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The SR-71 Blackbird
In the 1960’s, the US Air Force (USAF) developed the SR-71 Blackbird, a plane that could travel more than 3 times as fast as the sound produced by its own engines.
Throughout its nearly 24-year career, the SR-71 spy plane remained the world’s fastest and highest-flying operational aircraft. Flying at Mach 3+ from 80,000 feet, it could survey 100,000 square miles of Earth’s surface per hour. And in the off chance an enemy tried to shoot it down with a missile, all the Blackbird had to do was speed up and outrun it.
JP-7
The SR-71’s engineering was so cutting edge that even the tools to build the SR-71 needed to be designed from scratch.
In fact, given that the Blackbird became so hot because it cruised at a speed of Mach 3.2 conventional jet fuel could not be used in it. As told by former SR-71 pilot Richard H. Graham in his book SR-71 Revealed The Inside Story, Shell produced a special blend of fuel called JP-7, a one-of-a-kind fuel that used an additive to raise its flash point so the fuel would not break down at extreme temperatures.
SR-71 Blackbird needed TEB (Triethylborane) to light its engines and afterburners
Graham explains;
‘The high flashpoint brings up another problem. Most jet engines use igniter plugs, nothing more than a very hot spark plug, if you will. Using these igniter plugs they used with the JP-7 and just drowns it out, it won’t ignite. Kelly [Johnson] put his engineers to work, and he said, ‘OK, gentlemen, how are we going to start this?’ They came up with a very unique way. Triethylborane – TEB for short.
‘Each engine has a one-and-a-quarter pint. If I had it in a squirt gun and I squirted it into the atmosphere, it would go Kaboom! – it explodes with contact with the atmosphere. And that’s how we started the engines. As the engines rotate, at the right time, it sprays this amount of TEB into the turbine section, which goes kaboom, which in turn lights the engine. When you take the throttles up into the afterburner, it puts this metered amount of TEB in that lights up the JP-7. You get 16 shots for each engine.’
TEB was the most dangerous material after fissionable nuclear material
Mounted on each engine was a sealed tank, inerted with nitrogen gas and filled by maintenance with 600cc of TEB prior to each flight.
Former SR-71 Blackbird pilot David Peters adds: ‘An interesting note to this is the transport of it. If we landed away, servicing had to be hauled to our location. The NTSB lists TEB as the following most dangerous material, one step below fissionable nuclear material. The folks that handled this stuff were highly trained and good.’
How to light SR-71 Blackbird afterburners without Triethylborane
At this point, one may ask if there was a way to light the Blackbird’s afterburners if TEB wasn’t available.
Even though according to Peters in the 24 years the SR 71 flew, it never ran out of TEB, but there was a plan just in case.
John Olp, an SR-71 Mechanic from 1975-1985 at Beale AFB, explains;
‘The J58 engine had a unique way of lighting the afterburners if TEB wasn’t available for whatever reason.
‘Inserted into three rings of the flame holders were six catalytic ignitors. If TEB wasn’t available, the engines could be manually over-trimmed to increase the exhaust temperature and superheat the ignitors. When the throttles were advanced into afterburner, the glowing catalytic ignitors would light off the fuel, albeit somewhat harshly!
‘The catalytic ignitors were in place as a backup if TEB wasn’t available. There was a manual up-trim switch in the cockpit to control engine EGT. It was a hard light off if used, but was an option!’
Olp concludes;
‘Overtemping the engine would only be momentary to allow the afterburner light, probably not enough to cause any damage to the engines. That’s why the manual up-trim switches were available.’
Be sure to check out Linda Sheffield Miller (Col Richard (Butch) Sheffield’s daughter, Col. Sheffield was an SR-71 Reconnaissance Systems Officer) Twitter Page Habubrats SR-71 and Facebook Page Born into the Wilde Blue Yonder for awesome Blackbird’s photos and stories.
Photo credit: TSgt. Jose Lopez / U.S. Air Force
