Wind tunnel measurements of rectangular flat-plate wings of varying aspect ratios (AR = 2, 3, and 4) under different propeller-induced flow conditions were taken at Reynolds numbers from 60,000 to 90,000. The GWS 5×4.3 and GWS 3×3 propellers were used in both the tractor and pusher configurations at various advance ratios. In the tractor configuration, all wings tested showed a reduction in the wing lift curve slope for propellers rotating close to or in the windmill-brake state. As propeller rotation rate increased (decreasing advance ratio), the wing lift curve slope was observed to increase. Negligible variation in lift curve slope was found, however, for the propeller in the pusher configuration. In addition, all wings tested exhibited significant stall delay and increased maximum lift characteristics due to propeller-induced flow effects. The degree of stall delay and maximum lift increase was found to be related to the propeller advance ratio and the propeller diameter-to-wingspan ratio. Most notably, flat-plate wings with an aspect ratio of 2 (high propeller diameter-to-wingspan ratio) with the propeller in both tractor and pusher configurations showed the largest stall delay and maximum lift increase (＞40%) at the lowest advance ratios tested. As aspect ratio increased (larger propeller diameter-to-wingspan ratio), the degree of stall delay and maximum lift increase reduced. Also, propellers in the pusher configuration were found to have larger stall delay and maximum lift effects for wings of higher aspect ratio. The results found from these tests underscore the importance of accounting for propeller-wing interaction effects in the design of small-scale UAVs.
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