
JP-7 - win66
https://en.wikipedia.org/wiki/JP-7
======
dmurray
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.

~~~
throwaway0a5e
> 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.

~~~
masklinn
FWIW JP-7 was not the _only_ hydraulic fluid, it was only used as hydraulic
fluid in a few places where that was convenient, or possibly where they'd have
needed a different hydraulic fluid due to the temperature.

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pram
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.

~~~
savoytruffle
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.

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justin66
"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."

~~~
oasisbob
Can anyone verify this claim? It sounds too good to be true.

According to Wikipedia, FLIT was a product and large consumer-facing brand of
Standard Oil, not Shell.

~~~
refurb
I can’t verify that exact claim, but as a chemist, it wouldn’t be surprising.
Pesticides are mostly organic (carbon containing) compounds and oil is often
used as feedstock.

So I could see some key starting material for the pesticide being diverted to
make a fuel component.

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brazzy
> However, very high skin temperatures are generated at this speed due to
> friction with the air.

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.

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wil421
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.

[https://youtu.be/JjdyQpEUYzI](https://youtu.be/JjdyQpEUYzI)

~~~
dsb5
About 2:42 in this video you can hear the side by side V8's revving up and
then the J58's whirl.

[https://www.youtube.com/watch?v=nFO--
wzFfUs](https://www.youtube.com/watch?v=nFO--wzFfUs)

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aduitsis
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.

EDIT: oh yes [https://theaviationgeekclub.com/the-story-of-the-
sr-71-black...](https://theaviationgeekclub.com/the-story-of-the-
sr-71-blackbird-that-slid-on-jp7-fuel-residue-while-taxing-into-kadena-
hangar/)

~~~
phlipski
The SR-71 fuel tanks didn't fully seal until the plane was at cruising speed.
The heat on the airframe tightened up the tanks.

[https://en.wikipedia.org/wiki/Lockheed_SR-71_Blackbird](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.

~~~
0xffff2
Haven't seen the one in DC, but I've been within arms reach of one of the old
NASA SR-71's that's on display (not accessible to the public unfortunately)
several times. "Small" is just about the last word I would have ever used to
describe it.

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IgorPartola
Yeah but how does it compare to Skinny Fuel?

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The_rationalist
So this state of the art technology is no longer used for newer jets?

~~~
scoopertrooper
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.

