Restoration is easy.

[Nick]

Hi Nick, I'm not an expert on high velocity mechanics but how do they manage with aircraft props and jet turbine blades?

Just spoke to a pilot friend about this and he said its all very complex It seems that the speed of sound is related more to temperature than pressure - The Newton Laplace equation relates the speed of sound to the density of a gas, and the density is proportional to the temperature, so it seems that Mach 1 is proportional to the square root of the absolute temperature. Turbines & compressors run hot, so although the tips of the blades run at faster than Mach 1 if they were at STP, the air is at elevated temperature so not at STP and all is well... engines for supersonic craft go to great lengths to get the air flowing into the compressor sub-sonic before use - Concord was noted for this.

With standard prop-driven aircraft, supersonic tips are regarded as a "bad thing" - the prop makes a LOT of noise, laminar airflow over the blades is disrupted leading to a big loss in efficiency, and the shock wave can damage the blades, so again, lower revs, higher torque, more blades, dynamic pitch adjustment etc. all matter greatly.

There are planes where this can and does happen, but generally such behaviour is outside the SOA for the aircraft...