Effects of Wing Sweep on the Upwash at the Propeller Planes of Multiengine Airplanes.

摘要

An analysis has been made to give a qualitative picture of the effects of wing sweep on the upwash at the propeller planes of multiengine airplanes. The method used in this analysis is, in general, the same as that given in NACA TN 2528, 1951, with the necessary extensions as suggested therein. To provide a basis for Judging the effects of sweep, the method was applied to two hypothetical airplanes of the high-speed long-range type, one having an unswept wing and the other a swept-back wing. Included as a part of the report are charts which facilitate the prediction of upwash in the chord-plane region ahead of wings of various plan forms. Comparisons of the upwash characteristics of two wings, one unswept and the other swept back 400, indicated that the effects of wing sweep on wing upwash at the selected propeller locations were quite large. The average level of the upwash was considerably higher for the case of the swept wing. In addition to the higher level of upwash, the upwash distribution was more asymmetrical. With the wing swept, the upwash at the inboard side of a propeller disk was found to be approximately 100 percent greater than at the outboard side, whereas with the unswept wing the difference was 10 percent or less. When considering the complete airplane, nacelle-axis inclination was found to be a powerful factor in the reduction of the over-all upflow angles at the propeller disks (the angles of local flow with respect to the nacelle axis resulting from wing upwash, upwash of bodies, and geometric angle of nacelle axis). With the nacelles inclined, it was found that the upflow angles were only slightly greater in magnitude for the airplane having the swept wing than for the airplane having the unswept wing, indicating that first-order excitation would be little greater than in the case of the airplane with the unswept wing.