Possible Effects of Wing Flexibility on the Aerodynamics of Pteranodon

Notwithstanding the rapid development throughout this century of aircraft aerodynamics, the mechanics of animal flight remains poorly understood for three main reasons: (1) The structure of an animal wing is generally more complicated than that of an aircraft. Birds in particular have elaborate systems of feathers which may be used for control or changing the overall aerodynamic characteristics of the wing for different modes of flight. (2) In the case of flapping flight the movement of the wing is complex and the very fact that the airflow is unsteady makes it harder to analyze. (3) An animal's wing is not rigid and its shape depends upon the airflow which leads to a coupled aerodynamic and elastic problem. Some recent work has provided a broad understanding of the principles of gliding and flapping flight. Pennycuick (1968b) studied experimentally the gliding performance of the pigeon, producing a set of polar curves, and the same author (1972) has given a general theoretical account of gliding flight. Brown (1953) used high speed photography to study the flapping cycle of the pigeon and gave a qualitative explanation of lift and thrust generation. Pennycuick (1968a) measured experimentally the power requirements for flapping flight of a pigeon, and his 1972 book gives a method based on the concept of induced power, of estimating theoretically the power requirements for fast and hovering flapping flight. This book also contains some discussion of bird migration, optimum flying speeds, and estimates of the fuel needed:'A particularly detailed account of the flapping cycle, again based on high speed photography, has been given by Cone (1968) who discusses in a qualitative way problems (1), (2), and (3) outlined above and analyzes in some detail the structure of the vortex sheet in the wake of a flapping wing, discussing methods of drag reduction. Thus we have a reasonable qualitative understanding of the mechanics of flight but little calculation has been done on such problems as efficiency, and stability or control mechanisms are still poorly understood. This article is concerned with problem (3), the question of wing flexibility, and a particularly simple animal wing is chosen for analysis, that of Pteranodon. The wealth of fossil evidence has given us an accurate picture of the anatomy of