F-15X: USAF Seems Interested

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f119doctor

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Unread post05 Sep 2019, 18:05

sprstdlyscottsmn wrote:
sferrin wrote:
I still don't understand that. The -229 has a much hotter/higher exhaust velocity, which I thought contributes to high speed efficiency. (Why the old turbojets seem to be faster and fly higher than modern fighters, why the F119 uses a lower bypass ratio etc.)

If we are only looking at EGV, then I agree with you, but perhaps the magic is in the higher mass flow rate? I'm not speaking in hypotheticals or formulaic theory, I'm referring to flight manual data from flight tests.

I love P&W, but the GE is clearly the better motor for performance in the F-16. I see no reason it shouldn't translate to the F-15 as well.


It all depends on the engine configuration, temp & rotor speed limits as the inlet temp goes up with ram recovery, and integration with the airframe.

In the mid 90s, I was involved with a P&W proposal for the F-111F propulsion enhancement. The choices were to keep the TF30-PW-111 engine (250 lbs / sec airflow) with a new F100 style AB, the F100-229 (250 lbs/sec) and GE was proposing a F110-129 (270 lbs/sec).

Our analysis said that at subsonic speeds, both the 229 and 129 engines delivered higher installed thrust, as expected. But when you went supersonic on the deck, the TF30 had higher max AB thrust than either at 700 KTS or higher. I don’t know exactly why that was the result, that is what the analysis indicated.

Of course, the AF decided to retire the F-111F instead, so nothing came of the proposal...
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sprstdlyscottsmn

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Unread post05 Sep 2019, 18:26

Wow. I shouldn't be that surprised that the TF-30 was great supersonic. I've heard tell of F-111s and F-14As hitting stupid high mach numbers at altitude, 2.5+ region. Then again, I've also heard of F-14Bs accelerating through 1.35 on the deck and going fast enough to tear off Mx panels, but no high speed stories at high alt.
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sferrin

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Unread post05 Sep 2019, 19:02

f119doctor wrote:
sprstdlyscottsmn wrote:
sferrin wrote:
I still don't understand that. The -229 has a much hotter/higher exhaust velocity, which I thought contributes to high speed efficiency. (Why the old turbojets seem to be faster and fly higher than modern fighters, why the F119 uses a lower bypass ratio etc.)

If we are only looking at EGV, then I agree with you, but perhaps the magic is in the higher mass flow rate? I'm not speaking in hypotheticals or formulaic theory, I'm referring to flight manual data from flight tests.

I love P&W, but the GE is clearly the better motor for performance in the F-16. I see no reason it shouldn't translate to the F-15 as well.


It all depends on the engine configuration, temp & rotor speed limits as the inlet temp goes up with ram recovery, and integration with the airframe.

In the mid 90s, I was involved with a P&W proposal for the F-111F propulsion enhancement. The choices were to keep the TF30-PW-111 engine (250 lbs / sec airflow) with a new F100 style AB, the F100-229 (250 lbs/sec) and GE was proposing a F110-129 (270 lbs/sec).

Our analysis said that at subsonic speeds, both the 229 and 129 engines delivered higher installed thrust, as expected. But when you went supersonic on the deck, the TF30 had higher max AB thrust than either at 700 KTS or higher. I don’t know exactly why that was the result, that is what the analysis indicated.

Of course, the AF decided to retire the F-111F instead, so nothing came of the proposal...


There were actually proposed variants of the TF30, back in the day, all the way up to 30k lbs of thrust. :shock:
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sferrin

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Unread post05 Sep 2019, 19:03

“The F-15EX will act as a weapon ‘truck’, able to carry the kind of large hypersonic weapons that are in development, but will not fit inside a fifth-generation fighter weapons bay. ...
Source: Combat Aircraft Magazine Oct 2019 Volume 20 No 10

element1loop wrote:Because F-35A can't carry large external weapons ... :roll:


IIRC they're looking at weapons above 5,000lbs. (The current limit for F-15 & F-35 hardpoints.)
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Unread post06 Sep 2019, 04:38

sferrin wrote:“The F-15EX will act as a weapon ‘truck’, able to carry the kind of large hypersonic weapons that are in development, but will not fit inside a fifth-generation fighter weapons bay. ...
Source: Combat Aircraft Magazine Oct 2019 Volume 20 No 10

element1loop wrote:Because F-35A can't carry large external weapons ... :roll:


IIRC they're looking at weapons above 5,000lbs. (The current limit for F-15 & F-35 hardpoints.)


