In July, 1880 M. Biot exhibited to the French Society for Aerial Navigation an ingenious kite, invented by himself, which sailed without a tail and possessed great stability under all conditions of wind.
At the top of a flat plane of elongated elliptical shape two hollow cones were affixed, one on each side. The base or large end of these cones faced the wind, and the other end or point was slightly truncated, so as to leave an opening through which the wind could blow, and, by the action of the streams or columns of compressed air thus created, counteract any tendency of the plane to tip to one side or to the other. This provided for the lateral stability on the same principle as in the well-known Japanese kite, in which the side-pockets catch the wind and maintain the equipoise.
The fore and aft equilibrium was provided for by affixing a rotating screw at the lower end of the plane, pivoted on its central line. This screw had two vanes of coarse pitch and was free to rotate under the impulse received from the wind. It spun around with great speed when the kite was raised, and obviated any need of the usual tail by performing the same steadying office. It prevented any oscillations, without impeding the rising of the kite, and maintained it perfectly steady in all winds.
It was not agreed between the French aviators whether this effect was due to the action of the vanes, making an angle with the sustaining plane, as in the case of Pénaud's "planophore," or to "gyroscopic" action, but when the screw was omitted the kite swayed about, while when the screw was rotating, its twirling and tremor could be felt through half a mile of string, and the kite remained perfectly upright and steady,
M, Biot carried on quite a series of experiments with this apparatus. In the kite which he used the elliptical plane was 15 in. high, the two cones at the side were each 8 in. in diameter at the base by a height of 8 in., while the screw was 12 in. in diameter, its two vanes being each 1 3/8 in. broad.
The experiments were carried on in winds varying from 13 to 33 miles per hour, and the kite was found to be steady under all conditions, the only difference being in the height to which it would rise. When the wind blew from 13 to 18 miles per hour, 4,900 ft. of cord were paid out, the kite remaining at this distance during two hours. On other occasions, with stronger wind, as much as 6,500 and 8200 lineal feet of cord were paid out, and the kite mounted so high that it passed through several strata or currents of wind of varying direction, as was conclusively proved by the fact that the restraining cord as-timed a sinuous attitude when the full height was gained, and instead of approximating to a straight line or a regular curve, as usual, the line became serpentine in form, thus indicating that different trends existed in the various strata of air.
In one instance the kite, with 2,600 ft. of cord paid out, advanced against the wind and mounted directly over the head of the operator. This was attributed to an ascending trend in the wind, for the kite still tended to rise vertically and to advance against the wind, although the plane was horizontal, and the cord, now greatly bowed by the wind, tended to drag the apparatus backward. This attitude continued but a short time, when, the trend of the wind having apparently changed, the kite settled back to its original position, flying at an angle of 40 to 60 with the horizon,
M. Biot, who was an old experimenter with kites (having as early as 1868 been lifted up from the ground by a large apparatus of this kind), found the groscopic stability of the arrangement which has just been described so satisfactory, that he thereupon designed, in connection with M. Dandrieux, a full-sized aeroplane on the same principle, calculated to carry up a man. This design was submitted early in 1881 to a special committee of the French Society for Aerial Navigation, but this committee seems to have hesitated in recommending its construction, and no record has been found by the writer of its having been built or experimented with about that time.
When, however, the publication and discussion of M. Mouillard s "L'Empire de L'Air" had directed fresh attention to the soaring of birds on rigid wings, and given grounds for the belief that man could utilize the wind in the same way, M. Biot constructed in 1887 a soaring apparatus in the shape of an artificial bird 27 ft. across, and weighing 55 lbs., with which he hoped to reproduce the manoeuvres of the sailing birds.
It is known that a number of very interesting experiments were tried with this apparatus, but the writer has been quite unable to find in print, or to obtain from correspondents, a description of the machine or a record of its trials. He merely knows that these triads were many, and that on one occasion M. Biot suffered a tumble which was not encouraging to further experiment, but no account of them is to be found in the Aéronaute.
It is to be hoped that a full narrative may yet be given to the public of the results of experiments which must have been most instructive for other aviators who contemplate imitating the birds.
