstrips the horse, and the paddle-wheel and screw have, for large vessels, superseded the oar, so that it seems natural to expect that some rotating device shall be found the preferable propeller, should aerial navigation ever be accomplished.
It will be seen, from the accounts which follow, that the chief obstacle has hitherto been the lack of a sufficiently light motor in proportion to its energy; but there has recently been such marked advance in this respect, that a partial success with screws is even now almost in sight.
Curiously enough, the Aerial Screw considerably antedates the marine screw, although, unlike the latter, it has not been brought into practical use. We have already seen that Leonardo Da Vinci experimented with paper screws, which mounted into the air, as early as A.D. 1500, and we may add that a sketch has been found in his note books for a proposed aerial screw machine 96 ft. in diameter to be built of iron and bamboo framework, covered with linen cloth thoroughly starched. He probably abandoned all idea of constructing it when his experiments with models showed the power that would be required.
A similar proposal was made by Paucton, a learned mathematician, in 1768. when, in a treatise upon the Archimedean screw, he described an apparatus which he called a "Pterophore," consisting of two aerial screws, one to sustain and the other to propel, attached to a light chair. A man seated in the chair was expected to rotate these screws by means of gearing, and so raise himself through the air.
The first practical experiment known, however, is that of M. Launoy, a naturalist, and M. Bienvenu, a mechanician, who jointly exhibited before the French Academy of Sciences in 1784 the little apparatus shown in fig. 25. It consisted of two superposed screws, about one foot in diameter, each composed of four feathers inserted in sockets at the ends of a rotating axle. This axle was put into motion by the unwinding of a cord fastened to the two extremities of a bow and the report to the French Academy (May 1, 1784) says:
"The working of this machine is very simple. When the bow has been bent by winding the cord, and the axle placed in the desired direction of hight-say vertically, for instance- the machine is released. The unbending bow rotates rapidly, the upper wings one way and the lowerwings the other way, these wings being arranged so that the horizontal percussions of the air neutralize each other, and the vertical percussions combine to raise the machine. It therefore rises and falls back afterward from its own weight."
FIG. 25. -- LAUNOY & BIENVENU-- 1784.
Launoy & Bienvenu proposed also to build a large machine, and to go up in it themselves. It is not stated whether this was ever attempted but probably not, as a brief investigation must have satisfied them that they had no adequate primary motive power at hand to lift even its own weight in that way, and that with a secondary or stored power tile machine would fly but for a few seconds. Practically the same device was constructed by Sir George Cayley in 1795, and described by him in Nicholson's Journal for April, 1810; but whether he reinvented it or borrowed the idea from Launoy & Bienvenu is not stated. He mentions it merely as a toy, and his writings seem to indicate that he expected success to be achieved instead with an aeroplane to be driven by some sort of propelling apparatus, if only a sufficiently light first mover could be contrived.
Subsequently, Deghen, in 1816, Sarti, in 1823, and Dubochet, in 1334, all proposed and constructed models for flying machines on the vertical screw principle; but they did not discover the necessary light motor to transform their models into practical machines.
In 1842 Mr. Phillips, the inventor of the "Fire Annihilator," succeeded in raising into the air an apparatus weighing in the aggregate 2 lbs., by means of revolving fans inclined about 20° from the horizontal. The motive power was evolved by the combustion of charcoal, fire and gypsum making steam, as in the original fire annihilator and the engine consisted of rotating arms discharging steam direct into the atmosphere, and thus working by reaction, being the device known as the discovery of Hero, of Alexandria. Mr. Phillips exhibited a working model of his aerial machine at the Aeronautical Exhibition in London, in 1868; and in describing his experiment of 1842 he said:
"All being arranged, the steam was up in a few seconds, when the whole apparatus spun around like a top and mounted into the air faster than any bird; to what height it ascended I had no means of ascertaining. The distance traveled was across two fields, where, after a long search, I found the machine minus the wings, which had been torn off from contact with the ground." This is undoubtedly the first machine which has risen into the air by steam power; but the necessarily small capacity of the generator, and the wasteful though simple method of using the steam, limited its flight to a very few minutes, and removed it from the possibility of application on a practical scale.
In 1843 Mr. Bourne, the well-known English engineer, constructed some models of aerial screws, consisting of large fowl's feathers inserted in a cork, stuck on the top of a pine stick, to which a watch spring was attached, succeeded in making them rise by the force of the coiled spring to the height of some 20 ft.; but he recognized that the difficulty in the way of building a really navigable machine was to obtain "the right motive power."
