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USAF/US NAVY 6th Generation Fighter Programs - F/A-XX, F-X, NGAD, PCA

Dragon029

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As for the F-35, it would maybe give it a substantially higher speed in military power, but how much longer would its range in subsonic regime be would greatly depend on the maximum BPR the new engines provide, and even then, the higher the BPR, the more SFC worsens with speed.
The range would increase by the 30%+ as mentioned; the adaptive cycle AETP engines (GE's XA100 and P&W's XA101) are both specifically designed / sized to fit the F-35 (they're by no means plug and play, but the F135 and F-35's engine bay was the reference size to match).

Ok, I think my confusion comes from having seen TSFC data in different conditions. For the F135 I had read something like 0.7 or maybe a bit better, which makes sense for the bypass ratio of the engine, but this is probably static and at sea level (where did you see 0.57?). For the high-bypass turbofans you mention, the value I had seen was ca. 0.55, but that is in cruise mode, actually the flight regime that is relevant in this case. With TSFC at subsonic cruising speed for current fighter jets we could know if the claim of 30% reduction with newer engines makes sense or not, but I didn't find anything reliable yet...
I got numbers mentally mixed up; 0.57 is the F135's bypass ratio, not TSFC - for the F135's TSFC there's competing numbers - there's 0.7lb/lbf/hr from one website published in 2004 that's incorrect about some F135 figures (so I don't trust it that much), and another of 0.886lb/lbf/hr that's supposedly from Janes, but with no specific reference, plus that number is rather high for an engine that should be relatively fuel efficient (exceptionally high combustion temperatures, a reasonable bypass ratio, etc). In any case you can look at TSFC numbers of other military turbofans here, and they're generally in the 0.7-0.8 range: http://www.jet-engine.net/miltfspec.html

Regardless of what the F135's TSFC is however, the 30%+ range increase is coming directly from GE and (kinda) P&W.

GE's website claims that their "ACE" (XA100) will offer a 50% improvement in loiter time, 35% increase in range, 25% reduction in fuel consumption and 60% increased heat transfer rate for the engine's heat exchangers: https://www.geaviation.com/military/engines/ge-adaptive-cycle-engine

P&W haven't given numbers for their XA101 / "F135 Growth Option 2" engine, but their "Growth Option 1" option, which just swaps out one of the F135 modules (without adding a 3rd airstream / adaptive cycle capabilities) offers 5-6% lower fuel burn and 6-10% greater thrust across the entire flight envelope of the engine; so evidently there's been improvements made in things like compressor and turbine design that offer increased fuel burn at the same bypass ratio: https://www.ainonline.com/aviation-...-outlines-three-step-f135-development-pathway
 

_Del_

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An engine sitting on a bench, and an engine in flight at any given altitude and/or speed will have a different TFSC. Same with the engine throttle setting. All those figures could be exactly correct in different circumstances.
 

Sundog

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You also have to look at the electrical power generation of these new power plants. Remember, due to all of the onboard systems fighters are now using, these are also designed for higher power generation, besides just higher thrust and better TFSC.
 

marauder2048

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You also have to look at the electrical power generation of these new power plants. Remember, due to all of the onboard systems fighters are now using, these are also designed for higher power generation, besides just higher thrust and better TFSC.
"Power/Thermal Interaction within an Adaptive Turbine Engine" by Andrew K. DeSomma.

Injecting waste heat from electrical power generation into the 3rd stream:

Another consequence is that the additional heat causes the 3rd stream to behave like an impromptu burner
that increases the total engine thrust by about 113 lbf/MW. Due to this additional thrust the engine also
does not need to work as hard to achieve the required thrust.
 

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sferrin

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An engine sitting on a bench, and an engine in flight at any given altitude and/or speed will have a different TFSC. Same with the engine throttle setting. All those figures could be exactly correct in different circumstances.
Ugh. . .I hate this "argument". "But muh bench. . . " Nobody cares. OBVIOUSLY an engine sitting on a bench is going to behave differently than in the air. Do you really think GE and Pratt don't kn
You also have to look at the electrical power generation of these new power plants. Remember, due to all of the onboard systems fighters are now using, these are also designed for higher power generation, besides just higher thrust and better TFSC.
"Power/Thermal Interaction within an Adaptive Turbine Engine" by Andrew K. DeSomma.

