A methodology towards rotorcraft piloting autonomy for approach on moving offshore platforms

Helicopter operation on moving offshore platforms poses a challenge in terms of human factors and flight control. Higher control modes are essential to relieve pilot workload and enable autonomous shipdeck recovery. This paper focuses on control laws for fully autonomous approach guidance from cruise to relative hover on a moving shipdeck. First, the engagement geometry of a typical helicopter-ship combination is described. An instrument-like procedure including arrival and approach phases is defined and the necessary conditions for successful guidance based on ground track, altitude and ground speed parameters are specified. Second, outer loop control laws for real-time generation of the flight path vector commands are developed. The control laws use state feedback from the helicopter-ship system. Control gains are defined in terms of the distance to next waypoint to achieve smooth and gradual state tracking. Third, a model-based inner loop control is implemented to command the required collective, cyclic and pedal inputs for accurate flight path vector tracking, stabilization and axes cross-coupling compensation tasks. Simulation studies are performed using a comprehensive real-time capable helicopter flight mechanics code. Operational scenarios with nominal approach and steep approach profiles are simulated in still air and in wind up to 30 knots with gusts. Simulation results have demonstrated precise tracking of the shipdeck's position, course and speed with robustness to wind gusts and the feasibility to fly steep approaches.