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

[quellish]

Now you are contradicting yourself.

Your link just said they flew a full-scale prototype. The title of your link:

I would suggest reading the article:

“We’ve already built and flown a full-scale flight demonstrator in the real world, and we broke records in doing it,” Will Roper told Defense News in an exclusive interview ahead of the Air Force Association’s Air, Space and Cyber Conference. “We are ready to go and build the next-generation aircraft in a way that has never happened before.”

 

[RJMAZ]

I would suggest reading the article:

The link has the word demonstrator twice and the word prototype seven times.

With the digital design software they no longer need to create demonstrators or scaled models. They can model and simulate all of this with software. The full-scale prototype will then only need minor tweaks to go into low scale production.

The new Skunk Works advanced manufacturing facility is optimised for low rate production. Or as I like to call it full-scale prototype production. Lockheed recently hired 2000 staff to work at this new facility. All signs point to NGAD being produced at a rate of around one aircraft per month.

We will see in the next 12 months when there is still no NGAD contract points to it staying black.

Or if NGAD is awarded to Lockheed and they rapidly have a pair of production aircraft flying this points to them already being in production right now.

 

[quellish]

The link has the word demonstrator twice and the word prototype seven times.

And yet the source they quote (Roper) very specifically says demonstrator.

With the digital design software they no longer need to create demonstrators or scaled models. They can model and simulate all of this with software. The full-scale prototype will then only need minor tweaks to go into low scale production.

That would make validating the software models difficult. But it would also remove all need for the Groom Lake and RATSCAT facilities, which would be a win! Let's close them today and bet on the design software!

The new Skunk Works advanced manufacturing facility is optimised for low rate production. Or as I like to call it full-scale prototype production. Lockheed recently hired 2000 staff to work at this new facility. All signs point to NGAD being produced at a rate of around one aircraft per month.

It's not "full scale prototype production". It's low rate production - producing small quantities of things using manufacturing processes that do not scale up well, like 3D printing. That facility is being used for things like Speed Racer production.

We will see in the next 12 months when there is still no NGAD contract points to it staying black.

There are multiple NGAD contracts right now, that have been awarded in the past year, so I am not sure what you are referring to.

 

[aim9xray]

The link has the word demonstrator twice and the word prototype seven times.

Pedantically, and specifically, Valerie Insinna (the writer), used the word prototype seven times, and demonstrator once.

The source, Dr. Will Roper was quoted using the word prototype zero times and demonstrator once.

I would tend to go with the interviewee as the subject matter expert, but hey, that's just me.

 

[CV12Hornet]

What threats is it meant to be defending the fleet from? And which of these require supersonic performance?

It's not going to be much use against DF-21D from land/ship or H-6s launching ASBMs from 1,000nm away. So is it mostly just going to be doing outer layer cruise missile defence before they get to SM-6 range?

There are more aircraft threats than just H-6 with ASBMs. A majority of Chinese H-6s are going to be cruise missile carriers with YJ-12s for the foreseeable future, and YJ-12s don't have quite enough range to keep their launch platforms out of range of the CAP fighters. And much Chinese maritime strike capability still rests on fighters, quite a few of which still have to rely on even shorter-range missiles than the YJ-12.

 

[quellish]

"Take the Red Pill: Disruptive Agility For a Disruptive World."

View: https://youtu.be/bhngHlHjuEQ?si=gSKWmmGoLahO6lg5&t=2345

 

[paralay]

Do you feel that advances in composite materials could counter this?

I am not aware of the characteristics of modern composite materials. I assume that their heat transfer is worse than that of metals, but this is not accurate

This doesn't mean NGAD will be flying at Mach 3.5 during combat but it was simply a demonstration. NGAD flying it's entire mission supercruising at Mach 2 is already impressive. It will be very hard to intercept or shoot down once you add the low radar cross section.