This must also have been the conclusion of Mr. Cossus, who proposed, in 1845, the apparatus shown in fig. 26, which consists in three rotating aerial screws to be moved by steam power. The design is by no means devoid of merit, for by hinging the outer and smaller screws, and varying their angle with respect to the machine, the latter can be made to travel in any direction desired, while sustained by the rotation of the middle screw. It cannot be learned that Cossus tried any practical experiments, for a simple inquiry into the weights and relative energy of the steam engines of his day and an investigation as to the power required to sustain his apparatus must have speesily convinced him that it had better be abandoned.
FIG. 26. -- COSSUS-- 1845.
Analogous proposals were made in 1851 by Mr. Aubaud, who combined several screws with an aeroplane; and by Le Bris, who designed a car surmounted by two screws turning in opposite directions, in order to overcome the tendency of the apparatus to rotate on its own axis, as the consequence of the horizontal component of the thrust of a single screw.
It was to overcome this same objection that, in 1859, Mr. Bright designed and patented the apparatus shown in fig. 27, the axles of the screws consisting of tubes, rotating in opposite directions, one inside of the other. Mr. Bright seems to have planned the machine to be suspended beneath a balloon, and to be worked by man power, in order to alter or to maintain the altitude at will, and thus save the expenditure of ballast in rising or of gas in descending. Its beneficial effects, however, seem to have proved so small- solely, it may be said, from the inadequacy of the motive power employed-that it has not come into practical use.
FIG. 27. -- BRIGHT-- 1859.
These various efforts were somewhat desultory, and not followed up by anything like scientific experiments; but in 1863 there was in Paris a great "boom" in projects for navigating the air by means of aerial screws, and the French espoused its promotion with great enthusiasm. M. de Ponton d' Amécourt and M. de la Landelle had already studied the action of the screw upon the air, which, in July, 1863,, M. Nadar, a prominent photographer, invited to his reception rooms the élite of the press, of science, and of artists, and treated them to a first reading of his famous "Manifesto upon Aerial Automotion," which appeared the next day in the press, and was republished and commented upon throughout the whole of Europe.
In this manifesto, written with much eloquence, Nadar expressed the opinion that the principal obstruction in the way of navigating the air was the attention which had been given to balloons; that, in order to imitate nature, a flying machine must be made heavier than the air. Also that the surest means of success was the employment of the aerial screw -- "the sainted screw," as an illustrious mathematician called it, which was known to be capable of carrying up a mouse, and must, therefore, ? fortiori, be able to sustain an elephant.
The inanity of this argument was not apparent at the time; and Nadar proceeded to form a syndicate to promote "aviation" after the methods of opera bouffé. A journal was founded--the first Aéronaute--43 paying subscribers were obtained, and 100,000 copies of the first issue printed. This journal expired after its fifth issue. Then a monster balloon was built-the Géant-out of the exhibition of which it was expected to realize sufficient profits to build a screw machine which should put an end to ballooning forever. But the Géant met with all sorts of mishaps; it gave no profits, and entailed losses instead, which nearly ruined Nadar; and such experiments as were tried with aerial screws (outside of the little toys which were exhibited at the various meetings) demonstrated that the utmost weight which the exertion of one horse power could sustain, with a screw acting upon the air, was some 33 lbs., or, in other words, that if the apparatus were to weigh one ton, it would need 67 horse power continuously exerted to keep it afloat.
This is now clear enough to us. Assuming that in consequence of the rotation at high speed a smaller surface is required to sustain a given weight with a screw than with reciprocating wings or fixed aeroplanes, yet the motor for the screw would probably weigh about one-third of the whole weight of the apparatus (instead of one-quarter, as in the case of birds, and probably one-sixth in the case of aeroplanes), and so the utmost weight available for the motor of the screw and its supplies would be 1/3 of 33 lbs., or 11 lbs. to the horse power, while in 1863 there was no primary motor known then approximating such phenomenal lightness.
Now that Mr. Maxim has announced that he has built a steam engine, and its generator of 950 lbs. aggregate weight developing 120 actual horse power, or at the rate of 8 lbs. to the horse power, it is doubtless within his power to go up into the air with an aerial screw, and to perform therein various evolutions; but his trips would probably be short, and the consequences might be unpleasant were the machinery to break down while he is aloft.
He has, accordingly, with great good judgment, begun by applying his steam engine to an aeroplane, although this will involve greater difficulties in starting and in landing, as well as a less immediate demonstration.
Almost the only memento which now remains of the movement in favor of the aerial screw inaugurated by Nadar is the model of the flying machine designed in the Viscount de Ponton d' Amércourt, and which is shown in fig. 28. The following description is translated from that of M. Tissandier:
"M. de Ponton Amecourt constructed, in 1865, an aerial screw machine worked by steam, which was expected to rise with both its motor and its steam generator. This beautiful little model, which was exhibited at the London Aeronautical Exposition in 1868, is exquisitely finished. The boiler and frames are of aluminum, and the steam cylinders are of bronze. The reciprocating movement of the pistons is transmitted by gearing to a double pair of superposed screws of 41 sq. in. surface, one rotating in a different direction from the other. The apparatus, which is now in the collection of the French Society for Areial Navigation, weighs, without water or fuel, 6.1 lbs. The boiler is 3 1/4 in. high and 4 in. in diameter; the total height is 24 1/2 in. Unfortunately the boiler cannot be worked at sufficient pressure; when the machine is put into motion it possesses a certain ascensional force; it loses weight, but it does not rise."
