From a presentation at an EAA Chapter 1000 meeting (at Muroc, aka Edwards AFB). Feel free to mentally sub in A-12 wherever you feel like it, since this applies to both CIA and Air Force examples. This isn't very well organized, but hey.


The SR-71 was capable of accelerating for longer than any other vehicle at max power. It took 20 minutes and 250 miles to reach 3.2M. Even the Space Shuttle only takes 8 minutes. Calibrated airspeed at 3.2M was about 350 kts, although the true airspeed would be about 1820 kts.

Cabin air comes in at -40 degrees, but the cabin still gets hot. The U-2 has a heater for its tube food, but SR-71 crews just held their dinners against the 300 degree canopies for a minute or two.

Typically, the most challenging part of the mission was finding the tankers (pre-GPS, remember) without overshooting hundreds of miles to either side or in front. However, single engine approaches ( normal approach speed 175 kts, landing at 155 kts) were exceptionally difficult, requiring full rudder and 5-10 deg of bank. The drag chute was critical for stopping, and if it failed (it happened, due to door problems, which usually melted the chute), you could count of very hot brakes afterwards. The NASA guys copied the Shuttle's chute from the SR-71.

The SR-71 weighed about 60,000 lbs, but carried 80,000 lbs of fuel and 2,000 lbs of cameras. Thus, it was fairly fragile, and was limited to 2.5G and 30 degree banked turns. It was actually a very lightweight airplane for its size.

It was standard ops to sweep the runway before every flight, because debris and tires inflated with 450 psi of nitrogen just don't mix.

The J-58 engine is not a turbo-ramjet. At high speeds the air does not bypass the core (it always runs). However, ironically, for cooling purposes, air is diverted around the core and directly into the turbine, which can explain the confusion. The SR-71 never operates as a ramjet.

The SR-71's afterburner is unique because it is designed to run continuously This required gold plating for the oil coolers, lines, etc, since gold has just about the best thermal conduction properties of anything, and the heat must be radiated away.

The fuel tanks were never intended to leak. There was no sealant available that could do the job and contend with 300 degree fuel. The SR-71 does not seal up from heat expansion during flight, but a 10lb/hr fuel leak doesn't mean much when you're burning 60,000lb/hr.

The most complex part of the aircraft and the most masterful piece of engineering were the inlets. (There's a diagram that goes along with this that I can't show to explain the 5 different flight regimes).

Engine unstart. Go faster than 3.2 Mach, and before you burn up, you'll have an engine unstart, where the airflow in the inlet reverses (of course, this didn't just happen above 3.2M). Everything was optimized for 3.2M, and at that speed the inlet cone has the shock wave right at the very lip of the inlet, and is all the way in at the limit of its travel (the smallest opening). The way to remember which engine unstarted first (because when one goes, the other gets disturbed and you have a sympathetic unstart from it too) is to recall which side of the canopy your helmet smacked first.

JP-7 fuel cannot be re-ignited in the air. The SR-71 carried about 16 starts worth of TEB (TriEthylBorane) for each engine. TEB explodes upon contact with air, and thusly is an excellent ignition agent for either the core burner of the afterburner (so it takes at least 2 shots to get an engine going again). The real limitation for the SR-71's flight duration was the TEB capacity, followed by pilot endurance.

Starting an engine on the ground used either four -60 air carts manifolded together, or a special cart that had two 427 Chevy Hemis on it that manually spun the core to 1000 rpm.