The fact is that since the seventies, American military aviation has deliberately reduced the requirements for maximum speed. I do not know how this is justified, probably there is logic in this.
Flying at a speed of more than M = 2.1 forces the use of an adjustable air intake, which makes the structure heavier by ~ 300 kg and increases the RCS due to the presence of gaps in the front hemisphere.

I do not think that the glazing of the cabin is a serious limitation on the maximum speed. There are enough solutions in this area. For example, the nose fairings of hypersonic missiles are made of glass and its derivatives

 

[RJMAZ]

The fact is that since the seventies, American military aviation has deliberately reduced the requirements for maximum speed. I do not know how this is justified, probably there is logic in this.

The cruising speeds of fighters has steadily increased. Average speed has significantly increased. There is a huge advantage to supercruising. Faster is definitely better. The top speed haven't been as important due to the range being so low when travelling with Max afterburner.

A Mach 3.5 top speed of NGAD would not have been a design requirement. It would have simply been a result of the requirement for a high supercruise speed. If you build a design that can cruise at mach 2 without afterburner then it shouldn't be a surprise that it will be extremely fast with afterburner.

Flying at a speed of more than M = 2.1 forces the use of an adjustable air intake, which makes the structure heavier by ~ 300 kg and increases the RCS due to the presence of gaps in the front hemisphere.

It is easy to design the fixed intakes to be tuned for the mach 2+ range. The intake would then be a restriction at low speeds. There are multiple solutions that can solve that. Both the F-117 and B-2 have doors that opened at low speeds to increase airflow to the engines.

This also assumes the three stream engine behaves the same at high speed. The third stream could behave like the J58 engine in the SR-71. So instead of narrowing the intake the extra airflow can bleed into the third stream and dump into the afterburner. This would also explain the record breaking speed.

 

[paralay]

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.
The cost of NGAD has already become a problem for the world's largest military budget...

 

[RJMAZ]

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.

I'm not saying NGAD can fly above 2,500km/h for a long time. 2,500 km/h would surely be well above the supercruising speed of NGAD. Any bursts above 2,500km/h would be for a short time thus they do not require steel and titanium.

The F-22 has a supercruise speed listed at 1,870 km/h. I assume NGAD will have a supercruise similar or maybe around 2,000km/h but the key feature is it will be able to supercruise for much longer than the F-22.

 

[icyplanetnhc (Steve)]

Do you feel that advances in composite materials could counter this?

BMI composites such as the IM-7/5250-4 on the F-22 can have operating temperatures of 400 degrees Fahrenheit sustained, which is even better than aluminum, but these materials are quite expensive, and Mach 2+ speeds also make you much more visible in the IR spectrum.

The official F-15E fact sheet on the USAF website says Mach 2.5 plus. The F-15EX has engines with 23% more thrust than the original F-15E engines.

The static thrust of the F-15E with the F100-229 (29,160 lbs thrust) is negligibly different from the F-15EX with F110-129 (29,500 lbs thrust). The dynamic thrust of the -129 is better, but it tells nothing about the max speed of aircraft. In fact, the F-15E with -229 engines tops out at Mach 2.35 while the -220 engines top out at Mach 2.40

 

[RJMAZ]

I am not aware of the characteristics of modern composite materials. I assume that their heat transfer is worse than that of metals, but this is not accurate

Ceramic matrix composites or CMC are a modern composite materials that is now appearing in turbine blades of the latest engines. They have the highest heat handling ability and also absorb radar. The most flawless material for the leading edges of a high speed stealth fighter.

CMC is ridiculously expensive. The recent reports how they are redesigning NGAD for low cost could involve swapping out expensive high temp materials for lower cost less heat tolerant materials. This makes sense if the record breaking NGAD prototype far exceeded the operational need for speed. I can't think of any other way to design out cost besides changing the materials and simplifying the design such as removing active cooling systems.

 

[Forest Green]

Its OK. We dont need to debate over the exact terminology. Or which budget paid for the aircraft.

