Identification of AH-64D Dynamics to Support Flight Control Systems Evaluations

Integrated analysis tools have been used to evaluate the closed loop handling qualities of the AH-64D Longbow Apache. CIFER® (Comprehensive Identification from Frequency Responses) system identification techniques were used to identify a high-order linear model of the AH-64D at hover. The state-space model structure included the coupled dynamics of the rigid body, flapping, coning, dynamic inflow, lead-lag, and rotor rotational degrees of freedom. The identified model was linked to an analytic model of the baseline AH-64D flight control system to form a closed loop simulation in MATLAB®/Simulink®. This model was then integrated into CONDUIT® (Control Designer's Unified Interface) to evaluate existing flight control laws against pertinent military handling qualities and control system specifications. The purpose was to demonstrate the analysis tools and techniques which form an integral part of the overall process used by the US Army Aviation Engineering Directorate (AED) to evaluate and qualify advanced flight control systems for U.S. Army helicopters.