3.3.5: Aerodynamics of wings in compressible and supersonic regimes

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The evolution of the coefficients of lift and drag for a wing presents similarities with which has already been exposed for airfoils. However, instead of reducing the relative thickness and the use of supercritical airfoil to aft the divergency, in the case of wings there exist an additional resource: wing swept \(\Delta_{c/4}\).

The use of swept for the design of the wing permits reducing the effective Mach number (the reduction factor is approximately \(\cos \Delta_{c/4}\)). Then the behavior of the airfoils is as they were flying slower and consequently the divergence Mach can be seen as higher. However, the use of swept makes the aircraft structurally complicated and, moreover, both \(C_{L_{\alpha}}\) and \(C_{L_{\max}}\) decrease. That is why commercial aviation tends to develop supercritical airfoils to minimize the swept.

For supersonic flight, the wings are typically designed with great swept and small enlargement. The extreme case is the delta wing.