Future F-35 evolution - weight growth or performance gains?

[steve2267]

Pratt & Whitney is already proposing F135 engine upgrades that promise on the order of +10% thrust with 5-7% decreased fuel burn. If memory serves, GO 2 suggests even better performance increases. A future GE or P&W 3-stream engine could see up to 30% decreased fuel burn, and possibly more thrust.

However, the old adage is that all aircraft always gain weight.

Question for discussion: do you see the F-35 being no different in this regard, and it is inevitable that it gains weight?

IMO, there is an argument to be made that the F-35 may be an exception to this "rule." Why? Two reasons:

1. Concurrent development
2. Software

By adopting a concurrent development program, the US and her allies are receiving an aircraft that has already been continuously tweaked and upgraded. Problems have been identified, and fixed. The (in)famous stand-down also put a HUGE emphasis on weight reduction. And the -B model has definite limits on weight owing to its STO and VL requirements. So pretty much everything you could possibly want in an F-35 is already in it. Well, except for directed energy weapons. If a tactically useful laser comes along and can fit in the F-35, then all bets are off, IMO, regarding weight.

Secondly, the F-35 is largely defined by her avionics, specifically her software. For the most part, software has no weight... or, since storage capacity seems to be ever increasing within the same form factor, one does not have to add weight to add more software. Processors are also ever increasing in speed, for roughly the same form factor. They are also tending to use less energy as they advance, so their thermal footprint decreases. I would argue that as processor technology continues to increase, the F-35 could either become lighter (!), or increased capability will be realized for the same weight.

If weight, therefore, is staying roughly the same, but engine power increases, this bodes well for increased performance -- both kinematic and range/endurance.

My arguments assume the airframe stays the same. It also assumes no major structural issues are uncovered... but given the concurrent development process, and the extensive testing to date, I assign a low risk to any such possible problems.

On the other hand, if along comes a super-duper F-135 GO2 or GE 3-stream blower... and it is decided to lengthen the airframe to stuff MORE fuel into it (or maybe some new, hypersonic A2A vundermissile that HAS to be longer, and hence the weapons bays have to be longer), then increased performance is not a given.

Thoughts?

[Dragon029]

It probably will see weight gain, though I think it'll be less dramatic in comparison to jets like the F-16 - at least with the F-35 you already have a targeting pod, already have a high-end MAWS, already have a high-end jammer (though a non-towed 360 degree defensive jammer is still desirable and might be part of future weight gain), already have a software-defined radio / set of data links, already have SATCOM hardware, etc.

Things that I think might add weight in the future though:

1. DIRCM turrets
2. Serious offensive or defensive DEW
3. As mentioned above, additional EW equipment (perhaps the ASQ-239 wing and tail apertures will be refitted with transmitting AESAs).
4. Maybe in the case of some users, conformal fuel tanks (we know Israel is already looking at concepts for how that might work).
5. Possible weapons bay extensions (eg; the outer doors on each bay being strengthened and potentially bulged to accommodate an additional pair of hardpoints).

[hornetfinn]

I think you are very correct. F-35 might get DIRCM and laser weapon, but otherwise there is not much need for new sensors or equipment. Current systems will be upgraded or replaced, but new tech might well be lighter. Older fighters did get all kinds of new equipment as they matured, but even the latest 4th gen fighters have generally not gained weight. SH, EF Typhoon and Rafale are still pretty close to same weight they were when they were introduced to service.

[basher54321]

It probably will see weight gain, though I think it'll be less dramatic in comparison to jets like the F-16 - at least with the F-35 you already have a targeting pod, already have a high-end MAWS, already have a high-end jammer (though a non-towed 360 degree defensive jammer is still desirable and might be part of future weight gain), already have a software-defined radio / set of data links, already have SATCOM hardware, etc.

From what I can gather the majority of F-16 weight growth seems to have been structure related, not just the reinforcement programs but things like strengthening the intake at Block 15 for new hardpoints, and the structural redesign at Block 40 with bigger landing gear etc, then probably even more changes with CFTs.

The F-16A Block 10 had about a 35,000 lb MTOW, but LM advertise (last time I checked) about 48,000 lbs MTOW which I think might have been more than the F-16XL.

I know the decision to not fund the F-16F (XL) in the mid 1980s was probably correct and hindsight is a wonderful thing -
but wonder if anyone is looking at this thinking why didn't we just switch to the one designed for the role!

[mixelflick]

Interesting mental gymnastics..

I hope it doesn't gain weight or if it does, she gets a boost in power to compensate. Too many people trash talking her maneuverability (still) and acceleration...

[steve2267]

I hope it doesn't gain weight or if it does, she gets a boost in power to compensate. Too many people trash talking her maneuverability (still) and acceleration...

MF, if the F-35 avoids mid-life weight gain, but future engine performance increases, it stands to reason that the F-35's kinematic performance will get that much better. Yes, people still pooh-pooh the F-35's maneuverability, despite the Paris Air Show 2017 performance and all the testimonials from former F-16 / F-18 / F-15 drivers. But another 10% thrust certainly can't hurt.

While maneuverability / sustained turn rate would stand to get better, I think the possibility of a modest (1.2 Mach?) supercruise ability without re-heat is more tantalizing. That said, even at low supersonic speeds, drag increases a lot over subsonic, so fuel burn is going to be significantly higher.

The real benefits of weight neutral, improved engine performance is probably in decreased fuel burn, and corresponding increased range.

Increased range and improved durability / reliability / maintainability are probably the least sexy, but most important metrics that one can improve.

[SpudmanWP]

Mid-Life weight gains typically come from adding avionics and sensors.

Given that the F-35 already has all for the basic sensors (AESA Radar, ESM, EOTS, DAS), Towed Decoys, an extra ICP bay, and a software based CNI... I don't see it gaining a significant amount of weight.

The only thing that I can think of that will add weight would be DIRCM and AESA jamming in the ESM sensor bays.

[nutshell]

We should consider the fact that once deadly DEWs are in play, t/w str itr and everything else will not matter anymore.