Analysis of Rotorcraft Vibration Reduction Using a Center-of-Gravity Offset

Abstract

When a rotorcraft has N blades, N/rev vibration becomes large as the cruise speed increases. This article numerically examines the effect of Center-of-Gravity (CG) offset on rotorcraft vibration. A mid-sized rotorcraft, SH-60K, was selected for analysis with the use of CAMRAD II. A minimum of 60% decrease in the baseline z-acceleration was achieved at the pilot seat, which dominantly defines the vibration circumstance at a large offset CG. There exists a middle CG location between the baseline and the vibration minimum CG, where both the main rotor power characteristics and the trim attitudes are allowable. At that point, an approximately 20% reduction in the z-acceleration at the pilot seat can be achieved. Not only for preexisting helicopters, but also for rotorcraft in development, engineers should keep in mind that the CG positions are worth investigating to reduce vibration; although, the CG positions in almost all rotorcraft have been directly below the main rotor hub.