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

Thank you for confirming the higher bypass ratio giving more thrust at high Mach conditions. This is an advantage to the F110. The F110 not only has the highest thrust but also the highest bypass ratio of all F-15 engines.


At high speeds the F-15 intake ramps close to prevent too much air reaching the engine. At Mach 2.5 the Pratt engines hit their maximum airflow limit with the variable intake in the max position. The engines will begin to compressor stall above mach 2.5.

The F110 has a higher airflow limit which is why the F-16 needs the big mouth inlet. So in the F-15 when travelling at mach 2.5 with the inlets in max position the F110 engines can continue to handle more airflow as the speed increases above mach 2.5.

I'm sure you can explain this better. The original mach 2.9 makes perfect sense. This information has to be restricted as it would be a Pratt versus GE marketing issue.

Back on the NGAD topic. The F-15 speed was simply used to support a potential mach 3.5 top speed for the NGAD. I didn't realise we would dedicate two pages to the F-15. Lets forgeg about the F-15. What is your opinion about the NGAD top speed using the new engines? The highly swept frame. You know what is possible with engines. Mach 3.5 is totally realistic in a sprint?
I said high bypass can result in higher Hi-Mach AB thrust. There are a lot of variables between engine designs, and different configurations will reach a limit where thrust falls off for various reason. For example, the F-111F with the TF30-P-100/111 engine, rated at 25K at Max AB, has higher thrust at M2.5 than the F110-GE-129, rated at 29K at Max AB, that was proposed as a replacement.

Your understanding of the F-15 inlet is limited. The ramps of the inlet move to position the external shocks as close to the lower lip as possible, with a normal shock at the lower lip to the upper throat narrowest position. The higher the Mach number, the more deflected the ramps are to position the oblique shocks. If the intake is opened further to flow more air than the engine can take, spillage drag goes up. Smaller than the engine flow capability, the engine flow is choked off and thrust is reduced (see small mouth F-16 Block 30) The F-15 inlet is definitely more open at the throat to meet the -129 flow requirements, but the intake may run out of kinematic travel to properly position the shocks at the higher airflow as the Mach number increases. And, the -129 may have internal temperature or pressure limits that causes the core to cut back airflow, limiting either the fan airflow or fan pressure ratio (or both) at high Mn, high inlet temperature conditions. It is possible that the -220 powered F-15C is the fastest of all the variants at altitude.
 
I know three airplanes that flew for a long time at supersonic speeds of more than 2500 km / h, two of them are steel, one is titanium. The preparation for the flight of the latter is comparable to the preparation for a flight into space.
Lest people get the wrong impression, titanium's not magic, nor impossibly complex to use, just possessed of slightly different properties than steel that make it better for certain jobs. It doesn't necessarily need special preparations for use, I toss my titanium-framed wheelchair in and out of the car without a thought. If a titanium airframe needs spaceflight like preparations, that's more down to the other aspects of the airframe and operating environment, not the fact it's made of titanium.
 
It's not about melting, you don't need to reach melting temperature for an alloy structure to lose most of its structural integrity.

...

So no, the F-15 is not going Mach 2.9, period. It won't melt, but it will come apart from structural failure.

By the way, the old 'burning jet fuel can't melt steel beams' used by 9/11 conspiracy theorists misses the point. At whatever temperature it is (don't have the source to hand at the moment), steel expands by 10% and loses half its stiffness - so the carefully-engineered structures of the World Trade Center towers were suddenly the wrong shape and half as strong.
 
There are reasons other than speed to have highly swept wings.
Speaking of highly swept, if you derive the geometries from the landing gear doors from Boeings work and the canopy glass on Northrop Grumman's, the common benefactor is a wing sweep of around 45°, this sweep is nominal for speed in the range of the F-15, but may not be the sole benefactor as you said!
 
Steel structure are engineered in many case to handle a fire, as can be reasonably expected. That includes elastic property at higher temperature and collapsing scenario. 9/11 exposed the structure to unanticipated strain due to the massive area suddenly on fire resulting from the plane massive amount of fuel and generalized combustible construction material set ablaze.

