AEROPLANES -- i.e., thin fixed surfaces, slightly inclined to the line of motion, and deriving their support from the upward reaction of the air pressure due to the speed, the latter being obtained by some separate propelling device, have been among the last aerial contrivances to be experimented upon in modern times.
The idea of obtaining sustaining power from the air with a fixed, instead of a vibrating or a rotating surface is not obvious, and it was not till 1842 that an aeroplane, as we now understand the term, consisting of planes to sustain the weight, and of a screw to propel, was first proposed and experimented with. All aviators must have occasionally seen and marveled at the performances of the soaring varieties of birds, sailing in every direction at will upon rigidly extended wings (a performance concerning which more will be said in the progress of this discussion), but the happing birds are so much more numerous and easily observed, their action is so much easier of comprehension, that they have been the favorite model.
We shall see, however, in reviewing old traditions with perhaps a new understanding, that such faint approximations to success, as have hitherto been attained with artificial flying machines, were probably accomplished with fixed surfaces, either by gliding downward by the force of gravity, or in soaring upon the wind like a bird.
Although aeroplanes have been among the last devices to be experimented upon, they are now the favorite apparatus from which success is hoped for, and later designs have chiefly been in this direction. The very important labors of Professor Langley have shown that with the exertion of 1 horse power as many as 200 lbs. can be sustained in the air by an aeroplane, while Mr. Maxim states, as the result of his many experiments, that at least 133 lbs. can be sustained per horse power. lf we compare this with the results of vibrating wings, which may be assumed as supporting 77 lbs. per horse power,10 or with screws, which have been shown as affording generally 33 to 40 lbs. per horse power--chiefly, as the writer believes, because of the greater angle of incidence or of pitch which is required with alternating or rotating surfaces-we see that fixed surfaces possess a marked advantage over movable surfaces. The latter, it is true, can probably be made somewhat smaller and hence lighter, but this advantage is likely to be more than counterbalanced by the greater power required to work them.
Still the fact remains that almost all experiments with aeroplanes have hitherto been flat failures. This is believed by the writer to result from the difficulty of maintaining the equilibrium of that form of apparatus, both sideways and fore and aft. There seems to be no very great difficulty in obtaining proper balance and equilibrium with flapping wings or with screw apparatus, the motion of the parts apparently compensating to some extent for the tendency to tilt over, but fixed aeroplanes seem much more unstable--a single flat plane, for instance, of uniform weight throughout, possessing no sort of stability whatever when in forward rectilinear motion.
Perhaps the reader will best understand this, and at the same time obtain a glimpse of some of the laws of aerial equilibrium under forward motion, by experimenting with an aeroplane of his own.
Let him cut out a strip or parallelogram of stiff wrapping paper-say 15 in. long and 3 in. wide. Its sides should be straight and parallel, and the surface a true flat plane, free from folds or wrinkles. In this condition it may fall flatways a short distance with tolerable steadiness; but if allowed to fall edgeways, or projected forward without whirling, it will at once rotate upon its long axis, tumble over and over, and be seen to have very unstable equilibrium. This can be remedied with very slight changes; for next paste upon one of the long edges of the plane a strip of pasteboard 1/2 of an inch wide and the same length as the paper plane. Part of an ordinary pasteboard box will do very well; but the important point to be observed is that the apparatus shall balance on its middle line, and at a point 28 to 30 per cent. back from its front edge, or say, 7/8 of an inch. When the paste is dry, make a very slight fold in the paper strip near the edge opposite to the pasteboard strip and parallel to it. Let this fold or crease be about 5/8 of an inch from the rear edge, and form an angle of about 10° with the plane of the paper. Next bend the aeroplane parallel with the short sides and exactly in the center of the long sides, so that the two halves shall also stand at a dihedral angle of about 10° with each other, like a very obtuse letter V, care being taken that middle fold and the back fold shall be on the same side of the plane. It will then be noticed that the attitude of the apparatus somewhat resembles that of a soaring buzzard in the air minus its tail.
