Interest in high speed rotorcraft has directed attention toward the slowed-rotor, high advance ratio compound autogyro concept. Inherent features of this concept include partially unloading and slowing the rotor while maintaining autorotation. Unloading of the rotor results from transfer of the lift generation function to the more aerodynamically efficient wing at high flight speed, and slowing of the rotor is required to avoid sonic conditions on the advancing blade. This necessity for a reduction in rotor speed with increasing flight speed results in high advance ratio operation where the retreating side of the rotor is dominated by the reverse flow region. The use of conventional swashplate controls has been proposed as a means to unload and slow the rotor, as well as suppress large hub moments due to cyclic blade flapping. Rotors with low Lock number and high flapping stiffness were investigated in simulated wind tunnel experiments using the FLIGHTLAB rotorcraft modeling software. Performance analysis for rotors trimmed to autorotate with zero average hub pitching and rolling moments indicates that reduced rotor thrust is achieved primarily through rotor speed reduction at a lower shaft incidence angle with respect to the freestream velocity, and imposing hub moment trim constraints results in a thrust increment sign reversal with collective pitch angle above advance ratio my nearly equal 1.0. Rotor control strategies are developed including the use of variable shaft incidence to achieve rotor speed control while hub moment suppression is achieved through cyclic control. Quasi-steady analysis of a commanded rotor speed transition is presented for cases with and without hub moment suppression, further supporting the use of variable shaft incidence.
Performance and trim analysis of lightly loaded rotors in high advance ratio autorotation
Leistungs- und Trimmanalyse von schwach belasteten Rotoren im Autorotationsflug mit hohem Steigungsverhalten
2010
23 Seiten, 26 Bilder, 3 Tabellen, 15 Quellen
Conference paper
English
Performance and Trim Analysis of Lightly Loaded Rotors in High Advance Ratio Autorotation
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