Multibody Analysis of the Influence of Strut-Mounted Vibration Alleviation Devices on Rotor Aeromechanics

The struts that connect the main rotor and the gearbox to the airframe provide structural integrity to helicopters. They carry the weight of airframe and payload during flight in form of steady tension, support the main rotor on the ground in form of steady compression, and guarantee smooth operation to the drive system. These functions are typically well accomplished by very stiff struts; as a result, the vibratory loads originating from the main rotor periodic aerodynamic loading in forward flight are transferred to the airframe with almost negligible alleviation. One technique to solve this problem is to implement strut-mounted vibration alleviation devices. Aiming at providing global isolation of the airframe from the main rotor excitation, these devices are very typical in improving ride comfort in rotorcraft. However, the benefit comes at the cost of increased rotor and gearbox vibrations, possibly impacting also the rotor aeromechanics. The change can be significant, yet its evaluation is non-trivial; therefore a detailed investigation is necessary. This work presents a detailed multibody analysis of the influence of strut-mounted vibration alleviation devices on rotor aeromechanics. For this purpose, a multibody model of a helicopter is used to evaluate the changes in main rotor aeromechanics when vibration absorbers between the main rotor and the airframe are introduced.