What the F1 engine and the J-58 had in common: both were initially started with tetra-ethyl borane, TEB. A hypergolic fuel that ignites just by being exposed to oxygen.
The J-58 needed it because the Blackbird's fuel was notoriously inflammable. It had to have it on startup, and when bringing in the afterburners. on the throttle quadrant was a counter. It started at 50, and counted down. This was how many TEB shots the pilot had available. When it go to zero, if the engines flamed out (and they did, all too often!) the pilot had to figure out where to set her down because that was it. Even if they had full tanks of fuel, there was no way to restart the engines.
The F1 needed it because it had to ignite RP-1, basically Kerosene, super purified, with some additives, and liquid oxygen. The initial flow rate was measured in tons per minute and they had only one chance to light those engines up. Had to be done at the exact right time, in the right sequence*, or everybody went home much earlier than expected. TEB is such hypergolically nasty stuff that it would not fail to start the engine, even with two or three or four other engines right next to you, blasting away like crazy. It was literally the spark that could not fail.
*The five engines did not start at the same time, each was brought up in very specific order, starting with the middle, then going around the outside. Had to be started at the right time, not too early or late, and you can't let the engine next to you belching out 700 tons of power blow out the spark of igniting the next engine in the sequence.
The J-58 needed it because the Blackbird's fuel was notoriously inflammable. It had to have it on startup, and when bringing in the afterburners. on the throttle quadrant was a counter. It started at 50, and counted down. This was how many TEB shots the pilot had available. When it go to zero, if the engines flamed out (and they did, all too often!) the pilot had to figure out where to set her down because that was it. Even if they had full tanks of fuel, there was no way to restart the engines.
The F1 needed it because it had to ignite RP-1, basically Kerosene, super purified, with some additives, and liquid oxygen. The initial flow rate was measured in tons per minute and they had only one chance to light those engines up. Had to be done at the exact right time, in the right sequence*, or everybody went home much earlier than expected. TEB is such hypergolically nasty stuff that it would not fail to start the engine, even with two or three or four other engines right next to you, blasting away like crazy. It was literally the spark that could not fail.
*The five engines did not start at the same time, each was brought up in very specific order, starting with the middle, then going around the outside. Had to be started at the right time, not too early or late, and you can't let the engine next to you belching out 700 tons of power blow out the spark of igniting the next engine in the sequence.
