Helicopter autorotation landing trajectory optimization after tail-rotor total failure

The optimal landing trajectory and control process of helicopter autorotation after tail-rotor total failure is studied using optimal control method. A six-degree-of-freedom rigid-body flight dynamic model was developed with equations describing the tail-rotor total failure and the available shaft power as well as the rotor speed variation in the autorotation landing procedure. The autorotation landing procedure after tail-rotor total failure was transcribed into an optimal control problem and solved by numerical method. A single-rotor helicopter with tail rotor was taken as the sample, and the calculated optimal autorotation landing procedure in engine failure was in good agreement with the flight test data, which shows that the flight dynamic model and the optimal control method are feasible. Finally, the helicopter optimal autorotation landing procedure after tail-rotor total failure in cruising speed was investigated, and the results show that:when the tail-rotor fails, the airframe will experience large variations of yaw rate and sideslip angle under the effect of rotor anti-torque, which leads to a complex coupled flight. Therefore, the pilot who turned off the engine and is operating the autorotation landing needs an extra series of controls to stabilize the roll and yaw attitude through lateral cyclic pitch and sideslip. The optimal trajectory and the control process are in line with the qualitative conclusions and recommendations obtained from the engineering flight tests.