THE DEVELOPMENT OF THE COUPLED ROTOR-FUSELAGE MODEL (CRFM)

A collaborative programme in the United Kingdom, between Westland Helicopters Limited and the Defence Research Agency, has involved a multi-disciplinary team of researchers over the last 6 years, culminating in the first software release of the Coupled Rotor Fuselage Model. By coupling the dynamic systems of the rotor and fuselage using complex rotor modes the analysis accommodated the effects of hub motion on rotor load and vibration prediction. It has also allowed the range of hub types to be expanded to include; bearingless, multi-bladed teetering and gimbal configurations. A main feature of CRFM is to simulate manoeuvring flight conditions, to achieve this aim a model has been developed to mimic the pilot control logic to fly manoeuvres and a new wake model has been included to address the first order implications of manoeuvres on wake geometry. Algorithms for the timewise solution of modal response have been reviewed and prioritised on the basis of accuracy, efficiency and numerical stability. The calculation of rotor loads has shown benefits by the incorporation of a new modal curve fitting technique, providing improved accuracy and efficiency when determining loads using the Force Integration procedure. CRFM has been structured to provide versatility in computation and in application to multiple rotor and wing combinations of different aircraft configurations. The main technology modules are described with associated examples of the potential advantages of CRFM to enhance rotorcraft modelling.