[kach22i]

Originally Posted by Piotrsko

Thank you, I now understand why aircraft had a hard time going past 250 mph.

I had to double check myself, looks like my memory is intact - for now.


https://www.grc.nasa.gov/www/k-12/ai.../machrole.html

As an aircraft moves through the air, the air molecules near the aircraft are disturbed and move around the aircraft. If the aircraft passes at a low speed, typically less than 250 mph, it is observed that the density of the air remains constant. For higher speeds, some of the energy of the aircraft goes into compressing the air and locally changing the density of the air. This compressibility effect alters the amount of resulting force on the aircraft since the aerodynamic force depends on the air density. The effect becomes more important as speed increases. Near and beyond the speed of sound, about 330 m/s or 760 mph at sea level, small disturbances in the flow are transmitted to other locations isentropically or with constant entropy. Sharp disturbances generate shock waves that affect both the lift and drag of the aircraft, and the flow conditions downstream of the shock wave. On this slide, we will investigate the dependence of the density change on the Mach number of the flow.