SR-71 Blackbird engines used analog computing

Wow.... not just any ol' analog computer.... but a computer based off hydraulics!

When I think "analog computer", I think of something that's still an electrical circuit, but using op-amps instead of transistors. Hydraulics, wow - did not see that coming from the title.

That would explain why I couldn’t find any 400+ cubic inch Buick V8 engines back then. Had a blown piston. Not a total loss for the engine block. I had just preferred to do a swap out then, me being a weekend mechanic and all.

Had to toss the car then … to the junkyard, of which they probably bought it too and probably did in-house engine rebuildings.

We can probably safely surmise that those start cart guys transitioned into stock car racing once their military stint was up.

One of my college professors worked on long range ship gun munitions in the late 70s that were steerable through analog computers. He described the spinning of the round was used to drive an oil pump. Reservoirs around the circumference contained oil which could be moved from one side to another. As the round spun the oil was moved back and forth to change the center of mass, steering the round in flight. All controlled by a radio connection back to the ship. Very cool stuff.

An interesting overview of the J58 engine used in the SR-71 Blackbird by a Pratt and Whitney engineer on the project.

> This engine literally grows 6" in length when it's at cruise. And 2.5" in diameter. So how do you design to take care of that?