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

More than likely, F/A-XX will probably have to meet the original size requirements as dictated by the previous NATF (F-14 size) program. As for the unmanned element, MQ-25, that's obvious, their first unmanned platform. When F/A-XX begins carrier qualifications, you will see the mix of F-18 E/F, all required F-35Cs and the F/A-XX. I am curious if the USN will have F/A-XX assume the F-14 role, they already have two strike-fighter platforms. Hopefully, MQ-25 starts operational life as the tanker mission only and not a pseudo-strike/ISR/tanker whatever else then the aircraft gets screwed up, the USN does not need everything all at once, again depends on the leadership.
 
Hydroman said:
More than likely, F/A-XX will probably have to meet the original size requirements as dictated by the previous NATF (F-14 size) program. As for the unmanned element, MQ-25, that's obvious, their first unmanned platform. When F/A-XX begins carrier qualifications, you will see the mix of F-18 E/F, all required F-35Cs and the F/A-XX. I am curious if the USN will have F/A-XX assume the F-14 role, they already have two strike-fighter platforms. Hopefully, MQ-25 starts operational life as the tanker mission only and not a pseudo-strike/ISR/tanker whatever else then the aircraft gets screwed up, the USN does not need everything all at once, again depends on the leadership.
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I'd like to believe the USN is planning for larger unmanned aircraft to assist with IADS penetration alongside the F/A-XX if they are taking it seriously, but I honestly don’t have much insight into NAVAIR's current thinking for the Pacific.

It’s possible the unmanned side stays focused on fleet defense, tanker, and ISR roles... which would favor smaller, cheaper platforms, leaving the F/A-XX as the primary strike platform in the air wing.
 
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In other words a modern ATA for the twenty first century Scott Kenny, an ATA sized load would work for a modern carrier like the Ford class especially since it may carry the similar amount of weapons as the ATA was expected to carry.
 
FighterJock said:
In other words a modern ATA for the twenty first century Scott Kenny, an ATA sized load would work for a modern carrier like the Ford class especially since it may carry the similar amount of weapons as the ATA was expected to carry.
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It wouldn't literally be the NG ATA proposal, the newer weapons like AGM-158, JSM, and AARGM-ER are wider than the missiles they replaced.

But it absolutely could be based on the NG ATA proposal with modified weapons bays to fit the newer stuff.
 
That was exactly what I was thinking Scott Kenny about a modern ATA but with a much larger weapons bay, I will be highly surprised if it ends up being smaller than it considering as you say the much larger weapons than the original NG ATA design.
 
Before some posters get too carried away by F/A-XX sizing and engine options, consider that the F414 and F110 have core airflows that are actually not too different. The F414 with a BPR of 0.25 and fan airflow of 170 lb/s has a core airflow of 136 lb/s, while the F110-400 on the F-14B/D with a BPR of 0.87 and fan airflow of 269 lb/s has a core airflow of 144 lb/s, while the current F110-129 is about 153 lb/s. Incidentally, the F414 core airflow is also quite similar to the F100-220 (228 lb/s fan airflow, 0.63 BPR, so ~140 lb/s core airflow).

In other words, the difference between a derivative of the F414 or F110 may not be much different in practice especially if the fan is sized to what the Navy wants in terms of performance. An F414 class engine may be sufficient for something that's modestly larger than the F/A-18E/F, while structural engineering advances can mitigate the weight growth. Or if more thrust is needed, sizing the fan to something like 24,000-25,000 lbf of augmented thrust may be sufficient for the F/A-XX. After all, the Lockheed/Boeing/General Dynamics A/F-X proposal of the 1990s (AFX-653) was reportedly to be powered by a pair of PW7000 engines in the 25,000 lbf thrust range.
 
FighterJock said:
That was exactly what I was thinking Scott Kenny about a modern ATA but with a much larger weapons bay, I will be highly surprised if it ends up being smaller than it considering as you say the much larger weapons than the original NG ATA design.
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If it kept the "4 big weapons" concept for the bays, I'd want a bay long enough for 3 SDBs in tandem. That's ~5.7m long, 1.5m wide, and potentially as little as 0.5m deep. That said, the actual ATA bay ended up way way deeper, over 1.2m deep.


icyplanetnhc (Steve) said:
In other words, the difference between a derivative of the F414 or F110 may not be much different in practice especially if the fan is sized to what the Navy wants in terms of performance. Something like 24,000-25,000 lbf of augmented thrust may be sufficient for the F/A-XX. After all, the Lockheed/Boeing/General Dynamics A/F-X proposal of the 1990s (AFX-653) was reportedly to be powered by a pair of PW7000 engines in the 25,000 lbf thrust range.
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Fascinating how close the cores are (both are within 5% of the F110-400, and 11% from top to bottom).

