Robust Attitude Tracking Control of Aerobatic Helicopters: A Geometric Backstepping Approach

Robust attitude tracking control of a small-scale aerobatic helicopter using geometric and backstepping techniques is presented in this article. A nonlinear coupled rotor-fuselage dynamics model of the helicopter is considered, wherein the rotor flap dynamics is modeled as a first order system, while the fuselage is as a rigid body dynamically coupled to the rotor system. The robustness of the controller in the presence of both structured and unstructured disturbances is explored. The structured disturbance is due to uncertainty in the rotor parameters, and the unstructured perturbation is modeled as an exogenous torque acting on the fuselage. The performance of the controller is demonstrated in the presence of both types of disturbances through simulations for a small-scale unmanned helicopter. This work is, possibly, the first systematic attempt at designing a globally defined robust attitude tracking controller for an aerobatic helicopter which retains the rotor dynamics and incorporates the uncertainties involved.