Design and Evaluation of Control Laws for the CH-53E Low Speed Precision Control System

The United States Marine Corps often operate their helicopters in austere environments where degraded visual environments (DVE) such as brownout are regularly encountered. DVE significantly increase the risk to operations and have led to many mishaps across the Department of Defense. In response, engineers from the United States Navy are designing a system to augment the legacy flight control system (FCS) on the CH-53E. The system is designed to preserve the legacy FCS functionality to limit the impact on the current platform airworthiness and reduce developmental flight test. The Low Speed Precision Control (LSPC) system provides decel-to-hover with position hold functionality, allowing the pilot to modulate command references via trim beepers, cyclic fly through, and trim release. A piloted simulator test was performed with three test pilots to evaluate the handling qualities with and without LSPC engaged, in several fleet representative conditions. LSPC was found to reduce workload marginally in good visual environments and in low light conditions; however more substantial reductions were shown for approaches into brownout conditions. In addition, LSPC was shown to significantly reduce lateral drift during final approach into brownout and lateral and longitudinal drift in a hover. Inherent system bandwidth limitations were found to degrade the performance of the system for anything more than moderate control inputs. Overall, LSPC was successful in augmenting fleet representative approaches in the simulator for degraded visual environments.