Abstract

Actuators associated with control surfaces in aircraft, ships and underwater vehicles often introduce problems in terms of the control characteristics of the vehicle if significant saturation and rate limiting effects are present. Rate limits, in particular, have been linked to a number of well-publicised safety and handling-qualities issues for aircraft. Such limits also present difficulties in ship steering and ship autopilot systems. This paper describes an investigation of the effects of actuator nonlinearities involving a ship steering control application. The method of approach involves the use of inverse simulation to detect the onset of limiting. The paper shows that inverse simulation methods allow direct prediction of situations in which rudder saturation and rate limiting have significant effects in terms of the manoeuvrability of the vessel. It is also shown that a twostage inverse-simulation method allows direct assessment of the difference between desired and achievable manoeuvres.