Piezoelectric flapping wings as self-powering navigation sensors

Interest in flapping wing aircraft has grown considerably over the last several years, including the launch last year of a multidisciplinary university research initiative (MURI) to investigate means of controlling the leading edge vortex believed to be largely responsible for the success of biological fliers [[reference!]]. While this effort promises to substantially increase the performance of micro ornithopters, it fails to address one of the key enabling technologies for all small unmanned aircraft, autonomous flight. The work presented here is indented to address both problems, improving vehicle performance and utility by investigating the use of its wings as an organic power source, and autonomy by studying how measurements of the unsteady loads on the wings can be used to estimate the the acceleration of the vehicle. While piezoelectric materials have been proposed as both actuators and sensors for small flapping wing vehicles, such as the Micromecanical Flying Insect. The use of piezoelectric materials in the wings to generate both a navigation signal and supply a small amount of power in flight, essentially developing an inertial navigation system (INS) that ”pays for itself.” was proposed by the author. As a power source, active wing materials will likely be limited to powering low power devices such as microcontrollers or plasma actuators, see Post, and powering sensors while perched using a method similar to Priya. Their utility for navigation, however, is a function of the ability to interpret the signals generated by the film. These are be a combination of the wings’ acceleration, unsteady pressure loads and any loads induced by the structure’s movement. This work is focused on developing a set of equations that can be used to estimate the forces and moments produced by small flapping wings and the subsequent deflection of the wings themselves. These can be used in the design an extended Kalman filter (EKF) used to estimate the deflection of the wings and the movement of an aircraft propelled by them. While there is no specific reason why this method would not work for piezoelectrically driven flapping wings, the research this study supports assumes motor and gearbox driven wings. The basic design on which all the included assumptions are based is shown in Fig. 1. The frame is made from vacuum formed carbon fiber elements bonded to the clear PVDF membrane using cyanoacrylate glue. A 1/8” thick balsa wood plank along the leading edge provides a matrix to stiffen the wing for better thrust, as observed in Ho, et. al. and theoretically predicted by Garrick. Leads are connected to the membrane using conductive epoxy, and wings are flapped using either a crank-rocker mechanism, such as the Cybird gearbox or a revolutespherical-spherical-revolute (RSSR) such as the one that drives the Kestrel ornithopter and those built by the University of Arizona, shown in Fig. ??. The remainder of this paper is organized into three sections followed by a conclusion. The first covers the development of a process model for the deflection of a flapping wing including both the structural dynamics and aerodynamic forcing. The second covers the measurement model for the piezoelectric membranes, allowing them to be used with predictor-corrector algorithms such as an EKF. The final section will touch briefly on the power generation potential of the wings. The conclusion will summarize the models presented and suggest future improvements.