Tail Shake Vibration In Flight: Objective Comparison Of Aerodynamic Configurations In A Subjective Environment

Extensive computational fluid dynamic analysis and wind tunnel testing form part of the design of any new helicopter. Nevertheless, the so-called “tail shake” phenomenon is often encountered during early flight testing. A method is presented to characterise this wake related phenomenon in a tractable fashion. It is substantiated how a crew-correlated tail shake indicator was extracted from a subjective environment and developed into an objective characterisation. Amongst other rotorcraft, it was applied to the NH90 helicopter, used in this paper to demonstrate the method. The differences between two early aerodynamic configurations tested are quantified and wake behaviour highlighted, using the so-called “γ-α plot”. It is concluded that the proposed method allows objective comparison and gives insight into wake behaviour, supporting engineering decisions during development flight testing.