Abstract: The problem of enhancing tractor-helicopter system stability through controlling tractor rear steering angles was addressed, when the helicopter is towed by the tractor on the deck. Considering the inertial force on the helicopter traction system produced by coupled roll-pitch-heave motion of ship, a time varying, nonlinear 3DOF tractor-helicopter system dynamic model including steering system was established. To cope with the variation of aircraft parameters and ocean environment, tractor rear active steering controller and front compensative steering controller were designed based on constructive backstepping variable structure control method with the characteristic of steering subsystem taken into account. The simulation results show that the variable structure controllers can control the relative yaw angular velocity between the tractor and aircraft effectively, meanwhile, can follow the reference model and improve the handling of the system; the control system can restrict the effect of the uncertain outer disturbance and parameter perturbations, has strong robustness.

Key words: traction motion, stability, variable structure control, robust