Higher harmonic pitch link loads reduction using fluidlastic isolators

Fluidlastic isolators are proposed for higher harmonic pitch link loads reduction in helicopter rotors. 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. Using Hamilton's principle, the system equations of motion are derived based on the generalized force formulation. The results indicate that the application of the fluidlastic isolator can reduce the 4/rev pitch link load by 98.9% in high forward flight with small variations in the other harmonic loads. The isolator has significant influence on the higher harmonic torsional rotation of the blade tip. Increasing the tuning port area ratio can significantly reduce the tuning mass with little variation of the isolation ability. Within 5% variation of the normal rotor speed, the 4/rev isolator can reduce more than 80% of the 4/rev pitch link load. The effects of isolator's damping, forward speed, and thrust on the performance of the isolator are also studied. The ability to isolate other higher harmonic pitch link loads is also investigated.