Forum: F-35 Lightning II

Is it due to space, weight, or both? I've read that the internal bays' shape & size on version B were to be kept the same as on A & C, and that a set of SDBs can fit in there, either of which which would mean the limit excluding 2000-pound JDAMs has to be weight, since those (or at least the smaller type) would fit in such a space. But I've also read that a set of SDBs has to be missing one bomb in order to be put inside, which indicates that the issue must be space, and contradicts the "same as A & C" thing.

What makes me wonder is that, although the difference is always described in terms of what types of JDAM it can carry, it has implications for other kinds of weapons as well, which don't get mentioned. A space restriction limiting SDBs to three instead of four could also rule out JSM and/or JSOW, which are significantly longer than any JDAM or two SDBs, with fins sticking out in the back (and probably wings still protruding even when folded, on JSM, which is shorter but has bigger tail fins)... and while a weight restriction somewhere between the weights of "1000-pound" and "2000-pound" JDAMs certainly lets JSM in, since it's lighter than the former, it might exclude JSOW, which is slightly heavier.

My best guess (because it's what creates the fewest contradictions between different things I've read) is that the restriction for F-35B is a combination of a weight issue (which affects the heavier JDAMs) and a space issue (which affects the fourth SDB). But that could mean that either JSM or JSOW could be ruled out, for more than one possible reason apiece... or they might both be fine... yet I haven't seen anybody saying whether they are or not.

But then, exactly what is the weight limit? And exactly how much did the space get snipped, and where, and what does B have there instead that A and C don't? (Are there numbers for this or illustrations of it?) Since the idea of leaving the bays the same was ever even considered, it can't be the lift system that's intruding, so my guess is just fuel tanks to alleviate version B's loss of fuel capacity elsewhere...

F-16.net Sponsor

SWAT reshaped the bay in the F-35B in order to save weight. They accomplished this by not having to provide a weapons mount that needed to be stressed to 7 gs and 2000lbs, but 1000lbs instead. A bru-61 (SDB carrier) and an AMRAAM, but not a JSOW (not sure about JSM) can still fit.

Last edited by aaam on Oct 31, 2011 - 08:20 PM; edited 2 times in total

Something to keep in mind is that at first only the C was to have the larger bay. Then it was found early on that the larger bay could also be put in the A with minimum effect on that version's performance. Then it was decided to put the larger bay on the B, not so much because the Marines needed it but in the interests of commonality and a potential lowering of overall program costs. That didn't work out for weight reasons, so the B is back to the bay it originally was supposed to have all along. Keep in mind that for the Marines' mission, the B is going to be flying with external ordnance most of the time anyway.

http://www.youtube.com/watch?v=RQ5gmZ74YBY

aaam wrote:

Keep in mind that for the Marines' mission, the B is going to be flying with external ordnance most of the time anyway.

Not necessarily. Unless they need a bomb truck they'll keep 'em mostly clean. The reduction in drag index provides all kinds of benefits.

[quote="quicksilver.. Unless they need a bomb truck....[/quote]

The tactics for the "Bee" are greatly varied. Supersonic, stealth, AESA, mission system with internal weapons bay makes it a natural for an area HICAP. But, in the bombtruck mode with STOVL and forward basing plus that HICAP stuff, it becomes a very awesome CAS platform with a big hammer, not mention any of the ISR tatics. Not Worthy

There is also the issue of "bring-back" weight. The -B will not be able to RTB with as much unused ordnance as either the -A or -C.

http://www.aviationweek.com/aw/blogs/de ... 75779e6fc5

F-35B 'bring-back' to where though? On an LHA for the moment for the USMC it is likely that only vertical landings will be the go. Ashore a run on RVL will help with any extra bring back weight (depending on available minimum short runway length). If bring back weight is an issue then the ordnance can always be jettisoned. I guess some would rather the aircraft be jettisoned but I don't make mountains out of molehills myself. Some want to make hay with ordnance unable to be jettisoned but I gather there will be emergency procedures to cater for those eventualities (as is the case with any military aircraft with outside droppable stores). 'What if What if' games can be played ad nauseam but the aircraft NATOPS (for B & C variations will be quite clear on all these points).

The Sweetman report cited above is now almost ten months old, if the US date is the key. Time to move on.

spazsinbad wrote:

F-35B 'bring-back' to where though? On an LHA for the moment for the USMC it is likely that only vertical landings will be the go. Ashore a run on RVL will help with any extra bring back weight (depending on available minimum short runway length). If bring back weight is an issue then the ordnance can always be jettisoned. I guess some would rather the aircraft be jettisoned but I don't make mountains out of molehills myself. Some want to make hay with ordnance unable to be jettisoned but I gather there will be emergency procedures to cater for those eventualities (as is the case with any military aircraft with outside droppable stores). 'What if What if' games can be played ad nauseam but the aircraft NATOPS (for B & C variations will be quite clear on all these points).

The Sweetman report cited above is now almost ten months old, if the US date is the key. Time to move on.

Naw, the article contains relevant info. Aircraft routinely return with unused weapons. It gets expensive to jett smart weapons - this was supposedly one of the reasons the RN switched models to the -C.

maus92, no argument with anything however if you have been reading the KPPs are relevant and are being met. What could be better than that? More nitpicking about what the B model cannot do compared to the other two versions I suppose. Compare the B model to the Harrier and you will be amazed. OK?

maus92 wrote:

Naw, the article contains relevant info. Aircraft routinely return with unused weapons. It gets expensive to jett smart weapons - this was supposedly one of the reasons the RN switched models to the -C.

One of the reasons, no doubt. The primary one was attributed to the major sacrifice that goes into having STOVL capabilities. I'm still trying to find an article about the phenomenon of excessive costs going towards using small carriers with expensive aircraft (VSTOL). The overarching argument was that the savings which went into smaller carriers was lost in paying much more for the aircraft.

The article also referred to STOVL aircraft (harriers specifically) cost a lot more and were vastly less capable in comparison to something like an F-18 or a Rafale, resulting in each carrier having vastly less projection of air power. The major reason for endorsing a larger carrier with F-35C's comes down to having a greater range and reduced upkeep demands. While the 1k internal weapon limitation is a factor, it wasn't as significant an issue as extended range and improved power projection per aircraft carrier.

Aaaahhh but as I understand the small carrier debate (other than USN) is that it is the only carrier affordable to those countries with small carriers, with the F-35B being the ideal only replacement. Hmmm. When someone says 'sacrifice' I say 'flexibility'.

Akhck, now I realize that I had a big clue already and just didn't put the pieces together before. (I finally thought of checking it now because of the pilot's reference to "ductwork" in the video above.) Comparing a ventral view of B with a ventral view of A in another image with its bay doors open, it's easy to see that the back end of the full-size bay comes very close to, or might even slightly overlap, the ducts from the engine to the outlets in the bottoms of the wings. They might be able to fit without technically occupying the same space, with the bay below and the duct above, but just the fact that they're that close would mean there's not much room to squeeze anything else in that area between them, unless you open up the space between them by shortening the bay. (...since you couldn't move the ducts/outlets without fiddling with the plane's performance).

maus92 wrote:

There is also the issue of "bring-back" weight. The -B will not be able to RTB with as much unused ordnance as either the -A or -C.

Which is largely irrelevant since neither the A nor the C can land where the B can land.

maus92 wrote:

There is also the issue of "bring-back" weight. The -B will not be able to RTB with as much unused ordnance as either the -A or -C.

Which is largely irrelevant since neither the A nor the C can land where the B can land.

Forum: F-35 Lightning II

B's internal weapon restriction compared to A & C