F-35 Joint Strike Fighter News, Videos and pics Thread

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Re: F-35 Joint Strike Fighter Thread

Harrier didn't use fuel as a heat sink for its avionics . Therefore, Harrier could operate with nearly empty tanks, F-35 apparently cannot .

You gotta be kidding me? So therefore depending on how long it's been flying in accordance to low temperature in the atmosphere it has to return to base for refueling of sort if even if the fuel gauge is half?

Anyway here is another source.

The USAF Has To Re-Paint Its Trucks Because The F-35 Can’t Fly On Warm Fuel

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[Brumby]

Re: F-35 Joint Strike Fighter Thread

You gotta be kidding me? So therefore depending on how long it's been flying in accordance to low temperature in the atmosphere it has to return to base for refueling of sort if even if the fuel gauge is half?

Maybe it uses a combination of liquid and air cooling but on ground and with warm fuel is a unique situation. If not, it is a major screw in design.

 

[Equation]

Re: F-35 Joint Strike Fighter Thread

Maybe it uses a combination of liquid and air cooling but on ground and with warm fuel is a unique situation. If not, it is a major screw in design.

I wonder if the F-22 uses this same fuel as the F-35? If it does, it never been reported to have any problems at all.

 

[thunderchief]

Re: F-35 Joint Strike Fighter Thread

You gotta be kidding me? So therefore depending on how long it's been flying in accordance to low temperature in the atmosphere it has to return to base for refueling of sort if even if the fuel gauge is half?

Well, I'm not kidding you. Heat sinks are relatively simple devices, you certainly have some in your computer . They need to have good thermal conductivity and relatively high specific thermal capacity .

Good thermal conductivity is needed to easily transfer excess heat , in this case from avionics to heat sink and later to surrounding air . Usually electronic devices use metal (copper , aluminum ) directly attached to semiconductors for this purpose ,as metal has good thermal conductivity .

Unfortunately, metals have relatively low specific thermal capacity , and that means they would easily heat up themselves if not cooled . Anyone with broken fan on their computer cooler knows that . To cool your metal heat sink you would usually use air , either by fans or simply by moving . But, heat transfer between metal and air is not so great . Therefore, more expensive electronic devices use liquid coolers and usual medium is water . Water has relatively large specific thermal capacity, so you would need lot of energy (i.e. heat) . Also, thermal conductivity between metal and water is relatively good . Water would dissipate stored energy into surrounding air and everything would be fine .

In case of F-35, you cannot carry large quantities of water to cool down powerful avionics . What you could do is to use aviation fuel instead of water . It is not that good but it suffice . Problem arises when you use up your fuel . If certain amount of energy E1 raises temperature of 1000 liters of fuel by 1K , same amount of energy would raise temperature of 500 liters by 2K etc ...

If F-35 uses up most of its fuel and then turns radar on , it will start to raise its temperature rapidly because all of that excess heat has nowhere to go . And if that happens in warmer climate, temperatures will be initially very high and that is where fun starts ...

 

[thunderchief]

Re: F-35 Joint Strike Fighter Thread

I wonder if the F-22 uses this same fuel as the F-35? If it does, it never been reported to have any problems at all.

F-22 is larger (more place to store and dissipate heat) , I suspect it has somewhat less powerful avionics (in terms of energy) and generally flies higher (air is cooler ) and faster then F-35 . Therefore, it may not need same tricks for cooling down .

 

[kwaigonegin]

Re: F-35 Joint Strike Fighter Thread

Harrier didn't use fuel as a heat sink for its avionics . Therefore, Harrier could operate with nearly empty tanks, F-35 apparently cannot .

This is a very serious matter if true. Can you provide citation? If the F35 is basically useless at say less than 10 or 20% remaining fuel load we would have a lemon on our hands. Even if say 80% has more than adequate range we're still talking significant overhead in terms of weight and performance penalties.

 

[Brumby]

Re: F-35 Joint Strike Fighter Thread

I wonder if the F-22 uses this same fuel as the F-35? If it does, it never been reported to have any problems at all.

Don't think problem is fuel sourced but rather the F-35 is much more avionics centric as compared to F-22 (20 million lines of codes in F-35 vs. I believe 8 million in F-22). As mentioned by Thunderchief, all those heat generated needs to be dissipated. If avionics cooling was anticipated and planned for, the necessary operating scenarios and threshold would be known and solutions build-in. Maybe warm fuel is unique and doesn't necessarily point to a design misstep.

 

[93fiM5]

Re: F-35 Joint Strike Fighter Thread

Guys the tanks don't have to be painted white, the media is sensationalizing this issue.

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Also I'm pretty sure the issue is due to the bravo units V/STOL requirements, not avionics. Would be nice to find out the reason for the temperature threshold.

-Greg

 

[Air Force Brat]

Re: F-35 Joint Strike Fighter Thread

is it a hoax? it all seems to come from one source ...

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says

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but is it a credible source?

but now I found at the webpage of Luke AFB this:

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You guys really ought to check out Giuseppe Macri's twitter page,,,,,, yes he is a world renowned authority on the F-35-- actually his twitter page is full of lots of other really highly technical data, and Chief Thundercloud likes to "rain" on the F-35, yes the USAF did repaint 4 fuel trucks white to keep the fuel cooler, it does get up to 110 at Luke AFB, just like Texas, you can fry an egg on a sidewalk or a hot ramp... so come on guys, keep your shirts on, without a hat, it would fry your old "noggins" as well...

I think you boys need to take a "chill pill", if you've ever been around JP, it is a light, very light and highly refined light oil, basically kerosene. As you heat it, it becomes much less dense, and with far less ability to absorb heat, in extreme arctic conditions it must be preheated in order to burn properly, without treatment, it will "grow" things and gum up your injectors... and really guys, I mean really, they are painting the fuel trucks with reflective paint to keep the sunlight from being absorbed by the steel tanks of the fuel truck... I know none of you have ever owned a black car??? right, ask Jeff Head, he lived in Texas?

So, I've been around aircraft that won't start, or even fire on ONE cylinder after sitting on a HOT RAMP, the fuel in the injectors will vaporize, causing a vapor lock, this gentlemen, is an operational consideration, not design failure. To kool the F-35s systems with fuel that you will be carrying anyway, optimizes performance of equipment, and yes everything on an F-35 generates HEAT, and lots of it???

and to top it off, if you intended to operate your aircraft from a tropical forward area, you would park it all under camouflage netting??? I mean come on guys, use your noodles here.

You guys are going to tell me about "big-foot" sightings next, aren't you????

 

[Air Force Brat]

Re: F-35 Joint Strike Fighter Thread

F-22 is larger (more place to store and dissipate heat) , I suspect it has somewhat less powerful avionics (in terms of energy) and generally flies higher (air is cooler ) and faster then F-35 . Therefore, it may not need same tricks for cooling down .

Actually Chief, the F-22 is just plain KOOL dude, she is too KOOL for school! I guess that KOOLNESS just saturates her inside and out?