In the United States very few experiments seem to have been made with flapping wings, and no records of them are attainable. Investigation is, therefore, limited to such proposals as have been patented, and it is found that, aside from balloons, less than 30 flying machine patents have been taken out, of which four are for flapping wings.
The first of these, in order of date, seems to have been the proposal of Mr. W. E Quinby, who patented, in 1869, an apparatus to be operated by man power, consisting of a pair of side wings and a tail, all to be flapped by a series of cords attached to the operator, who is encased in a cuirass which maintains the wings at about the height of his waist. The surfaces shown in the drawings are quite insufficient to sustain the weight, and in 1872 Mr. Quinby took out another patent for a modification of his apparatus, in which he added dorsal surfaces, so that the wings and the tail were continuous and resembled the supporting surfaces of a bat. The arrangement for imparting motion was ingenious but futile, because of the inefficiency of muscular power, which has already been stated.
In 1876 Mr. F. X. Lamboley patented a framework shaped like the wings of a bird, and covered with a wire netting to which birds' feathers were fastened so as to give a valvular action. Human power as relied upon to impart motion through a trapeze-bar and platform, and of course it would prove inadequate.
In 1877 Mr. M. H. Murrell patented an apparatus consisting of a pair of pivoted side wings and a tail, to be also operated by man power. The wings were furnished with slats similar to those of a Venetian blind to close on the down stroke, and open when going up. An investigation of what others had attempted would probably have saved the inventor some misspent time and ingenuity.
So little has been effected with flapping wings that a number of American inventors seem to have turned their attention to various arrangements of revolving vanes. Of these A. P. Keith patented, in 1870, an aerial car with paddle-wheels revolving in a transverse plane, for the purpose of lifting and propelling. Thomas Green patented, in 1873, an apparatus with two wheels, each with four revolving blades passing through the air flatwise on the down stroke and edgewise on the up, and M. H. Baldwin patented. In 1890, an aerial vessel in which weight is to be supported by a set of wheels containing feathering vanes; the wheels revolving in opposite directions on longitudinal shafts. All of these are worthless, as is also the patent of I. M. Wheeler of 1887, which covers the arrangement of a number of oscillating frames superposed to each other on a mast, and carrying slats similar to those of a Venetian blind; these various devices only being mentioned to illustrate how ingenuity has been wasted upon mechanical details, while scarcely any attention seems to have been given to the devising of the lightest possible motive power. Each fresh inventor of winged machines is apt to imagine that his predecessors did not succeed because they did not hit upon the right method of imitating the complicated and swift motions of the birds. Thus Mr. H. Sutton, of Australia, communicated to the British Aeronautical Society, in 1888, that experiment and observation had convinced him that the tips of the bird's wings describe, when viewed from the side, the outline of an inverted cone with rounded base, instead of the figure of 8 motion described by Dr. Pettigrew and Professor Marcy. He had accordingly made a model, driven by clockwork, to test the truth of his theory. This model was not capable of free flight (steel springs and clockwork being much heavier than rubber, in proportion to their stored energy), but when suspended at the end of a counterweighted lever, resting upon an upright support with a ball-and-socket joint, it flew in a circumference of about 12 ft. by the flapping action of the wings. By slightly modifying the stroke of either wing it was made to fly from right to left or from left to right. By altering the guide-rods, which governed the direction of the stroke it could be made to fly upward at any desired angle, but the important, the vital question of an efficient motor was left untouched by the inventor.
Still, earnest attempts are occasionally made in the direction of light motors. At the meeting of the British Aeronautical Society, in 1890, a photograph was shown of a steam- bird machine, designed and built by Mr. E. P. Frost, which is represented in fig. 22. The wings, which are 30 ft. from tip to tip, are in exact imitation of those of the crow, and the various positions which they assume during a stroke are shown in the picture. The weight of the machine, including engine and boiler, is about 650 lbs. It was expected to carry m addition the weight of a man in the air, but it was said that the maker of the engine failed in his contract to secure the necessary power, and the apparatus did not fly.
FIG. 22. -- FROST-- 1890.
