We have seen that if , shocks form above the airfoil. This causes a large increase in drag.

In addition, the expressions for the supersonic wave drag coefficient have  in the denominator. Thus, the supersonic wave drag coefficient also becomes very high in the transonic range. Some people believe that linear theory could be close to the truth at , so that . Thus, they hypothesized the existence of the "sound barrier". In practice,  does become quite high at , but fortunately stays finite, so that powerful engines can still accelerate the aircraft through  without needing infinite thrust.
 

Conclusions:

1. Good aerodynamic design dictates that the surface slopes should be smooth and gentle to avoid sharp peaks in the pressure distribution.
2. The value of  must be kept high for transonic flight.
3. Flight at  should be kept to a short duration.