The Response of Helicopter Rotors to Vibratory Airloads

Abstract

Abstract : Structural response data from flight or wind tunnel tests of eight full-scale rotors were examined and compared for high-speed flight conditions and in the absence of blade stall or maneuvers. Both similarities and differences in the behavior of the rotors were observed, and these findings are useful in determining appropriate tests for development of theoretical methods. Limited use is made of airload measurements and theoretical calculation in examining these data. Major similarities observed in the rotor behavior include: 1) 3/rev vibratory flap bending moments are remarkably similar among all the rotors at high speed; 2) the root oscillatory chord bending induced by lag dampers is similar for three of the articulated rotors despite differences in the damper type; and 3) torsion moment and pitch-link loads show same positive- negative loading over the advancing side of the disk caused by the unsteady pitching moments at the blade tip. Differences that were observed include: 1) the vibratory chord bending-moment behavior appears to be dependent on rotor stiffness in part, but differences seen are not easily explained; 2) the CH-53A root oscillatory chord bending-moment data do not show the damper-induced loads that are seen on the other articulated rotors with hydraulic lag dampers; and 3) the AH-1G torsion response is very different from that of the articulated rotors. Rotor blades; Rotary wings. (edc)