Pentagon fails 7th audit in a row, eyes passing grade by 2028 - Breaking Defense

“This result was not a surprise, and I know that on the surface it doesn't sound like we're making progress. However, that is not the case,” said DoD comptroller Michael McCord.

breakingdefense.com

 

[RJMAZ]

Mach 2+ speeds also make you much more visible in the IR spectrum.

Forcing the enemy to spend tens of billions of dollars developing an integrated IR sensor network that is datalinked to provide guidance to SAM missiles. Sounds like a great idea. The USAF only needs a small silver bullet fleet of aircraft but the enemy has to develop countermeasures.

 

[icyplanetnhc (Steve)]

That is usually what happens when someone accidentally says restricted information. They have to say they misspoke. He originally said mach 2.9. When misspeaking it is common to get two numbers the wrong way around. But he said "nearly mach 3". Mach 2.497 is not "nearly mach 3."

"Nearly mach 3" matches his "mach 2.9" quote.

The official F-15E fact sheet on the USAF website says Mach 2.5 plus. The F-15EX has engines with 23% more thrust than the original F-15E engines.

Let's put this ridiculous myth to rest. Again, keep in mind that the F100-229 engines have practically the same static thrust as the F110-129 on the F-15EX, and more powerful than the F100-220.

 

[RJMAZ]

Let's put this ridiculous myth to rest. Again, keep in mind that the F100-229 engines have practically the same static thrust as the F110-129 on the F-15EX, and more powerful than the F100-220.

I'm not sure if posting graphs from a flight test done 34 years ago will help put this to rest.

Both of the graphs include the lower powered Pratt 220 engines.

 

[flateric]

I'm not sure if posting graphs from a flight test done 34 years ago will help put this to rest.

I'm not sure if you even understand what that graphs mean.

 

[flateric]

Assuming a 22.5° 2D wedge, the 40.8° oblique shock wave corresponds to about Mach 3. For a 3D cone, the Mach number is around 2.

Sure. As legit as these.

 

[RJMAZ]

Currently trying to use this to make a good model of it.

Intakes will not be on the upper surface. That cockpit looks looks far too big relative to the aircraft size. That looks like a F-35 sized aircraft yet NGAD will have twice the thrust of the F-35.

 

[VTOLicious]

...NGAD will have twice the thrust of the F-35.

How do you know? I would suggest to use terms like "assumed", "most probably", "imho", etc.

 

[quellish]

The most flawless material for the leading edges of a high speed stealth fighter.

The leading edges need to smoothly transition from the electrical properties of free space (air) to that of the rest of the aircraft structure. Ceramic matrix composites can't do that.

 

[icyplanetnhc (Steve)]

I'm not sure if posting graphs from a flight test done 34 years ago will help put this to rest.

Both of the graphs include the lower powered Pratt 220 engines.

https://tacg218.com/wp-content/uploads/2023/04/F-15E-Flight-Manual-15-April-1993.pdf

Go check page 772, this is clearly the -229 engines.

The F-15EX does not go Mach 2.9, period. The PM misspoke at the spur of the moment and explicitly clarified Mach 2.497.

 

[overscan (PaulMM)]

Note that the F-15E clean can reach about Mach 2.5 maximum only on a colder day (-10degrees) and for a brief period of time. On a warmer day (+10 degrees) it barely breaches Mach 2.

This shows the stupidity of a single number.

 

[RJMAZ]

Go check page 772, this is clearly the -229 engines.

The F-15EX does not go Mach 2.9, period. The PM misspoke at the spur of the moment and explicitly clarified Mach 2.497.

First you posted the Pratt 220 engines from a 34 year old flight test. Now you post the Pratt 229 engines from a 31 year old flight test.

