US Navy 6th Gen Fighter - F/A-XX

[Training_Dummy]

Could be anything. The Navy already pays north of $100 Million per F-35 IIRC. Part of the reason could be that they don't want to spend more money at this time. Whatever it is, they are not getting adaptive engine on the carrier deck for the forseable future. And that decision seems to have been made some years ago.

I meant examining if the specific reason USN is not using an adaptive three stream engine for F/A-XX might roughly be extended as to a notional A100/101 F-35 or derivative, but sounds like aside from the same tea leaves Josh_TN are reading, there isn’t much to point as to reasons; could be cost, tech risk, technical/operational reasons unique to US naval aviation, none or all.

 

[Scott Kenny]

The USN seems to think adaptive engines are a non starter for FAXX; I cannot imagine their view on F-35C is much different.

My understanding was that it was because of development time. USN needs planes to replace Super Bugs NOW (well, 10years from now), so isn't willing to fight needing both new engines developed out as well as new airframes.

Edit: they did that with the F-14 and got screwed with TF30 Tomcats when the F401 was cancelled.

 

[Jimmo952]

My understanding was that it was because of development time. USN needs planes to replace Super Bugs NOW (well, 10years from now), so isn't willing to fight needing both new engines developed out as well as new airframes.

Edit: they did that with the F-14 and got screwed with TF30 Tomcats when the F401 was cancelled.

I think you are right. The Navy is taking the conservative approach.

 

[H_K]

I think F414s, even maxed out in their development, aren't going to be enough power for an ~80,000lb aircraft expected to do fighter missions in addition to striker, while F110s are.

Where am I getting ~80klbs? Carrier limits. Max takeoff weight is limited by the steam catapults because we're going to have Nimitz classes in service till ~2050. Max landing weight is limited by what the arresting gear can stop, and IIRC the Ford-class Advanced Arresting Gear isn't capable of much higher weights, it's capable of safely stopping much lighter aircraft (as in UAVs/CCAs).

Weight wise, the MTOW of a Tomcat is ~78klbs, the KA-3 "Whale" was ~83klbs, and the F-111B was up to 88klbs. Since we're unlikely to have swing wings to help out low-speed handling, so something in the 75-85klbs range is not unreasonable to launch.

But the trick comes from the landing weight. Recovery weight of an F-14 was 55klbs, it's why they so rarely flew with 6x Phoenix missiles. They'd have minimal fuel left, Tomcat pilots said it was "make your trap on the first pass or hit the tanker". So that says what our "Empty weight plus weapons weight plus ~3000lbs of fuel" can be. I'm assuming a weapons load for the FAXX as roughly equal to the ATA (possibly with more AAMs): ~12,000lbs in ground-attack mode, ~9500lbs for 4xSM6 and at least 2xAMRAAM, and 5-6,000lbs for pure AMRAAMs.

55-3-12=40klbs empty.

And a reasonable rubric for MTOW is 2x Empty Weight (checks with pretty much every jet from Teens on up). That means 80,000lbs ish MTOW, which checks with catapult max.

80-12-40=28klbs of fuel onboard.

I like this math. Another good example would be the A-5 Vigilante, as it's non swing wing (vs. Tomcat or F-111B).

https://www.aahs-online.org/images/Navy_SAC/A-5C.pdf

RA-5C weighed 39klbs empty, 80klbs MTOW. Combat radius was 950nm (hi-hi) with 24,500lbs internal fuel. A radius of 1,000nm+ should be possible with modern engines burning at least 10-15% less than old J79s and ~25klbs internal fuel. Installed weight of F110s would be about the same as J79s, with almost 2x the thrust. However the F110s have more airflow so might require bigger ducts.

Now put all that in a stealthy delta-canard (a little like NATF, the navalized YF-23 proposal), scaled to roughly Vigilante size. I think structural weight would have to increase somewhat (even with composites) to accommodate internal weapons, bigger ducts, increase the max structural load factor from ~4.5g to 7.5g, add stealth features etc. So 40-45klbs empty weight might be a reasonable target.

80klbs MTOW - 45klbs empty - 25klbs fuel = 10kbs payload

Payload would probably be a little higher that as I doubt that 80klbs is the upper catapult limit (RA-5Cs required only 16 knots WOD on a C13 catapult at 80klbs).

Landing might be a bigger constrain. RA-5C at max trap weight of 50klbs had a stall speed of 112 knots and approach speed was 140 knots, and most importantly required 28 knots of WOD, which is quite high... I'm not sure if the limit was due to airframe strength or the Mk 7 arrestor wire. Max bring back was ~11,000lbs, less ~3,000 lbs fuel leaving enough for ~8,000 lbs weapons. So if the empty weight was increased to 45klbs empty, then a trap weight of ~55klbs or more would be desirable.

 

[B2Blain]

I meant examining if the specific reason USN is not using an adaptive three stream engine for F/A-XX might roughly be extended as to a notional A100/101 F-35 or derivative, but sounds like aside from the same tea leaves Josh_TN are reading, there isn’t much to point as to reasons; could be cost, tech risk, technical/operational reasons unique to US naval aviation, none or all.