If, now, this aeroplane be allowed to drop edgeways, with the weighted side downward, from a height of 7 ft. or more, its behavior will be entirely different from that in its former condition. Instead of tumbling over and over, it will sail downward and forward upon a curve until the increasing pressure balances the weight, and then glide on a straight path to the floor, some 15 or 20 ft. from the operator. It may not glide on a straight line upon the first trial, but in that event very slight changes in the angles of the back crease and of the middle fold, and a smoothing out of the plane will be sure to produce the desired forward flight and steady glide.
Still better results can be obtained by pasting a strip of tin 1/4 in. wide in a fold in the forward edge of a plane 4 in. wide. For this purpose it will be well to have the strip of tin 15 in. long, and to cut the paper plane 20 in. long by 5 in. wide, so that 1 in. of the latter can be folded quite over and pasted down over the tin. The latter should be accurately spaced 2 1/2 in. from each end, so that the apparatus shall balance exactly on the middle line lengthways, and 1.2 in. from the weighted edge, crossways. The corners beyond the tin may be rounded off if desired, provided care be taken not to disturb the balance. Then by bending the apparatus very slightly in the center of its length, and turning up the rear edge about 10° in the same direction, an aeroplane will be produced which will sail steadily forward in still air, sweep to the right, if the right-hand back corner be slightly curved up, or go to the left when the left-hand corner is similarly treated.
The principle on which this aeroplane sails is the same as that upon which the bird glides downward on outstretched wings, The preponderance of the weight in front determines the angle of incidence, and brings the center of gravity to coincide with the center of pressure, the latter varying approximately as per Joessel law, already given, which, however, it must be remembered, probably only applies lo square planes; the horizontal component of the pressure (inasmuch as the plane is inclined forward acts in the direction of the flight, and furnishes the motive power while the back fold supplies automatically the longitudinal stability by counteracting such tendency as the aeroplane may have to tilt fore and aft; and she dihedral angle in the middle gives lateral stability, by reacting against the air on that side toward which the apparatus may begin to tip.
These compensations are effective in still air, but it may be doubted whether they are sufficient in the open air. When a bird soars in a gusty wind (and almost all winds are gusty and irregular in velocity near the surface of the ground), the automatic effects obtained by the dihedral angle of the wings and the upward angle of the tail do not seem to act quickly enough. The bird will be seen, by observation at close range, to be almost constantly balancing himself by slight, almost unconscious movements. He advances the tips of his wings or thrusts them back; he flexes one or the other, and quite often he advances or draws back his head, or uses his legs as a pendule from the knee joint, in order to maintain his equilibrium. All birds are acrobats, but the soaring kind, if closely observed in a gusty wind, will be seen to perform feats of balancing more delicate and wonderful than those of any human equilibrist.
We shall hereafter see that even if the aeroplanes experimented with had been provided with adequate motors, as they were not, this difficulty in maintaining a proper equilibrium with fixed surfaces is probably sufficient to account for most of the failures of experiments upon a practical scale with that form of apparatus, and for their abandonment by their designers, a brief trial having probably satisfied them that aside from the question of a motive power, which they were confessedly unable to solve, they were not yet masters of such reasonable stability and commend over their apparatus, as to warrant them in proceeding further. Now that the all-important question of a light motor seems to be in a fair way of being solved through the achievements of Mr. Maxim, M. Trouvé, and others who are known to be laboring in the same direction, the question of the equilibrium of aeroplanes increases in relative importance, and warrants making this somewhat prominent in criticizing past experiments and proposals. For this and other reasons we shall pass in review a number of mere designs as well as forms of apparatus which was actually subjected to the test of experiment, and endeavor to inquire into the causes of failure.
Failures, it has been said, are almost as instructive as successes, as tending to remove, if we can understand the cause, at least one of the difficulties in the way. and the reader will probably agree that there has been hitherto no lack of failures in aerial experiments.
