INDUCED DRAG OF A CRESCENT WING PLANFORM

Comparative study, both computational and experimental, has been carried out on the possible drag reduction at low speeds of two wings of same aspect ratio 6, but different wing planforms; one is crescent and the other is elliptic. Computational results, using two inviscid panel programs, indicate that the crescent wing planform is capable of reducing the drag, interpreted from the integrated surface pressure distributions. The benefit has been attributed to a high suction pressure loading in the tip region in the case of the crescent wing. However, such a potential in drag reduction cannot be verified experimentally at the Reynolds number based on the mean chord 0.25 x 10(6). There has been no expected gain in the effective aspect ratio associated with the crescent wing, based on the results of balance tests. Detailed wake surveys at a downstream distance behind these wings reveal substantial differences in the wake structures at an approximate lift coefficient of 0.35, but the vorticity in the wake vortex cores shows similar magnitudes. One explanation for the misleading computational findings is that there exists a residue drag at no-load condition, possibly arising from the errors in the discretization of the highly curved tip shape. This residue drag tends to contaminate the calculation at lifting conditions.