F-15X: USAF Seems Interested

[sprstdlyscottsmn]

So 5 of the 8 are woefully underpowered. Got it.

[mixelflick]

Thank you for the links to the EX...

So the new engines put out nearly 60,000lbs of thrust in full afterburner... Which is around 10,000lbs more thrust than the current F-100's. I took the following figures from the F-15QA page, insofar as weight is concerned..

USAF F-15Es used/use both the F100-PW-220 (25Klbs ea) and the F100-PW-229 (29K lbs ea) - don't know the current ratio of each.

3 squadrons out of 8 use the F100-PW-229

viewtopic.php?p=417826#p417826

333rd FS "Lancers" - F100-PW-220
334th FS "Fighting Eagles" - F100-PW-220
335th FS "Chiefs" - F100-PW-220
336th FS "Rocketeers" - F100-PW-220
389th FS "Thunderbolts" - F100-PW-220

391st FS "Bold Tigers" - F100-PW-229
492nd FS "Madhatters" - F100-PW-229
494th FS "Panthers" - F100-PW-229

Interesting.. thank you.

I wonder then why the EX will use GE engines? One would think given all Eagles (both C's and E's) are flying using P and W engines, the EX would continue to do so. Especially where thrust levels in the 229 are already at 29,000lbs of thrust. I know it's not all about thrust, but with a much larger weapons payload... you'd think that would be the primary driver.

[marsavian]

The GE-129 has more dynamic thrust especially supersonically, produces more acceleration and is already standard with the current production line. Considering the first two are coming straight from Qatar's order looks like the engine choice has already been made.

[mixelflick]

The GE-129 has more dynamic thrust especially supersonically, produces more acceleration and is already standard with the current production line. Considering the first two are coming straight from Qatar's order looks like the engine choice has already been made.

It's going to be a beast then, as the current engines already give eye watering acceleration. I suppose they'll be used primarily in a homeland defense type mission(s), although some being deployed as air superiority birds sounds plausible as well. They must have a hell of a jammer on it though, because it sounds like the RCS will be bigger than ever. So it'll be fast, carry lots of weapons to a high altitude, have a monsterously powerful radar and have long legs too.

I surmise they'll be used after F-22 sanitize the airspace, as the F-15EX will be used to maintain that.

[sferrin]

So 5 of the 8 are woefully underpowered. Got it.

Basically a bigger F-4.

[southerncross]

It's going to be a beast then, as the current engines already give eye watering acceleration.

F-15C with the PW-220 and very rough numbers gives TWR around 1.669 empty, the SA with the GE-129 gives around 1.547 so it will apparently not improve on what is already in service. I wonder why not to use the extremely light F-15C as a basis instead, that would really be a beast, even beyond F-22's TWR (not to talk about what a F119-derived engine would do). Maybe they need the added features of the -E, more fuel and also want to lose as little time and money as possible, hence use the most developed F-15 model as a basis.
A non-stealthy but otherwise high-performance complement in the USAF is actually a very rational decision IMHO, it will increase the capacities fast and form a force that has less weak spots.

[vilters]

What the "E" actually needs are 2 fuselage plugs.
2 feet in front and 2 feet behind the wing to carry more fuel internally.
Get rid of the external tanks and use the wing stores for weapons.

[sprstdlyscottsmn]

F-15C with the PW-220 and very rough numbers gives TWR around 1.669 empty, the SA with the GE-129 gives around 1.547 so it will apparently not improve on what is already in service.

Empty T/W is the most irrelevant of all T/W numbers. No plane ever flies empty. Pick a load and use that to measure T/W. Even then, the result is fairly irrelevant as it doesn't account for drag, installation losses, altitude losses, or ram effect increases.

[southerncross]

F-15C with the PW-220 and very rough numbers gives TWR around 1.669 empty, the SA with the GE-129 gives around 1.547 so it will apparently not improve on what is already in service.

Empty T/W is the most irrelevant of all T/W numbers. No plane ever flies empty. Pick a load and use that to measure T/W. Even then, the result is fairly irrelevant as it doesn't account for drag, installation losses, altitude losses, or ram effect increases.

Sure, hence my "very rough numbers" remark, the point being the comparison and not the final value. Empty weight is of no real practical application but still an important reference, even more for versions of the same platform, given the claim that the plane was going to improve a lot in that regard. A F-15C may be not as good with EFTs but they can still drop them in case of need, a thing the SX is probably not going to be capable of with the CFTs. I wonder why the AF selected a version of the Strike Eagle instead of developing further the C version for air-to-air role, and also where the great weight increase from the C to the SA versions comes from, it is like 4 tons that cannot be CFTs and avionics alone, I hope.