What you say may have been proposed, but there's this from last week, which suggests a hypersonic surprise strike would be launched via USAF VLO platforms. The article suggests a Mach 5 glider, perhaps to keep heat down, and still be able to use an integrated terminal sensor at the end.

In which case why not use a big booster to arc it out nice and high glide it a bit, then fire ramjet second stage to cruise the glider at around 100K ft, then a fast powered terminal dive, to release the glider much lower down, for a faster agile terminal phase (Mach 6 at release perhaps) without bleeding off energy short of ground targets, thus remaining fast, fairly agile and hard to kill, all the way to impact.

Hypersonics: Army Awards $699M To Build First Missiles For A Combat Unit
SYDNEY J. FREEDBERG JR.
August 30, 2019 at 9:02 AM

" ... The Air Force version of the C-HGB, has to be mounted on a strategic bomber, and or a fifth-generation fighter jet, needs a slightly different glide body but uses 70% of the same components from the Amry's Dynetics contract. ..."

https://breakingdefense.com/2019/08/hyp ... mbat-unit/


As I understood it F-15X is based on an improved F-15E airframe but is A2A focused, proposed to replace C and D Eagles and to supplement low F-22A numbers. Not as a strike jet.

I expect the new hype-weapon has a serious reward COG, so the longest part of it is likely to be forward of the pylon, as opposed to over-hanging the rear and creating problems. Thus sorting the clearance issue in terms of length. Seems likely F-35A would get that gig rather than F-15X.
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sferrin

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Unread post06 Sep 2019, 12:11

element1loop wrote:I expect the new hype-weapon has a serious reward COG, so the longest part of it is likely to be forward of the pylon, as opposed to over-hanging the rear and creating problems. Thus sorting the clearance issue in terms of length. Seems likely F-35A would get that gig rather than F-15X.


It's less about clearance and more about pylon capacity. The F-35 is limited to 5,000lbs. ISTR the EX would be higher than that. Silver Sparrow, for instance, weighs almost 7,000lbs.

https://www.rafael.co.il/wp-content/upl ... parrow.pdf

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element1loop

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Unread post06 Sep 2019, 15:26

sferrin wrote:It's less about clearance and more about pylon capacity. The F-35 is limited to 5,000lbs. ISTR the EX would be higher than that. Silver Sparrow, for instance, weighs almost 7,000lbs.


Has the D (I) wing always been able to support 7,000 lb? Or cleared later at lower G limits for a target missile? F-35A may be capable of doing same given it's a strike optimized fighter and will replace F-15 variants. With the payload overhead it would be tempting to maximize the wing/pylon combo during LRIP to allow A to evolve to heavier weapons that exploit VLO plus standoff to make their attacks. So is 5,000 lb really the design limit?
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Unread post06 Sep 2019, 16:02

[quote=“sferrin”]There were actually proposed variants of the TF30, back in the day, all the way up to 30k lbs of thrust. :shock:[/quote]

In the mid-90s analysis, it was a plain vanilla 25k TF30-P111 that had superior thrust to the -129 and -229 along the right side of the flight envelope 700+ KCAS / M2+
Last edited by f119doctor on 06 Sep 2019, 16:10, edited 2 times in total.
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sferrin

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Unread post06 Sep 2019, 16:03

element1loop wrote:
sferrin wrote:It's less about clearance and more about pylon capacity. The F-35 is limited to 5,000lbs. ISTR the EX would be higher than that. Silver Sparrow, for instance, weighs almost 7,000lbs.


Has the D (I) wing always been able to support 7,000 lb? Or cleared later at lower G limits for a target missile? F-35A may be capable of doing same given it's a strike optimized fighter and will replace F-15 variants. With the payload overhead it would be tempting to maximize the wing/pylon combo during LRIP to allow A to evolve to heavier weapons that exploit VLO plus standoff to make their attacks. So is 5,000 lb really the design limit?