Steel is the material of choice in many popular hot structure like boilers. This hot steel is tailored to have good properties at high temperature while remaining economical.
A boiler with a pressure vessels to hold steam can have a functioning temperatures as high as 600K for example.
 
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Speaking of highly swept, if you derive the geometries from the landing gear doors from Boeings work and the canopy glass on Northrop Grumman's, the common benefactor is a wing sweep of around 45°, this sweep is nominal for speed in the range of the F-15, but may not be the sole benefactor as you said!
F-117 is subsonic ;)
 
I said high bypass can result in higher Hi-Mach AB thrust. There are a lot of variables between engine designs, and different configurations will reach a limit where thrust falls off for various reason. For example, the F-111F with the TF30-P-100/111 engine, rated at 25K at Max AB, has higher thrust at M2.5 than the F110-GE-129, rated at 29K at Max AB, that was proposed as a replacement.
Yes. The TF30 has an even higher bypass ratio than the F110. This helps explain the higher thrust at Mach 2.5. The TF30 is also larger diameter than the F110. It is not surprising that the TF30 will outperform the F110 at M2.5

Generally the higher the bypass ratio the thrust with afterburner at high Mach levels.

Your understanding of the F-15 inlet is limited.
I was saving everyone from reading a complex 5,000 word essay on the variable inlets. I was keeping things limited to bypass ratio and air flow as these are easier for members to understand.

It is possible that the -220 powered F-15C is the fastest of all the variants at altitude.
It is also possible the F110 is the fastest by a significant margin. There has been many changes in the F-15QA and F-15E model to optimise the F110 engines.
 
Lest people get the wrong impression, titanium's not magic, nor impossibly complex to use, just possessed of slightly different properties than steel that make it better for certain jobs. It doesn't necessarily need special preparations for use, I toss my titanium-framed wheelchair in and out of the car without a thought. If a titanium airframe needs spaceflight like preparations, that's more down to the other aspects of the airframe and operating environment, not the fact it's made of titanium.
The main advantage of Ti over steel is lower weight for similar strength and temperature capability. There are a few handling issues like no chlorine solvents or cadmium plated hand tools, but it can take most day to day abuse just fine if designed properly for the specific application. Ti is much more difficult to use in the manufacturing process such as requiring inert atmospheres to weld and form, although these requirements have become pretty much industry standard after much learning on the A-12 / SR-71.
 
At a typical cruising altitude of 40-50,000 ft with an ambient static temperature of about -70 F (216 Kelvin), total/stagnation temperature is 415 F at Mach 2.5, and 583 F at Mach 2.9. That's a substantial temperature increase that's well beyond what many of the F-15's aluminum structural components such as wing leading edges can handle, and I can assure you it doesn't just take "a few seconds" to accelerate from Mach 2.5 to 2.9.
It is the duration of the heat rather than the peak heat. During a high speed run the F110 engines would hit Mach 2.5 in far less time than the best F100 engine. Less time is then less heat.

The F110 could then get "close to Mach 3" in the same duration as the F100 engine reached Mach 2.5.

So no, the F-15 is not going Mach 2.9, period. It won't melt, but it will come apart from structural failure.
Definitely no structural failure. It is rated for 9G. Flying at high speed in a straight line won't have the wings falling off. Anyway back to NGAD.
 
Yes. The TF30 has an even higher bypass ratio than the F110. This helps explain the higher thrust at Mach 2.5. The TF30 is also larger diameter than the F110. It is not surprising that the TF30 will outperform the F110 at M2.5

Generally the higher the bypass ratio the thrust with afterburner at high Mach levels.


I was saving everyone from reading a complex 5,000 word essay on the variable inlets. I was keeping things limited to bypass ratio and air flow as these are easier for members to understand.


