The rotor shaft bending moments are produced by mΩ dynamic flapping forces, unbalanced components of static flapping forces, dynamic drag forces, dynamic centrifugation forces and unbalanced components of static centrifugation forces of the arms on spheriflex hub helicopters. The amplitude, frequency, phase position and distribution laws of rotor shaft bending moments are analyzed in this paper. After the flight load measurement for a helicopter is performed, the characteristics of the measured rotor shaft bending moments are analyzed, establishing the effectiveness criteria, distinguishing the non-effective data, and finally compiling the measured fatigue load spectrums. The analysis of the helicopter shows that in the rotor coordinate system, the dynamic moments are much larger than the static moments while the unbalanced static flapping force and static centrifugation force are small. The main components of rotor shaft bending moments are 1Ω moments produced by the 1Ω flapping force, the drag force and the centrifugation force. The combined bending moments exhibit the same amplitude in one section rotating around the rotor shaft, the similar amplitude and the same phase difference with the different circumferential position along the shaft.
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