Matt:

There are 1/4" gaps between some of the surfaces on the one at Wright-Pat. Airframe does indeed expand quite a bit as it heats up, and it does dribble fuel and hydraulic oil some cold (not a huge amount, or it would explode!).

First fly-by-wire, too, IRCC. "necessary" because of the change in length. Note that this is also a problem in high speed fighters (not that they go THAT fast, or so so long), and that the Russians didn't use fly-by-wire in any of their fighters that I know of, certainly not the MIG-23 anyway. Some advantages there. The current US fighters have a bundle of wires several inches across -- a shrapnel splinter in that tube pretty much trashes the aircraft.

Peter

fuel
 

the fuel was made spesily for the sr71 it took a lot of heat to bern



some facts

http://www.sky-flash.com/sr.htm

JP-6, I believe.

Very high boiling point, necessary as it is used to keep the rest of the aircraft cool and as the heat sink for the cabin AC.

The engineering on that plane still amazes me, considering it was almost all done without digital computers!

Peter

just good old Brain power

Actually, slide rules and one of the greatest aircraft design teams that ever existed!

Peter

It is rather interesting to read how the Lockheed Skunk works put that plane together in an incredibly short period of time. Something like that could never be done today in the huge conglomerates.

Large monster organizations never get anything done quickly. The great advantage of the Skunk Works was the fact they were all crammed in together. Everyone knew what everyone else was working on, and you just had to walk out the door and look over the railing to see the assembly guys doing their job. Didn't take long for information to travel around -- they guy doing the wing was right next to the guy working on the engine nacelle or the tail!

Not like GM these days, where you get a "box" to fit your part in. That leads to things like parts installed inside welded frame sections, or needing to pull the engine to remove a bolt.... The guy working on what your part connects to is probably in India or Australia, not the next desk over.


Peter

And, like my Mazda Capella, where you need to take the head off to access the IP bolts, to permit timing adjustments.

Good planning for maintenance activity eh?

The change in length was definitely part of it.

However, the two main reasons for implementation of a stability augmentation system in the SR-71/A-12 was first, to maintain some semblance of control when the ship went into augmented thrust (afterburner) mode and second, maintain control of the ship at cruise in the event of an engine 'unstart.'

When the pilot engaged the afterburners, there was no way to insure that both the 'burners would simultaneously produce the additional thrust. With the wide spacing and power of the J-58 engines, even a momentary assymetrical thrust condition caused by one engine lagging into afterburner could put the ship out of control. On conventional twin-engined jet fighters this isn't a serious issue because the two engines and their thrust lines are relatively close together and a momentary assymetrical thrust condition can be corrected with a small application of the rudder.

At cruise, engine 'unstarts' were common in early days of the J-58. Fuel and engine management was crude at best and coupled with the additional complication of having to control the inlet spike position and nozzle configuration, sometimes the system would loose control and self-inflict what amounted to a Mach2+ compressor stall or, 'unstart' on one of the engines. The resulting assymetric thrust condition when this took place was responsible for the crash of at least one SR-71 early in the program.

Improved stability augmentation and engine control eventually reduced this to a 'minor' inconvenience but even with the SAS, an unstart at cruise would slam the crew's heads into one side of the cockpit.

PW4000 Engine temps
 

I had to get out my book on the engine temps. The PW 4000 is 1225-1350C at takeoff power! That is at the end of the burner can just before the first set of turbine blades. The only way they keep the blades from melting is using a boundary layer of high pressure air coming out of holes through the hollow blade. I've got more info if you want it.