It is also possible the F110 is the fastest by a significant margin. There has been many changes in the F-15QA and F-15E model to optimise the F110 engines.
Yes, the TF30-100 is higher bypass than the F110-129, but not by much. The F101 is higher than both, but I doubt very much that it would be a good M2.5+ engine.

And the highest performing engine in the M3+ envelope has been the J58, which functions as a very low bypass single shaft turbofan with the bleed bypass open at cruise speeds.
 
I will admit, I am expecting a higher supercruise speed for NGAD than for the F-22. Simply because the Pacific Ocean is stupid big and it takes time to fly from a base 1500+nmi from the fighting to where you're dropping ordnance. There may even be some Blackbird/XB70 style optimization for having good range at high speed, so the plane really can cruise at say Mach 2.2 for 3000nmi. Instead of the F-22 crap range while supercruising

Equally, I am expecting a physically large airframe due to range requirements, roughly F-111 sized/weight. What I hope happens is that the designers of NGAD make the weapons bays large enough for 2000lb class bombs and AGM-84s, so that the NGAD in a ground-attack loadout could pack the same load as the A-12 was intended to. Not that I totally expect the USAF to want a replacement for the Strike Eagle, but the USN will want a decent attack load.

In Air-to-air loadout, I expect the NGAD to be packing on the order of 10-12x BVRAAMs and 2-4x WVRAAMs. This is because of how long it would take to return to base and rearm. And then we start talking about the joys of CCAs as semi-disposable quivers.

At some point, probably in the 2060s or so, I expect the NGAD etc to be a single manned plane flying in control of an entire strike package of CCAs. Pre- and post-strike recon in the shape of an absurdly VLO ISR plane** marking targets, NGAD plus probably 3x air-warfare CCAs as fighter cover, maybe another NGAD plus 3x bomber CCAs or just 4x bomber CCAs for the strike, plus at least 1 Growler-replacement EW CCA.

** The kind of VLO that you look for by the "hole" in the received data, not the actual returns.
 
I will admit, I am expecting a higher supercruise speed for NGAD than for the F-22. Simply because the Pacific Ocean is stupid big and it takes time to fly from a base 1500+nmi from the fighting to where you're dropping ordnance. There may even be some Blackbird/XB70 style optimization for having good range at high speed, so the plane really can cruise at say Mach 2.2 for 3000nmi. Instead of the F-22 crap range while supercruising

Equally, I am expecting a physically large airframe due to range requirements, roughly F-111 sized/weight. What I hope happens is that the designers of NGAD make the weapons bays large enough for 2000lb class bombs and AGM-84s, so that the NGAD in a ground-attack loadout could pack the same load as the A-12 was intended to. Not that I totally expect the USAF to want a replacement for the Strike Eagle, but the USN will want a decent attack load.

In Air-to-air loadout, I expect the NGAD to be packing on the order of 10-12x BVRAAMs and 2-4x WVRAAMs. This is because of how long it would take to return to base and rearm. And then we start talking about the joys of CCAs as semi-disposable quivers.

At some point, probably in the 2060s or so, I expect the NGAD etc to be a single manned plane flying in control of an entire strike package of CCAs. Pre- and post-strike recon in the shape of an absurdly VLO ISR plane** marking targets, NGAD plus probably 3x air-warfare CCAs as fighter cover, maybe another NGAD plus 3x bomber CCAs or just 4x bomber CCAs for the strike, plus at least 1 Growler-replacement EW CCA.

** The kind of VLO that you look for by the "hole" in the received data, not the actual returns.
I'm fairly certain this is the goal. Cruising up a 60K, being VLO, and moving fast with great efficency, maybe turn performance and close in fighting will take the back burner for good. I imagine this concept being something that quickly dashes overhead undetected while dropping ordnance and being completely displace from it's release point before anyone could see where it came from. This is just the start, whose to even know what other kinds of implementations any sixth generation fighter will have. I completely agree that this will be a missileer quarterback that sends the unmanned vehicles in for the close in dirty work. We often talk of how those spooky planes from area 51 were mistaken for looking like UFOs, but what about when they start acting like it? Gives big mothership vibes.
 
