F35 variants, which is the most capable version?

Discuss the F-35 Lightning II
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exorcet

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Unread post15 May 2012, 05:18

archeman wrote:So just doing some quick calculations from your table numbers shows what a high price the Navy paid to get that greater control at lower speeds.
* C version gets only 1.66% greater range than the A. That low of a % puts it in the 'statistically insignificant' category. That has always been one of the quotes that attends the C version "has greater range", well not really enough to talk about.
* C version stores 7.6% more fuel than the A. Those big wings sure chew up that 7.6% fuel bonus in a hurry don't they???
* C version weighs 15.8% more than the A. Is this where the max G is going?

Given the above stats I would have thunk that the Navy would have looked into a more complex/larger flaps and leading edge solutions to get their control and landing speed solution. If they succeeded then the other partners may have been able to adopt those solutions instead of having the the one-off C version.


Some of the weight on the C probably comes from strengthening the frame to handle carrier landings and not just the wing. And as already mentioned, if the plane can't land on a carrier it's useless. LM probably did what needed to be done to get the most performance out of the F-35C.

Also, those ranges are requirements I think, and not the actual ranges, which could be higher. There is also payload to consider, which could be nearly 20,000 lbs. That would significantly cut range compared to a lighter payload that is more likely to be carried most of the time.

Using the Breguet range equation on the F-35A carrying 18,000 lbs at Mach .75 at 30,000 ft (standard temp), .886 1/hr TSFC, and L/D = 8; I get a range of 1318 nm. Change the payload to 2500 lbs and it comes out to 1830 nm. Of course, I don't have the info to do an accurate calculation on the F-35, and the equation I'm using is only so accurate, but it should give an idea of how much performance parameters can vary.

For comparison I get 1265/1693 out of the F-35C, assuming it has the same L/D and cruise Mach.
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archeman

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Unread post15 May 2012, 05:34

Some of the weight on the C probably comes from strengthening the frame to handle carrier landings

Yes Exo, good point there.

Can you speak to the reduced max G? Is that just a factor of the weight or is there a higher life expectancy play at work here also?
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Unread post15 May 2012, 05:49

And don't forget the catapulting. The entire airframe spine has to be strong with the nosewheel being especially strong and with twin tyres to handle the catapult forces (which has to cope with steam and the lesser load of EMALS). I have seen several theories about lower G - the USN is OK with that for whatever reason, be it longer life with some structural components less robust than in the F-35A for example to save weight? Obviously the required 'naval' bits are very strong in comparison.

http://www.asdnews.com/news-27850/Vough ... for_LM.htm

Not forgetting the main wheels/oleos are especially strong to deal with the increased no flare descent rate for carrier landings. Thankfully all that has been tested (except hook) successfully. Other threads have that detail.

Some chitchat about drop testing the F-35C here: F-35C drop testing picture

http://www.f-16.net/f-16_forum_viewtopic-t-13899.html
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firstimpulse

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Unread post15 May 2012, 06:11

Just a side question about G-ratings, does the A model's G rating signify an agility advantage over the others in all types of flight? Even at low speed (compared to the C), or put up against the B's ability to VIFF?
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1st503rdsgt

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Unread post15 May 2012, 06:27

firstimpulse wrote:Just a side question about G-ratings, does the A model's G rating signify an agility advantage over the others in all types of flight? Even at low speed (compared to the C), or put up against the B's ability to VIFF?


Who said the F-35B could VIFF?
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firstimpulse

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Unread post15 May 2012, 06:31

It can't? :shock:
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delvo

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Unread post15 May 2012, 09:37

Different range estimates have been listed a few times before. The numbers change depending on how you calculate them, since they are from calculations, not the results of anybody actually flying one until it falls. In other reports about their ranges, the gap between "C" and "A" was larger. So the real difference might be more in favor of "C" than the table posted here looks. I think the range for "C" got cut when the Navy beefed up the amount of fuel to require it to bring back from a mission as a safety margin, which in turn reduces the amount of the total fuel being carried that you're allowed to include as contributing to its official range. Anyway, in addition to drag, another part of the reason why "C" doesn't have even more range than it does is that its landing gear intrude into some of the space that's occupied by fuel tanks in one or both other versions, which counteracts part of the fuel-carrying gains "C" gets from its bigger wings and lack of an internal gun.

Part of the g-force issue with "C" could be the stress on the wings. Being longer/wider, they might experience more force when doing the same maneuvers, especially out toward the tips and away from the roots, and they have those joints partway out instead of a continuous solid structure.

As for "C" making sacrifices in general in order to be able to use an aircraft carrier: yes, it requires some trade-offs for any plane that's going to do it. Getting a plane up to and down from a modern fighter's minimum air speed in a few hundred feet is hard work, so that ability won't just happen to exist in just any design that didn't go out of its way to have it. That's why the Navy and Air Force have different kinds of planes to begin with. If carrier operations could be carried out by entirely conventional planes, then air bases on land and aircraft carriers would have the same kinds of fighters at them.

Why would VIFF ability have been given to "B" but not to "A" and "C"? If one version had it, they'd all have it, or maybe only "A" and "C" would but not "B" because it could interfere with the kind of thrust vectoring that "B" actually needs and has.
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Unread post15 May 2012, 13:15

firstimpulse wrote:It can't? :shock:


It uses a lift fan, not thrust-vectoring nozzles a la Harrier. I don't think the system would work in forward flight. Even if it could, I'm not sure that it would offer significant tactical advantages.
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That_Engine_Guy

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Unread post15 May 2012, 20:56

delvo wrote:
asianviper wrote:So it would seem that the A model would be better for air to air missions as it seems to be quite a bit lighter than the B and C has the internal cannon and is also able to handle up to 9g?
"A" lighter than "B"? This comment confuzzles me.


The A has the 'base' F135-PW-100, the B has the "STOVL" F135-PW-600.

Compare the photos of the engines below, the weight question should be obvious. (Note they are NOT to scale!)

Official weight figures on the respective 'propulsion' systems have not been released, but it is a given the added components add weight.

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-600.jpg
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Unread post15 May 2012, 21:26

Time for some recent LM F-35 specifications.... :-)

06 Feb 2012 from: http://f-35.ca/wp-content/uploads/2012/ ... 6-2012.pdf
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