> different fuel then any other military plane, I'm not sure if it was because > of high flight temps or the ambient temps and lack of oxygen at their > cruising altitude.
Well, it was lots of things. But a major one was to stop the fuel boiling away at the operating temperatures; the fuel was also used as refrigerant fluid to keep the wings cool. (pushing air out of the way at Mach 3 heats the leading edge of the wings quite significantly). The whole business of building an engine that works at those speeds is pretty arcane, anyway. The engine gets reconfigured in a big way to adapt to the differences in airflow. More than that I know not, although I'm sure there are several references available on the net.
