Aerodynamics and Flight Control of Flapping Wing Flight Vehicles: A Preliminary Computational Study

Abstract

The dexterity and gracefulness of winged creatures have captured the imagination of humans for a long time. Insects have evolved sophisticated flight control mechanisms that permit a remarkable range of maneuvers. To replicate the flight behavior of insects it is first necessary to obtain a good understanding of the kinematics of insect flight and the physics of the fluid flow around the body of the insects. This in turn might allow for the identification of efficient aerodynamic shapes and control mechanisms that can be replicated in unmanned robotic vehicles. These robotic vehicles can then be used to perform tasks that are not possible with conventional fixed wing or rotary flight vehicles. If one agrees that insects have highly optimized wing shapes and control mechanisms, then a study into the flight control of insects can also be used to validate optimization techniques that recover the optimal wing shape, pitching frequency, stroke amplitude and other control inputs. Insect flight control has been studied extensively from a physiological perspective, but its mechanics are less well known. Even when the kinematic changes elicited by a given stimulus have been defined, their consequences for aerodynamic force production often remain obscure. Quasi-steady aerodynamics has been largely supplanted by unsteady theories and is widely accepted as the mechanism that leads to the forces produced by insects in flight. 4 Lighthill performed some of the earliest theoretical studies on the aerodynamics of insect flight and Weis-Fogh and Jensen determined the variation of the positional angle of fore and hind wings during flight of Schistocerca gregaria. A variety of experimental studies has enabled a better understanding of the nature of wing articulation by insects in hover and forward flight. 6, 7 While these studies enabled the authors to propose a possible theories for insect flight, the lack of a complete understanding of the flight control mechanisms has prevented a more comprehensive understanding of insect flight control. It is not clear how many degrees of freedom an insect controls to enable it to perform its various maneuvers. Further, insects in controlled laboratory environments tend to produce lift and drag forces that are different from those observed in nature, leading one to look for alternate analysis tools. It is also difficult to replicate subtle shifts in the center of gravity or even get a good estimate of the center of gravity of the insect and this further clouds our understanding. Finally, there is a wide body of evidence that suggests that unlike conventional aircraft/flight vehicles, the control inputs are typically the pitching frequency, the stroke amplitude, the change in angle of attack during the pitching cycle and the twist in the wing. Each of these control inputs produce coupled motions in roll, yaw and pitch motion and this non-orthogonal nature of the response to the control inputs complicates the process of using separate control inputs to generate specific maneuvers. The ability of insects to devise control inputs for particular manouvers is interesting