MINIMUM LANDING APPROACH DISTANCE FOR A VUK-T SAILPLANE

Abstract

Because of the extremely low drag associated with modem high-performance sailplanes, the landing approach trajectory can become critical if aerodynamic deceleration devices are not used. In the paper it is assumed that the sailplane approaches the landing strip head-on in still air with too much speed, altitude, or both, to allow a conventional approach glide. It is also assumed that the initial altitude is too low for any kind of go-around maneuver. The treated problem is then formulated as an optimal control problem, and this problem is one of transferring the sailplane from a prescribed initial state to a prescribed terminal state in minimum distance. The flight is confined to a vertical plane, sideslip or other lateral maneuvers are not allowed (heated in the analysis). It is shown that the most obvious, and perhaps startling, feature of the optimal trajectory is its highly oscillatory nature. Presented solution provides useful qualitative information for high L/D of sailplanes,but also the light aircraft. The lowerbound on speed is necessary for the problem to have a solution. The altitude inequality constraint provides a realistic solution. All calculations were performed on modern high-performance Yugoslav sailplane VUK-T.