Ocular demonstration being always more satisfactory than description, those readers who have been sufficiently interested in the subject to try the experiments which have been described with paper planes (falling by gravity) may also like to see for themselves how an aeroplane behaves when motive power is applied. They can probably obtain in a shop one of the toys which have already been alluded to, under the head of "Screws to Lift and Propel," as one of the series produced in 1879 by M. Dandrieux, and which is shown in fig. 59.
FIG. 59. -- DANDRIEUX -- 1879.
This is a true aeroplane, the wings being fixed, and the propulsion being produced by the screw at the front, which represents the antennae of the butterfly. This screw is driven by the unwinding of the rubber threads, and has practically no pitch except that produced by the yielding of the posterior edge of the gold-beater's skin, of which the vanes are composed. Its peculiar shape, giving a maximum of surface near the outer end, with a rigid an. terior edge and an elastic posterior edge, is the result of a good deal of experiment, and may furnish a useful hint for those desiring to experiment upon a larger scale. The wings are also of gold-beater's skin, and instead of being stretched tightly upon the frame. the anterior margin only is made rigid, the rest of the surface being left quite loose, so that it may undulate when under forward motion, as in the case of M. Brearey's device, which will presently be described. This feature in construction, which differs greatly from that which obtains in the case of birds and insects, whose wings are elastic, but do not undulate, is said to be intended to compensate for defects in workmanship and equilibrium. Upon being tested in still air within doors, the toy will be found quite erratic in flight. It will generally go up to the ceiling, and then flutter in various directions until the power is exhausted, and seldom twice pursue the same course. Out-of-doors it will rise some 20 or 30 ft., dart about, or drift with the wind, until the rubber threads are unwound, and then glide down to the ground sustained by its aeroplane alone.
As a matter of course the sustaining surfaces have to be made very large in proportion to the weight, in order to prevent injury in alighting. One of these little toys, computed by the writer, weighs 86 grains or 0.0123 lbs., and measures 50 sq. in. in aeroplane surface, or 0.3472 sq. ft.
this being in the proportion of 28 sq. ft. to the pound, or about 0.7 of that of the real butterfly, which, being much smaller, measures some 40 sq. ft. to the pound, and which in consequence is capable of but slow flight, although it is not infrequently found by aeronauts floating about in the upper air a mile or so above the earth, a fact to which further reference will be made when we come to consider the prevalence of upward trends in aerial currents.
The propulsion of a loose undulating surface was at about the same time, somewhat differently and quite independently, proposed by M. F. W. Brearey, the Honorary Secretary of the Aeronautical Society of Great Britain. He patented, in 1879 the apparatus shown in fig. 60, in which a flexible fabric is attached to a central spine and to vibrating wing arms at the front, which latter beat up and down like the wings of a bird. The effect of this action is to throw the fabric into a state of wavelike motions, both lengthwise and in a smaller degree also laterally, which are said to cause the apparatus to be both supported and propelled in the air, while an adjustable tail regulates the angle of incidence. The wing arms are flexible and stayed to a bowsprit by cords, and the power for an actual machine is to be placed in a car or body affixed along the central spine.
FIG. 60. -- BREAREY -- 1879.