I don't know. I read (wish I could find the source) that that was part of the justification for the F-15EX.
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element1loop

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Unread post09 Sep 2019, 09:25

sferrin wrote:
element1loop wrote:
sferrin wrote:It's less about clearance and more about pylon capacity. The F-35 is limited to 5,000lbs. ISTR the EX would be higher than that. Silver Sparrow, for instance, weighs almost 7,000lbs.


Has the D (I) wing always been able to support 7,000 lb? Or cleared later at lower G limits for a target missile? F-35A may be capable of doing same given it's a strike optimized fighter and will replace F-15 variants. With the payload overhead it would be tempting to maximize the wing/pylon combo during LRIP to allow A to evolve to heavier weapons that exploit VLO plus standoff to make their attacks. So is 5,000 lb really the design limit?


I don't know. I read (wish I could find the source) that that was part of the justification for the F-15EX.



Another reference to intentions for external hype weapons on F-35.

F-35 Looks to the Future
by David Donald
- June 17, 2019, 6:56 AM

" ... Anti-ship capability is also under study, as is the external carriage of a new family of hypersonic missiles that are now in the early stages of development. ... "

https://www.ainonline.com/aviation-news ... oks-future
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Unread post10 Sep 2019, 13:50

I agree the F-15EX will be geared for air superiority... at least at first.

But I have a hard time believing they won't be used as eventual F-15E replacements/supplementals. The USAF is absolutely in love with that bird, and rightfully so. They've been used in every major conflict, can haul lots of weapons to high altitude and has the legs necessary too.

The F-35 can do all that and more, but if I'm not mistaken there were no plans to replace the F-15E fleet as the F-35 came on board. They won't last forever, but those new F-15EX's will be able to take over when its time.

Still can't believe we're buying this thing. Has there been any official word or is Congress still hashing it out??
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Unread post10 Sep 2019, 16:08

mixelflick wrote:The F-35 can do all that and more, but if I'm not mistaken there were no plans to replace the F-15E fleet as the F-35 came on board. They won't last forever, but those new F-15EX's will be able to take over when its time.


I hope they don't that would rarefy resources on a small fleet that's fully redundant within the same service. Far better to get rid of all F-15s (sell what remains of their 20,000 hrs) when the E goes, and put the recouped operating budget into what needs to be built next.

And the new Sec-Def looks for things to axe ...
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Unread post11 Sep 2019, 13:59

http://www.airforcemag.com/Features/Pag ... tives.aspx

"Members of the Senate’s defense appropriations subcommittee on Sept. 10 endorsed the Air Force’s plan to buy the F-15EX from Boeing, signaling authorizers and appropriators in the House and Senate will all back the idea in the final defense policy and spending bills.

The panel’s version of the 2020 defense spending bill includes nearly $1 billion for eight of the new fighter jets, two of which will be used as test aircraft, according to a summary of the bill. Earlier this year, the Senate and House Armed Services committees as well as the House Appropriations Committee included eight F-15EXs in their own legislation, and lawmakers in both chambers must now agree on how much money to offer the program.

Senate appropriators also offer nearly $1.9 billion to plus up the Pentagon’s request for F-35s, bringing total Joint Strike Fighter procurement to 96 airframes in 2020. That includes an extra 12 F-35As for the Air Force and 60 overall for the service. The summary also notes an additional $156 million to jumpstart F-35A procurement in fiscal 2021."
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Unread post11 Sep 2019, 23:20

What?
8? ?
Is that one for each museum in 50 years? Or how did they calculate that number?

Ah, 2 test AC; Probably one to test the static pressure system and one for the dynamic pressue system.

And somebody puts that on paper? A toilet lady does a better job.

Or do they need airframes to test the 737 AOA probes?
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Unread post12 Sep 2019, 00:52

vilters wrote:What?
8? ?
Is that one for each museum in 50 years? Or how did they calculate that number?

Ah, 2 test AC; Probably one to test the static pressure system and one for the dynamic pressue system.

And somebody puts that on paper? A toilet lady does a better job.

Or do they need airframes to test the 737 AOA probes?



Pulling a page from the Su-57 program.
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