It's crazy to me that once they had this high-performance jet fuel, they also used it as a coolant and as hydraulic fluid.
I guess the main requirement for the latter two purposes is that it doesn't break down at really high temperatures. The jet fuel needs to be stable at high temperatures too (additionally, you need to be able to burn it to make the engine go) so once you put all this research into finding the right jet fuel you have a liquid that will do OK on the other jobs.
Edit: and also it was used for lubrication! Good fuels definitely do not necessarily make good lubricants...it must just be really hard to find anything with the right thermal stability.
> they also used it as a coolant and as hydraulic fluid.
Potentially a much smaller headache than pumping one or two more fluids around inside a jet engine and keeping them from breaking down. The jet fuel only needs to not break down for a single pass through the engine. A closed lube or cooling system would need to not break down for multiple passes (i.e. much longer duration at high temperature).
>it must just be really hard to find anything with the right thermal stability.
A total loss lubrication system doesn't need to be actively cooled (assuming your lubricant input is of suitable temperature) which saves a ton of weight and complexity which is why rocket and jet engines often use the fuel as a lubricant.
The F-1 rocket engine on the first stage of the Saturn V used a similar arrangement, with the fuel also doing double duty as hydraulic fluid, coolant and lubricant.
Many tactical aircraft to this day use their fuel for the same purposes. I know the F-35 uses its fuel as a heat sink. The F-35B variant specifically uses fuel as the hydraulic working fluid (aka "fueldraulics")for much of the work of the 3 bearing swivel nozzle.
I was an inflight-refueling technician in the USAF and there was a variant of the tanker (KC-135T) that had isolated tanks to specifically carry this stuff, for refueling an SR-71. Sadly that was before my time. A neat little factoid tho, I guess.
Wikipedia indicates it was originally KC-135Q with the unique fuel system (which separates the exotic SR-71 fuel payload from the typical fuel to fly the refueling plane). KC-135T was the re-engined variant using modernized engines like the rest of the fleet.
"Manufacturing several hundred thousand gallons of the new fuel required the petroleum byproducts Shell normally used to make its Flit insecticide, causing a nationwide shortage of that product that year."
They used two massive Buick V8s to get the turbines started. They eventually switched to Chevy V8s. Another person commented about fuel leaking, it must have been a sight to watch one start up.
I've read many years ago that in low temperatures, the SR-71 was prone to leaking fuel while in its hangar. But that was not dangerous because JP-7 won't catch flame without TEB.
If ever in Washington D.C. I highly recommend the Udvar-Hazy Center at Dulles airport. There is an SR-71 on display there (along with just about every other important plane in US aviation history) that you can walk right up to. It's surprisingly small IMO.
The fuel was formulated to meet the engineering requirements of a very particular product that was rendered outmoded by developments in satellite and UAV technology.
[+] [-] dmurray|5 years ago|reply
I guess the main requirement for the latter two purposes is that it doesn't break down at really high temperatures. The jet fuel needs to be stable at high temperatures too (additionally, you need to be able to burn it to make the engine go) so once you put all this research into finding the right jet fuel you have a liquid that will do OK on the other jobs.
Edit: and also it was used for lubrication! Good fuels definitely do not necessarily make good lubricants...it must just be really hard to find anything with the right thermal stability.
[+] [-] throwaway0a5e|5 years ago|reply
Potentially a much smaller headache than pumping one or two more fluids around inside a jet engine and keeping them from breaking down. The jet fuel only needs to not break down for a single pass through the engine. A closed lube or cooling system would need to not break down for multiple passes (i.e. much longer duration at high temperature).
>it must just be really hard to find anything with the right thermal stability.
A total loss lubrication system doesn't need to be actively cooled (assuming your lubricant input is of suitable temperature) which saves a ton of weight and complexity which is why rocket and jet engines often use the fuel as a lubricant.
[+] [-] iggldiggl|5 years ago|reply
[+] [-] euler_angles|5 years ago|reply
[+] [-] kube-system|5 years ago|reply
[+] [-] raverbashing|5 years ago|reply
[+] [-] pram|5 years ago|reply
[+] [-] savoytruffle|5 years ago|reply
[+] [-] justin66|5 years ago|reply
[+] [-] oasisbob|5 years ago|reply
According to Wikipedia, FLIT was a product and large consumer-facing brand of Standard Oil, not Shell.
[+] [-] brazzy|5 years ago|reply
I remember reading somewhere that this is a common misconception and that most of the heat is generated not by friction but by air compression.
But that may have been about the Space Shuttle re-entry, which has considerably higher speeds.
[+] [-] wil421|5 years ago|reply
https://youtu.be/JjdyQpEUYzI
[+] [-] dsb5|5 years ago|reply
https://www.youtube.com/watch?v=nFO--wzFfUs
[+] [-] aduitsis|5 years ago|reply
EDIT: oh yes https://theaviationgeekclub.com/the-story-of-the-sr-71-black...
[+] [-] phlipski|5 years ago|reply
https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird
If ever in Washington D.C. I highly recommend the Udvar-Hazy Center at Dulles airport. There is an SR-71 on display there (along with just about every other important plane in US aviation history) that you can walk right up to. It's surprisingly small IMO.
[+] [-] cbm-vic-20|5 years ago|reply
https://oppositelock.kinja.com/favorite-sr-71-story-10791270...
[+] [-] win66|5 years ago|reply
[+] [-] IgorPartola|5 years ago|reply
[+] [-] The_rationalist|5 years ago|reply
[+] [-] scoopertrooper|5 years ago|reply
[+] [-] throwanem|5 years ago|reply