I think the big driver for the Navy was money. What irritates me is that they were so close to the finish line. I believe the adaptive engine was supposed to have been operational by the 2027 timeframe. The AF or the Navy could have scraped together a few billion a year to finish it. The Navy might not have seen value in it or wanted to increase the flyaway cost of the C. Frank Kendall's statements indicated the AF would have liked it. I understand why the AF might not have wanted to be the sole bill payer. I don't think it was ever disclosed much it would added to the price tag.

I personally don't buy the commonality argument. The three versions are not exactly the same. The C has a more robust landing gear, different wings, and a more robust hook. The B has a lift fan and a different weapons bay.

Re: the F/A-XX Sam Lagrone from USNI News was on CAVASSSHIPS. Some takeaways...

• Described F/A-XX as on ice.
• Observed that the Navy has not made a clear argument regarding the requirements of the F/A-XX and what it is for.
• Range is a concern. Raised the issue of that the CVW that went to sea when the Nimitz was commissioned had greater range. Some will say that the CVW will have MQ-25s, but there the number of MQ-25 will be limited.

Saying that it is a strike fighter is not enough. I really wonder whether OSD or the SecNav is not allowing them to proceed. It surely seemed they were going to announce an award but something happened.

 

[dark sidius]

Is it possible that the return of Lockheed with a boosted F-35 C could be the explanation for the delay of Award ?

 

[EmoBirb]

Described F/A-XX as on ice.

Huh? What happened?

 

[EmoBirb]

Is it possible that the return of Lockheed with a boosted F-35 C could be the explanation for the delay of Award ?

If the Navy didn't even want new engines for the F-35, it's doubtful they'd pick up a heavily upgraded (and thus more expensive) version. Which still would most likely not match a clean sheet next gen design in various areas. Especially not without an adaptive cycle engine.

 

[Josh_TN]

Heavily modified F-35s are just LM marketing on the long shot chance someone with some power is willing to pick up the idea as a cost savings measure. Its contractor equivalent “wouldn’t it be crazy if we had a threesome! Unless your interested…”. It should not be treated as something that has even been considered by any service.

 

[NMaude]

If the Navy didn't even want new engines for the F-35, it's doubtful they'd pick up a heavily upgraded (and thus more expensive) version.

As @Scott Kenny has pointed out in a number of posts the USN needs the F/A-XX ASAP has it is needed urgently to replace their current inventory of Super Hornets which are getting worn out rather quickly. What they want is something good enough to do the job and not some hideously expensive gold-plated hanger queen subject to requirements creep, in that case that means relying on either mature off-the-shelf already in production equipment or with a TRL of 6 or higher.

 

[Training_Dummy]

We just saw a radical reshaping of the US Army and who’s to say if they’re done with the changes. USN might be next, arguably needing more change, given the numerous operational and procurement dilemmas. Perhaps USN recent air-launched hypersonic weapon news were a harbinger of F/A-XX getting paused or worse (if true).

Kudos to the USAF for executing on B-21 (growing the buy too) and apparently making a resoundingly successful argument for CCAs and NGAD.

In the end I can’t rule out a scenario where Boeing gets both F-47 and Navy’s next fighter buy, but with Block 3 Hornet.

 

[quellish]

I think the big driver for the Navy was money. What irritates me is that they were so close to the finish line. I believe the adaptive engine was supposed to have been operational by the 2027 timeframe. The AF or the Navy could have scraped together a few billion a year to finish it. The Navy might not have seen value in it or wanted to increase the flyaway cost of the C. Frank Kendall's statements indicated the AF would have liked it. I understand why the AF might not have wanted to be the sole bill payer. I don't think it was ever disclosed much it would added to the price tag.

The Department of Defense was looking to solve the problem of the F-35 engines having a short life and expensive sustainment due to them running hotter/harder than originally projected. The AETP program was originally a technology development program, then was refocused to provide an engine for the F-35.

In FY22 the Department of Defense conducted a business case analysis / analysis of alternatives for solving the F-35 engine program. They looked at three options. 1. Modifications / upgrades to the existing engine (ECU). 2. AETP XA100 engine, which would only work for the F-35A. 3. A proposed "Tri-Variant" AETP engine that would be intended for all 3 variants. The analysis made clear that the best way to solve the F-35 engine life/cost issue was the ECU option. The other options were higher risk and much higher cost.

The Department of Defense chose the ECU path, and while it would have liked a new engine and new capabilities for the F-35 this was high risk and cost. The Department of Defense felt that they simply could not afford the $7b development cost for the AETP engine for the F-35A, much less the "tri-variant" engine which would have been substantially more expensive.

Neither the AETP engine nor the "tri-variant" engine were anywhere close to being ready.

None of this is at all relevant to the F/A-XX but for some reason the AETP engine for the F-35 keeps coming up in this thread like a flu you can't shake, and most of the information posted about it is incorrect and misinformed.

