Testing coupled rotor blade–lag damper vibration using real-time dynamic substructuring

In this paper, we present new results from laboratory tests of a helicopter rotor blade coupled with a lag damper from the EH101 helicopter. Previous modelling of this combined system has been purely numerical. However, this has proved challenging due to the nonlinear behaviour of the dampers involved—the fluid filled lag damper is known to have approximate piecewise linear force–velocity characteristics, due to blow-off valves which are triggered at a certain force level, combined with a strongly hysteretic dynamic profile. The novelty of the results presented here, is that the use of a hybrid numerical–experimental testing technique called real-time dynamic substructuring, allowed a numerical model of the rotor to be combined with the physical testing of a flight certified lag damper unit. These hybrid tests, which are similar in concept to hardware-in-the-loop, were carried out in real-time such that there is bi-directional coupling between the numerical blade model and the experimental lag damper. The new results obtained from these tests (for steady-state flight conditions) reveal how the inclusion of a real damper produces a more realistic representation of the dynamic characteristics of the overall blade system (during operational flight conditions) than numerical modelling alone.