Determination of Ground Effect from Tests of a Glider in Towed Flight,
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON DC
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An investigation was made to find the effect of the ground on the aerodynamic characteristics of a Franklin PS-2 glider. The lift, the drag, and the angle of attack of the glider in towed flight were determined at several heights from 0.14 to 1.19 span lengths and at various speeds for each height. Two wing arrangements were tested the plan wing, and the wing with a nearly full-span 30-percent-chord splot flap deflected 45 deg. For both wing arrangements, the results showed a decrease in the drag coefficient and the angle of attack for a given lift coefficient when the wing was affected by the ground for the flapped wing, which was the only one tested at two different heights near the ground 0.14 and 0.33 span length, the reduction in drag was greater at the smaller height by the change in angle of attack was approximately the same at both heights. The experimental results for the plain wing were in good agreement with theoretical values calculated by the method of Weiselsberger for both the angle of attack and the drag coefficient at a height of 0.21 span length Tanis refinement of the theory had a practically negligible effect on the computed values in this case. For the flapped wing, the ground effect on the drag coefficient as calculated by the extended treatment of Tani was in better agreement with experiment, in general, than the predictions by Weiselsbergers method. With regard to ground effect on the angle of attack of the wing with split flap, the results did not indicate either treatment as definitely preferable although it appeared that, in this case, Wieselsbergers method probably agreed better with experiment.
- Gliders and Parachutes