Wind tunnel tests on a nacelle fitted with two lifting fans in tandem

Abstract

Summary. Results are given of wind-tunnel tests of a nacelle-shaped body fitted with two lifting fans in tandem. Lift, drag and pitching moment were measured both with the fans installed with axes vertical and also in a modified arrangement with 15 deg rearward tilt. In the latter case, the effects of simple inlet and exit cascades were also examined. The effects of aerodynamic interaction between efflux and mainstream were almost as serious for this slab-sided nacelle as when the same fan was installed in a large wing. The adverse effect on lift was slightly reduced by rearward movement of the fan when only one fan was in use and the other duct sealed, but a greater improvement was obtained when the front fan was used and allowed to induce additional downflow through the open rear duct thus reducing the magnitude of the lower surface suctions. Five-tube yawmeter traverses in the two vertical fan ducts just above the fans showed much less flow maldistribution at forward speeds compared with the fan in wing because of the 1-diameter length of duct between surface and traverse station. The decay of the cross flow with depth and the effect of variation of one fan rotational speed upon the flow in the other duct were also examined.