I will admit, I am expecting a higher supercruise speed for NGAD than for the F-22. Simply because the Pacific Ocean is stupid big and it takes time to fly from a base 1500+nmi from the fighting to where you're dropping ordnance. There may even be some Blackbird/XB70 style optimization for having good range at high speed, so the plane really can cruise at say Mach 2.2 for 3000nmi. Instead of the F-22 crap range while supercruising

Equally, I am expecting a physically large airframe due to range requirements, roughly F-111 sized/weight. What I hope happens is that the designers of NGAD make the weapons bays large enough for 2000lb class bombs and AGM-84s, so that the NGAD in a ground-attack loadout could pack the same load as the A-12 was intended to. Not that I totally expect the USAF to want a replacement for the Strike Eagle, but the USN will want a decent attack load.

In Air-to-air loadout, I expect the NGAD to be packing on the order of 10-12x BVRAAMs and 2-4x WVRAAMs. This is because of how long it would take to return to base and rearm. And then we start talking about the joys of CCAs as semi-disposable quivers.

At some point, probably in the 2060s or so, I expect the NGAD etc to be a single manned plane flying in control of an entire strike package of CCAs. Pre- and post-strike recon in the shape of an absurdly VLO ISR plane** marking targets, NGAD plus probably 3x air-warfare CCAs as fighter cover, maybe another NGAD plus 3x bomber CCAs or just 4x bomber CCAs for the strike, plus at least 1 Growler-replacement EW CCA.

** The kind of VLO that you look for by the "hole" in the received data, not the actual returns.

The aircraft you're describing is similar to what I was expecting for the last couple of years, until the reassessment done this year in context of various fiscal pressures and review of technological availabilities.

But now it seems somewhat in the air, and everything from the manned NGAD aircraft itself, along with the new generation tanker, and the shape of CCA procurement in the near term, feels a bit unclear at present.
 
Yes, the TF30-100 is higher bypass than the F110-129, but not by much. The F101 is higher than both, but I doubt very much that it would be a good M2.5+ engine.

And the highest performing engine in the M3+ envelope has been the J58, which functions as a very low bypass single shaft turbofan with the bleed bypass open at cruise speeds.
I would disagree on the J58 being called a very low bypass engine. When at M3+ it is acting with a higher bypass ratio than most fighter jet engines. All that bleed bypass air is being dumped into the afterburner.


There may even be some Blackbird/XB70 style optimization for having good range at high speed, so the plane really can cruise at say Mach 2.2 for 3000nmi. Instead of the F-22 crap range while supercruising

Equally, I am expecting a physically large airframe due to range requirements, roughly F-111 sized/weight.

I agree with this completely it will be very big. I always say mach 2 supercruise for NGAD because it is a nice round number.

I think NGAD will have a higher MTOW than the F-111 due to the huge internal fuel capacity in that blended, delta wing. Even the Flanker series of aircraft is very close to the F-111 in size.

Look at the SR-71 it has 37 ton of fuel in an aircraft that weighs 30 ton empty. A very high fuel fraction. Speed does not need a very high thrust to weight ratio. A high thrust to weight ratio is only needed for dogfighting.

Take all the specifications of the F-22 and SR-71 and average them to exactly half way. That is the specs of NGAD.

Length: 25.83m
Wingspan: 15.25m
Wing area: 124m2
Top operational speed: Mach 2.725
Empty weight: 25,158kg
Internal fuel: 22,600kg
MTOW: 58,009kg
Service ceiling: 75,000 feet

It probably won't be the greatest dogfighter at very low speed. But it is very easy to sustain 9G at high cruising speeds.
 
It is the duration of the heat rather than the peak heat. During a high speed run the F110 engines would hit Mach 2.5 in far less time than the best F100 engine. Less time is then less heat.

