Simulation of an Ornithopter with Active Flow Control and Aeroelestic Energy Harvesting

Abstract

A six degree of freedom simulation of a small flapping wing vehicle is presented here based on aerodynamics developed by DeLaurier for a larger ornithopter. This model compares well with existing experimental data provided the vehicle is close to steady, level flight. When that assumption is relaxed, the model slowly departs from the region in which it is valid, showing its promise as a plant model for control system development. Also shown are simulations of the effect of Single Dialectric Barrier Discharge plasma actuators for performance and maneuverability enhancement. Power generation and force sensing from piezoelectric membranes in the wings is presented as means of increasing range and autonomy of a micro air vehicle. Ornithopters have several advantages over fixed wing and rotorcraft micro air vehicles (MAVs). The success of biological flappers such as birds and insects suggests that this motion is optimal in this size range. They are quieter and efficient, as they combine lift and thrust in one relatively largesurface. They have been proposed as man-portable systems for urban surveillance and other environments. Additionally, their resemblence to biological fliers makes them useful to study bird behavior. However, man-made flapping wing vehicles have a number of limitations that have restricted their use to toys and lab equipment. Chief among these is that they combine the energy density problems of other MAV planforms with the added complexity, and weight, of a flapping mechanism. In addition, they are very stable in forward flight, and thus difficult to maneuver in confined environments. On top of this, the vehicle dynamics change continuously, making controller design more difficult. This paper presents a simulation based of a small ornithopter that includes equations to model methods to allieviate some of the restrictions mentioned above. The functions developed can be used for either geometry optimization to meet mission requirements, performance estimation for mission planning, or, as presented here, to create a virtual vehicle to study the flight mechanics of flapping wing vehicles. This simulation focuses on the possibility of using Single Barrier Dielectric Breakdown (SBDB) plasma actuators embedded in the wings to increase lift and add direct roll control to the platform through differential actuation. In addition, to attempt to alleviate the energy density problem, this simulation models the energy produced by piezoelectric film in the wings. The rest of this paper is broken into four sections. The first covers the aerodynamic modeling of the vehicle, including the modeling of the unsteady lift on the wings. Next, the vehicle dynamics, including moment of inertia, center of gravity and body coordinate systems are covered. Third in this list are the results of an example vehicle in free simulated flight. Finally, there is a conclusion and discussion of future work.