Reconfigurable Fault-Tolerant Tilt-Rotor Quadcopter System

In this paper, fault-tolerance characteristics of a reconfigurable tilt-rotor quadcopter upon a propeller failure are presented. Traditional quadcopters experience instability and asymmetry about yaw-axis upon a propeller failure but the design and control strategy presented here can handle a complete propeller failure during flight. Fault-tolerance is achieved by means of structural and flight controller reconfiguration. The concept involves conversion of a tilt-rotor UAV into a T-copter. The dynamics and control of the tilt-rotor quadcopter are presented for ideal flight condition and for the reconfigured system in case of propeller failure. Analytical solution for trim flight conditions yielding zero angular rates for the UAV is derived. It has been shown that the structurally reconfigured UAV is controllable and completes the flight mission without much compromise in flight performance. The controllability and observability analysis of the reconfigured system is shown by state space formulation. The flight controllers for both dynamic models are analyzed and the applicability of the proposed concept is presented by propeller failure simulation during the way-point navigation.

Limit-Cycle Oscillation Suppression of Bioinspired Ornithopter: Wind Tunnel Testing

This study experimentally shows that an oscillatory behavior observed in a trim flight of an ornithopter has a stable limit-cycle oscillation (LCO) characteristics and that the magnitude of the LCO in body pitch dynamics can be suppressed by active tail motion. A free flight of the tested ornithopter is emulated in the wind tunnel using a specially devised tether that provides the minimal mechanical interference to the flight of ornithopter. Due to the symmetric wing motion in forward trim flight, the longitudinal flight dynamics is more focused than the lateral one. The non-contact type sensors are used to measure the time histories of the flight state variables such as wing and tail motions, body pitch angle, and altitude. The tail motion for the pitch LCO reduction is achieved by two actuators: 1) Servo motor for the rigid-body motion of the tail elevation angle, and 2) Macro-Fiber Composite strain actuator for the elastic deformation of the tail camber. The performances of the LCO suppressions are compared in the root-mean-square-error sense and the harmonically activated in-phase tail motion linked to wing motion is observed to effectively reduce the pitch LCO.