Flight Question Skin temperature at mach 0.8 (xr-2)

[n72.75]

T0/T for mach 0.8 is 1.128.

That would mean the ambient temperature would have to be ~280C

 

[Hlynkacg]

No.

You would need a much higher EAS for compensating for higher air density. For 300°C, which is the skin temperature of a SR-71 at 90,000 ft (0.05 atm) and Mach 3.2 (473 EAS), you would need about (Different materials and air temperature ignored) 690 EAS at sea-level, or Mach 1.05.

So, not just near-supersonic, but actually almost at the limit speed possible for a F/A-18 at sea-level with clean config.

I'l admit that I'm not up on the math in this particular case but I do know that the thermal protection strips on the leading edges of our helicopter's rotor blades could get up to 250 C durring normal operations.

(A crew-mate of mine had the misfortune to illustrate this fact rather graphically)

I also know that there are numerous cautions/warnings in the F/A-18 NATOPS (Operations/Flight Manual) about temperature tolerances and low-altitude transonic flight. It may not be 300 C but it is certainly in that ball park.