In 1882 M. Jobert exhibited before the French Society for Aerial Navigation the model of a proposed apparatus designed by himself, in order to test the possibility of imitating the manoeuvres of the soaring birds, as described by M. Mouillard. This aeroplane was to be hinged and jointed, so that it might be folded up like an umbrella for convenience in transportation, or opened out and stiffened by sliding bars in order to make the wing rigid. With this M. Jobert proposed to experiment on various areas of surfaces in proportion to the weight, and to test the efficacy of both fixed and adjustable sustaining surfaces. He does not seem to have met sufficient encouragement to carry out his design, for the writer has been quite unable to learn that he ever completed a full-sized aeroplane capable of sustaining a man.
Having begun where M. Biot terminated--ie., with the design for a soaring apparatus--M. Jobert next turned his attention to kites, and proposed in 1887 the apparatus shown in fig. 67, which he termed a "ropebearing kite," designed for establishing communication with wrecked vessels. It consisted of a hollow truncated cone C, under which was rigidly connected a kit e P, from which depended two light lines terminating in a ring, the latter carrying a light cord steadied by the drag 0. The object of this arrangement was to ensure a rapid and certain connection with the shipwrecked mariners, who, by seizing the light cord, could at once haul down the kite and thus gain access to the main carrying rope, with which to haul aboard the usual life-saving cable. This carrying rope was fastened to a bridle attached to the top cross-stick of the kite, and to the top of the cone at V, which arrangement was claimed to produce perfect stability, and to ensure that the apparatus should travel straight back in the line of the wind without rising to any great elevation. In order to regulate the height, the angle of the plane could be varied by means of a light string (not shown), extending from the lower cross-stick to the carrying rope and fastened by a hook in one of a series of loops.
FIG. 67. -- JOBERT -- 1887.
The sustaining plane was, like the cone, formed of calico, in which hems were turned at the top and at the two sides, in order to form cases for the sticks of the frame, the lower edge of the kite being left uncaged, in order to produce bagging and consequent increase of lifting power. At the small end of the cone a couple of thin metallic tongues were fastened, which, thrown into vibration by the wind rushing through the cone, produced a howling sound which might notify the shipwrecked sailors of the approach of the apparatus, and the whole arrangement, as will readily be perceived, was quite cheap and readily rigged up or folded away, no matter how large it might be.
The writer does not know whether this apparatus ever came into practical use. It has here been figured in order to show how a cone can be applied to a kite in order to impart stability to the latter, but the arrangement would need to be greatly modified in order to admit of its utilization in an aeroplane, so as not unduly to increase the resistance to forward motion.
In 1886 and 1887 M. Maillot a French rope-maker, tried quite a series of experiments with the kite represented in fig. 68. This was constructed of poles and canvas, in the shape of a regular octagon; it measured 775 sq. ft. in area, about 32 ft. across, and weighed 165 lbs. It had neither balancing head nor tail, and was so poised by the bridle of attachment that the center of pull corresponded to a point only one-third of the distance back from the front edge, or to a spot, therefore, decidedly forward of the center of pressure, at the comparatively coarse angle; (30 to 60 ) usually assumed by kites. This angle of incidence it was intended to regulate by a cord, attached to the rear edge and carried to the seat swung beneath the kite for the operator, who might then, by hauling in or paying out this cord. regulate the angle of incidence and cause the kite to rise or to fall. This was intended to furnish the longitudinal stability, while (there being no provision for automatic lateral equilibrium) the side oscillations caused by the varying intensity and directions of the wind were restrained by side ropes attached to the kite and handled by men standing on the ground.
FIG. 68. -- MAILLOT -- 1887.
In the first experiments (May, 1886) M. Maillot was dissuaded from ascending beneath the kite, and he therefore substituted for his person a bag of ballast weighing 150 lbs., tied just below the seat. The kite was raised by first securely anchoring the main rope, which was 800 ft. Iong. and then lifting up the front edge so that the wind might sweep under the surface; upon which the kite rose to such height that the bag of ballast swung some 30 ft. above the ground, where M. Maillot and two assistants managed the two side ropes and the tail cord (not shown in the figure), which latter regulated the angle of incidence by depressing or raising the rear of the kite.
Allowing 33 lbs. for half the weight of the main rope, it was estimated that the apparatus sustained, on this occasion, an aggregate weight of 348 lbs., or in the proportion of 2.32 sq. ft. per pound. The wind was variously estimated at 15 to 22 miles per hour; but as this speed was not measured, nor the pull upon the various ropes ascertained, while the angle of maximum incidence was merely guessed at, as about 45 no accurate computation can be made of the various reactions. The kite was easily controlled by the three men, hauling or paying out the two side ropes and the tail cord, but it plunged about with the varying intensity of the wind, and in one of the oscillations so produced the bag of ballast was whipped about and broke the rope by which it was suspended.
