Wenham[103] has advocated the employment of superimposed planes, with a view to augmenting the support furnished while it diminishes the horizontal space occupied by the planes. These planes Wenham designates Aëroplanes. They are inclined at a very slight angle to the horizon, and are wedged forward either by the weight to be elevated or by the employment of vertical screws. Wenham’s plan was adopted by Stringfellow in a model which he exhibited at the Aëronautical Society’s Exhibition, held at the Crystal Palace in the summer of 1868.
The subjoined woodcut (fig. 110), taken from a photograph of Mr. Stringfellow’s model, gives a very good idea of the arrangement; a b c representing the superimposed planes, d the tail, and e f the vertical screw propellers.
Fig. 110.—Mr. Stringfellow’s Flying Machine.
The superimposed planes (a b c) in this machine contained a sustaining area of twenty-eight square feet in addition to the tail (d).
Its engine represented a third of a horse power, and the weight of the whole (engine, boiler, water, fuel, superimposed planes, and propellers) was under 12 lbs. Its sustaining area, if that of the tail (d) be included, was something like thirty-six square feet, i.e. three square feet for every pound—the sustaining area of the gannet, it will be remembered (p. [134]), being less than one square foot of wing for every two pounds of body.
The model was forced by its propellers along a wire at a great speed, but, so far as I could determine from observation, failed to lift itself notwithstanding its extreme lightness and the comparatively very great power employed.[104]
The idea embodied by Henson, Wenham, and Stringfellow is plainly that of a boy’s kite sailing upon the wind. The kite, however, is a more perfect flying apparatus than that furnished by Henson, Wenham, and Stringfellow, inasmuch as the inclined plane formed by its body strikes the air at various angles—the angles varying according to the length of string, strength of breeze, length and weight of tail, etc. Henson’s, Wenham’s, and Stringfellow’s methods, although carefully tried, have hitherto failed. The objections are numerous. In the first place, the supporting planes (aëroplanes or otherwise) are not flexible and elastic as wings are, but rigid. This is a point to which I wish particularly to direct attention. Second, They strike the air at a given angle. Here, again, there is a departure from nature. Third, A machine so constructed must be precipitated from a height or driven along the surface of the land or water at a high speed to supply it with initial velocity. Fourth, It is unfitted for flying with the wind unless its speed greatly exceeds that of the wind. Fifth, It is unfitted for flying across the wind because of the surface exposed. Sixth, The sustaining surfaces are comparatively very large. They are, moreover, passive or dead surfaces, i.e. they have no power of moving or accommodating themselves to altered circumstances. Natural wings, on the contrary, present small flying surfaces, the great speed at which wings are propelled converting the space through which they are driven into what is practically a solid basis of support, as explained at pp. [118], 119, [151], and 152 (vide figs. [64], 65, 66, [82], and 83, pp. 139 and 158). This arrangement enables natural wings to seize and utilize the air, and renders them superior to adventitious currents. Natural wings work up the air in which they move, but unless the flying animal desires it, they are scarcely, if at all, influenced by winds or currents which are not of their own forming. In this respect they entirely differ from the balloon and all forms of fixed aëroplanes. In nature, small wings driven at a high speed produce the same result as large wings driven at a slow speed (compare fig. [58], p. 125, with fig. [57], p. 124). In flight a certain space must be covered either by large wings spread out as a solid (fig. [57], p. 124), or by small wings vibrating rapidly (figs. [64], 65, and 66, p. 139).