Lift Enhancement of Pliant Wings Through Bio-Mimicry

Flexible aerodynamic surfaces have been shown to favorably influence flight characteristics by increasing lift, angle of attack at stall, and resistance to perturbation. The objective of the research presented within this thesis is to investigate the influence of two aspects of flight observed in biological flyers, a suction-surface flap and dynamic stall, when applied to pliant wings. A rigid flat plate and membrane wing, both with an aspect ratio of 2, were tested at Reynolds numbers between 50,000 and 100,000 in two sets of experiments to quantify the effects on the membrane wing of a passively actuated pop-up flap and dynamic stall. The first set of experiments presented examines the effect of the suction-surface flap for various Reynolds numbers and various pre-strains, and compares the results to a rigid plate. The results of this experiment show that there is a relationship between membrane camber and flap effectiveness, and that an optimum level of membrane camber exists for a given membrane and flap condition. The second set of experiments presented evaluates the differences in dynamic stall behavior between a rigid plate and a pre-strained membrane wing. A similar form of lift hysteresis is observed for the pliant wing as has been studied for rigid wings. Both the static and the dynamic lift curves reach a higher maximum lift for the membrane wing in comparison to the rigid plate.