3 ms·

SR-71 Blackbird engines used analog computing

20 points by djmips 4y ago

djmips 4y ago
An interesting overview of the J58 engine used in the SR-71 Blackbird by a Pratt and Whitney engineer on the project.
- egberts1 4y ago
  And transitioned to a program manager, to say the least.
daveslash 4y ago
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.
- kingcoleman 4y ago
  https://www.researchgate.net/figure/Complete-hydraulic-circuit-of-the-DP0-automatic-gearbox_fig9_266055377 https://www.researchgate.net/figure/Complete-hydraulic-circu... Pretty wild huh? Once upon a time the gear shifts in automatic transmissions were handled by a hydraulic "computer".
  - daveslash 4y ago
    Very wild indeed! Thank you for sharing that. Though, I don't even know what I'm looking at ! (*and don't say 'automatic transmission gearbox' :-p ~ I mean to say this is all foreign to me and while I can appreciate it, I certainly don't understand it)
    - kingcoleman 4y ago
      Hydraulic fluid goes brrr, car goes vroom! That's about the extent of my understanding.
- jjk166 4y ago
  It's important to remember that while the SR-71 was introduced in the late 60s, its engine was developed in the 50s, based off a pre-existing design from the 40s. They were actually initially developed for a boat plane.
phibz 4y ago
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.
karmakaze 4y ago
> 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?
- DeadMouseFive 4y ago
  springs
egberts1 4y ago
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.

20 points by djmips 4y ago

djmips 4y ago

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

egberts1 4y ago
And transitioned to a program manager, to say the least.

daveslash 4y ago

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.

kingcoleman 4y ago
https://www.researchgate.net/figure/Complete-hydraulic-circuit-of-the-DP0-automatic-gearbox_fig9_266055377 https://www.researchgate.net/figure/Complete-hydraulic-circu... Pretty wild huh? Once upon a time the gear shifts in automatic transmissions were handled by a hydraulic "computer".
- daveslash 4y ago
  Very wild indeed! Thank you for sharing that. Though, I don't even know what I'm looking at ! (*and don't say 'automatic transmission gearbox' :-p ~ I mean to say this is all foreign to me and while I can appreciate it, I certainly don't understand it)
  - kingcoleman 4y ago
    Hydraulic fluid goes brrr, car goes vroom! That's about the extent of my understanding.
jjk166 4y ago
It's important to remember that while the SR-71 was introduced in the late 60s, its engine was developed in the 50s, based off a pre-existing design from the 40s. They were actually initially developed for a boat plane.

phibz 4y ago

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.

karmakaze 4y ago

> 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?

DeadMouseFive 4y ago
springs

egberts1 4y ago

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.