Abstract: To avoid overturning caused by ground constraints, longitudinal and lateral skidding and vertical bumping against the ground, attitude control, skidding control and vertical velocity control are the crucial considerations in an unmanned helicopter takeoff and landing. In this article an autonomous takeoff and landing control strategy for unmanned helicopters is proposed, in which the longitudinal and lateral control is based on the ground force, attitude and skidding feedbacks, and the vertical control includes takeoff and landing judgment by the ground force and velocity control based on height demand traction. Ground force feedbacks are used to keep in balance the longitudinal and lateral force and the moment so that the helicopter can take off vertically while losing the ground constraints; attitude and skidding feedbacks are used to keep the unmanned helicopter horizontal and prevent its longitudinal and lateral movement in the process of takeoff and/or landing; together they constitute an essentially parallel control mechanism. The strategy is verified successfully during the flight test of an unmanned helicopter, which provides useful experience for the development of unmanned helicopter autonomous takeoff and landing technology.

Key words: takeoff, landing, unmanned vehicle, attitude control, skidding, force feedback