The fountain flow signature around a generic tandem-rotor helicopter hovering near the ground

Abstract

A multi-purpose test rig has been manufactured to perform an in-depth study of the flow field around a tandem-rotor generic helicopter in hovering flight. The survey includes the flow field study around the blades and also the overall trust and power measurements near the ground for both overlapped and non-overlapped blades. A single-rotor configuration has also been tested as a baseline. The results have approved the existence of a fountain flow region between the twin rotors, about which, very limited experimental data are available in the literature. It has been shown that in tandem rotors, the ground effect increases the pressure within the fountain flow which gives rise to the lift. For the overlapping blades, this favorable effect has been shown to be more prominent than the non-overlapping configuration. It has also been found out that the ground proximity remarkably enhances the tandem-rotors’ trust in comparison with the single rotor. As increasing the overlap between the rotors, both the power required by the blades and the thrust produced in the ground effect increase.