There probably have been in all ages of the world men, whose imaginations were fired by the sight of the soaring birds and some who tried to imitate them. In early times mechanical and mathematical knowledge was too crude to render such experiments numerous, and before the invention and diffusion of printing, even the records of such failures would generally perish; but a few legends have come down to us in abbreviated shape, which indicate that some then celebrated attempts and failures had taken place. No great faith can be attached to these legends, yet some of them are curious, if considered as the relation of attempts to sail upon the wind like soaring birds with rigid fixed surfaces.
Passing over as too scanty of record the myths of an antiquity perhaps the earliest legend of an experiment which we may fairly suppose to have been tried with an aeroplane is stated to be found in the somewhat fabulous chronicles of Britain,11 wherein it is related that King Bladud, the father of King Lear, who is supposed to have reigned in Britain about the time of the founding of Rome, caused to be built an apparatus with which he sailed in the air above his chief city of Trinovante, but that, losing his balance, he fell upon a temple and was killed. This is about all there is of the legend, and as even that concerning King Lear, which Shakespeare worked up into his tragedy, has been suspected of being a myth, it is difficult to comment intelligently upon such a tradition; yet it is not impossible that King Bladud (who was reputed to be a wizard, as were all investigators in ancient times), should have attempted to imitate the ways of the eagle in the air, and should have succeeded in being raised by the wind, when, for lack of the balancing science of the bird, he should have lost his equilibrium, and with a shear, a plunge, or a whirl have come in disaster to the ground.
A better authenticated legend seems to be that of Simon the Magician who, in the thirteenth year of the reign of the Emperor Nero (about 67 A.D.), undertook to rise toward heaven like a bird in the presence of everybody.12 The legend relates that "the people assembled to view so extraordinary a phenomenon and Simon rose into the air through the assistance of the demons in the presence of an enormous crowd. But that St. Peter, having offered up a prayer, the action of the demons ceased, and the magician was crushed in the fall and perished instantly."
"It seems, therefore, certain" (adds M. de Graffigny) "from this tale, which has come down to us without any material alteration, that even in that barbarous age a man succeeded in rising into the air from the earth by some means which have unfortunately remained unknown."
The writer has seen the feat performed by soaring birds many times. He has seen a gull, standing upon a pile-head within 20 ft. of him, float up into the air without flapping, by simply facing the wind, opening his wings to their full extent, and keeping them rigidly extended to a sea breeze blowing at the rate of 14.40 measured miles per hour. The gull rose vertically about 2 1/2 ft. above the pile-head, then drifted back about 5 ft., still rising slightly, when he altered by a trifle his angle of incidence, advanced against the wind, losing a little height, and was thenceforth in full soaring activity. Many other writers have seen the same kind of performance, including the still more difficult feat seen by M. Mouillard13 who observed in Africa an eagle spring from the top of an ash-tree and without a single flap first descend from 7 to 10 ft., going against the wind, and upon this freshening to a squall, rise directly and slowly some 300 ft. into the air, while advancing against the wind some 150 ft. at the same time
The reader may be further interested by the account of a somewhat similar feat, published in L'Aéronaute of October, 1890 by Mr. Charles Weyher and which he describes as follows:
"One day when I was close to the Aqueduct of Buc, and the wind was blowing strongly down the valley, and therefore at right angles to the aqueduct, I saw a sparrow hawk come out of a hole marked A (fig. 36) on the sketch, near the top, and on the leeward side.
"The bird left his hole and dove downward, his wings scarcely opened, and thus reached like a dart a point about the center of the opening of one of the arches. At this moment, when at B, he stretched his wings wide open and began circling, continued his orbits, drifting with the wind, until he attained an elevation of 800 to 1000 ft. At this elevation, or the point C, the sparrow hawk folded his wings almost completely and dove forward again upon a steep inclination, making use of the height gained to recover against the wind the distance which he had drifted, and to regain his hole, into which he entered gently, by simply opening his wings wide when within 7 to 10 ft. of the wall.