Injecting waste heat from electrical power generation into the 3rd stream:

Another consequence is that the additional heat causes the 3rd stream to behave like an impromptu burner
that increases the total engine thrust by about 113 lbf/MW. Due to this additional thrust the engine also
does not need to work as hard to achieve the required thrust.
113lbs for a 50,000lb thrust engine is almost in the noise.
 

marauder2048

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An engine sitting on a bench, and an engine in flight at any given altitude and/or speed will have a different TFSC. Same with the engine throttle setting. All those figures could be exactly correct in different circumstances.
Ugh. . .I hate this "argument". "But muh bench. . . " Nobody cares. OBVIOUSLY an engine sitting on a bench is going to behave differently than in the air. Do you really think GE and Pratt don't kn
You also have to look at the electrical power generation of these new power plants. Remember, due to all of the onboard systems fighters are now using, these are also designed for higher power generation, besides just higher thrust and better TFSC.
"Power/Thermal Interaction within an Adaptive Turbine Engine" by Andrew K. DeSomma.

Injecting waste heat from electrical power generation into the 3rd stream:

Another consequence is that the additional heat causes the 3rd stream to behave like an impromptu burner
that increases the total engine thrust by about 113 lbf/MW. Due to this additional thrust the engine also
does not need to work as hard to achieve the required thrust.
113lbs for a 50,000lb thrust engine is almost in the noise.
The engine thrust in the paper at those conditions is ~ 9500 lbs.
 

sferrin

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An engine sitting on a bench, and an engine in flight at any given altitude and/or speed will have a different TFSC. Same with the engine throttle setting. All those figures could be exactly correct in different circumstances.
Ugh. . .I hate this "argument". "But muh bench. . . " Nobody cares. OBVIOUSLY an engine sitting on a bench is going to behave differently than in the air. Do you really think GE and Pratt don't kn
You also have to look at the electrical power generation of these new power plants. Remember, due to all of the onboard systems fighters are now using, these are also designed for higher power generation, besides just higher thrust and better TFSC.
"Power/Thermal Interaction within an Adaptive Turbine Engine" by Andrew K. DeSomma.

Injecting waste heat from electrical power generation into the 3rd stream:

Another consequence is that the additional heat causes the 3rd stream to behave like an impromptu burner
that increases the total engine thrust by about 113 lbf/MW. Due to this additional thrust the engine also
does not need to work as hard to achieve the required thrust.
113lbs for a 50,000lb thrust engine is almost in the noise.
The engine thrust in the paper at those conditions is ~ 9500 lbs.
Wonder how that would translate to the bigger engine.
 

_Del_

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Ugh. . .I hate this "argument"
I wasn't making an "argument".

He seemed confused that there were varying figures for the TFSC.

for the F135's TSFC there's competing numbers...
He followed with numbers he didn't "trust".

I just tried to explain that there is no absolute figure. The TFSC will depend on the circumstances. None of the numbers he quoted from various sources need to be "wrong" or not trusted. They can all be true for some given set of variables. High, medium, low altitude, military power, cruise setting, best endurance speed, best cruise speed, etc will all result in a different TFSC.
 

marauder2048

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An engine sitting on a bench, and an engine in flight at any given altitude and/or speed will have a different TFSC. Same with the engine throttle setting. All those figures could be exactly correct in different circumstances.
Ugh. . .I hate this "argument". "But muh bench. . . " Nobody cares. OBVIOUSLY an engine sitting on a bench is going to behave differently than in the air. Do you really think GE and Pratt don't kn
You also have to look at the electrical power generation of these new power plants. Remember, due to all of the onboard systems fighters are now using, these are also designed for higher power generation, besides just higher thrust and better TFSC.
"Power/Thermal Interaction within an Adaptive Turbine Engine" by Andrew K. DeSomma.

Injecting waste heat from electrical power generation into the 3rd stream:

Another consequence is that the additional heat causes the 3rd stream to behave like an impromptu burner
that increases the total engine thrust by about 113 lbf/MW. Due to this additional thrust the engine also
does not need to work as hard to achieve the required thrust.
113lbs for a 50,000lb thrust engine is almost in the noise.
The engine thrust in the paper at those conditions is ~ 9500 lbs.
Wonder how that would translate to the bigger engine.
Good question. I just thought it was a "cute" result that waste heat isn't really wasted.
 

sferrin

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Good question. I just thought it was a "cute" result that waste heat isn't really wasted.
Read somewhere of a Martin Baker design (MB-5 maybe?) had its exhaust pipes oriented such that they produced forward thrust. (Maybe everybody did that.) Got hot air, may as well use it.
 

Bhurki

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Geez, take it easy..
Its not so much the heat from the electrical system that needs to be used to create some extra thrust, but the requirement of efficiently dumping that heat into streams that are already present to direct that heat out of the jet without any negative impact to the electric internals.

So looking at the adaptive stage to be something that harnesses heat from the components to add thrust is trivial, since its mostly working as a heat pump to cool everything down. The extra thrust is just a little free obvious bonus.
 

