Inherent errors in asynchronous, redundant digital flight controls

In current aerospace research, redundant digital computers, operating asynchronously for low cost and high reliability, are being considered for the control of high-performance aircraft. Asynchronous sampling in the control loops leads to inherent errors even under normal, failure-free operation. Such errors are defined and characterized by a useful approximation, and state equations are derived for their description in a dual-redundant, closed-loop system. A covariance analysis of the inherent errors is developed. The state equations and the covariance analysis are applied to a simulation based on a digitized version of the U. S. Air Force A-7D pitch-axis control system, with the aid of a specially-prepared, packaged computer program.