"It is well to observe that the bird in taking this journey, both going and coming back, expended no muscular work whatever, save the utterly inappreciable exertion of opening and folding up his wings twice."
FIG. 36 -- THE SPARROW-HAWK'S EXCURSION.
The legend of Simon the Magician which has led to the above digression, is clearly of Christian origin, as evidenced by the intervention of St. Peter, who is supposed to have been martyred in Rome about A.D. 64. It is not known to he confirmed by any Roman record, such records having been largely destroyed during the dark ages; but if the tradition be founded upon a fact, we may suppose Simon after some preliminary trials, to have attempted to imitate, with a fixed aeroplane, in public, some of the evolutions of a soaring bird and being unable to perform skillfully the necessary manoeuvers to have lost his equilibrium and his life.
There is another monkish tradition of the eleventh century concerning Oliver of Malinesbury who in some of the accounts is styled "Elmerus de Malemaria" and who was an English Benedictine monk, said to have been a deep student of mathematics and of astrology, there by earning the reputation of a wizard. The legend relates14 that "having manufactured some wings, modeled after the description that Ovid has given of those of Dedalus and having fastened them to his hands, he sprang from the top of a tower against the wind. He succeeded in sailing a distance of 125 paces; but either through the impetuosity or whirling of the wind, or through nervousness resulting from his audacious enterprise, he fell to the earth and broke his legs. Henceforth he dragged a miserable, languishing existence (he died in 1060 attributing his misfortune to his having failed to attach a tail to his feet."
Commentators have generally made merry over this last remark, but in point of fact it was probably pretty near the truth. To perform the manoeuvre described, of gliding downward against the breeze, utilizing both gravity and the wind, Oliver of Malmesbury must have employed an apparatus somewhat resembling the attitude of a gliding bird, but being unable to balance himself fore and aft, as does the bird by slight movements of his wings, head and legs, he would have needed even an ampler tail than the bird spreads on such occasions in order to maintain his equilibrium. He would have failed of true flight in any event, but he might have come down in safety.
A more explicit tradition of the same kind comes from Constantinople, where under the reign of the Emperor Manuel Comnenus probably about the year 1178 a Saracen (reputed to be a magician of course), whose name is not given, undertook to sail into the air from the top of the tower of the Hippodrome in the presence of the Emperor.
The quaint description of this attempt, as taken from the history of Constantinople by Cousin and given both by Graffingy and by Bescherelle, so clearly describes an aeroplane as distinguished from movable wings, and so well indicates the difficulty of obtaining and maintaining a proper balance with such an apparatus, that it is worth quoting:
"He stood upright, clothed in a white robe, very long and very wide, whose folds, stiffened by willow wands, were to serve as sails to receive the wind. All the spectators kept their eyes intently fixed upon him, and many cried, 'Fly, fly, O Saracen! do not keep us so long in suspense while thou art weighing the wind!'--i.e., adjusting the angle of incidence and the equilibrium of the machine.
"The Emperor, who was present, then attempted to dissuade him from this vain and dangerous enterprise. The Sultan of Turkey in Asia, who was then on a visit to Constantinople, and who was also present at this experiment, halted between dread and hope, wishing on the one hand for the Saracen's success, and apprehending on the other that he should shamefully perish. The Saracen kept extending his arms to catch the wind. At last, when he deemed it favorable, he rose into the air like a bird; but his flight was as unfortunate as that of Icarus for the weight of his body having more power to draw him downward than his artificial wings had to sustain him, he fell and broke his bones, and such was his misfortune that instead of sympathy there was only merriment over his misadventure."