The Pratt 220 engine actually goes slightly faster than the Pratt 229 despite having much lower thrust. This shows that the engine design plays a very big part. You can not assume the GE F110 will be similar. A primary reason for the lower powered 220 having a higher top speed is because the bypass ratio dropped from 0.63:1 in the 220 to 0.36:1 in the 229. Less bypass air means less oxygen for the afterburner and lower exhaust velocity.

The F110 in the EX not only has a higher maximum thrust than both Pratt engines but it's bypass ratio is 0.76:1 giving more oxygen to the afterburner. It has the highest peak exhaust velocity of all F-15 engines. The F-15EX and F-15QA also has aerodynamic tweaks including a full fly by wire system. You can clearly see a massive improvement in the air show performance. All of this is what gives the Mach 2.9 top speed. Period.

Note that the F-15E clean can reach about Mach 2.5 maximum only on a colder day (-10degrees) and for a brief period of time. On a warmer day (+10 degrees) it barely breaches Mach 2.

This shows the stupidity of a single number.

Of course but we must compare apples to apples. All the maximum speeds are from ideal conditions. All aircraft suffer performance drops with suboptimal altitude and temperature.

 

[Rhinocrates]

I would think that extraordinary performance under ideal conditions would be irrelevant to the required operation of an aircraft. If a stripped F-15 could graze Mach 2.5, what could it actually do at that speed, which it could only hold briefly, without weapons and radar? The question is, what is it required to do and how well does it do it compared to its rivals?

A superfast fighter would require specialised design for that superfast regime. The F-15 doesn't have it (that said, I think that it's one of the all-time classic designs). In any case, it was conceived before people were thinking about 'generations.'

Remember, it took a Hell of a lot of specialised engineering with Blackbird and a Foxbat inlet, material, structure and engine design to allow them to reach Mach 3. The Foxbat wrecked it engines with every high speed dash and every Blackbird mission was like a space launch. That just isn't apparent in an F-15. None of the published concepts for NGAD/FAXX indicate specialisation to achieve, let alone sustain extreme speed.

Nowadays, with very long cycles of development and production, each new generation of any military system strives to transcend, not merely improve upon the present state of the art. I don't think that any next-generation fighter will be just somewhat faster than its opponents; instead, it will operate in another realm where it is intended to be unreachable. That's the doctrine behind stealth and hypersonics. If NGAD were required to be faster, it would be much faster - Mach 5, say, not 3. If it's stealthy, it's extremely stealthy, if it's networked, then it's very networked and can control fleets of CCAs and even Roombas. The evidence indicates that NGAD/FAXX is not notably faster - i.e., not hypersonic - so it's something else - such as super-stealthy, super-networked, super long-ranged, super-cruise, whatever.

 

[Scorpion82]

First you posted the Pratt 220 engines from a 34 year old flight test. Now you post the Pratt 229 engines from a 31 year old flight test.

The Pratt 220 engine actually goes slightly faster than the Pratt 229 despite having much lower thrust. This shows that the engine design plays a very big part. You can not assume the GE F110 will be similar. A primary reason for the lower powered 220 having a higher top speed is because the bypass ratio dropped from 0.63:1 in the 220 to 0.36:1 in the 229. Less bypass air means less oxygen for the afterburner and lower exhaust velocity.

The F110 in the EX not only has a higher maximum thrust than both Pratt engines but it's bypass ratio is 0.76:1 giving more oxygen to the afterburner. It has the highest peak exhaust velocity of all F-15 engines. The F-15EX and F-15QA also has aerodynamic tweaks including a full fly by wire system. You can clearly see a massive improvement in the air show performance. All of this is what gives the Mach 2.9 top speed. Period.

