Engineering Evaluation, AH-56A Compound Helicopter with Advanced Mechanical Control System

The United States Army Aviation Systems Test Activity conducted an engineering evaluation of the AH-56A compound helicopter with the advanced mechanical control system. This evaluation was primarily a handling qualities evaluation to determine the relative merits of the advanced mechanical control system versus the improved control system previously tested. The testing consisted of 20 test flights totaling 18.2 hours. The advanced mechanical control system corrected the major problem of the AH-56A with the improved control system. This problem was loss of aircraft control within the flight envelope resulting from blade moment stall. Some additional benefits of the advanced mechanical control system were a reduction in pilot workload during transition and elimination of the tendency for pilot-coupled roll oscillations, longitudinal trim shift with sideslip, and roll due to lift coupling. One deficiency identified during improved control system testing is still present. This deficiency is the inability to effectively perform low-speed low-level mission tasks below 120 knots calibrated airspeed under reduced visibility conditions due to the lateral-directional stability characteristics. There were four shortcomings identified, all of which existed with the improved control system.