LMFS

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If the new engine has an option for a higher bpr than a F135 and lower possible bpr than a F119 and is similarly sized, it gives better efficiency all across the envelope. Or say the F135 size engine is the same bpr at max, but also allows lower bpr than the F135 by forcing air through the core, the F-35 will now have better supersonic efficiency (and possibly thrust) and lower spool times available as needed, but retains subsonic efficiency.
Yeah, that is exactly what I mean. Since the engine diameter is not going to change a lot, BPR may be increased compared to F135, but will it be by a big margin? Odds are that it is not going to be turned into a high bypass engine, and 30% reduction in consumption is a lot compared to an engine that is very modern and efficient already, and has been designed for subsonic flight. But I admit I dont have proof that is not the case. 30% less TSFC than a F119 in subsonic regime is realistic IMHO.

The range would increase by the 30%+ as mentioned; the adaptive cycle AETP engines (GE's XA100 and P&W's XA101) are both specifically designed / sized to fit the F-35 (they're by no means plug and play, but the F135 and F-35's engine bay was the reference size to match).
Ok I will read their statements with detail

I got numbers mentally mixed up; 0.57 is the F135's bypass ratio, not TSFC - for the F135's TSFC there's competing numbers - there's 0.7lb/lbf/hr from one website published in 2004 that's incorrect about some F135 figures (so I don't trust it that much), and another of 0.886lb/lbf/hr that's supposedly from Janes, but with no specific reference, plus that number is rather high for an engine that should be relatively fuel efficient (exceptionally high combustion temperatures, a reasonable bypass ratio, etc). In any case you can look at TSFC numbers of other military turbofans here, and they're generally in the 0.7-0.8 range: http://www.jet-engine.net/miltfspec.html
Maybe that value from Janes is cruise related? It would make sense...
Relatively high BPR in fighters go below 0.7 in uninstalled conditions, like the AL-31F for instance. It should be the case for F135 too, since it has similar BPR and way better technology.

GE's website claims that their "ACE" (XA100) will offer a 50% improvement in loiter time, 35% increase in range, 25% reduction in fuel consumption and 60% increased heat transfer rate for the engine's heat exchangers: https://www.geaviation.com/military/engines/ge-adaptive-cycle-engine
25% less consumption, 35% more range, 50% more persistence... it reads definitely like sales pitch / best case figures to me. They don't indicate what engine they are taking as reference, it may be F135 as you say but until now I have seen no proof, I will look further.

They also mention 60% more heat transference, in fact I seem to remember reading in an official document that the adaptive engines were critical to remove current restrictions regarding usable fuel and its temperature from the F-35. It may have an impact in those numbers, if for instance the fuel consumption is reduced a 25% plus due to better heat sink properties the engine allows to reduce the amount of non-usable fuel on board, they may in some circumstances reach that 35% extra range they announce. And of course, at high speeds it may not be possible to bypass so much air so that the heat sink function would not operate as effectively in that regime... it is a complex technology

P&W haven't given numbers for their XA101 / "F135 Growth Option 2" engine, but their "Growth Option 1" option, which just swaps out one of the F135 modules (without adding a 3rd airstream / adaptive cycle capabilities) offers 5-6% lower fuel burn and 6-10% greater thrust across the entire flight envelope of the engine; so evidently there's been improvements made in things like compressor and turbine design that offer increased fuel burn at the same bypass ratio: https://www.ainonline.com/aviation-...-outlines-three-step-f135-development-pathway
Exactly, the idea would be to decouple those technological improvements from the layout derived ones. It is not easy, though.
 
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Firefinder

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Another thing to consider for the range is any fuel increases or mods to the frame.

Say the navy decided to give the F35 a crank arrow delta wing, that will give you more fuel in the wings to have fun with. Design it well you may even get some better aerodynamics at cruise speeds.

So say the new adaptive engines just give a flat 20 percent increase to efficiently and range 90 percent of the time. And the new fuel load is about 20 percent more too, that will easily allow 1000 mile combat radius.

Then you have a conform fuel tank type of deal, that I sometimes sees toss around.

Honestly it be easier to just design a fresh design with all the new thing built in....
 

_Del_

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Yeah, that is exactly what I mean. Since the engine diameter is not going to change a lot, BPR may be increased compared to F135, but will it be by a big margin? Odds are that it is not going to be turned into a high bypass engine, and 30% reduction in consumption is a lot compared to an engine that is very modern and efficient already, and has been designed for subsonic flight
Say the BPR is exactly the same, but you can increase exhaust velocity by sending everything through the core like a turbojet. Will you see a 30% reduction in consumption? Maybe. It won't be in the subsonic regime.
The increased efficiency will be at the higher airspeeds where you are now getting more thrust for less fuel burn. Maybe that let's you supercruise. Maybe that just substantially increases the airspeed you can cruise with a tolerable fuel burn, but it's not hard to see how that could translate to more speed, range, and operational possibilities for the F-35 in either case.
 