I'm not an engine expert, but to much understanding it's exactly the opposite, lower bypass means better supersonic performance, not the other way round. Hence the low BPR of 0.2 on the supercruising F119, or 0.4 on the EJ200 etc. A lower SFC and specific static thrust requires the higher BPR. Hence the very high BPR on civil turbofan engines and the higher BPR of the RB199 or F135 compared to the above mentioned fighter engines, compares to the striker engines emphasising fuel economy at subsonic cruise over dynamic thrust output at supersonic speeds. A key limitating factor of attainable Mach/EAS is structural integrity (temperature limit). I doubt the F-15EX airframe has been comprimised for a much higher speed, as it's of little utility from an operational point of view. It would be a waste of money! And for that matter FBW doesn't change the aerodynamics of an aircraft, unless the CG is moved aft. The spectacular MANEUVERABILITY demonstrated by the F-15QA proves nothing with regard to a stunning Mach 0.4 increase which you claim based on a misspoken statement of an official. Airbus has recently sputed nonsense about Typhoon's top speed being Mach 2.4 equivalent to 2900 km/h. Both doesn't add up, is nonsense and simply not true. I'd rather trust a flight manual than a spokesman of whatever entity. And yes the F110 is a different engine, but as stated above a higher BPR has the opposite impact of what you state. Let alone that the F-15EX isn't the first Ragle with that engine, nor has it increased the F-16 Block 50s max speed or supersonic performance, compared to the F100-PW-229 powered Block 52. There are many factors at stack including airflow, pressure recovery and airframe related temperature limits.

 

[paralay]

It would be logical to assume that the demonstrator is an aircraft without a complete set of equipment with two F135 engines. Naturally, it will have enormous excess power and set records in the minimum takeoff length, rate of climb and cruising supersonic. It is possible to assume an RCS at the level of a cruise missile - 0.2 m2 (according to the Russian measurement method)

Although most likely the demonstrator is a reduced scale model of 76%, with two F414.

 

[zebra159357]

It is possible to assume an RCS at the level of a cruise missile - 0.2 m2 (according to the Russian measurement method)

Im curious how did you come up with that number for a supposed demonstrator, one that we have zero clue about as far as its capabilities go.

 

[F119Doctor]

First you posted the Pratt 220 engines from a 34 year old flight test. Now you post the Pratt 229 engines from a 31 year old flight test.

The Pratt 220 engine actually goes slightly faster than the Pratt 229 despite having much lower thrust. This shows that the engine design plays a very big part. You can not assume the GE F110 will be similar. A primary reason for the lower powered 220 having a higher top speed is because the bypass ratio dropped from 0.63:1 in the 220 to 0.36:1 in the 229. Less bypass air means less oxygen for the afterburner and lower exhaust velocity.

The F110 in the EX not only has a higher maximum thrust than both Pratt engines but it's bypass ratio is 0.76:1 giving more oxygen to the afterburner. It has the highest peak exhaust velocity of all F-15 engines. The F-15EX and F-15QA also has aerodynamic tweaks including a full fly by wire system. You can clearly see a massive improvement in the air show performance. All of this is what gives the Mach 2.9 top speed. Period.


Of course but we must compare apples to apples. All the maximum speeds are from ideal conditions. All aircraft suffer performance drops with suboptimal altitude and temperature.

There is no chance that the F-15EX goes M2.9. If the airframe exceeds M2.3 for any length of time, the polycarbonate windscreen is being replaced due to fissure cracks caused by the aero heating. You’ll notice the “time limited” area of the flight envelope at the high Mach numbers.

Each engine will have different limiting factors as the speed and inlet temperatures increase. The lower bypass / higher nozzle pressure ratio of the -229 is better for Mil power supersonic thrust, but that isn’t an issue at the M2+ speeds. Higher bypass of the -220 and -129 can mean better Max AB thrust at high Mach conditions, if the high temperature inlet air doesn’t result in major core power cutback. The -100/200/220 control system has a variable vane schedule that gets more aggressive at high inlet temperatures to increase core airflow without overspeedong the core, but if you let the core decelerate at those conditions the compressor blades will immediately flutter and break off (internal throttle is locked up at Mil power minimum above M1.4). The -229 doesn’t have this schedule, because M2.3+ isn’t a requirement. I don’t know if the -129 has any high Mach tricks in its schedules.

