Pitch link loads reduction using fluidlastic isolators

Fluidlastic isolators are proposed for higher harmonic pitch link loads reduction in rotorcraft. Frequency responses of one degree-of-freedom system with a fluidlastic isolator are conducted to investigate the dynamic characteristics of fluidlastic isolators. The results illustrate that the force transferred to the base can be effectively reduced. An aeroelastic simulation of a soft in-plane rotor in high forward flight is conducted to investigate the dynamic characteristics of the coupled rotor and fluidlastic isolators. Leishman-Beddoes dynamic stall model is utilized to capture the unsteady aerodynamics. System equations of motion are derived based on the generalized force formulation. The results illustrate that the introduction of fluidlastic isolator can reduce the 4/rev pitch link load by 98.4% in high forward flight with the variation of other harmonic loads. The variation of hub loads is substantially small. The 4/rev isolator has significant influence on the higher harmonic torsional rotation of blade tip. Within 5% variation of the normal rotor speed, the 4/rev isolator can reduce more than 75% 4/rev pitch link load. The effects of pitch link stiffness, isolator's damping, forward speed, and thrust on the ability of the isolator are also studied.