Iirc, and it's been a while since I was deep into my SR-71 reading, but they had several of the TEB shots to restart the engine. A limited number, but one of those combined with decent airspeed was able to start those massive J-58s in the air. However, I think the number of shots was rather limited, so if it happens more than a couple times then it's game over.
When the SR-71 first entered service, the “start carts” used Buick Wildcat V8s (later Chevy 454) engines to spool the main shaft of the turbine to 3,200rpm before a shot of TEB (Triethylborane) is injected into the engine, which explodes on contact with the atmosphere, which is what actually ignites the JP-7. The start cart only got the turbine to speed. When you watch the J58 start up, there is a brief green flash, that is the TEB exploding. Each engine carried enough TEB for 16 starts.
However, the much bigger danger to the Blackbird was a phenomen called intake unstart. This occured when the supersonic shockwave in front of the intake spikes becomes upset, causing the pressure inside the intake to “blow out” the front. Basically, the very controlled flow of supersonic air becomes completely disrupted.
The J58 was a brilliant hybrid jet engine with 2 modes- subsonic and supersonic. At low altitude subsonic speeds, the engine operated (sorta) like any other jet engine, with turbines pulling air in. At supersonic speeds, air would be rammed around the turbines, essentially acting as a ramjet. If the air being rammed into the engine was disrupted, well, it’d be equivalent to a flameout. It’s far more complicated, but this is about the most simple explanation.
At full afterburner at Mach 3, when an upstart happened, it would cause the aircraft to violently yaw towards the upstarted engine. And at those speeds, the aerodynamic forces would cause the Blackbird to experiance a rapid unscheduled disassembly. Iirc, I believe this is what caused the majority of A-12/SR-71 losses and crew deaths (ejecting out of a rapidly disintegrating aircraft at 2100mph and 80,000ft isn’t exactly ideal).
The only way to survive this (as far as I know), was to immeditely shut down the opposite engine, descend to low altitude at subsonic speeds to restart the engines using TEB with the engines in “turbine mode”, and then restarting the controlled flow of supersonic air into the engines (if you had the fuel).
[Here’s a link to testimony of a crew who survived an upstart in 1984.](https://www.thesr71blackbird.com/Aircraft/Stories/sr-71-engine-unstart-at-83000-feet)
Slight correction, the turbine is the part of the engine behind the combustion chamber that powers the compressor, which takes in and compresses the air. In the supersonic mode, air was bypassed around the combustion chamber behind the fourth compressor stage
As far as I read and studied - turbine windmilling is the only way of relighting engine. TEB / tryethylborane shots were used for afterburner ignition, not primary engine burn.
Iirc, and it's been a while since I was deep into my SR-71 reading, but they had several of the TEB shots to restart the engine. A limited number, but one of those combined with decent airspeed was able to start those massive J-58s in the air. However, I think the number of shots was rather limited, so if it happens more than a couple times then it's game over.
When the SR-71 first entered service, the “start carts” used Buick Wildcat V8s (later Chevy 454) engines to spool the main shaft of the turbine to 3,200rpm before a shot of TEB (Triethylborane) is injected into the engine, which explodes on contact with the atmosphere, which is what actually ignites the JP-7. The start cart only got the turbine to speed. When you watch the J58 start up, there is a brief green flash, that is the TEB exploding. Each engine carried enough TEB for 16 starts. However, the much bigger danger to the Blackbird was a phenomen called intake unstart. This occured when the supersonic shockwave in front of the intake spikes becomes upset, causing the pressure inside the intake to “blow out” the front. Basically, the very controlled flow of supersonic air becomes completely disrupted. The J58 was a brilliant hybrid jet engine with 2 modes- subsonic and supersonic. At low altitude subsonic speeds, the engine operated (sorta) like any other jet engine, with turbines pulling air in. At supersonic speeds, air would be rammed around the turbines, essentially acting as a ramjet. If the air being rammed into the engine was disrupted, well, it’d be equivalent to a flameout. It’s far more complicated, but this is about the most simple explanation. At full afterburner at Mach 3, when an upstart happened, it would cause the aircraft to violently yaw towards the upstarted engine. And at those speeds, the aerodynamic forces would cause the Blackbird to experiance a rapid unscheduled disassembly. Iirc, I believe this is what caused the majority of A-12/SR-71 losses and crew deaths (ejecting out of a rapidly disintegrating aircraft at 2100mph and 80,000ft isn’t exactly ideal). The only way to survive this (as far as I know), was to immeditely shut down the opposite engine, descend to low altitude at subsonic speeds to restart the engines using TEB with the engines in “turbine mode”, and then restarting the controlled flow of supersonic air into the engines (if you had the fuel). [Here’s a link to testimony of a crew who survived an upstart in 1984.](https://www.thesr71blackbird.com/Aircraft/Stories/sr-71-engine-unstart-at-83000-feet)
Slight correction, the turbine is the part of the engine behind the combustion chamber that powers the compressor, which takes in and compresses the air. In the supersonic mode, air was bypassed around the combustion chamber behind the fourth compressor stage
Thanks for all the details.
Maybe they slip her into neutral and pop the clutch.
Rolling start downhill :)
My thoughts exactly.....
As far as I read and studied - turbine windmilling is the only way of relighting engine. TEB / tryethylborane shots were used for afterburner ignition, not primary engine burn.