Alternative approach to aeroservoelastic design and clearance

The in-flight interaction between an aircraft´s flight control system (FCS), structural dynamics and unsteady aerodynamics has been of concern to aircraft designers for many years. Frequently, due to a limited understanding of the array of complex issues involved, a very conservative approach is essential to achieve a FCS which will obtain flight clearance. The paper examines the impact of the nonlinear nature of the servo-hydraulic actuation system on the aeroservoelastic interaction. A method of predicting the occurrence of a limit cycling condition in such a system is presented, with comparisons made to experimental results. In addition, the paper demonstrates how an application of actuator performance limits can be used to predict a maximum level of structural response. Finally, the possibility of reducing the current clearance requirements from a consideration of this maximum structural response is discussed