The Steady-State Response of a Cantilevered Rotor With Skew and Mass Unbalances

The steady state response of a cantilevered rotor with skew and mass unbalances is studied, with special attention to the effects due to skew. A disk misaligned with its drive shaft receives active gyroscopic moments which force pitch changes in the disk, much as mass unbalance centrifugal forces induce disk translation. These active gyroscopic moments affect the rotor in ways unpredicted by passive gryoscopics; that is to say the moments acting on a perfectly aligned disk which changes pitch solely due to its precession. Under the combined influences of disk skew and mass unbalance the precessing rotor exhibits an unconventional phase lag response, and it need not be in line with the mass unbalance at low spin rates. This can significantly alter rotor balancing procedures. Rotor critical speeds are studied for their number and severity, with results presented in a compact nondimensional form.