M. Maillot repeatedly experimented with this and other kites (but smaller) on the same principle during the year 1887. He states that he succeeded in sustaining as much as 594 lbs., but whether he ever went up himself beneath the kite the writer has been unable to ascertain. There would have been little or no risk in doing so, provided the wind was steady and strong, for it is evident that the three lines carried to the ground would give almost complete command over the apparatus, but then such a performance would have taught very little toward the management of an aeroplane free in the air. Changes were made from time to time in the modes and points of attachment of the various ropes, and the endeavor seems to have been directed to the discovery of some arrangement by which automatic equilibrium could be secured, under all conditions and varying velocities of wind, without the use of a tail. From the discontinuance of the experiments it is interred that they did not succeed, and the writer attributes this failure (if failure it was) to the employment of a single rigid plane;; for it will be remembered that M. Pénaud obtained a stable kite, on the principle of his "planophore," by adding to the upper pair of planes a second set, inclined at a slight angle to the first, the effect of which was to regulate the incidence.
On the same principle, M. Barrett, whose proposed aeroplane has already been noticed, obtained stability with a tailless kite many years ago, by shaping the plane like a laundry "flat-iron," cutting out a portion of this from the rear or broad end, and adjusting the band so obtained at an angle with the rest of the surface, so that the kite would fly steadily.
M. Copie, on the other hand, obtained partly the same effect by inserting a hemispherical pocket in the body of the kite, but this did not prove quite satisfactory until an opening was cut in the apex, on the same principle as the hole which is provided in the top of a parachute, after which the wind, rushing through the pocket, produced much the same effect as in the Jobert regulating cone; but the device is not one which can be profitably applied to an aeroplane in forward motion.
Upon the whole, M. Maillot's kite was rather crude, and decidedly inferior to Pocock's "charvolant," heretofore described, in which the pilot kite might be used to regulate the carrying kite. The stability of the Maillot arrangement could probably have been improved, and the side ropes dispensed with, by breaking up the surface into two planes, forming a diedral angle with each other, like the attitude of a bird gliding downward, or the same effect might have been partially produced by providing the plane with a keel
Very good results with central keels have been obtained by M. Boynton with his various forms of "Fin" kites, which are now sold in the shops. They consist of a plane, to which is affixed at right angles a "fin" or keel located in the lower part of the kite, and raised slightly above its surface. They fly without a tail, with a steadiness depending somewhat upon the form of the main bearing surface, and seem to afford a good opportunity for further experiment as to the shape of greatest stability; for keels have been frequently proposed for aeroplanes, in which they will produce less resistance to forward motion than obtains with other arrangements, but few seem to have tested how such keels should be applied.
These remarks chiefly apply to plane rigid kites, and to the various adjuncts and forms which have been tried in order to confer stability upon a main plane surface sus-. taining the weight; but still better results have been obtained with flexible surfaces, and it seems not improbable that this is the arrangement which will give the greatest amount of stability to a kite, by producing automatic ad. justment to the wind's varying intensity.
As an example of such action may be mentioned the "Bi-Polar" kite of M. Bazin, who experimented with it in 1888. It consists of a main sustaining surface like a boy's "bow" kite, or practically the same in shape as the kite surface in fig. 66. The frame is composed of two sticks, one of them a flexible rod at the head, bent to a bow. and the other a main central spine at right angles, to which the bow-strings are fastened. The peculiarity of the "Bi-Polar" kite is that this central spine is also made flexible, and that to its lower end (projecting some distance below the supporting surface of the kite) three triangular fins are attached, just like the tail of a dart, omitting one fin. This arrangement obviates any necessity for a tail and confers automatic stability, for the lateral equilibrium is obtained through the elasticity sideways of the main surface or head, which is blown back by the pressure to a convex surface with a diedral angle, which angle varies in accordance to the violence of the wind, while the longitudinal equipoise is likewise maintained by the balancing pressures on the head and on the fins, as the flexible spine yields more or less to the breeze. The kite is thus made stable in both directions, and flies steadily without a balancing tail. M. Basin sailed it with two strings, one attached at the top and the other at the bottom of the main sustaining surface; these strings were both carried to the ground, and attached at each end of a stick of equal length with the vertical distance which they spanned at the kite, and with this stick in his hand the operator could vary the angle of incidence. This was intended to secure measurements of this angle of incidence in connection with the pull, but the results thus obtained have not as yet, to the writer's knowledge, been published.
