A new approach to the prediction of helicopter rotor performance using a free wake analysis was developed. This new method uses a relaxation process that does not suffer from the convergence problems associated with previous time marching simulations. This wake relaxation procedure was coupled to a vortex-lattice, lifting surface loads analysis to produce a novel, self contained performance prediction code: EHPIC (Evaluation of Helicopter Performance using Influence Coefficients). The major technical features of the EHPIC code are described and a substantial amount of background information on the capabilities and proper operation of the code is supplied. Sample problems were undertaken to demonstrate the robustness and flexibility of the basic approach. Also, a performance correlation study was carried out to establish the breadth of applicability of the code, with very favorable results. Quackenbush, Todd R. and Bliss, Donald B. and Ong, Ching Cho and Ching, Cho Ong Unspecified Center COMPUTER PROGRAMS; FREE FLOW; HELICOPTER PERFORMANCE; HELICOPTER WAKES; HOVERING STABILITY; INFLUENCE COEFFICIENT; COMPUTERIZED SIMULATION; CONVERGENCE; LOADS (FORCES); PERFORMANCE PREDICTION; RELAXATION METHOD (MATHEMATICS); ROBUSTNESS (MATHEMATICS); TIME MARCHING...