The design of control systems for helicopters in hover and at low speed is a basic requirement for the extension of mission profiles and new mission demands. A special task for various applications is the position hold under wind and gust conditions above a ground fixed or moving target, like a shipboard reference, or a small vessel or lifeboat in rescue missions. For the solution of this problem a controller concept was developed and the feasibility was proven and successfully demonstrated in flight tests.
The in-flight helicopter simulator ATTHeS of the DLR has been equipped by the Institute of Flight Mechanics with an innovative measurement system for the hover position above a target. A video camera in combination with a highly parallel computer system for processing the optical information was used as an integra ted sensor system for the measurement of the relative position of the aircraft to a target. Based on the existing well-proven flight control laws of ATTHeS for the forward flight condition, which are implemented for handling qualities investigations, these control laws were modified and adapted to fulfil the special requirements of the position hold task, including altitude hold and heading hold capabilities. The integrated system of optical position sensor and control computer enables the helicopter to hover automatically above a defined target in constant altitude and with constant heading. Flight tests above a moving car under wind and gust conditions underline the future potential of the overall system to be used under operational conditions.