EXPERIMENTAL COMPARISON OF TWO WING TIPS

Abstract

Systematic tests of six wing tip configurations chosen for a general aviation application had shown a sharp edged tip to be best for a range of conditions. A full-sized model was made from the outer five feet of a 15-meter glider wing having a drooped tip. The model was made to allow tips to be interchanged, and a sharp-edged tip like that developed for the general aviation application was tested on a direct comparison basis with the original glider tip. At full scale Reynolds numbers, the model tests showed the new sharp-edged tip to be superior for all values of lift coefficient above 0.4. In addition to gains in L/D of up to 6%, the climb parameter was significantly improved by as much as 6% and the increase in maximum lift coelficient of 4% could offer a reduced stall speed. From earlier tests of a general aviation application, an increase in effective dihedral at high angles of attack can also be expected. Flow field surveys were made of the wake downstream of the tips to determine the nature and location of the vortices. These showed a distinct effect on the location and strength of the vortices, and appear to corroborate the higher lift of the new tip.