Identification of Flight Dynamics of a Cylcocopter Micro Air Vehicle in Hover

This paper discusses the control methodology, flight dynamics identification, and disturbance rejection analysis in hover of a revolutionary horizontal-axis rotary-wing concept: the twin cyclocopter. The vehicle has a gross weight of 500g (1.25 by 1.67 by 1ft in dimensions) and comprises two highly optimized cyclorotors along with a tail rotor for pitch control. Stable hover flight required fast control of the rpm and thrust vectoring of the rotors through onboard feedback regulation. A six-degree-of-freedom flight dynamics model of the vehicle was extracted through input excitation and time-domain identification. The longitudinal and heave degrees of freedom were decoupled and independent from the rest of the dynamics. Longitudinal translation damping was higher than in the heave mode, indicating differences in restoring forces at different blade azimuth positions due to the different pitch angles. Strong gyroscopic coupling was observed between lateral and yaw degrees of freedom because the rotors spin in the same direction, resulting in unbalanced angular momentum, which is an important characteristic of the twin cyclocopter. Coupling between lateral velocity perturbation and yaw response was also observed. Analysis based on a control-theoretic framework indicated sufficient maneuverability potential of the vehicle in open-loop condition. The longitudinal and lateral gust tolerances were calculated to be about 7.9 and 17 m/s, respectively.