great white
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The story: synthetics started in the aviation industry, and not because they are/were any better. They don't burn! The theory was that crashing a plane full Of synthetics as aposed to castor oils is much less of a flame infested scenario. It took them three years to meet "MilSpec" 5606 with a synthetic oil. It took that long to make a synthetic come close to a castor oil for performance.
Actually, synthetic oil did not start in aviation. Synthetic oil was "created" in the late 20's by Germany to deal with their shortage of oil stocks "in country" and it was used in vehicles fro everything from fuel to lubricants: http://www.caer.uky.edu/energeia/PDF/vol12_5.pdf
The World Wars kicked it's production into high gear, especially when Germany was "cut off" from the oil field it was "accessing" in the south.
5606 is hydraulic oil. It is used in everything from oleos and struts to brake systems and hydraulic rams in systems and flight controls. Mil-H-5606, Mil-PRF-5606 and Nato H-515. They're all mineral oil based. H-5606 isn't really used in military avaiation any more. We've switched to PRF-5606, which is a higher "grade".
The 5606 "family" is fire resistant, not fire proof. Skydrol is more so, but that's dirty, deadly, toxic stuff. Carcinogenic, heavily carcinogenic. I've lost a couple friends to it that worked with it on the Boeing 707. Well, cancer where they got hit with it. Employer denied it was the cause.
And yes: 5606 definitely does burn. It burns rather well in a crash: http://www.skybrary.aero/index.php/Hydraulic_Fluid_as_a_Fire_Source
So does the F34/JP8 and the 23699 engine oils. So does 555 gearbox oil and etc.....
They all burn.
Quite spectacularly actually.
It's one of our biggest fear in a crash, other than the sudden stop that is....
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