Originally posted by dtango
Otherwise we could call different planes supersonic including the P-47 or the P-51 that I believe have recorded hit or exceeded mach 1 in dives.
In WWII there were prop planes that, by looking at the indicated speed on their airspeed indicators and correcting to true airspeed, indicated that they were going past Mach 1. I think, though, that the pitot-tube-based airspeed indicators of WWII became inaccurate as they approached Mach 1 in ways that were not corrected by the standard correction tables and that the aircraft were thus not actually travelling at Mach 1 or higher.
I think I remember reading that people have done some research that shows that the WWII prop fighters could not have gone faster than Mach 1, even in a vertical dive with full power from 45,000 ft straight down. The airframes and propellers created too much drag at higher speeds for the terminal velocity to get that high.
Airflow over the wings, though (airflow over the top of the wing is faster than true airspeed of the aircraft), and tip speed of the propellors did become supersonic at high enough speeds in dives. The supersonic airflow over wings is the cause of compressibility for WWII fighters and was worse for wings with thick cord (faster air over the top), like the P-38, than for those with thinner cord (like the P-51). Thick-cord wings hit compressibility at lower speeds than thin-cord wings.
