In this part of the paper the theoretical considerations underlying the design of an autopilot system for helicopters are discussed, in particular, the system investigated has three modes of operation, viz —

1. (i) Stabiliser

   In this mode, whilst the pilot still exercises overall control, the autopilot introduces artificial stabilisation so that the helicopter becomes more easy to fly

2. (ii) Cruising

   Here the pilot establishes a desired attitude and heading in straight-line flight, on selection the autopilot maintains this mode of flight automatically

3. (iii) Automatic Hover

   Assuming that signals are available defining the plan-position of the helicopter with respect to the point on the ground over which the pilot wishes to hover, on selection the autopilot maintains this hover condition automatically