Development of transonic area-rule methodology

Abstract

This study presents an innovative method for area ruling in the transonic regime. The method applies a weighting function to the sonic area rule that generally accounts for the physical nature of transonic flow. In sonic flow, changes in pressure are communicated with negligible dissipation along Mach planes. As a result, drag becomes a strong function of the cross-sectional area development of the aircraft. Transonic flow has the added complexity of mixed subsonic and supersonic regions. In this flow, the communication between the aircraft fuselage and its external parts has dissipation due to embedded subsonic regions. Therefore, the sonic area rule no longer strictly applies. The new transonic area-rule methodology, described in this article, utilizes a weighting function that adjusts for the effects of the mixed flows. The shaping methods resulting from this new transonic area-ruling technique are much less severe than the standard sonic area-ruling method and require substantially less body modification. Furthermore, the new transonic area-ruling technique maintains drag rise delays that are the same as the traditional sonic area rule. Nomenclature A = stream-tube area CD = drag coefficient M = local Mach number Wm = wingtlp parameter v = velocity ACD = wave drag coefficient