The F110 could then get "close to Mach 3" in the same duration as the F100 engine reached Mach 2.5.
How do you know the F110 can even reach Mach 2.9 without hitting some kind of temperature limit (i.e. TIT, FTIT, compressor discharge, etc.)? No F110-equipped aircraft has ever hit that kind of speed, nor were they ever designed to. The F-15E is already time-limited above Mach 2.3, the time it takes to accelerate another 0.6M above that is not a short duration at all, and the F110 is simply not designed for it.

Definitely no structural failure. It is rated for 9G. Flying at high speed in a straight line won't have the wings falling off. Anyway back to NGAD.
It's not simply the static load factor, but also things like flutter and the ability for the structure and the actuators to handle that.

You are basing your entire supposition on a single (mis)statement by a Boeing PM that he later explicitly retracted, and you are refusing to let go. This is like arguing with a creationist.
 
I think we'll see that endurance will win out over raw speed. I had thought for some time we'd see an F-111 size fighter, but I'm not real convinced anymore. Trend is moving against that and towards cheaper distributed assets. Hopefully one of the lessons we are learning watching the Ukraine situation is that we will need to be able to build our next generation of combat aircraft quickly, and at home. Cheap would be a plus, too, but I suppose if the balloon goes up, they punt the bill to our grandchildren.
 
How do you know the F110 can even reach Mach 2.9 without hitting some kind of temperature limit (i.e. TIT, FTIT, compressor discharge, etc.)? No F110-equipped aircraft has ever hit that kind of speed, nor were they ever designed to.
How do you know that it can't?

You are basing your entire supposition on a single (mis)statement by a Boeing PM that he later explicitly
We have had someone from Boeing who had to retract the restricted information they accidentally leaked and reduced it to the publicly known information. No one would say the words "close to Mach 3" if the speed was below Mach 2.5.

I have based the assumption on the F110 having
1) Higher max thrust than any F-15 engine.
2) Higher bypass ratio than any F-15 engine.
3) Higher bypass ratio has proven to give more thrust at high Mach speeds.
4) Fly by wire and intake adjustments.
5) 50 years of service history to improve things regarding flutter.

I'm only saying it's 16% faster than the 31 year old flight test data someone has provided.

Anyway. Let's get back to NGAD.
 
All fighter jets rapidly lose speed when pulling 9G. If an aircraft starts from a higher speed it can sustain 9G for longer.

An aircraft cruising at mach 2 and 60,000 ft has enough energy to trade that it can pull enough G to kill the pilot.
 
We have had someone from Boeing who had to retract the restricted information they accidentally leaked and reduced it to the publicly known information. No one would say the words "close to Mach 3" if the speed was below Mach 2.5.

Let's look at the PM's statement in detail, shall we? He not only said Mach 2.9, but also said 2,225 mph, a value that would correspond to that Mach number at sea level. I don't even need to begin with how preposterous that is.

So what is more likely, that he made an error in an off-the-cuff remark, and later corrected himself on record to Mach 2.497, or that there's some deep conspiracy that somehow defies logic? I'm sure when the F-15EX -1 becomes available eventually, it will not reflect your absurd beliefs at all.


Not to mention, at Mach 2.9 the shock cone will be impinging on the wing structure, creating all sorts of loads that it wasn't designed for. Combine that with the severe aero heating, and it's all the more reason that the F-15EX won't touch that speed, period.
 
Yes we are about NGAD not F-15 EX
Wouldn't have gone down this rabbit hole if he didn't double down on his preposterous claims.

Back on the topic of NGAD, this article was posted a few pages ago, but here are the parts I thought was interesting.

“Our original plan was—and the funding that was laid in—was for two increments. … You don’t have to get everything into this Increment 1. What we need to do is get it out there, with the minimum viable capability, on time or early, and on-budget or under budget. But Increment 2 …. we are close to getting started in earnest on that.”

There is a government analysis underway for Increment 2 “with other parties…and internal government agencies” to determine the needed attributes of the system.

“And then next year—actually this fiscal year—we will kick off concept refinement, where we then bring in industry to help us further define what those attributes are and whittle down those use cases,” Helfrich said. “It’s really the same approach that we did for CCA Increment 1.”

