A major source of helicopter drag, about 30% of the total, is from the rotor hub. It is important that the drag generated by a helicopter, and hence emissions, is reduced.

This research programme was undertaken to investigate this subject and investigate potential techniques to achieve reductions in hub drag. A wind tunnel test programme was carried out to provide a large, high-quality experimental data set. A 5 bladed scale helicopter model was designed and manufactured.

The model was designed to enable the effect of model geometry to be examined by using a range of 5 rotor caps and 5 hub fairings. The overall model aerodynamic loads were measured and the loads generated by the rotor hub and rotor cap were independently obtained using internal load cell balances. Two Particle Image Velocimetry systems, 3D and time resolved, were employed in parallel to acquire flow field data in regions of interest around the model.

A range of representative flight conditions were simulated. These acquired data were processed to allow the significant features of the helicopters model’s aerodynamic characteristics to be obtained. This exposed the salient sources of rotor hub drag and so identified techniques that may be employed to reduce the magnitude of this force. The data was also available for the development and validation of CFD codes.