A Generalized Dynamic Balancing Procedure for the AH-64 Tail Rotor

摘要

The tail rotors on the AH-64A Apache and AH-64D Longbow Apache incorporate a unique design, which includes two, two-bladed teetering rotors that have an azimuth spacing of 55°, instead of the more usual 90°. Maintainers have observed that some Apache tail rotors can be very difficult to balance dynamically. This investigation uses RCAS numerical simulations of tail rotor response when mass is added to the tips of single and adjacent blades to investigate possible causes for this balancing difficulty. The simulations show that the vibratory vertical force response due to added tip mass varies as a function of the mass distribution between two adjacent blades, and the azimuth spacing between the two blades. As a result, the tail rotor balance sensitivity coefficients can be quite inaccurate, and could be a prime contributor to the observed problems balancing tail rotors. An analytical model of the tail rotor, with characteristics similar to the RCAS model is then used to develop method for correcting the balance sensitivity coefficients measured for single blade response to account for the phase angle when adjacent blades have defects.