Experimental work on unsteady helicopter rotor hub wakes

Abstract

Helicopter tail shake phenomenon is a topic of main distress for the rotorcraft industry since it adversely affects the overall performance, occupants' comfort and handling qualities of helicopter. This research work is intended to investigate the unsteady aerodynamic wake characteristics induced by the helicopter rotor hub that lead to this tail shake phenomenon by executing a wind tunnel campaign. The experiments were carried out in the UTM wind tunnel with a test section of 2m (width) × 1.5m (height) × 5.8m (length) with the maximum wind speed of 80m/s. Dynamic pressure measurements inside the wake due to the effect of helicopter advance ratios and pylon configurations were performed. The dynamic analysis conducted through the power spectral density and root-mean-square methods, has successfully managed to quantify the frequency and the amplitude of unsteadiness of the hub wakes that lead to the tail shake problem. The analyses tell that by employing pylon to the rotor hub, it could significantly reduce the wake unsteadiness up to 99.31%. Subsequently the findings of this research have potential to minimize this long running problem that undoubtedly could benefit the entire growing helicopter industry.