Originally Posted by
Concours77
if inlet air would have melted the machinery, why not the exhaust nozzle?
thanks for responding!
Because the issue is a combination of centrifugal loading in rotating turbomachinery (typically 2/3 of the stress in the blade) and the effect of the temperature. Failure mode of a cooked blade is typically plastic stretching due to the centrifugal load, making contact with the case.
I think the propulsion system was termed turboramjet.
Sorry, my bad, not hypergolic.
From Wikipedia:
Triethylborane was used to ignite the
JP-7 fuel in the
Pratt & Whitney J58 turbojet/
ramjet engines powering the
Lockheed SR-71,
[2] and its predecessor
A-12 OXCART. Triethylborane is suitable for this because of its
pyrophoric properties, especially the fact that it burns with very high temperature. It was chosen as an ignition method for reliability reasons, and in the case of the Blackbird, because the
JP-7 fuel has very low volatility and is difficult to ignite. Conventional ignition plugs posed a high risk of malfunction. It was used to start each engine and to ignite the
afterburners.
[3]