The power of simulation as a design and training tool has long been recognized and successfully exploited by the fixed-wing aircraft community. This in turn has begun to influence the helicopter industry which until now used simulation to a much lesser extent. This is evidenced by the emphasis on simulation by the U.S. Army in the procurement of the next generation light helicopters (LHX) and the investments currently made by the helicopter companies on simulation equipment and facilities. The approach to fixed-wing aircraft simulation has become fairly uniform within the Industry despite advances in aircraft technology and capabilities. On the other hand, rotorcraft simulation has taken divergent paths. There is a plethora of techniques and more are in the offing. One reason is that the rotor wake, rotor dynamics, and the interaction between the rotor, airframe, engine and drive train are extremely complex and difficult to model, even to achieve a credible offline non-realtime simulation. Consequently, designers of helicopter engineering/training simulations face a bewildering array of techniques for real-time, man-in-the-loop simulation.

This paper surveys the different rotor modeling techniques from a real-time simulation user's perspective. It describes the most commonly used techniques, their underlying assumptions and simplifications, computing requirements, and strengths and weaknesses. It is hoped that the paper will provide a potential designer/user with an understanding of the options available to him and help him choose an approach that will best meet his needs.