Hello
In the Fundamental of Aerodynamics by Anderson (Chapter 12) shows that maximum lift-to-drag ratio decreases as Mach number increases. He asked this question:
"This is a fact of nature that progressively causes designers of supersonic airplanes grief as they strive toward aerodynamically efficient airplanes at higher supersonic Mach numbers. What physics is nature using against the airplane designer in this case, and how might the designer meet this challenge?"
I would like to know your opinion about that.
Best Regards
Most of high mach no planes are marginally stable and burns more fuel. Mostly they concerned about decrease of Drag
I've heard some supersonic jets, like the newer sukhoi series, use forward-swept wings. Apparently this design effectively maintains a low drag at sonic speeds, however it can cause slightly more drag at subsonic speeds. But since some fighter planes are intended to fly mostly at super sonic speeds, this design seems to be accepted.
in such planes, the flow moves inwards (towards the plane) on the wings, thus reduces wing-tip vortices
Aerodynamics drag is also depend on surface of the body and designed of the structure is more important to decrease drag. when drag reduces mach number eill increase.
Total Drag consists of Skin friction drag, wave drag and the base drag. Due to the mission requirement you can not avoid the skin friction drag. If the nose fineness ratio is in the range of 2.5 to 4, will lead to minimum wave drag. Then we are left with base drag which one should try to reduce. At sonic Mach numbers the base drag could be 60 to 70 % of the total drag. Hence, designers should look at the base drag and the ways to reduce the base drag.
Active and passive techniques are available in the literature.
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