Posted on 09/16/2016 3:05:10 PM PDT by Chode
The F-35 uses the fuel in the tanks to cool the avionics. Because of this, the Air Force has had to build special shade canopies for their F-35s and to paint their fuel trucks white, in hopes of keeping the fuel temperatures low.
I'm not sure what happens when the aircraft goes bingo fuel. I guess you have to shut down the radar and mission computers.
SR-71 used fuel for heat sink as well as for hydraulic fluid.
Yeah, you wouldn't want the electronics to be further damaged by crashing into the ground while in the powered-up state.
the readiness of the f35, like my death, is greatly over-exaggerated.
“SR-71 used fuel for heat sink as well as for hydraulic fluid.”
Not sure what SteelyTom’s source could have been for this information.
The SR-71 flight manual states (on page 1-86) that the aircraft had four hydraulic systems and states required fill levels. No mention is made of any use of fuel, except as a heat sink for hot hydraulic fluid.
Fuel would make a poor hydraulic fluid: insufficient lubricating qualities, and probably poor compressibility ratio as well.
Using onboard fuel as a heat sink for avionics is a relatively mature technology in use since the 1950s. I vaguely recall that it was used on the B-58 and XB-70, but have no reference at present. The B-1B has used fuel to cool avionics for decades with no incidents.
Fuel over-temperature problems only arise when ground operations last longer than planned, or if malfunctions occur. During flight, fuel flow is always high enough to avoid excessive temperature increases. And in some designs heat-exchanger systems cool the fuel by dumping the waste heat into the external air (heat-exchangers of that sort don’t receive sufficient airflow unless the aircraft is flying).
If the F-35 fuel state falls so low that the avionics heat-exchangers no longer function, the problems have become more urgent and more immediate than over-temp avionics. Difficult as it is for many freepers to accept, designers and engineers do devote some thought to these contingencies beforehand.
It’s probably the J-8 fuel recipe. That stuff is nasty.
— SR-71A Flight Manual, Section I, page 4
JP-7 is a mixture composed primarily of hydrocarbons, including alkanes, cycloalkanes, alkylbenzenes, indanes/tetralins, and naphthalenes, with addition of fluorocarbons to increase its lubricant properties, an oxidizing agent to make it burn better, and a cesium containing compound known as A-50, which aided in disguising the radar and infrared signatures of the exhaust plume.
— Wikipedia page on SR-71
Both references above were taken from the Wikipedia page on JP-7, the very specialized fuel that powered the SR-71.
I erred in my recollection to this extent: my memory was that JP-7 was used in the entire SR-71 hydraulic system, when in fact it was used in the engine hydraulic system. Thank you for correcting me on that.
The Free Republic audience is remarkably well informed, as many others have remarked.
And for their next impression of a defense force all F-35s will be swept into the dustbin of history as a multibillion dollar nearly two decade long failed project.
It isn;’t the troops. Iti s the leadership.
That's why, if you want your fuel pump to last a long time, you keep the fuel level above 1/4 and preferably above 1/2.
This is a good idea anyway, because should anything from a small, local SHTF event happen, or a major SHTF, at least you have fuel.
“...The fuel is not only the source of energy but is also used in the engine hydraulic system. ...
... I erred in my recollection to this extent: my memory was that JP-7 was used in the entire SR-71 hydraulic system, when in fact it was used in the engine hydraulic system. Thank you for correcting me on that. ...”
Many thanks to Steely Tom for such a courteous and succinct reply.
Glad to defer to him on SR-71 powerplant and fuel system details. My own experience was limited to avionics: hydraulic and fuel systems were involved only occasionally, and superficially.
Hydraulic systems must withstand a broad range of ambient conditions while still functioning. The SR-71 may have faced the greatest range of conditions of any aircraft USAF ever operated.
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