Investigation On Helicopter Flight Trajectory Optimization After Engine Failure

A single-engine helicopter have to autorotate when encountered engine failure. The technic of autorotation is one of the most important factors to safe landing. The trajectory of helicopter in autorotation is studied theoretically in this paper and optimal control theory is applied to the calculation of optimal autorotation.Horizontal, vertical and pitch movements are considered when establishing the mathematical model of autorotative helicopter. Let horizontal movement x, vertical movement z, horizontal velocity u, vertical velocity w, pitch altitudeΘ, pitch rate q and rotor speedΩbe the state variable. Let collective pitchθ0 and cyclic pitchθs be the control variable. Let the velocity of the helicopter at touch down be the cost function. The calculation of autorative course is converted to an optimal control problem. In this study, control delay of the pilot is taken into account, and the limits of rotor speed, collective pitch and pitch angle is also considered.A parameter optimization algorism is used here. The optimal control problem is converted into parameter optimization form, which can be solved by the software SnOpt. Sicosky S-58 helicopter is ued as a sample.The solution of numerical calculation agrees with the flight test data. The influence of pilot control delay and variation of rotor inertia is also studied here. The scope of helicopter in autorotaion is studied, and the height-velocity diagram is given.