M. Brearey records that he took the idea from watching the movements of a "skate" fish in an aquarium, which in swimming undulated its whole body, and that he found that when applied to propulsion in air the loose fabric greatly added to the stability, so that the device might be considered as a sort of dirigible parachute, which would come down safely if the motive power became exhausted from any cause. In the various models which he made to illustrate the experimental lectures, with which he was accustomed to popularize "the problem of flight ' in Great Britain, he used the torsion of indict-rubber to produce the revolution of the crank which vibrated the arms, thus getting a dozen strokes or so, and he claimed that the smaller model (5 ft. X 8 ft.) flew from his hand, on one occasion at least, perfectly horizontally to the extent of 60 ft., no angle of incidence of the apparatus being perceptible. The larger model was 6 ft. wide by 10 ft. long, with about 16 sq. ft. of surface, and a weight of 3.1 lbs. (of which 0.44 lbs was added ballast, which it easily carried), being thus in the proportion of some 5.15 sq. ft. per pound of weight, with which the falling velocity would be about 9 ft. per second, or equal to a descent from a height of 1.27 ft., but which was nevertheless found to be too heavy to be safely used in public experiments over the heads of an audience. From his experiments M. Brearey drew the following conclusions as to the possibilities of his apparatus:
We are thus at liberty to contemplate the construction of an aerial vehicle whose dimensions would suffice to maintain, in wave-action, 600 or 700 sq. ft. of canvas, actuated by steampower, and capable of supporting the additional weight of a man, whose weight, together with the machine, would certainly not exceed 500 lbs.; and we can contemplate the man as being able to move a few feet backward or forward without much affecting the stability of the machine. His descent under the parachute action can thus be graduated at will. This can also be effected by a cord attached to the tail, which by that means can be elevated or depressed at pleasure. Placed upon wheels it has, of course, yet to be ascertained what distance of pre. liminary run would be required, assisted by the action of the fabric, before it would rise from the ground.
Subsequently (his second American patent is dated in 1885 M. Brearey further proposed the superposition of two or more sets of such "wave-action" aeroplanes, and the important addition of what he calls the "pectoral cord," which consists in an elastic cord (or suitable spring) attached to some point underneath each of the lower set of wing-arms and passing underneath the carriage, car or central spine, so that it may be thrown into tension on the up stroke, and restore the power thus stored upon the down stroke of the wing-arms This device is designed to imitate in its action the functions of the pectoral muscle of a bird. The tension of this cord or spring is regulated in accordance with the weight to be sustained, and is said to be perfect when, upon the whole apparatus being committed free to the air, the wing-arms are retained at a suitable diedral angle against the upward pressure. It follows from this action that the up stroke, being assisted by the air pressure which sustains the weight of the apparatus, expends less power than the down stroke, and that nearly all the power can be used in depressing the wing-arms to compress a wave of air, which undulating backward and outward along the loose fabric may assist the air pressure already due to the forward speed in sustaining the aeroplane, and serve at the same time to propel it.
M. Brearey, however, seems to have applied this "pectoral cord" chiefly to those of his models which showed the wing-action proper, and in the practical demonstration which he gave to the Aeronautical Society of Great Britain, at its meeting in 1882 he said:
Working in the field of experiment, I am enabled to state that the power requisite to propel and-sustain a body in the air has been greatly overestimated, even by those who took the more favorable estimate in view of the ultimate attainment of flight. I am not aware, however, that the true reason for the minimum display of actual power exerted in the flight of birds has ever been propounded. Certainly it has never before been demonstrated by actual experiment.
The action of the pectoral muscles of the bird alone accounts for this. Consequently the advantage would be altogether lost in anything but a reciprocal action. The bird commits himself to the air, and the pressure of the air underneath the wings forces them upward. The weight of the bird is indicative of the pressure; and as a consequence of this automatic raising of the wing by the pressure of the air underneath, we should imagine that the elevator muscle need not be strong. As a matter of fact, we find it is weak. I doubt whether any muscular effort is made to elevate the wing at all in flight, but when not in flight, the bird of course requires the power to elevate its wing in preparation for it.
Committed, then, to the air, the elastic ligaments connected with the winks are stretched to that degree which allows of the wings being sufficiently raised for effective support without flapping, and without, as I conceive, any muscular exertion upon the part of the bird. The limited power of the elevator muscle may here come into use occasionally in aid of the under air-pressure, and with the further effect of stretching the ligaments. Now it will be argued that' in the downward stroke there must be as much muscular force employed as will raise or, at least, prevent from falling, the weight of the bird; but this is not so, because the reaction of these ligaments, which have been stretched entirely by the weight of the bird, assists materially the action of the depressor muscle.