Dragon029

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I wasn't making an "argument".

He seemed confused that there were varying figures for the TFSC.

for the F135's TSFC there's competing numbers...
He followed with numbers he didn't "trust".

I just tried to explain that there is no absolute figure. The TFSC will depend on the circumstances. None of the numbers he quoted from various sources need to be "wrong" or not trusted. They can all be true for some given set of variables. High, medium, low altitude, military power, cruise setting, best endurance speed, best cruise speed, etc will all result in a different TFSC.
At the time those articles had been published no F135 had actually flown in the air (the X-35s used F119 variants that, while they would've been similar, were still several years of development away from being refined into the F135), so unless the source had referencing calculated / simulated performance figures for different flight regimes they would've been sea level test-stand figures (which as far as I'm aware the vast majority of engine performance brochure figures come from anyway).

Also the numbers that I didn't trust from the 0.7lb/lbf/hr figure website were things like claims that the F135 has a 0.2 bypass ratio, which is definitely incorrect; P&W have officially published numbers of 0.57 for the CTOL/CV engines and 0.56->0.51 for conventional and STOVL mode (not counting the lift-fan as bypass). The F119-PW-611 used on the X-35 might have been notably different, but it must've retained relatively similar BPR, etc figures to today's F135 to make the lift-fan work and fit the (roughly) same engine bay dimensions on the X-35.

25% less consumption, 35% more range, 50% more persistence... it reads definitely like sales pitch / best case figures to me. They don't indicate what engine they are taking as reference, it may be F135 as you say but until now I have seen no proof, I will look further.

They also mention 60% more heat transference, in fact I seem to remember reading in an official document that the adaptive engines were critical to remove current restrictions regarding usable fuel and its temperature from the F-35. It may have an impact in those numbers, if for instance the fuel consumption is reduced a 25% plus due to better heat sink properties the engine allows to reduce the amount of non-usable fuel on board, they may in some circumstances reach that 35% extra range they announce. And of course, at high speeds it may not be possible to bypass so much air so that the heat sink function would not operate as effectively in that regime... it is a complex technology
You're right that they don't explicitly name the F135 as the baseline that they're referencing, but I'm skeptical that it'd be any other engine (*maybe* it could be their F136) considering that the engines are meant to fit the F-35.
 

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marauder2048

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Flyaway

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i.e. - The USAF, after decades of trying, thinks they have finally found a way to get rid of the A-10.
You could say that about the B-1 now as that seems to have a lot of issues.
 

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My problem is, after reading the document, I have no idea what he is advocating. It's a puff piece. There isn't any concrete action listed in the document and most of what he is talking about with regard to "integration" and "networking", etc., has been going on for years. It's a full on Powerpoint Warrior document. Get back to me when he has something substantive.
 

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IMO the target are all the C-135 based airframe: AWACS, JSTAR, RC, KC... They all could have to go.
 
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At some point in the article, it is mentioned it is a "virtual version"... Is it just simulation or a "true" plane?
 

sferrin

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At some point in the article, it is mentioned it is a "virtual version"... Is it just simulation or a "true" plane?
Yeah, I'll be surprised if there isn't some marketing stretching of the truth there. "Already successfully flown" in the simulator maybe.
 

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Just my view, but I don't think this is stretching the truth at all. Anyone who knows Roper knows that isn't his style. In 2016, the Government gave GE and Pratt $1B contracts for a new fighter engine. It seems unlikely to me that they would award engine contracts without a near simulteneous airframe contract. Also, the funding for the 6th generation aircraft jumped significantly in FY19 and FY20. Adding it up, it seems likely they would be flying a demonstrator now. I'd sure like to know what records they broke with the vehicle.
 

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Wasn't this flown as part of that DARPA program started in 2015 or 2016?
 

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I don't know and You may be correct. But I would think that if you were correct, it would be a different vehicle. If the engine contracts were issued to Pratt and GE in 2016, it's just my view, but I doubt that funding level is sufficient to pay for engines plus flight test.
 

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I recall the reports 2 years ago about a small demonstrator of the SR-72 being spotted. This would probably be the new fighter instead.
 

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I recall the reports 2 years ago about a small demonstrator of the SR-72 being spotted. This would probably be the new fighter instead.
Wouldn’t that have been too early for this program.
 
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