DYNAMIC FLIGHT MANEUVERING USING TRAPPED VORTICITY FLOW CONTROL

Closed-loop feedback control is used in a series of wind tunnel experiments to effect commanded 2-DOF maneuvers (pitch and plunge) of a free airfoil without moving control surfaces. Bi-directional changes in the pitching moment over a range of angles of attack are effected by controllable, nominally-symmetric trapped vorticity concentrations on both the suction and pressure surfaces near the trailing edge. Actuation is applied on both surfaces by hybrid actuators that are each comprised of a miniature [O(0.01c)] obstruction integrated with a synthetic jet actuator to manipulate and regulate the vorticity concentrations. In the present work, the model is trimmed using position and attitude feedback loops that are actuated by servo motors and a ball screw mechanism in the plunge axis. Once the model is trimmed, the position feedback loop in the plunge axis is opened and the plunge axis is controlled in force mode so to maintain the static trim force on the model, and alter its effective mass. Meanwhile the servomotor in the pitch axis is only used to alter the dynamic characteristics of the model in pitch, and to introduce disturbances. Attitude stabilization and position control of the model is achieved by closing the position loop through the flow control actuators using a model reference adaptive controller designed to maintain a specified level of tracking performance in the presence of disturbances, parametric uncertainties and unmodeled dynamics associated with the flow. The controller employs a neural network based adaptive element and adaptation laws derived by a Lyapunov-like stability analysis of the closed loop system.

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