Another issue is the F-15 variable inlet scheduling. The -220 max airflow is 228 pps, while the -229 is 248 pps, and the -129 is 275 pps. The higher airflow requirements may result in the inlet not being in the optimum position for ram recovery or aircraft drag at the M2.3+ conditions as it was for the original -100 /-220 airflow characteristics it was designed for.

 

[icyplanetnhc (Steve)]

First you posted the Pratt 220 engines from a 34 year old flight test. Now you post the Pratt 229 engines from a 31 year old flight test.

The Pratt 220 engine actually goes slightly faster than the Pratt 229 despite having much lower thrust. This shows that the engine design plays a very big part. You can not assume the GE F110 will be similar. A primary reason for the lower powered 220 having a higher top speed is because the bypass ratio dropped from 0.63:1 in the 220 to 0.36:1 in the 229. Less bypass air means less oxygen for the afterburner and lower exhaust velocity.

The F110 in the EX not only has a higher maximum thrust than both Pratt engines but it's bypass ratio is 0.76:1 giving more oxygen to the afterburner. It has the highest peak exhaust velocity of all F-15 engines. The F-15EX and F-15QA also has aerodynamic tweaks including a full fly by wire system. You can clearly see a massive improvement in the air show performance. All of this is what gives the Mach 2.9 top speed. Period.

Yeah, let's ignore the thermal limits of the windscreen and the aluminum alloy of many structural components, increasing temperatures from inlet heating, and all other factors that make Mach 2.9 a complete absurdity for the F-15EX that simply doesn't happen.

That is why I am using it as supporting evidence for the NGAD prototype hitting Mach 3.5 in a very short sprint. Top speed is the most likely record that was broken on the test flight.

Back to the topic of NGAD, this is also an extreme non-sequitur.

 

[paralay]

Im curious how did you come up with that number for a supposed demonstrator, one that we have zero clue about as far as its capabilities go.

This is the limit for a maneuverable fighter that can be reached without active means of protection

 

[zebra159357]

This is the limit for a maneuverable fighter that can be reached without active means of protection

Limit assessed by who ?

 

[quellish]

To get back on the topic of NGAD....

The demonstrator program began in FY16. Two demonstrators (or sets of demonstrators, i.e. 2 each) were built: One for the Air Force, one for the Navy, from different contractors. The demonstrator program was under DARPA and the services. At the time the vision for the program was based around the "Penetrating Counter Air" concept of having a lot of capability in one manned aircraft. DoD had identified 5 key (immature) enabling technologies for the program. Most of these technologies would have been demonstrated by the demonstrator aircraft. At the time manned-unmanned teaming was still speculative and may not have been a priority for the demonstrators.

The demonstrator aircraft likely started flying in 2017 or 2018.

Later in the course of development DoD moved away from a single manned aircraft having these key technologies. Instead, these technologies would be matured in parallel and applied to legacy platforms as appropriate. The manned "6th generation" platform would then have some portion of those technologies.

The goals of the program have evolved quite a bit since then. Manned-unmanned teaming has become a much higher priority. Many of the capabilities or technologies originally envisioned for the "6th generation" manned aircraft are now distributed elsewhere in the "system of systems".

 

[FlyGuy369]

I would think that extraordinary performance under ideal conditions would be irrelevant to the required operation of an aircraft. If a stripped F-15 could graze Mach 2.5, what could it actually do at that speed, which it could only hold briefly, without weapons and radar? The question is, what is it required to do and how well does it do it compared to its rivals?

A superfast fighter would require specialised design for that superfast regime. The F-15 doesn't have it (that said, I think that it's one of the all-time classic designs). In any case, it was conceived before people were thinking about 'generations.'

Remember, it took a Hell of a lot of specialised engineering with Blackbird and a Foxbat inlet, material, structure and engine design to allow them to reach Mach 3. The Foxbat wrecked it engines with every high speed dash and every Blackbird mission was like a space launch. That just isn't apparent in an F-15. None of the published concepts for NGAD/FAXX indicate specialisation to achieve, let alone sustain extreme speed.