M. Brearey here produced a model having wings measuring 4 ft. from tip to tip. He showed the elastic cord underneath the wings but for the purpose of the first experiment he detached it. He then wound up the indict-rubber strands 32 times, and showed that this, although sufficient to flap the wings with energy while held in the hand, was insufficient to cause the model to fly. This was demonstrated by letting the model free. He explained its inability to fly from its want of power to bring the wings down with sufficient force.
He now unwound the action and proceeded to wind it up again 32 times, and attached the pectoral cord. Holding the model in his hand, he called attention to the fact that it was powerless to flap the wings because the two forces were in equilibrium. It required the addition of another force to effect flight, and he asked what that other force could be except weight? If now It flew, he proved beyond the possibility of doubt that weight was a necessity for flight. The model was then set free, and flight was accomplished.
He also showed that the model would only fly without the attached pectoral cord when wound up 40 times. With the cord it would fly when wound up only 13 times, thus showing the great saving in power which accrued through the action of the pectoral cord.
M. Brearey then produced a model of his "wave aerial machine," having 4 sq. ft. of loose surface weighted to 1/2 lb., and he demonstrated by its flight that the principle was equally applicable to that.
It may be questioned whether this "wave action" is likely to prove economical of power in either sustaining or propelling an aeroplane, for it seems difficult to conceive that a wave of air compressed at the front by the wing arms should travel back to the rear, unconfined as it is either at the bottom or sides. Still, the loose surface may add to the stability, as claimed for the Dandrieux toy, and it would certainly diminish by its yielding the strains that would otherwise occur at the points of attachment of a rigid surface in an aeroplane; but M. Brearey's wave action seems to be chiefly applicable as a dirigible parachute, and a small model upon this principle, but without motive power, was once liberated as an experiment by Captain Templer, from a balloon which had risen 200 ft. or 300 ft. from Woolwich Arsenal, and it traveled back again to the arsenal, half a mile, against the wind.
It seems somewhat singular that so few efforts have been made to devise dirigible parachutes, a system which M. de Ia Landelle constantly extolled, as constituting the first requisite step toward eventual flight by working out the problem of absolute stability and safety. The only one of these devices which the writer has been able to find recorded is that of M. Couturier, patented in France in 1875 and this is so briefly described in the Aéronaute for November, 1878 that its mode of operation cannot be made out.
The "pectoral cord" attachment is probably a valuable device for flapping wings, as furnishing that inequality of effort between the up and the down stroke which undoubtedly obtains in bird flight. This effect was produced in a "wave-action" model exhibited by M. Brearey at the aeronautical exhibition of the Aeronautical Society of Great Britain of 1885 by a "trunk engine" designed and built by M. Hollands, which, however, was not shown under steam, as the boiler was only just completed in time for the exhibition; but M Hollands said that the model flew well, and supported weights, when the engine was supplied with compressed air through an indict-rubber tube. He does not seem to have stated what power was exerted.
While almost all inventors and experimenters of aeroplanes have proposed some sort of motive power, and have found their designs paralyzed very soon by the want of a sufficiently light motor, there have been at various times, as already intimated, keen observers of the flight of soaring birds, who have held that once under way in a sufficient breeze, the performance involves no muscular movement whatever, save in balancing, and that the wind alone furnishes sufficient motive power (if blowing from lo to 30 miles per hour) to enable man to soar and to translate himself at will in any direction even (paradoxical as it may seem) against the wind itself.
Chief among these observers in recent days stands M. Mouillard, of Cairo, Egypt, who has spent over 30 years in watching birds soar in tropical latitudes, and who published, in 1881 a very remarkable book (in French), "L'Empire de l' air," which should be read by all those seriously interested in the solution of the problem of flight. This book, the result, as the author explains, of a passionate, vocation which began at the age of 15 is almost wholly a record of personal observations and deductions. Its sub-title designates it as an "essay upon ornithology as relating to flight," but it is far more than that, for it not only describes the flight and manoeuvres of birds, and gives good reasons for the author's belief that they can be imitated by man, but it describes four attempts which he has made to do 50 with various forms of apparatus.
