An Experimental Investigation of Ground Effect on a Quad Tilt Rotor in Hover

Abstract

The performance of a 0.031 geometrically scaled fuselage/wing model of a Quad Tilt Rotor (QTR) operating in helicopter mode while hovering in-ground effect (IGE) and out-of-ground effect (OGE) was experimentally studied. The effect of ground proximity was tested by varying the height of the model above the ground. Measurements included download on the airframe; thrust, torque, and rpm of the rotors; and static pressures along the centerline of the bottom of the fuselage. Fixedpitch propellers were used to model the rotors. The downwash distributions of the rotors were measured and compared well with large-scale V-22 rotor measurements. Tuft flow visualization was used to identify the physical processes causing changes in the download and static pressure measurements. The uncertainty of the measured quantities was determined to 95% confidence levels. A significant download (9 ± 0.5% of the rotor thrust) was observed in hover, OGE. The download reduced substantially IGE and become an upload (8.5 ± 0.5% of the rotor thrust) when the wheels of the QTR were on the ground. Flow visualization and pressure measurements suggest that the upload IGE is caused by the interaction of the wakes from the four rotors that are turned parallel to the ground and meet under the fuselage. The measured download, coupled with power measurements, indicate that for a given power the available vehicle thrust significantly increases IGE.