Automated Measurment of Backlash and Stiffness in Electro-Mechanical Flight Control Actuation

Abstract

Electro-mechanical actuation of primary flight control surfaces is expected to increase the efficiency of future commercial aircraft. More specifically, the effort and cost of manufacture and maintenance will be reduced due to the omission of hydraulic supply and actuation systems. However, backlash is inherent to electro-mechanical actuation, whereas it does not occur in conventional hydraulic servo-actuation. Due to wear, backlash increases over the lifetime. With regard to electro-mechanical actuation of primary flight control surfaces, excessive backlash can cause detrimental effects such as limit cycle oscillations or, as a worst case, lead to jamming. Therefore, efficient and simple-to-deploy methods for monitoring backlash are sought after. This paper describes time domain methods for automated measurement of backlash and stiffness that use available sensor signals of an electro-mechanical aileron actuation system. So far, feasibility of the methods has been verified by experiments on appropriate test benches.