M. Mouillard underrates, perhaps, the value of mathematical investigation, and he sometimes errs in his explanation of physical phenomena; but his observations are unrivaled, and they are presented with a particularity of circumstance, a vivacity and a charm which photograph them at once on the mind of the reader. He begins by explaining the difference between useful and unfruitful observations of creatures so willful, so swift, and so shy as the birds; then he describes the various modes of flight (both rowing and sailing), and the movements of the various organs, such as the wings and the tail; the influence of their shape in determining the mode of progression and the speed of the various species, and he shows conclusively that if these organs are properly shaped therefor, the heavier the bird the more perfectly he soars, and can, once initial speed is gained, sail indefinitely upon the wind without further flapping his wings This is the keynote of the book; observation after observation is described, anecdote after anecdote is related, to impress upon the reader that there need be no flapping whatever, if only the wind be strong enough; and that when there is no wind, the soaring bird must come down to the ground or resort to flapping, like the rowing birds.
Then the effect of the speed of the wind is discussed. It is shown that certain species of soaring birds with broad wings, such as the kites, the eagles, and the vultures can sail upon a wind blowing at 10 to 25 miles per hour, but must seek shelter when it increases to a gale, while the sea-birds, with long and narrow wings, such as the gulls, the frigate bird, the albatross, sport indefinitely in the tempest blowing at 50 or more miles per hour. He arrives at the conclusion that when man succeeds in imitating the manoeuvres of the soaring birds, he will utilize the moderate winds, and attain to speeds of about 25 to 37 miles per hour.
M. Mouillard also passes in review the individual mode of flight and characteristics of the various species of birds, both the rowers and the sailers; comprising some 13 different types, and giving tables from his own measurements of weights, surfaces, dimensions, etc., which have been compiled by M. Drzcwiecki, and have already been quoted by the writer under the head of "Wings and Parachutes;" while he finally expresses a strong opinion that the easiest type for man to imitate is the great tawny vulture of Africa (Gyps fulvus), which weighs some 16.50 lbs., and spreads some 11 sq. ft. of surface to the breeze.
M. Mouillard explains how, in his opinion, the manoeuvres of this bird can be imitated, so as to obtain both a sustaining and a propelling effect from the wind, and he describes (much too briefly) the four several attempts which he had then made to demonstrate the correctness of his theory of the possible soaring flight of an aeroplane for man.
The third of these aeroplanes, as described in 1881, is shown in fig. 61. It consisted of two thin boards, properly stiffened, to which were attached ribs of "agave" wood (an African aloe, exceedingly light and strong), which ribs carried the fabric constituting the two wings. The two boards were hinged vertically together (somewhat imperfectly) at the center, and the operator stood upright in the central space at c, suspended by four straps attached to the boards near the hinge; two of these straps passing over the shoulders and two between the legs. Moreover, light wooden rods extended from the feet to the outer ends of the boards, so that the angle of the wings with each other could be varied at pleasure.
Standing upright, with this apparatus strapped on, the hinge was about at the height of the pit of the stomach, the arms being extended out flat upon the boards, and slipping under straps; M. Mouillard trusting to such shifting of his body within the space c as he could effect by resting his weight on his arms, to produce the necessary changes in the center of gravity of the apparatus, which were required by the changes in the angles of incidence.
The whole apparatus weighed 33 lbs., but was found unduly light, as the parts yielded and the wood cracked when tested with vigorous thrusts of the legs. It had been hastily constructed, with such materials as the country afforded, and the builder was not satisfied with it.
