The resistance divergence Mach value is typically greater than 0.6 making it a transonic effect. The resistance divergence Mach is normally close and is always greater than the critical Mach number. Generally, the resistance coefficient reaches its highest value when reaching Mach 1.0 and begins to decrease again once the supersonic flight regimes over Mach 1.2 are passed. The increase in resistance is given by the formation of a shock wave on the upper surface of the profile, which can induce detachment of the flow and the adverse pressure gradient in the final portion of the wings.
This effect forces planes that intend to fly at supersonic speeds to have high-thrust engines. In early developed transonic and supersonic aircraft, a tapping was frequently used to provide them with the acceleration necessary to overcome the zone of high resistance around Mach 1.0. In the early days of aviation, this consequent increase in resistance led to the belief that the sound barrier could not be reached, as it was thought that it would not be technologically possible to build an engine with such considerable thrust or an aircraft with sufficient authority to control in flight to overcome said barrier.
In fact, one of the most popular analytical methods for calculating resistance at high speeds, the Prandtl-Glauert Rule, predicted an infinite amount of resistance in Mach 1.0. Two of the most important technological advances that resulted from attempts to conquer the sonic career were: The Whitcomb Area Rule and the supercritical profile. A supercritical profile is molded to make the resistance divergence Mach as high as possible, allowing aircraft to be able to fly with relatively low resistance at high subsonic speeds and at low transonic speeds.
These advances in conjunction with Computational Fluid Dynamics (CFD) have been able to reduce the resistance increase factor by 2 to 3 times for modern design aircraft. [2] allowing aircraft to be able to fly with relatively low drag at high subsonic speeds and low transonic speeds. These advances in conjunction with Computational Fluid Dynamics (CFD) have been able to reduce the resistance increase factor by 2 to 3 times for modern design aircraft. [2] allowing aircraft to be able to fly with relatively low drag at high subsonic speeds and low transonic speeds. These advances in conjunction with Computational Fluid Dynamics (CFD) have been able to reduce the resistance increase factor by 2 to 3 times for modern design aircraft. [2]
Sources
