Abstract: A system (1) responds to inputs (2) in parallel with a state estimator (4). The controller (6) provides the inputs (2) in response to ordered state inputs (14) and state estimator inputs. An external disturbance vector (f) affects the system (1) so that the observed values of the state variables are not the same as the estimated values. The estimated and measured values are compared (8) to give an error signal (9). The error values are fed to an Ordered State Corrector (11) which computes the error that the order state variable would have in the steady and applies it in the opposite sense to increment the input ordered state (14). If more than one state variable is to be corrected, the correction is applied directly to the control inputs using Multi-State Correction, in which the steady state errors are used to find the control inputs which would cause the errors and then a correction is applied to the control inputs.

Abstract: This invention relates to a system including an autopilot, with a simulator, for a fluid borne vehicle, and, in particular, to such a system including novel means to compute, in real time, and for depth keeping, and pitch keeping, purposes, any change of, or `out-of-trim`, heave force, and any change of, or `out-of-trim`, pitching moment, acting on the vehicle. For simplicity the general term out-of-trim forces is used when both are referred to.