M. Mouillard gives but a scanty description of his experiments with this aeroplane in "L'Empire de l'Air," so little, indeed, as to suggest further inquiry; but he has since written another book, which he entitles "Le vol sans battements" (flight without flapping), which is now nearly ready for the press, and wherein he records further observations, explains more fully his ideas and the results of his meditations, giving freely, as he expresses it, "all that he knows" and in which there is a fuller account of the experiment in question.
From this forthcoming book M. Mouillard has kindly furnished the following extract concerning the experiment with the apparatus shown in fig. 61.
It was in my callow days, and on my farm in the plain of Mitidja, in Algeria, that I experimented with my apparatus, No. 3, the light, imperfect one, the one which I carried about like a feather.I did not want to expose myself to possible ridicule, and I had succeeded by a series of profound combinations and pretexts in sending everybody away, so that I was left all alone on the farm. I had already tested approximately the working of my aeroplane by jumping down from the height of a few feet. I knew that it would carry my weight, but I was afraid to experiment in the wind before the home folks, and time dragged wearily with me until I knew just what the machine would do; so I finally sent everybody away-to promenade themselves in various directions-and as soon as their backs were turned, I strolled into the prairie with my apparatus upon my shoulders. I ran against the air and studied its sustaining power, for it was almost a dead calm; the wind had not yet risen, and I was waiting for it.
Near by there was a wagon road. raised some 5 ft. above the plain. It had thus been raised with the soil from ditches about 10 ft. wide, dug on either side.
Then came a little puff of wind, and it also came into my head to jump over that ditch.
I used to leap across easily without my apparatus, but I thought that I might try it armed with my aeroplane; so I took a good run across the road, and jumped at the ditch as usual.
But, oh horrors! once across the ditch my feet did not come down to earth; I was gliding on the air and making vain efforts to land, for my aeroplane had set out on a cruise. I dangled only one foot from the soil, but, do what I would, I could not reach it, and I was skimming along without the power to stop.
At last my feet touched the earth. I fell forward on my hands, broke one of the wings, and all was over; but goodness ! how frightened I had been ! I was saying to myself that if even a light wind gust occurred, it would toss me up 30 to 40 ft. into the air, and then surely upset me backward, so that I would fall on my back. This I knew perfectly, for I understood the defects of my machine. I was poor, and I had not been able to treat myself to a more complete aeroplane. All's well that ends well. I then measured the distance between my toe marks, and found it to be 138 ft.
Here is the rationale of the thing. In making my jump I acquired a speed of 11 to 14 miles per hour, and just as I crossed the ditch I must have met a puff of the rising wind. It probably was traveling some 8 to II miles per hour, and the two speeds added together produced enough pressure to carry my weight.
I cannot say that on this occasion I appreciated the delights of traveling in the air. I was too much alarmed, and yet never will I forget the strange sensations produced by this gliding.
Fig. 61. -- MOUILLARD -- 1865
Then M. Mouillard repaired the injured aeroplane, and he tried it again a few days later. Of this later experiment he says in "L'Empire de l'Air":
I had no confidence, as I have already stated, in the strength of my aeroplane. A violent wind gust came; it picked me up; I became alarmed, did not resist, and allowed myself to be upset. I had one shoulder sprained by the pressure of the two wings, which folded up against each other like those of a butterfly when at rest.
M. Mouillard then determined to make no more experiments with this incomplete machine, but to build a better one, with which he could control all the manoeuvres necessary for soaring, but shortly afterward his circumstances led him to leave the farm and to remove from Algeria to Cairo, Egypt. Here, in a great city, he no longer had the facilities for experimenting that he possessed on the farm, for he had to go out some distance to secure space and privacy for each experiment. Then came illness; the former gymnast became a cripple, so that he could no longer perform for himself the acrobatic manoeuvres necessary to experiment with a soaring apparatus, but still he persevered, and he describes in "L'Empire de L'Air" the design for the fourth apparatus, of which he began the construction in 1878, but which was interrupted by ill-health.
