1. Ch14 Transonic Flow
－drag divergence phenomena, rapid shift of center of pressure unsteady and somewhat unpredictable effects of shock waves on the control surfaces
－Typical cruise Mach number of jet transports ( )
( now concept to push MDD →1 )

2. c.f.

3. 14.7.4 The Transonic Area Rule and the Supercritical Airfoil
－Product of transonic wind tunnels at Langley by Richard Whitcomb
－to reduce drag in the transonic regime

4. Area Rule: the cross-sectional area of the body should have a smooth variation with longitudinal distance along the body; there should be no rapid or discontinuous changes in the cross-sectional area distribution.
( wasp-like or coke-bottle shape for the body; the body cross-section should be decreased in the vicinity of the wing. )

5. The area rule reduces the peak transonic drag by a considerable amount.

6. Supercritical airfoil: shaped somewhat flat on the top surface in order to reduce the local Mach number inside the supercritical region below what it would be for a conventional airfoil under the same flight conditions.
The shock strength is lower; the B.L. separation is less severe.
MDD ↑
i.e. Mcr, supercritical airfoil = Mcr, an equivalent standard airfoil
MDD, supercritical airfoil >> MDD, standard airfoil (slightly >Mcr)
“Super-critical”