Friday, November 24, 2017

Pratt & Whitney J58 SR-71 engine - Hot!


Would those be Mach Diamonds?

3 comments:

  1. I recall reading 'Popular Mechanics' or some such, that during development, they were having problems with bolt head failures. They backtracked through their records, and discovered that the mechanic's wrenches were chrome plated. Tiny flecks of chrome would flake off during assembly, and then alloy with the bolt head when red hot, changing metal composition and causing the failure.

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    1. Indeed. Chrome tools were nit allowed anywhere near the plane.

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  2. I forget which Blackbird book I read it in but they used one J-58 to direct its exhaust into the intake of test engines to simulate supersonic air moving past the spike. If you look closely at hot J-58's the titanium actually becomes translucent at operating temps.

    The spike was used to protect the turbine blades from supersonic air which would damage the compressor stages. The excess supersonic air was shunted past the compressor stages via six large coffee can sized tubes and fed into the afterburner stage which resulted in the SR-71 getting better fuel mileage at supersonic speeds than at subsonic speeds. The J-58 was the only engine ever designed to operate continuously at full afterburner.

    At mach speeds the pilots main job was to manage this airflow into, through and around the compressors to prevent engine "unstarts". Basically he was managing the position of the supersonic shockwave itself and the J-58 was pretty particular about where she wanted it! Unstarts were bad because they were physically violent and could lead to sympathetic unstarts of the other engine resulting in a very pretty, black rock falling out of the sky at supersonic speed.

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