FIG. 28. -- D'AMÉCOURT -- 1863.
The illustrated papers also published about 1865 views of a great steam flying machine, attributed to M. de la Landelle. These showed a hull flanked with aeroplanes, and surmounted with two masts, each carrying four sets of screws, and also a partly folded umbrella, presumably to open into a parachute. It is to be found reproduced in most works upon aerial navigation, and in encyclopeadia articles, and is not given here, because it possesses no merit whatever, being probably a newspaper fancy, like the flying ship attributed to Mr. Edison, which went the rounds of the press some years ago, and which is also reproduced in M. Dieuaide's chart.
M. de la Landelle was a persevering man, as well as one of considerable scientific acquirements. He continued making experiments upon screws of various shapes long after M. Nadar and Ponton d' Amércourt had given them up in disgust; and he encouraged M. Pénaud, then a rising young man, to take up the study of Aviation. The latter produced in 1870 the little apparatus shown in fig. 29, which has remained the best of its kind.
FIG. 29. -- PÉNAUD -- 1870.
Pénaud's flying screw, which is called by the French a "Helicoptère," consists of two superposed screws rotating in opposite directions, and actuated by the force of twisted rubber strings. The principle is the same as the apparatus of Launoy & Bienvenu and of Sir George Cayley, but the twisted rubber is far more effective than the bow, whether the latter be of whalebone or steel, and this change in the motor constituted the chief merit of Pénaud's modification. He first experimented with rubber in tension, but found that the increased weight of the frame (to resist the strains) more than compensated for the weaker effects of torsion, and that the latter application enabled him to construct models which were simple, cheap, efficacious, and not easily broken. These models, when built in varying proportions, would either rise like a dart to a height of some 50 ft., and then fall down, or sail obliquely in great circles, or, after rising some 20 or 25 ft., hover in the same spot for 15 or 20 seconds, and sometimes as many as 26 seconds, which was a much longer flight than had ever before been obtained with screws.
For lack of a sufficiently light primary motor, Pénaud's further experiments in this direction brought forth no practical results, and his apparatus has remained a toy, which has been varied in many ways.
The most popular of such toys have been the various single spinning screws, either of cardboard or metal, which are attached to a spindle around which a string is wound, and which are set in rapid rotation by briskly pulling and unwinding the cord These are of many shapes, with two, three, or more arms, and of various angles of pitch. Those with heavy rims are most effective, sometimes rising as much as 200 ft. into the air; but they have led to accidents and proved dangerous. In such devices the source of power is not taken up into the air, as in Pénaud's apparatus, but it is stored in the momentum of the screw and encircling ring (if any) by the original muscular effort. Mr. Wenham measured the force expended in unwinding the coiled string by attaching thereto a small spring steelyard, and noting the time of ascent of a flying screw of tin plate with three equidistant vanes. He computed that to maintain the flight of the instrument, weighing 396 grains, a constant force is required of near 60 foot-pounds per minute, or in the ratio of about 3 horse power for every 100 pounds.
Many modifications have also been made of the double screw arrangement, which takes up its secondary motor in the shape of twisted rubber. These have been produced by many people; but the cleverest are probably those of M. Dandrieux, who, in November, 1879, presented before the French Aeronautical Society5 no less than 10 different types, the best known of which is that of the butterfly, which is still to be found in the toy shops, and which comes to us both from Paris and from Japan. M. Dandrieux modified the shape and proportions of the screw, and effected a material improvement in its efficiency.
Flying screws driven by clock springs have been frequently made. Such an arrangement was constructed by Sir George Cayley, "the flying baronet," at the beginning of the century, and is described in his paper on "Aerial Navigation," in Vol. XV of Nicholson's Journal. Sometimes the attempt has been made to substitute man power. Of such was the experiment of Mr. Mayer, a stair-builder, who, about 1828, constructed an aerial screw proportioned to sustain 126 lbs., and rotated it with his own muscular power. In giving an account of the result, forty years later, he said, naively: 6
"The result was very flattering, though not perfectly successful. My pecuniary resources were exhausted, and other work in my own business being then offered to me, ascending by wings (screws) was abandoned until a more convenient season, and the more certain and substantial method of making stairs, and ascending them step by step, was substituted in its place."
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