 

[Scott Kenny]

None of this is at all relevant to the F/A-XX but for some reason the AETP engine for the F-35 keeps coming up in this thread like a flu you can't shake, and most of the information posted about it is incorrect and misinformed.

Mostly in the sense of Lockheed making a stretched "FB-35" or "F-35XL" that is sized for carrier elevators not LPH elevators. Lots (5-10klbs) more fuel and a more efficient engine would give the nice big range needed, but you're still only carrying 2x 2000lb class weapons internally as the downside.

 

[TSARb]

XA100 and XA101 engines extend the range of F-35 about +30%

 

[NMaude]

Mostly in the sense of Lockheed making a stretched "FB-35" or "F-35XL" that is sized for carrier elevators not LPH elevators.

How long an aircraft can one of the CVN's lifts accomodate?

 

[bring_it_on]

I think the big driver for the Navy was money. What irritates me is that they were so close to the finish line. I believe the adaptive engine was supposed to have been operational by the 2027 timeframe.

On the F-35? The EMD program for an F-35 adaptive engine had not even started by the time it was decided that they were not going down the route of an adaptive engine option. JPO/LM have not managed to bring to service tech refresh EMD's in 3-5 years, and you think they could whip up a completely new engine EMD in 4 years (2023 when they decided to not go ahed with EMD and 2027)?

Even the significantly lower risk / lower technical capability F-135 engine core upgrade won't become operational till 2029 at the earliest. Realistically, they would have been lucky to have fully developed operational engines in the fleet in the early 2030s had they stuck with the program and transitioned it to a formal EMD phase in FY24/25. That's basically when I suspect NGAP will deliver and both of these would have a fairly similar EMD schedule.

 

[Josh_TN]

How long an aircraft can one of the CVN's lifts accomodate?

IIRC an extra 9 feet longer than F-35. Gator freighters set the length limit.

 

[NMaude]

IIRC an extra 9 feet longer than F-35.

Which sets the upper-limit on how big a fuselage plug could be and if split into fore and aft plugs (The former in front of the wings and the later aft of the wings) each no more than 4.5ft long.

 

[Josh_TN]

Which sets the upper-limit on how big a fuselage plug could be and if split into fore and aft plugs (The former in front of the wings and the later aft of the wings) each no more than 4.5ft long.

No one is buying an F-35 with plugs. Those A/C would be non standard and suffer from a different parts stream than the rest of the world, and no one is doing that. Any upgrade will apply to the entire fleet for the life of a/c or else the economy of scale falls apart.

My comment on length was just to highlight how much including the ISMC kneecapped the performance of all the other machines.

 

[red admiral]

How do you even put plugs in a F-35 fuselage to lengthen it? Forward fuselage screws up the intakes and more. Centre fuselage makes the weapon bays have a kink in them. Don't see it being realistic.

 

[Sferrin]

IIRC an extra 9 feet longer than F-35. Gator freighters set the length limit.

Vigilante was 76 feet long.

 

[joewee]

No one is buying an F-35 with plugs.

Oh I hope not. To paraphrase Forest Gump: marketing is as marketing does.

Let's not forget that in the post-A12 era (1991-1996) Lockheed put on an extensive (and shameless) marketing push for a "navalized" F-117 to various OPNAV and NAVAIR offices. They worked two avenues and approaches: (1) in the special-access world they tried to sell the Navy on a "silver bullet" capability; (2) in the acknowledged world they offered it as a JAST alternative.

With a straight face, Lockheed suggested the so-called F-117N would a "mod" to the proven F-117A. As we used to say, the rudder pedals would be the only thing in common with a "derivative" like that.

Along with a larger F404 engine (the F412, later the F414) and a radar, nearly the entire airframe would be of new design.

Not to be unfair to Lockheed, McDonnell Douglas went on to successfully lobby for the Super Hornet aka Hornet 2000, as an ECP to the F/A-18C/D.

 

[H_K]

Vigilante was 76 feet long.

Yes. Vigilante folded down to ~65ft (nose and tail), just a tad more than the YF-23 NATF proposal (62.5ft). Both were much longer than F-35C (51.5ft)... the extra 11-14ft translates into better aerodynamics especially in transonic / supersonic flight.

Here's a size comparison of F-35C vs. YF-23 NATF / A-5 and Mirage IVA.

A-5A: 21klbs max internal fuel / 34 klbs empty = 0.617 fuel fraction​

Mirage IVA: 26klbs max internal fuel / 32 klbs empty = 0.812 fuel fraction​

I like these 2 because they were 2 different approaches to solving the same problem - high supersonic performance and high fuel fraction - and ended with nearly identically sized aircraft with similar engines (the Mirage IVA had more internal fuel volume though). What they were lacking was FBW and canards to maximize low speed lift and combat maneuverability... the Mirage 4000 shows what was possible in this respect (as it was basically a Mirage IV in size but optimized for strike fighter missions). NATF represents a further refinement in this direction with moving canards and stealth (although we don't know NATF's fuel fraction, it was probably also quite good).