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A four‐bladed scissors rotor was evaluated in model and full‐scale tests. Flight speeds over 150 knots were reached and high‐speed maneuvers over two g's. Hub mobility was instrumental in greatly reducing oscillatory blade loads. With respect to these loads, as
well as with respect to acoustics and vibrations, the scissors rotor resembles more a two‐bladed rotor than a four‐ blader. The single seesaw hinge combined with a hub spring gave essentially a constant hub moment with flapping, which contributed noticeably to stability and to
controi power. Some degradation of hovering power was noted in comparison with the performance of a symmetric four‐bladed spacing, and at high speed, a slightly higher power required was measured due to increased hub drag. In high‐gross‐weight hover a blade motion instability
was encountered in the reactionless mode. This instability could be explained and eliminated.
Bell Helicopter Company, Fort Worth, Texas
Publication date: July 1, 1975
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