Even better results can be attained with the "Malay" kite, which is in shape a lozenge, composed of two flexible sticks crossing each other at right angles. The cross or horizontal stick is the longest, being preferably 1.14 times the length of the upright stick, and fastened to the latter at a point 0.18 of its length below the top; a string is then carried (in notches at the ends of the sticks) around the periphery of the resulting lozenge, and this is covered with paper or with muslin in the usual way. This surface, when impinged upon by the wind and restrained by the bridle, is bent back by the pressure and adjusts itself to the varying irregularities of the breeze, the kite flying without a tail with great steadiness and rising to great elevations.
M. Eddy, of Bayonne, N. J., who has been constantly experimenting with kites during the last few years, and who is recognized as an expert in such matters, prefers the "Malay" kite to all others. He has improved it by so fastening the cross-stick and tying its outer ends as to produce a slight initial convexity, which is further increased by the action of the wind, and which materially adds to the steadiness of the flight. With this arrangement M. Eddy has succeeded in causing a single kite to ascend to a height of 2400 ft, with 3000 ft. of line, and then bringing it to the zenith directly over his head, or even a little back of his hand, where its attitude strongly suggested the advance of the soaring bird against the wind. Upon a previous occasion he had succeeded in attaining a height of 4,coo ft., with a string of five kites flying in "tandem"--that is to say, each kite attached by a string of its own to the string of the preceding kite already raised, so as to take up the slack or sagging of the line, and thus enable the upper kite to rise to an altitude otherwise unattainable. This performance seems to suggest an easy way for the exploration of the upper air by the Weather Bureau, for by affixing to the upper kite self registering instruments (thermometer, barometer, hygrometer, etc.), or, preferably, by connecting such. instruments (and an anemometer besides) electrically with recording instruments on the ground (through a series of fine wires insulated in the kite string), observations of the conditions prevailing aloft can be easily obtained. The French have lately been making such observations by means of "free balloons" of medium size, and they are said to be of material assistance in forecasting the weather; the records obtained from the top of the Eiffel Tower showing that even at that moderate height coming changes in wind and in temperature are indicated several hours in advance of their prevalence at the ground.
The same principle of obtaining stability without a tail, by means of an elastic frame, can be applied to other forms than the "Malay" or the "Bi-polar" kites but it requires a good deal of delicate adjustment and balancing. It has been done with the common hexagonal form of kite by M. C. E. Myers of Frankfort, N. Y., the aeronautical engineer who furnished and operated the balloons and kites by means of which the recent (1891) rain-compelling experiments were tried in Texas.
It will be remembered that the explosions intended to produce rain were in some cases produced by exploding dynamite suspended below kites, and fired by electricity. In providing for this, M. Myers, who has for several years been conducting systematic experiments with kites, evolved some very interesting facts, and he has published part of his experience in the Scientific American Supplement (No. 835) for January 2 1892 from which the following is extracted:
The originating cause of my interest in kite flying is aerial navigation, and by successive steps I have adapted kites to fly without tails, to fly with considerable weight attached, and, finally, to fly without the restraint of the usual kite-string; and, rising higher and higher, finally to disappear miles in height and miles away on the verge of the distant horizon.
Theoretically, there should be no difficulty in attaining these results. Practically, there is as much difficulty as with a child learning to walk or a youth learning to manage a bicycle. In a word, it is the art of balancing....
Theoretically, the kite should be light or possess much surface with little comparative weight. It should balance at the flattest possible angle, nearly horizontal, and its surface should be widespread, like the wings of a soaring bird. As a fact. I have obtained the best results with this model, but had great difficulty at first to induce it to fly at all, and was finally forced to attach a compromise tail--not a kite tail, but a bird-like tail, which, being flexible, vibrated or undulated with the vertical oscillations of the kite, and thus acted as a propeller, so that this kite actually moved against the wind....