At the same meeting Mr. H. Middleton, who has been advocating for several years winged apparatus as superior, in his judgment, to aeroplanes, exhibited two bird machines, one weighing 20 lbs., with a wing-spread of nearly 12 ft., and the other of between 10 and 12 lbs. weight with a wingspread of some 9 ft. He also showed an aeroplane weighing somewhat over 20 lbs., with sustaining planes of 14 ft. across and a screw of 4 ft. diameter, in order to compare its performance with those of the bird machines. Only the smaller of these latter was shown in action, but its balance was not properly adjusted, and although it raised itself from the sustaining horizontal rope during the first few strokes, it soon rested again upon the rope, and on the pressure being raised during a subsequent run, the right wing broke and terminated the experiment.
The aeroplane, being similarly suspended, moved along the rope at a moderately good pace, but without raising itself on the air, and that experiment was brought to an untimely end by the rupture of a joint on the propeller shaft.
Probably the most original conception ever presented for a flying machine is that of M. G. Trouvé, who has just revived (1891) the proposal for his mechanical bird, which was first presented to the French Academy of Sciences in 1870. This is shown in fig. 23, and consists of two wings, A and B, connected together by a "Bourdon" bent tube, such as is used in steam gauges. The peculiarity of this tube, as is well known, is that as pressure increases within it the outer ends move apart, and as pressure diminishes they return toward each other. M. Trouvé increases the efficiency of this action by placing a second tube within the first, and in the experimental model he produces a series of alternate compressions and expansions by exploding 12 cartridges contained in the revolver barrel D, which communicates with the tube. This produces a series of energetic wing strokes which propel and sustain the bird in the air in connection with a silk sustaining plane indicated at C.
FIG. 23. -- TROUVÉ-- 1870.
The manner of starting the bird is equally ingenious and peculiar, and is shown in fig. 24. The bird is suspended from a frame by a thread, which, being attached to the hammer, keeps the latter off the cap. A second thread holds the bird back from the perpendicular, while a common candle A and a blow-pipe flame B complete the preparations. Upon the thread being burned at A the bird swings forward from position 1 to position 2, where the suspending thread is burned by the blow-pipe B, the hammer falls on the cap, an explosion ensues, the wings strike downward violently, and the bird flies on an upward course, as shown in position 3. Then the gases escape from the Bourdon tube, this recovers its shape, raises the wings and actuates two pawls which rotate the revolver barrel and work the hammer, so that a fresh explosion occurs and the bird continues to fly. When the 12 cartridges are exhausted the bird glides gently to the ground, being sustained by its wings and aeroplane as by a parachute. It has thus flown 75 to 80 yards.
FIG. 24. -- STARTING TROUVÉ'S BIRD-- 1890.
This motor is evidently very simple and very light, and for a practical flying machine M. Trouvé proposes to substitute for the cartridges a supply of compressed hydrogen gas, which, when mixed with about three parts of air, becomes an explosive mixture to be fired by the electric spark. Thus the motor would derive the greater portion of its power direct from the atmosphere as wanted, there would be no danger of premature explosion as with fulminates, and, hydrogen being only of the weight of air the weight and the equilibrium of the apparatus would vary but little when supplies became exhausted. Moreover, it is probable that no cooling agent would be required , as in ordinary gas engines, because the tube exposes so great a surface that it is to be expected that the heat would pass into the air while under motion, and that, as there is no piston to be lubricated, a moderate heating would not prove objectionable.
M. Trouvé started out with the assumption that a motor for aerial navigation should not weigh over 8 lbs. to the horse power. He presented to the French Academy of Sciences, in 1886, an electric motor, weighing but 7.7 lbs. per horse power, working an aerial screw, which will be more fully noticed when that subject is treated, and on August 24 last (1891) he deposited with the same body a sealed letter containing the drawings and description of an aeroplane and screws, which, he confidently believes, provide a final solution for the problem of aerial navigation, and which will also be noticed under the head of Aeroplanes.
Meanwhile other inventors are also working in the same field, and the English papers have contained sundry paragraphs, within the last few months, concerning a flying machine some 45 ft. across, in the form of a bat, which is being built in Coventry for Major Moore, of India. It is to be driven by an electric motor, but the descriptions do not make it clear whether this is to be by beating wings or with fixed wings, as in an aeroplane. The cost incurred is stated at over $5000, and the trial is to take place at the Crystal Palace. Should this take place in time, it will be noticed, as well as the great apparatus now being completed by Mr. Maxim, when we come to discuss aeroplanes.
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