COMBINATION HAVING A TRIANGULAR WING

A study was undertaJsento evaluate a method for predicting the-downwash in a transverse plane behind a wing-body combination throughout an angle-of-attack range from 0 ° to 20°. The predicted duwnwash was cal-culated by a numerical method in which an array of discrete vortices was allowed to roll up”. The wing vortices were assumed to emanate from the trailing edge of the wing with their positions and strengths determined from the measured spanwise distribution of load. The wing-body combination had a ratio of maximum body diameter to wing spsn of 0.259, a triangular wing with an aspect ratio of 2.0, and a body of revolution with a fineness ratio of 12.5. Comparisons are made between the experimental and predicted values for the downwash and for the spanwise distribution of load at a Mach number of 0.25. The positions of the vortex cores indicated by the tuft-grid technique, the water-tank techniggej and the numerical method are also compared. The downwash predicted by the numerical method showed general agree-ment with the experimental downwash at angles of attack up to about 6° to 8°. Above these angles considerable disagreement existed between the predicted and experimental downwash. These differences are attributed in part to flow separation effects since flow studies have indicated that the vortex sheet emsnates ahead of the wing trailing edge rather than at the wing trailing edge as assumed in the numerical methd