Propeller induced flow effects on wings at low Reynolds numbers

Signficant performance benefits have been found for a wing with a propeller in the tractor configuration at low Reynolds numbers (30,000 to 80,000) based on the wing chord. Propeller induced flow experiments on a wing with an aspect ratio of 4 using the Wortmann FX 63-137 airfoil show that an increase in propeller rotation rate (decreasing advance ratio) results in lift-to-drag ratios as high as 10 to 12 (a maximum of 80% increase in lift-to-drag ratio from a clean wing configuration) at both low and high angles of attack up to stall (0 to 16 deg). Experiments performed using trips and upper surface oil flow visualization results show that the turbulated nature of the propeller slipstream induces early transition to turbulent flow over the central portion of the wing. The result is a reduction of pressure drag and an increase in lift of the wing. The effect is greatest at low angles of attack. Additionally, results are presented where the location of the propeller was varied with respect to the wing, including having the propeller in a pusher configuration. The results show that to maximize the performance of small-scaled unmanned aerial vehicles (UAV) it is critical to properly integrate the propeller in a way that minimizes adverse low Reynolds number flow effects on the aerodynamics of a small-scaled UAV.