This account seems to be given with such circumstance as to preclude the idea that it is merely the idle tale of some lover of the marvelous. We may, therefore, fairly seek to draw some inferences therefrom, which have not been heretofore mentioned by other writers. The first is that the apparatus was some form of aeroplane, because it is likened to a robe instead of a pair of wings, and also because no mention whatever is made of any flapping action. The only active exertion described on the part of the operator is that of the adjustment of the apparatus to the prevailing wind, implying that it was so adjustable that the angle of incidence might be regulated to obtain an ascending effect, and the center of pressure be brought to coincide with the center of pressure to produce fore and aft equilibrium. The second inference is that the force of the wind was the only motive power relied upon, and that the apparatus was not blown away, but rose upon the wind like the gull which has been already described. This being possibly an instance of that mysterious phenomenon of "Aspiration" which was alluded to at the beginning of this account of "Progress in Flying Machines," and which will be found further exemplified when an account is given of the various experiments of Captain Le Bris The third inference is that the defect lay in the maintenance of the equilibrium. That the apparatus started off properly balanced, but that so soon as a change occurred in the conditions, perhaps an erroneous manoeuvre on the part of the Saracen, or perhaps a gust of wind on one side, the aeroplane lost its balance, and disaster ensued.
Only brief allusion need be made in this discussion to the writings of Roger Bacon the eminent philosopher of the thirteenth century 1214-94 He seems to have prophesied both the balloon and the flying machine but not to have tried or related any experiments. His writings will be found noticed in some of the encylopaedias and in Wise's "History and Practice of Aeronautics,'' the latter book containing, moreover, references to the traditions which have here been mentioned, as well as to others which have been omitted.
One of the most celebrated traditions of partial success with a flying machine refers to J. B. Dante an Italian mathematician of Perugia, who toward the end of the fourteenth century seems to have succeeded in constructing a set of artificial wings with which he sailed over the neighboring lake of Trasimene.15 We have no description of the apparatus, but this was presumably an aeroplane, soaring upon the wind, for we have seen abundantly that all experiments have failed with flapping wings, man not having the strength required to vibrate with sufficient rapidity a surface sufficient to carry his weight in the air. Moreover there would be a stronger and steadier wind over a lake than over the land, and the selection of a sheet of water to experiment over was very happy. as it would furnish a yielding bed to fall into if anything went wrong, as is pretty certain to happen upon the first trials. A similar selection has been recommended by D'Esterno and by Mouillard and cannot be too strongly urged upon any future inventor who desires to make similar experiments. With adequate extent of surfaces, and (if he goes up at all) some prudence as to the height to which he allows the wind to carry him, he can thus acquire some insight into the science of the birds, with no greater danger than that of numerous dunkings
Whether Dante grew overbold with some preliminary successes, or whether he was impatient to display his achievement before his fellow-citizens and his sovereign, he attempted to repeat the feat in Perugia, on the occasion of the marriage of Bartholomew Alviano with the sister of Jean Paul Baglioni. Starting from the top of the highest tower in the city of Perugia, he sailed across the public square and balanced himself for a long time in the air, amid the acclamations of the multitude. Unfortunately the iron forging which managed his left wing suddenly broke, so that he fell upon Notre Dame Church and had one leg broken. Upon his recovery he seems to have given up further experiment, but went to teach mathematics at Venice, where he died of a fever before he had reached forty years of age.
Granting the tradition to be true, the apparatus used by Dante must have been more manageable than any of its predecessors, for the accident is said to have been due to a breakage instead of a loss of balance. The latter, however, must have been still deficient, or Dante would have renewed his experiments with a stronger forging. He may have reasoned, moreover, that as the wind does not blow with the requisite speed every day, and he knew of no sufficiently light motor to take its place, the use of a soaring machine would be very limited; but it is very unfortunate that we should have no description of the machine and its mode of operation.
10 Assuming a bird in horizontal
flight to develop 425 ft. lbs. per minute for each pound of his weight, the
sustaining reaction will be 33.000/425 = 77 lbs. per horse power.
11Bescherelle, Histoire des Ballons, 1852.
12Fraffigny, La Navigation Aérienne, 1888.
132. Mouillard, L'Empire de l'Air, 1881. Page 22.
15Bescherelle, Histoire des Ballons.
16 Tissandier, La Navigation Aérienne. Bescherelle, Histoire des Ballons.
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