FULL SCALE GROUND AND AIR RESONANCE TESTING OF THE ARMY-BOEING VERTOL BEARINGLESS MAIN ROTOR

This paper presents ground and air resonance test results for full scale tests of the Boeing Vertol-Army Bearing-less Main Rotor (BMR) flown on a BO-105 helicopter. The BMR has the advantage of simplicity due to elimination of the pitch bearing and the flap and lag hinges used in articulated rotor designs. This results in potential improvements in performance, reliability and life cycle costs. The aircraft was tested for ground and air resonance damping at conditions which were expected to be critical, including level flight, climbs, descents, maximum power dives, and auto-rotations; in addition, testing during loads evaluations included banked turns, pull-ups, and push-overs. The aircraft encountered no air resonance mode instabilities during any of these flight conditions. Initial testing disclosed that ground resonance mode damping had to be improved by stiffening the existing landing gear skid. Analytical results are also presented which were used in developing the rotor design and in preparing the flight test procedures. Model rotor test results are also shown which gave an accurate preview of what was to have been expected during full scale flight testing.