Aerodynamic interference and unsteady loads for a trimming intermeshing rotor compound propeller helicopter at level forward flight

Abstract

Traditional trim methods for isolated rotor helicopters are not suitable for intermeshing rotor compound propeller helicopters (IRcPHs) due to inherent structural differences. This study aims to establish a novel trim method for an intermeshing rotor with an auxiliary propeller. First, the relationship between the rotor cyclic pitch and the flapping response in the fully articulated rotor system with hinged extension is derived. The study then formulates the equilibrium state equations and the corresponding flight conditions for trimming the IRcPH in level forward flight. In addition, the unsteady vortex lattice method is employed to calculate the periodic averaging states on the rotor disk and correct for induced losses in flight dynamics. Finally, the paper focuses on the aerodynamic interference, blade–vortex interaction, and harmonic load patterns of the IRcPH, serving as a guide for rotor active control systems. Results show that the positions of the mutual aerodynamic interference occur constantly at 160° and 340° azimuths on the intermeshing rotor disk, serving as the phase basis for suppressing vibration. Moreover, the propeller enters the comfort zone as the forward flight speed increases, and the loads only have frequency orders of (2/nw)/rev with respect to the main frequency of the intermeshing rotor.