Analysis of Estimated and Experimental Transonic Downwash Characteristics as Affected by Plan From and Thickness for Wing and Wind- Fuselage Configurations.

摘要

As part of a transonic research program the sensitivity of downwash at the tail plane to fairly systematic changes in wing plan form and thickness has been evaluated over a Mach number range of approximately 0.6 to 1.1, utilizing the transonic-bump technique. This paper presents a summary of information obtained from 11 transonic-bump investigations of wing and wing- fuselage configurations and compares the experimental results with theoretical estimations made for subsonic and supersonic Mach numbers. Of the many variables investigated, the most powerful single factor influencing the character of downwash variation with Mach number appears to be wing thickness ratio. If the wing thickness is such that erratic lift variations are present at transonic speeds, similar effects on downwash can be expected. Available methods for estimating the downwash slope de/dCL at high subsonic speeds or low supersonic speeds are probably sufficiently accurate for preliminary design purposes when applied at low lift coefficients, particularly for wings of small thickness ratio. With increases in sweep angle or aspect ratio, and decreases in taper ratio, the nonlinear downwash characteristics occurred at lower lift coefficients and were more severe; whereas changes in thickness ratio had little effect. The onset of nonlinear downwash characteristics was delayed to considerably higher lift coefficients and the severity of the nonlinearities was reduced considerably as the speed was increased from subsonic to low supersonic.