[sprstdlyscottsmn]

You first have to understand that the F-15C empty weight is ~31,000lb, not 28,000lb. Also the F100-PW-220 is closer to 23,500lbt. This means an empty F-15C has a TWR closer to 1.5. And since it has less excess thrust it is more susceptible to weight and drag effects than the heavier F-15EX with the same TWR.

[southerncross]

You first have to understand that the F-15C empty weight is ~31,000lb, not 28,000lb. Also the F100-PW-220 is closer to 23,500lbt. This means an empty F-15C has a TWR closer to 1.5. And since it has less excess thrust it is more susceptible to weight and drag effects than the heavier F-15EX with the same TWR.

My data surely can be wrong, I was taking the engine thrust from wiki and the F-15C's weight from 1992 SAC. With all data from SAC (engine 23,450 lbf, weight 28,476 lb) it results TWR 1.647. I admit I am not aware if currently F-15C is much heavier than that.

[sprstdlyscottsmn]

My data surely can be wrong, I was taking the engine thrust from wiki and the F-15C's weight from 1992 SAC. With all data from SAC (engine 23,450 lbf, weight 28,476 lb) it results TWR 1.647. I admit I am not aware if currently F-15C is much heavier than that.

I'll need to go through my data on the F-15C empty weight. At least you were working from the right thrust values and not the "25,000 class" number. If you want to look at empty weight then I would suggest using excess thrust not thrust to weight ratio. So, for the numbers you have from the SAC (the FM I have lists 28,000 for F-15A and 29,500 for F-15C) then an F-15C has 18,424 lb of excess thrust to accommodate fuel and munition and drag and maintain "unity". An F-15EX with no CFT (~34,000lb weight) has ~24,000lb of excess thrust available. As they have the same platform and layout we can see that even a heavier EX will maintain a thrust advantage over a C at any loading.

[southerncross]

If you want to look at empty weight then I would suggest using excess thrust not thrust to weight ratio.

Thanks for the tip, for the same platform it makes sense indeed, only issue I had is that the EX is (I guess) expected to operate with the CFTs which necessarily have some aero effect, even when reduced, apart from the weight.

So, for the numbers you have from the SAC (the FM I have lists 28,000 for F-15A and 29,500 for F-15C) then an F-15C has 18,424 lb of excess thrust to accommodate fuel and munition and drag and maintain "unity". An F-15EX with no CFT (~34,000lb weight) has ~24,000lb of excess thrust available. As they have the same platform and layout we can see that even a heavier EX will maintain a thrust advantage over a C at any loading.

This is what I don't completely get: why to keep developing a much heavier version when a lighter one is there. The C with the -129 engine would be much better even. According to your data, the C is 3 tons lighter, both without CFTs. Why not to put the F119-PW-611 (in case it has the right size, I could not find that information) or some other modern layout engine on those C planes, together with modern, lighter avionics? I think the structure of the E was reinforced and it has more equipment, but three tons? Who needs a 20,000 h service life? A WSO is not needed currently either, no 5th gen plane uses it anymore, though it is unclear to me whether the F-15X will actually be single seat. The advantage in kinematics would be brutal and offer a different kind of capability that can be useful, or rather, the lack of which can be exploited, say create the USAF fighter specialised in energy maneouverability. A 6+ ton heavier F-22 (or essentially any stealth fighter) would never be in conditions to match it, no matter the engines, and better even, the basis is already at hand, a reliable and well known plane. Just for the fun of it, two F119-thrust engines on a F-15C airframe would result in TWR of 2.45, and they are in the same size class as current engines

I assume there are reasons for this that I am simply not aware, otherwise it would be rather silly. But an airframe of the size and capabilities of the F-15C for that weight is almost a miracle one would expect the air force not to let go easily.

[Corsair1963]

The F-15EX is just a slightly modified version of the Saudi/Qatar Eagle currently on the St Louis Production Line. Which, is why it was selected....

[southerncross]

The F-15EX is just a slightly modified version of the Saudi/Qatar Eagle currently on the St Louis Production Line. Which, is why it was selected....

Are all those twin seaters? It was previously reported that the F-15X would come in two versions, single and twin seater.