I'm still leaning more towards the core being a development off the F110, because the CFM56 has had a LOT of development and the CFM56-7 has a whole new HP compressor in it. I was thinking CFM-56-7 HP compressor with F101 fan on it. Or similar.
 
For the engine big brains, sorry but this remains murky for me: would a bigger fan for the F414 be compatible with the current LPT or would the core need a redesign?
 
What about a three-spool turbofan like a 21st century equivalent of the RB199?
 
The Typhoon's EJ-200 would be a better equivalent I would think, that also has if I remember correctly limited supercruise capability.
 
icyplanetnhc (Steve) said:
Before some posters get too carried away by F/A-XX sizing and engine options, consider that the F414 and F110 have core airflows that are actually not too different. The F414 with a BPR of 0.25 and fan airflow of 170 lb/s has a core airflow of 136 lb/s, while the F110-400 on the F-14B/D with a BPR of 0.87 and fan airflow of 269 lb/s has a core airflow of 144 lb/s, while the current F110-129 is about 153 lb/s. Incidentally, the F414 core airflow is also quite similar to the F100-220 (228 lb/s fan airflow, 0.63 BPR, so ~140 lb/s core airflow).

In other words, the difference between a derivative of the F414 or F110 may not be much different in practice especially if the fan is sized to what the Navy wants in terms of performance. An F414 class engine may be sufficient for something that's modestly larger than the F/A-18E/F, while structural engineering advances can mitigate the weight growth. Or if more thrust is needed, sizing the fan to something like 24,000-25,000 lbf of augmented thrust may be sufficient for the F/A-XX. After all, the Lockheed/Boeing/General Dynamics A/F-X proposal of the 1990s (AFX-653) was reportedly to be powered by a pair of PW7000 engines in the 25,000 lbf thrust range.
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Your core airflow size does not consider the core airflow inlet conditions. The F414 has a fan pressure ratio of approximately 4:1, while the F110 is in the 3:1 range. If the F414 had the F110 fan discharge pressure, the core airflow would be reduced by 25%, only around 100 pps vs the 150 pps approximate size of the F110, so physically the F414 core is significantly smaller. You have to consider the inlet flow conditions (both pressure and temperature) when comparing the core size.

Other considerations in comparing various engines is the pressure ratio split between the fan and core compressor. Higher bypass engines tend to have lower fan pressure ratio and higher core pressure ratio, while the lower bypass tends to move a higher percentage of the OPR from the core compressor to the fan. Of course, there are technical limits on the pressure ratio you can achieve with either compressor, although the state of the art has advanced a long way over the years.
 
icyplanetnhc (Steve) said:
The F101’s size and diameter makes that a non-starter.
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If you're designing around an F101 or F118 fan it doesn't really matter. You size for the inlet mass flow (of about 350lbs/sec for the F101). F101 and F110 are both 182" long, and the F101 is about 400lbs heavier (4300lbs instead of 3900). If you chop the afterburner off, you are now comparing with the F118 and that is only 101" in length and ~3200lbs.

And the CCA mission profile greatly leans towards a very low fuel consumption engine. F101 burns ~0.562lb/lbt/hr, the CFM56-7B core would scrape another ~8-10% off that burn number, bringing you down to ~0.5 or so.
 
So for the F/A-XX, @F119Doctor, how well would a turbofan with a three-spool architecture fare compared to two-spool architecture?
 
One of the problems with compressor design is the mismatch in flow capacity between the front and rear stages at off design rotor speeds. As the rotor speed and compression ratio decreases, the flow velocity increases in the small rear stages, choking the flow and overloading the forward stages towards flow separation and compressor stall. This flow mid-match gets worse the higher the design pressure ratio.

One solution is to split the compressor into smaller sections, each with a lower pressure ratio and turning at their own speed on separate shafts. The P&W J57 had two rotors, RR went with three shafts on their RB211 (and subsequent large turbofans) and the RB199.

Other solutions to the flow mismatch are bleed valves that vent the excess front end flow before it gets to the small back end, and variable vanes that reduce the front end blade angle of attack to reduce front end airflow at lower rotor speeds. J79 was one of the first with 6 stages of variable vanes out 17 compressor stages.

Most modern engines have a combination solution of split rotors, variable vanes, and compressor bleed to handle the higher Overall Pressure Ratios (OPR) of 30-35:1 for supersonic fighter engines and 50:1+ for high bypass transport engines.