The most practical form of kite for general purposes seems, however, to be the six sided. Those created by me as part of my apparatus for the Government rainfall expedition in Texas were composed of an X, formed of two spruce sticks, each 6 ft. long, tapering, with a top section of 1/4 in. X 1/4 in. and bottom section of 1/4 in. X 1/2 in. tacked flatwise together with a very small pin-nail, and bound with hemp cord at the joining. Five in. below this crossing (which was about 2 ft. from the top) was a similar piece of timber, but 14 in. shorter, and tapering each way, placed crosswise of the X, horizontally, so as to form a 5-in. triangle, which stiffened the frame more than if all crossed at one point. The outer end of each stick was creased with a knife and notched around, so that a hemp cord passed first through the crease and was "half-hitched' around each stick to prevent splitting. The kites were covered with red calico, pasted on tight, and bits of cloth were also pasted across the sticks where the kite-strings attached. These strings were attached as long loops--one loop to the top sticks about 6 in. from their tips, one loop to the two bottom sticks about 30 in. from the bottom, and one loop to the cross-bar about a foot from each end. All these loops were then gathered together and drawn through one hand as the kite lay on the ground, held in place by one foot on its crossing, and being adjusted carefully and equally to draw from a point somewhere midway between the cross-stick and top, best attained by trial, were then tied together.
The kite was thus rather stiff and light at top, elastic and heavier at the bottom, and suspended at a point above its center of gravity and center of surface. To the loop at the bottom was usually hung a narrow strip of cloth to afford greater steadiness in supporting the kite's burden of dynamite to be exploded. I have been thus particular to describe minutely this construction because many have written me for this information.
The first trial kite flown at Midland Tex., escaped. I had built it all myself, as a model, and it had drawn up one ball of hemp twine, and an assistant was holding the string preparatory to running out another ball when the cord parted at a flaw, and the kite flew into space. When last seen with a glass, it was estimated to be about 3 miles high and 8 or 10 miles away, a fading red dot in the distance....
In ordinary light winds this kite floats well, is steadier than many other kinds I have tried, and would seem to be well adapted for photography. If hung very near its top, it is prone to advance upward and forward against the wind till over and beyond the party holding the string, and literally floats on the air as if propelled by its fluttering triangular section at or near the bottom of the kite.
The accidental escape of this kite exhibited a very interesting example of partial "aspiration," and it is understood from additional information, kindly furnished by M. Myers, that he succeeded in reproducing this effect on several occasions. The kites were hung, after considerable experiment, so that they floated nearly flat on the air, with as little tail as possible, and sometimes none at all. They rose upon a light breeze, and drew away as long as the string was let out. When checked or pulled, they rose higher and higher until quite overhead, when the string had to be released. If suitably balanced the kite then rose still higher and drifted back, but not as fast as the wind blew, its rearward flap vibrating more or less, and making its action a progressive one relative to the wind thus producing "aspiration" with respect to the breeze. A long string, or small weight at the end of a shorter string, was sufficient to keep it balanced, so that it might remain up for hours and go floating out of sight.
The possibility of this progressive action against the wind without loss of height (or of "aspiration") has been strenuously denied, and yet it is easily explained if, instead of assuming the wind to blow horizontally, as we generally do, we consider that it has at times a more or less ascending trend, this being a not unusual condition over the sun broiled plains of Texas. It is clear, from the description of the mode of attachment of the string, that its weight when released would tilt the kite forward, so that the plane would point below instead of above the horizon, In this position the direction in which the "drift" is exerted would be reversed--that is to say, the horizontal component of the pressure, instead of pushing backward, would be pulling forward, and thus become a propelling force against the wind, provided, of course, that the latter still exerted its pressure on the under side of the kite. Thus an upward trend in the breeze of but 3° or 5°, operating against a kite inclined forward 2° below the horizon, would be sufficient to cause it to advance relatively to the wind, somewhat as a vessel "close hauled" advances against the breeze which furnishes its motive power. In point of fact, therefore, that which has herein been termed the "drift" may act upon a plane surface, as a force pushing backward or propelling forward, according as that plane is inclined to the front above or below the horizon; but in the latter case there needs be an ascending trend in the wind in order to produce a sustaining pressure on the under side, for otherwise the horizontal wind would strike the upper surface of the plane and press it downward instead of upward. The effect may be quite otherwise with concavo-convex surfaces.
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