He also said that studies and experiments so far indicate that pilots of crewed fighters will likely be able to control many more CCAs than originally thought.

Senior USAF leaders have speculated that the CCA program could eventually achieve a rhythm of introducing a new design every two to four years, which would be better for staying abreast of both changing technological opportunities and threats.

Helfrich emphasized that Increment 2 is not a derivative or growth version of Increment 1.

Just because it’s called Increment 2 doesn’t mean it “has more capability … we’re still looking to figure out … the right balance and do the analysis” of the needed capability “to maximize low cost,” he said. The Air Force may yet decide to “change the focus” of CCAs “from a missile truck to something else,” perhaps an electronic warfare platform.

“I think it’s a little too early to say whether or not we’re going to do “Increment 1B or 1C. We’ll have to learn as Increment 1 rolls out and as Increment 2 rolls out, but we do expect them to be complementary,” and that there will be “multiple Increments in the force at the same time.”

Helfrich said the life expectancy of a CCA is also not yet determined. Early concepts called for using the craft for a number of sorties, and then divesting them on one-way missions, with the idea of avoiding the creation of a sustainment enterprise to support them.

“A lot has to do with how you use them,” he later told Air & Space Forces Magazine. While a small number of CCAs may be used for training, most of their missions would likely be practiced in simulators, and the aircraft themselves would be stored in a crate until needed for operations.

If the CCA is being treated as an attritable item, I suppose that it makes sense that their missions would be practiced in simulators rather than being expended in exercises, but I have to wonder what the fidelity of that would be, especially in LFE where I've sometimes seen "magic fairy dust" taken too far.
 
I will admit, I am expecting a higher supercruise speed for NGAD than for the F-22. Simply because the Pacific Ocean is stupid big and it takes time to fly from a base 1500+nmi from the fighting to where you're dropping ordnance. There may even be some Blackbird/XB70 style optimization for having good range at high speed, so the plane really can cruise at say Mach 2.2 for 3000nmi. Instead of the F-22 crap range while supercruising

Equally, I am expecting a physically large airframe due to range requirements, roughly F-111 sized/weight. What I hope happens is that the designers of NGAD make the weapons bays large enough for 2000lb class bombs and AGM-84s, so that the NGAD in a ground-attack loadout could pack the same load as the A-12 was intended to. Not that I totally expect the USAF to want a replacement for the Strike Eagle, but the USN will want a decent attack load.

In Air-to-air loadout, I expect the NGAD to be packing on the order of 10-12x BVRAAMs and 2-4x WVRAAMs. This is because of how long it would take to return to base and rearm. And then we start talking about the joys of CCAs as semi-disposable quivers.

At some point, probably in the 2060s or so, I expect the NGAD etc to be a single manned plane flying in control of an entire strike package of CCAs. Pre- and post-strike recon in the shape of an absurdly VLO ISR plane** marking targets, NGAD plus probably 3x air-warfare CCAs as fighter cover, maybe another NGAD plus 3x bomber CCAs or just 4x bomber CCAs for the strike, plus at least 1 Growler-replacement EW CCA.

** The kind of VLO that you look for by the "hole" in the received data, not the actual returns.

I think a large long ranged super cruiser was the original idea, though probably not with more speed or that extreme warload. I think all bets are off now.

As for demonstrator record breaking, while the discussion has taught me a lot about trade offs in engine design, I think the assumption that speed records were broken seems misguided: there are any number of very minor performance records the quote might have referred to. And in any case the demonstrator might no longer be especially representative of the program’s end product.

ETA: we are going to have a hard time pinning down what NGAD is when it seems clear USAF does not know what NGAD is.
 
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B-21 + dual panel upscaled APG-85 in dem cheeks.

Simple and elegant.

I actually think B-21 would be ideal had it been adept in the supersonic regime. It already got all spectrum all aspec VLO, payload, range, sensors, avionics, etc nailed down.
 
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