The three shaft design is very effective and allows more of the compressor stages to run closer to their optimum rotor speeds. But it is a heavy and complicated design with the three shafts, and bearings / seals / supports for the three shafts. It appears that most new designs are converging on the two shaft design with variable vanes with wide chord high stage loading airfoils. Geared high bypass fans allow the two shaft design to work without having the low pressure turbine to be so large.
 
F119Doctor said:
Your core airflow size does not consider the core airflow inlet conditions. The F414 has a fan pressure ratio of approximately 4:1, while the F110 is in the 3:1 range. If the F414 had the F110 fan discharge pressure, the core airflow would be reduced by 25%, only around 100 pps vs the 150 pps approximate size of the F110, so physically the F414 core is significantly smaller. You have to consider the inlet flow conditions (both pressure and temperature) when comparing the core size.
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Interesting. Typically, what does the bypass ratio number indicate? The geometric inlet area ratio, if not the airflow ratio? Based on this, what would be the method for deriving core airflow rate? Evidently it appears to involve more than what fan airflow and BPR would indicate.
 
Will be interesting to see what engine will be selected to begin with until the advanced engine is available.
 
icyplanetnhc (Steve) said:
Interesting. Typically, what does the bypass ratio number indicate? The geometric inlet area ratio, if not the airflow ratio? Based on this, what would be the method for deriving core airflow rate? Evidently it appears to involve more than what fan airflow and BPR would indicate.
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You are correct in the actual pounds per seconds airflow thru the core ( I haven’t checked your math, assume it is correct ). But the higher fan pressure ratio of the F414 is packing that airflow into a physically smaller core flow path.

If you put a 4:1 fan in front of the F110 core, you would either have a much lower BPR, or you would have to increase fan airflow significantly to keep the same BPR (all else being equal)
 
Hydroman said:
Will be interesting to see what engine will be selected to begin with until the advanced engine is available.
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As F/A-XX is planned to operate a derivative of an in service engine and no current plans to operate an adaptive engine which engine it is equipped with at the start will likely be what powers it at the end as well.
 
F119Doctor said:
You are correct in the actual pounds per seconds airflow thru the core ( I haven’t checked your math, assume it is correct ). But the higher fan pressure ratio of the F414 is packing that airflow into a physically smaller core flow path.

If you put a 4:1 fan in front of the F110 core, you would either have a much lower BPR, or you would have to increase fan airflow significantly to keep the same BPR (all else being equal)
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Okay, I see what you mean now with regards to physical size.

On another note, do you have any more information regarding the PW7000? It was the proposed 25,300 lbf thrust engine for the A/F-X in the early 1990s, and in the early 2000s, Pratt pitched it as an F414 alternative for the F/A-18E/F Super Hornet. Evidently it would use a core derived from the PW6000 with a scaled fan and LPT from the F119, and sized to have the same F414 footprint.

https://www.flightglobal.com/fixed-wing/2001/04/usn-urged-to-re-engine-f-a-18e-f/
 
@Hydroman to my knowledge the USN has said F/A-XX will not use an ACE and - while I’m not sure anymore given the sheer amount of tidbits we’ve consumed over so long if this has been confirmed or just speculative - the working assumption (for me, right now) is F/A-XX will use a derivative of a currently in-service engine. We can rule out the F135 as a twin F135-engined -XX would be huge (and probably anti polar to what F/A-XX eventually becomes, personal POV). So that leaves the F100, F110 and F414. Depending on how evolved the ultimate F/A-XX engine is, there may or not be part, sustainment or logistical commonality with the F414 currently embarked with CAW SuperHornets (now and in the future since and I am assuming the USN would spend every penny on F/A-XX vs a new engine for SuperHornet).

My silly assumption is that the USN may not want as much of the electronic part of the NGAD next gen leap as the USAF. Furthermore, the USN may well be very happy with a 7G/M1.5 airframe vs a presumptive F-47 with a way more exotic flight envelope / profile that would rapidly and robustly stand up a blue-suit pants-tent. The thrust profile, power generation and cooling needs of a tailless, signature-optimized, 400kW, 7G, M1.5ish dash speed but still supercruising class fighter with a 50% range improvement over SuperHornet can definitely be conceptualized without much technological squinting. It certainly seems a more relaxed design exercise than what the USAF may desire from F-47.

Again quellish did the simplified aeromath in a prior post on how you do this with a pair of F414+ engines. What Q didn’t say but seems worth kicking around as a consequence of his logic, is that a smaller, less-capable, cheapish-to-operate, strike-optimized F/A-XX may be a crucial element of the program if the USN hopes to get -XX into a glide slope for a price that gets the USN the airframes it needs, and soon.

