Editing Area rule (section)

==Sears–Haack body==

A superficially related concept is the [[Sears–Haack body]], the shape of which allows minimum wave drag for a given length and a given volume. However, the Sears–Haack body shape is derived starting with the [[Prandtl–Glauert transformation|Prandtl–Glauert equation]] which approximately governs small-disturbance subsonic flows, as well as Ackeret Theory, which closely describes supersonic flow. Both methods lose validity for transonic flows where the area rule applies, due to assumptions made in their derivations. So although the Sears–Haack body shape, being smooth, will have favorable wave drag properties according to the area rule, it is not theoretically optimum.<ref>{{cite web |url=https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670030792.pdf |title=Studies of optimum body shapes at hypersonic speeds |website=NASA Technical Reports Server |author=Spencer, B. Jr |author2=Stivers, L. S. Jr |date=October 1967 |access-date=4 November 2022}}</ref>