Nowadays, with very long cycles of development and production, each new generation of any military system strives to transcend, not merely improve upon the present state of the art. I don't think that any next-generation fighter will be just somewhat faster than its opponents; instead, it will operate in another realm where it is intended to be unreachable. That's the doctrine behind stealth and hypersonics. If NGAD were required to be faster, it would be much faster - Mach 5, say, not 3. If it's stealthy, it's extremely stealthy, if it's networked, then it's very networked and can control fleets of CCAs and even Roombas. The evidence indicates that NGAD/FAXX is not notably faster - i.e., not hypersonic - so it's something else - such as super-stealthy, super-networked, super long-ranged, super-cruise, whatever.

The only thing I have found that eludes to a mission profile was in the SERN invention from Northrop Grumman. Mach 2.2 at FL600 with loitering periods at Mach .08 (probably .8) at FL300. As far as what I can see as well, Northrop has also invented their own version of a DSI. My research has shown that the design closely resembles that of the superbowl commercial Easter eggs. But hey, since we are talking high speed stuff, look at this canopy from Northrop last year. Looks absolutely wild.

 

[paralay]

Limit assessed by who ?

statistiques, mon ami

 

[RJMAZ]

I'm not an engine expert, but to much understanding it's exactly the opposite, lower bypass means better supersonic performance, not the other way round. Hence the low BPR of 0.2 on the supercruising F119, or 0.4 on the EJ200 etc.

That is for maximum exhaust velocity at dry thrust. For supercruising a lower bypass generally gives higher exhaust velocity.

We are talking about maximum speed in full afterburner. Notice how the B-1B is by far the loudest aircraft at every airshow. Noise is linked to exhaust velocity. The B-1B has the highest bypass ratio of any afterburning engine.

Yeah, let's ignore the thermal limits of the windscreen and the aluminum alloy of many structural components, increasing temperatures from inlet heating, and all other factors that make Mach 2.9 a complete absurdity for the F-15EX that simply doesn't happen.

It's only for a few seconds. Going from Mach 2.5 to Mach 2.9 won't suddenly have the F-15EX melting. Period.

Back to the NGAD prototype. Mach 3.5 for a few seconds breaking the record seems highly likely. Everything from the inlets to canopy would be designed for sustained heating from supercruise. They are designed to handle high heat.

 

[RJMAZ]

The lower bypass / higher nozzle pressure ratio of the -229 is better for Mil power supersonic thrust, but that isn’t an issue at the M2+ speeds. Higher bypass of the -220 and -129 can mean better Max AB thrust at high Mach conditions,

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.

 Another issue is the F-15 variable inlet scheduling. The -220 max airflow is 228 pps, while the -229 is 248 pps, and the -129 is 275 pps. The higher airflow requirements may result in the inlet not being in the optimum position for ram recovery or aircraft drag at the M2.3+ conditions as it was for the original -100 /-220 airflow characteristics it was designed for.

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?

 

[FlyGuy369]

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.

I don't know much on engines and their related sciences, but a quoted NPR of 1:7 was mentioned. What does this mean?

 

[quellish]

The highly swept frame.

There are reasons other than speed to have highly swept wings.

 

[icyplanetnhc (Steve)]

It's only for a few seconds. Going from Mach 2.5 to Mach 2.9 won't suddenly have the F-15EX melting. Period.

Back to the NGAD prototype. Mach 3.5 for a few seconds breaking the record seems highly likely. Everything from the inlets to canopy would be designed for sustained heating from supercruise. They are designed to handle high heat.

It's not about melting, you don't need to reach melting temperature for an alloy structure to lose most of its structural integrity.

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. And that total temperature is just from isentropic compression, actual aerodynamic heating will be more severe.

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