A typical value of this critical Mach number is of the order of

Question

The critical value of Mach number for a subsonic airfoil is associated with sharp increases in drag due to local shock formation and its interaction with the boundary layer. A typical value of this critical Mach number is of the order of

(a) 0.4 to 0.5                (b) 0.75 to 0.85

(c) 1.1 to 1.3                (d) 1.5 to 2.0