‘During that pass we had “13 fireballs” come out of the SR-71’s exhaust. It looked beautiful, and people wanted to know if it could be done again,’ former Blackbird RSO, Lt. Col. Doug Soifer.
Former Blackbird RSO, Lt. Col. Doug Soifer, tells about the accidental making of this unique SR-71 picture in Richard H. Graham’s book SR-71 Revealed The Inside Story.
‘On our very first TDY to Mildenhall, Mike Smith [the pilot] and I were lucky enough to be there for Air Fete—the big annual air show at Mildenhall. We got to fly the first day and thought we did a good job. During the 20 minute sortie we had a real hard kick during one pass when we went to afterburner and pulled up tight. We didn’t think much about it until we landed and were overwhelmed by people as we stepped off the jet and asked us what we did. We had no idea what they were talking about until someone brought over his camcorder and showed us the tape.
‘During that pass we had “13 fireballs” come out of the plane’s exhaust. It looked beautiful, and people wanted to know if it could be done again. They used the picture of us with the flames coming out for the next year’s Air Fete poster. Mike and I became known as the “Fireball Twins.” The maintenance people figured it was the TEB [triethylborane] shooting out of its container and igniting the JP-7. With that start, we had an exciting six weeks in England.’
The SR-71 burned JP-7 fuel. 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. In an emergency situation, crews were authorized to refuel with JP-4 or JP-5, however, this limited the aircraft to Mach 1.5. These emergency fuels were to be used only if the crew was low on fuel and had to use any tanker he could find to avoid the loss of the aircraft.
To ignite the JP-7 for engine start, and to light the afterburner section, a liquid chemical ignition system was used. Talk about “unique!” The liquid chemical, triethylborane (TEB), had the physical property of exploding when exposed to air. Mounted on each engine was a sealed tank, inerted with nitrogen gas and filled by maintenance with 600cc of TEB prior to each flight. During engine start, rising fuel pressure in the fuel control signaled the ignition system that a metered amount of TEB could be injected into the engine combustion section, after the pilot moved the throttle from cut-off to the idle position. Preceded slightly by fuel, the TEB exploded and ignited the JP-7. Anyone watching an engine start from behind the aircraft could see the tell-tale green flash of the TEB exploding, igniting the engine.
Each time a throttle was lifted up and moved forward into the afterburner range, another metered shot of TEB would light the AB fuel. Each engine’s tank contained enough TEB for at least 16 metered shots to light either the engine or afterburners. Located on the throttle quadrant were TEB remaining counters for each throttle, reset to 16 by maintenance or crews, and mechanically clicked down a number every time the throttle was moved to start the engine or the AB was lit. The AB’s lit hard and rarely together. In the event you ran out of TEB, or had a leaking tank, the afterburner could be lit by a catalytic ignitor. The catalytic ignitors are made up of a ceramic disk and two sets of pure platinum screening disks. When the turbine gets hot, the platinum glows and allows afterburner fuel to light off. Since the SR-71 cruised in AB, its AB throttle range was relatively large, allowing for vernier control at all speeds.
The aircraft performance charts provided data for “minimum,” “mid-range,” and “maximum” afterburner throttle positions.
Photo credit: US Gov Employee via Wikipedia