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.