Since the publication of his book in 1881 M. Mouillard is understood to have been continuously engaged in perfecting and simplifying his proposed soaring apparatus, and in trying experiments (by proxy) with models on a small scale. He says that he will soon be prepared to have the matter tested on a large scale, and that he has never wavered from absolute conviction in the truth of the principles which he laid down in "L'Empire de l'Air," in which he expresses himself as follows:
I hold that in the flight of the soaring birds (the vultures, the eagles, and other birds which fly without flapping) ascension is produced by the skillful use of the force of the wind, and the steering, in any direction, is the result of skillful manoeuvres so that by a moderate wind a man can, with an aeroplane unprovided with any motor whatever rise up into the air and directed himself al will, even against the wind itself.Man therefore can, with a rigid surface and a properly designed apparatus repeat the exercises performed by the soaring birds in ascension and steering and will need to expend no tone whatever save to perform the manoeuvres required for steering.28
"The exact shape of these aeroplanes need not be discussed in this chapter, for it will be seen further on that there are scores of shapes and devices which can be employed, but all forms of apparatus, however dissimilar, must be based upon this idea, which I repeat."
Ascension is the result of the skillful use of the power of the wind, and no other force is required.
M. Mouillard then continues:
It will doubtless be very difficult for many persons to admit that a bird can with a moderate wind, remain a whole day in the air with no expenditure of power. They will endeavor to suppose some undetermined pressures or some unseen flappings. In point of fact, the human understanding does not readily admit the above truth; it is astonished, and seeks for all the evasions it can find. All those who have not seen say, when ascension without expenditure of force is mentioned to them, "Oh, well, there were some motions which escaped your observation. "It even occurs sometimes that a chance or superficial observer, who has had the luck to see this manoeuvre well performed by a bird, when he turns it over in his mind afterward feels a doubt invading his understanding; the performance seems so astonishing, so much against ordinary experience, that the man asks himself whether his eyes did not deceive him For this observation, in order to carry absolute conviction, must hear upon the performance of the largest vultures, and they alone; and this is the reason: it is because all the other birds which ascend into the air by this process do not perform the necessary decomposition of forces required in all its naked simplicity."29
To be convinced, a man must see; for to see the performance even once is better than a whole volume of explanations. Therefore, O reader, if you are interested in this subject, go and see for yourself, and be edified. Go to the regions where dwell the birds which perform these demonstrations; and when you have beheld them for a few instants, being already initiated as to what to observe, comprehension will at once come into your understanding.
Whoever has seen a boy's kite ascend into the air, and considered that the string may be replaced by a weight, if only the equilibrium be secured and maintained, will have no difficulty in granting the correctness of M. Mouillard's assertion that the power of the wind is quite sufficient to secure ascension, but it will not so readily be understood how it is also sufficient to secure progression even against the wind. It will, indeed, be conceived that an aeroplane possessed of initial velocity can soar in a circle in the wind like a bird, and by changing its angle of incidence, descend somewhat when going with the wind. and rise again in consequence of the greater "lift" when facing the wind, thus gaining in height at every lap, and eventually utilizing the elevation thus gained in gliding in any desired direction, always provided that the equilibrium be maintained but this involves very delicate manoeuvres, which will be further considered when we come to sum up the results of all the experiments with soaring devices, and indeed the subject warrants a paper by itself which may be placed in an appendix.
It may, however, be said here that the French aviators., after having long doubted the reality of the performance of sailing flight by the birds, whose evolutions they were unable to watch in their climate, have had so many corroborations furnished to them by trustworthy witnesses, that they now generally admit that a soaring bird can sustain himself indefinitely on a wind, without flapping, and that man may learn to imitate him if only a proper apparatus be designed, and the operator possesses the necessary knowledge and skill to work it, so as to perform the right manoeuvres and at the right time.
28 The italics are M.
Mouillard's own.
29
The present writer has seen the feat performed by gulls many times.
| List of Illustrations | Table of Contents | Index |