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Bash the F-35 thred.


Belesarius

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How short-legged is the F-35?  Because I just noticed something surprising:

 

Per the USAF's page on the F-22, the raptor has 18,000 lbs of internal fuel.

 

Per LockMart's page on the JSF, all variants save the B carry more than that.
 

So either the JSF isn't really as short-ranged as we've been led to believe, or the F-22 has insanely short legs.

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How short-legged is the F-35?  Because I just noticed something surprising:

 

Per the USAF's page on the F-22, the raptor has 18,000 lbs of internal fuel.

 

Per LockMart's page on the JSF, all variants save the B carry more than that.

 

So either the JSF isn't really as short-ranged as we've been led to believe, or the F-22 has insanely short legs.

 

2214.jpg

 

 

the F-22 has insanely short legs

 

GeEuVIM.png

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How short-legged is the F-35?  Because I just noticed something surprising:

 

Per the USAF's page on the F-22, the raptor has 18,000 lbs of internal fuel.

 

Per LockMart's page on the JSF, all variants save the B carry more than that.

 

So either the JSF isn't really as short-ranged as we've been led to believe, or the F-22 has insanely short legs.

 

This wouldn't be the first time that the military deliberately leaked incorrect information about a program as a misdirect regarding its capabilities.

Hell, they did that for M855A1 of all things.

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This wouldn't be the first time that the military deliberately leaked incorrect information about a program as a misdirect regarding its capabilities.

Hell, they did that for M855A1 of all things.

 

That's one possible explanation.  My immediate guess was that the F-22A was designed the same was as the F-15A was.

 

The F-15C carries about 760 liters more fuel than does the F-15A; not because the F-15A was designed haphazardly or anything, but because a bunch of spaces were left deliberately open in case new avionics needed to be fitted.

 

F-22A has, IIRC, provisions for future installation of sideways-looking cheek radar arrays and IRST.  It may have some empty space elsewhere that was deliberately not filled with fuel tanks for future contingencies.

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NUMBERS AND MATH INCOMING

 

 

Per this official USAF maintenance book on the raptor, it carries 36,515 pounds of fuel when carrying a full internal load and 4x 2503 liter external tanks.  Based on the density of jet fuel that's about 17,000 pounds of fuel in the external tanks, so the raptor is carrying 19,500 pounds of fuel or so internally.  That's a little bit more than quoted above, but only a little more than the F-35A and actually less than the F-35C.

 

(Unless the Maskirovka extends to official maintenance books, in which case, hats off)

 

Now, how does this compare to other fighters?

 

These numbers give the raptor a substantially higher fuel fraction than many idiot reformer detractors would claim.  Per Lockheed Martin's website it weighs 43,340 lbs empty, so the F-22 has a respectable fuel fraction of .31.  That's about what the old time fighter mafia white papers from the '80s consider ideal.  Considering that the internal space for fuel is competing with the internal space for the weapons bays, this is pretty impressive, and suggests that there aren't huge tracts of unused space in the raptor.  Most contemporary fighters manage around .3, so the raptor is actually pretty middle of the road on fuel fraction.  It's a bit worse than a superhornet, but a bit better than a eurofighter, a bit better than a MiG-35, and way better than a MiG-29 or Gripen (Note that this post gives a lower FF for the raptor, but not the insanely low .27 that reformists have parroted.  He probably used the AF's official fuel figures, which appear to be rounded down somewhat).  Again, considering that it has internal bays eating up so much of the available internal volume, this is a pretty impressive engineering accomplishment.

 

Given the above, the raptor might have somewhat longer legs than average because it cruises faster than most fighters.  According to everything I've seen, the raptor's combat radius drops significantly if it supercruises for much of the mission.  However, even in subsonic cruise the raptor is probably faster than other fighters, and its most economic speed may be high transonic, while other fighters (especially with weapons on) cruise at low transonic or even high subsonic.

 

Also, the F-35A has a fuel fraction of .39 according to the official figures, which matches or betters most flanker variants!  In terms of stuffing fuel into an airframe, the F-35 is absolutely at the top of the heap for fighters. This is completely insane, because the main bays on the F-35 are about as big as those on the F-22 (F-35 lacks sidebays, however)!

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Putting it another way, the F-35C carries about 23% more internal fuel than a freaking tomcat.  That's not relative to its mass or anything; it actually carries that much more fuel.

 

When the JSF gets the block 2 F135 engine, which is supposed to deliver 7-10% more thrust and 5-7% less fuel burn (their words, not mine.  Not sure if that's absolute fuel consumption or TSFC), then it's going to be respectably long-ranged.

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Do you think the lack of a of hydraulics system has much to do with that freed up space? Lost was mentioning on TS that it's probably a volume vs weight deal... but, how much space and weight does having the actuators save?  Not to mention the lack of having hydraulic fluid around to deal with as a hazard.

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I'd assume that any modern fighter aircraft is probably more volume limited than weight limited (because of all the avionics and shit that gets crammed in there), but I could be wrong. Either way, the saving on the hydraulic system could definitely be part of the explanation for the high fuel fraction.

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Do you think the lack of a of hydraulics system has much to do with that freed up space? Lost was mentioning on TS that it's probably a volume vs weight deal... but, how much space and weight does having the actuators save?  Not to mention the lack of having hydraulic fluid around to deal with as a hazard.

 

It probably has something to do with it.  As I understand it, the design benefits of the F-35's EHA are largely indirect.  That is, the system on its own really isn't much smaller or lighter than conventional actuators.

 

But the system can be made much thinner, so critical areas on the wing and tails and whatnot can be made more streamlined.  EHA also generates less waste heat than conventional hydraulics, and since the fuel is used as a heat sink, perhaps more of it can be safely consumed (unusable fuel is accounted as dry mass).

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F-35A internal fuel tanks:

 

kvcdeA5.gif

 

 

I wonder what the best way to make a longer-ranged version of the F-35 would be?  There definitely would be a market for that sort of thing.  Canada and Australia, because they have enormous airspace they need to patrol, and Israel, because they want a strike fighter that can nail targets in Iran, all come to mind.

 

Just stretching out the fuselage seems like a more efficient option than enlarging the wings.

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