To the extent these assumptions underestimate the USNs ultimate aspirations, I would be not be surprised and even impressed, yet sobered by the observation that current US DOD/W leadership does not prioritize carriers (and therefore carrier aviation) as much as it does B-21 or even F-47. But I still think F/A-XXs engine is more like F414 than F100/110 and ditto for F119 or F135, if not more.
 
Is the F414 in a good place where it can deliver strong performance while still meeting the electrical power requirements for the F/A-XX’s subsystems (sensors, EW, etc)?
 
icyplanetnhc (Steve) said:
Okay, I see what you mean now with regards to physical size.

On another note, do you have any more information regarding the PW7000? It was the proposed 25,300 lbf thrust engine for the A/F-X in the early 1990s, and in the early 2000s, Pratt pitched it as an F414 alternative for the F/A-18E/F Super Hornet. Evidently it would use a core derived from the PW6000 with a scaled fan and LPT from the F119, and sized to have the same F414 footprint.

https://www.flightglobal.com/fixed-wing/2001/04/usn-urged-to-re-engine-f-a-18e-f/
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I worked the engine supportability proposal for the PW7000 engine for the Lockheed A/F-X proposal. It preceded the commercial PW6000 engine, which did not include the somewhat exotic dual disk single stage HPT, running slower and at higher HPC compression ratio than the PW7000, according to the Program Manager during a after work bar debrief. The 5 stage HPC didn’t work well in the PW6000 application, and was replaced with an MTU designed HPC. There were several variations of the PW7000 proposed for the various AF-X contractor proposals, with different sized fans and LPTs. The bigger fans had a 1&1/2 stage LPTs, with the first 1/2 stage having no inlet guide vane between the HPT and LPT blades

While the core was run as the XTE67 development items under the ATEGG program, I don’t know if any full up engines were ever run before the A/F-X program was cancelled and replaced by the JAST program that created the F-35.
 
In_A_Dream said:
Is the F414 in a good place where it can deliver strong performance while still meeting the electrical power requirements for the F/A-XX’s subsystems (sensors, EW, etc)?
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That is likely dependant on the set of requirements that the USN has around size, weight, performance, necessary subsystems like radar and sensor size etc. We haven't seen that whole set yet, just glimpses or small subsets, so it is hard to make a statement of complete confidence in one engine over another.
 
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F119Doctor said:
The 5 stage HPC didn’t work well in the PW6000 application, and was replaced with an MTU designed HPC.
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Right, the reporting at the time (2001) seems to be when Pratt was still trying to work out the 5-stage HPC from the XTC/XTE-66 for the PW6000, hence the earlier connection, but I think 2002 is when that got replaced by the 6-stage MTU HPC.

Beyond the initial 25,300 lbf thrust PW7000 reported for the Lockheed/Boeing/General Dynamics A/F-X, I believe I’ve seen at least 2 variants publicly reported by the late 1990s and early 2000s, both seemingly based on the XTE-66 5-stage HPC core tested for IHPTET Phase II. There’s the version with a scaled F119 fan and LPT proposed as an F414 alternative for the Super Hornet, and also one with an advanced 2-stage fan, although I don’t think that one had a specific application identified.

Currently, it appears that the PW9000 family has replaced the PW7000 for potential future military applications.
 
Last I heard (as reported in Aviation Week 10+ years ago) the PW9000 proposal was the PW1100G core (also with an MTU designed compressor) with a scaled F135 fan. There are rumors that a non afterburning version of this engine is the B-21 powerplant. The high speed low rotor of the PW1100G, minus the geared high bypass fan, would be a reasonable starting point for a lower bypass military turbofan.
 
If I heard it right - The 3 stream powerplants cannot right now do rapid cycling through their phases - 90 seconds IIRC for the open / shut - so for a carrier-based aircraft that is suicide if they snap a wire and have to hit reheat and go.
 
TerraFirma said:
If I heard it right - The 3 stream powerplants cannot right now do rapid cycling through their phases - 90 seconds IIRC for the open / shut - so for a carrier-based aircraft that is suicide if they snap a wire and have to hit reheat and go.
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That doesn't sound right to me.

If you're at sea level bolter conditions, there's no need to shift modes at all. If you're currently running in high-bypass mode you stay in high-bypass mode and light the AB in that condition. That's the higher AB thrust mode, anyways, since less air is being burned in the core.
 
TerraFirma said:
If I heard it right - The 3 stream powerplants cannot right now do rapid cycling through their phases - 90 seconds IIRC for the open / shut - so for a carrier-based aircraft that is suicide if they snap a wire and have to hit reheat and go.
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You can allways light the burners especially at SL but I think you are confusing with the spool-up time from idle to MIL RPM which does take a few seconds.
Usual landing procedures do ask for 100% if I recal right.
 

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