A high-fidelity blade-element mathematical model for the AH-64A Apache Advanced Attack Helicopter has been developed by the Aeroflightdynamics Directorate of the U.S. Army's Aviation and Troop Command (ATCOM) at Ames Research Center. The model is based on the McDonnell Douglas Helicopter Systems' (MDHS) Fly Real Time (FLYRT) model of the AH-64A (acquired under contract) which was modified in-house and augmented with a blade-element-type main-rotor module. This report describes, in detail, the development of the rotor module, and presents some results of an extensive validation effort. Mansur, M. Hossein Unspecified Center AERODYNAMIC CHARACTERISTICS; AH-64 HELICOPTER; MATHEMATICAL MODELS; PROPELLER BLADES; ROTOR AERODYNAMICS; ROTOR DYNAMICS; AERODYNAMIC FORCES; AIRCRAFT MANEUVERS; EQUATIONS OF MOTION; FLIGHT CHARACTERISTICS; ROTORS...