On the Structural Specilization of Flying Fishes from the Standpoint of Aerodynamics

Abstract

A LARGE variety of flying animals has been studied by the early designers of aircraft, but it was not until there was a radical departure from any of these that a real conquest of the air was made with heavierthan-air machines. We may consider those animals that have been examined for such purposes, beginning with the lower groups. Except for the ballooning spiders, which simply drift by means of their wide flung silk on light breezes, or the flying squids that are little more than animated darts, there are no flying invertebrates except the insects. These are highly diversified and exceedingly successful. Their wings are usually of light stiff membranes stretched on supporting rods and superficially, at least, somewhat resemble the wings of a modern aeroplane. There are two important and interlocked differences, however. The first is that in all cases they are locomotor in function, and no insect attains a large (absolute) size. With such small sizes the manipulation of delicate structures is mechanically possible and indeed advantageous, if not absolutely necessary. Long continued gliding is impractical for bodies of such light weight, whereas, on the other hand, the manipulation of such thin expansive areas in a larger size is out of the question for either animals or machines, due partly at least to the fact that the weight increases by the third power of the length. Thus it is evident that such superficially aeroplane-like insects as dragon flies are really not miniature planes at all, but are working on radically different principles inl which the paired outstretched wings vibrate practically all through flight in such a manner that their tips describe a figure. eight in addition, to rotating slightly back and forth along their long axis. Considering the vertebrates, we may examine, the birds, which for so long have been studied by would-be fliers. The flapping flight of the bird wing is conditioned by its peculiar lattice-like fenestration due to the complicated form and placement of the feathers. All the smaller birds fly by rapid wing beats, only the larger, such as buzzards, hawks, condors, albatrosses, etc., sustain long continued flight by soaring. Such flight is by far the closest approach to that of a plane (a motorless glider) that we have examined as yet, although it is still a far cry from a plane in its methodof getting under way, control, or appearance in the air. The flying mammals, such as bats and flying squirrels, although having solid wings are still further from the successful plane. The bats with their elaborate wing flapping have as yet never been successfully repro-