CSBA Analyst Calls For F-35C Redesign

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steve2267

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Unread post21 Feb 2019, 00:40

disconnectedradical wrote:
Something about the A-12 trailing edge being straight means there's a big RCS spot right in front. Apparently neither Northrop or Lockheed wanted to bid so General Dynamics got the contract but at that time they didn't have the stealth experience.


lbk000 wrote:I also recall reading that the A-12 had major LO issues with the trailing edge (really, its a planform issue). AFAIU the aircraft's skin will retain the incoming energy which nevertheless needs to go somewhere, so when it hits a discontinuity it'll get radiated, which is why in LO designs you see serrations along edge lines to radiate at oblique angles. The A-12's trailing edge would basically catch radar waves and then kick them straight back at it, a pretty big booboo for the design. I believe they tried to bandaid it with RAM solutions to dissipate the traveling waves, but the trailing edge was a fundamental problem baked deeply in the design.

The USN received little or no input from the USAF about LO design, and GD did not have the experience of LM and Northrop.


Contrast the A-12 trailing edge with any of
  • NG B-2
  • NG X-47B (I mentioned this earlier, but was poo-pooed away)
  • NG B-21 -- stories discussing trailing edge (e.g. compromises forced upon B-2 by some requirements when it was designed)
  • possibly Boing X-45
  • LM MQ-25 entry

None of these designs had a trailing edge perpendicular to the longitudinal axis of symmetry.
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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steve2267

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Unread post21 Feb 2019, 00:44

The LM MQ-25 design entry appears at first blush to be closest to the A-12 in planform concept, excepting obvious differences such as single engine (LM MQ-25) vs twin (A-12), and no cockpit in the MQ-25:

Image
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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steve2267

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Unread post21 Feb 2019, 00:46

I was disappointed when NG threw in the towel on the X-47B. Mebbe it lives on in the B-21? Who knows.
Image

Image
Last edited by steve2267 on 21 Feb 2019, 01:00, edited 1 time in total.
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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steve2267

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Unread post21 Feb 2019, 00:58

And, last, but certainly least, lest I forget the Boing boyz:
Image

Image
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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steve2267

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Unread post21 Feb 2019, 01:05

And lastly, some images Google coughed up from globalsecurity.org that compares and contrasts the X-45 and the X-47, planforms which probably woulda been a whole lot mo betta than the ill-fated A-12:

A contrast of the two shapes / designs:

Image

I assume (dangerous) this is a worthwhile image showing planforms scaled to the Viper & Bug:

Image

A 3-view comparison:

Image
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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Unread post21 Feb 2019, 13:10

X-47B wins for me (aesthetics, anyway).

Big fan of cranked arrow designs, going back to the F-16XL.
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ricnunes

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Unread post21 Feb 2019, 19:25

steve2267 wrote:
disconnectedradical wrote:
Something about the A-12 trailing edge being straight means there's a big RCS spot right in front. Apparently neither Northrop or Lockheed wanted to bid so General Dynamics got the contract but at that time they didn't have the stealth experience.


lbk000 wrote:I also recall reading that the A-12 had major LO issues with the trailing edge (really, its a planform issue). AFAIU the aircraft's skin will retain the incoming energy which nevertheless needs to go somewhere, so when it hits a discontinuity it'll get radiated, which is why in LO designs you see serrations along edge lines to radiate at oblique angles. The A-12's trailing edge would basically catch radar waves and then kick them straight back at it, a pretty big booboo for the design. I believe they tried to bandaid it with RAM solutions to dissipate the traveling waves, but the trailing edge was a fundamental problem baked deeply in the design.

The USN received little or no input from the USAF about LO design, and GD did not have the experience of LM and Northrop.


Contrast the A-12 trailing edge with any of
  • NG B-2
  • NG X-47B (I mentioned this earlier, but was poo-pooed away)
  • NG B-21 -- stories discussing trailing edge (e.g. compromises forced upon B-2 by some requirements when it was designed)
  • possibly Boing X-45
  • LM MQ-25 entry

None of these designs had a trailing edge perpendicular to the longitudinal axis of symmetry.


steve2267, disconnectedradical and lbk000,

Thanks for the more detailed info guys.
Yes, what you mention regarding the A-12 trailing edge makes sense and could/should indeed be a problem. But wouldn't this problem affect the A-12 RCS when or if the radar source was behind the aircraft or resuming it would affect the A-12's rear aspect RCS and not so much its frontal RCS?

Moreover, couldn't an airframe modification (hopefully not so extensive) of the currently known A-12 design solve this issue?
I always felt (although I could be wrong) that the A-12 design that we all know (and which schematics have been previously posted here) was more of a "demonstrator design" instead of what would be its "final design" (if the program didn't get cancelled), this akin to the YF-22 or the X-35 which were demonstrators and also relatively different compared to their respective final airframe designs which were respectively the F-22 and F-35.
A 4th/4.5th gen fighter aircraft stands about as much chance against a F-35 as a guns-only Sabre has against a Viper.
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botsing

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Unread post21 Feb 2019, 20:10

Here is some more explanation about traveling waves:

https://basicsaboutaerodynamicsandavion ... ermeasure/

Image

And of course this picture:

TravelingWave_001.png
"Those who know don’t talk. Those who talk don’t know"
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steve2267

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Unread post22 Feb 2019, 00:25

What Botsing posted.

The illustration on the right gives a peek into the F-35's display of it's RCS in 360° so the pilot can orient his aircraft to minimize his RCS values in the direction of known threats / emitters.
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.
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Unread post22 Feb 2019, 00:29

ricnunes wrote:Moreover, couldn't an airframe modification (hopefully not so extensive) of the currently known A-12 design solve this issue?
I always felt (although I could be wrong) that the A-12 design that we all know (and which schematics have been previously posted here) was more of a "demonstrator design" instead of what would be its "final design" (if the program didn't get cancelled), this akin to the YF-22 or the X-35 which were demonstrators and also relatively different compared to their respective final airframe designs which were respectively the F-22 and F-35.

It would have required extensive changes to the design. Again, if memory serves, LM was consulted after the A-12 design was laid down to test the LO properties and it rated poorly so they (LM) proposed some changes which would have altered the trailing edge "significantly" as well as adding what got referred to as a "stealth bra" to the front end which by accounts resulted in a cranked arrow leading edge. One might surmise that the resultant planform would have looked fairly close to a longitudinally squashed X-47.
Apparently the intake design was also a source of grief. Don't ask me how, I don't know any more than that.
The A-12 was likely unsalvageable because of two very fundamental factors:
1. The Navy's LO requirements were not "aggressive" compared to ATF and ATB.
2. The Navy just didn't want to pony up the money for a proper LO design. Northrop was "too expensive".

I've seen some suggestions that the USAF tacitly sabotaged the A-12 by feeding the USN partial truths about LO so as it wouldn't compete with ATF funding -- effectively vegging it, the line of thinking being that if the A-12 succeeded, the USN would want more funding to buy them, but if the A-12 failed too soon, then the USN would want more funding to find a replacement. That might be off towards the tinfoil-hat end of the spectrum, but if you're already having fun speculating about making the A-12 viable then you might as well consider the alternatives.
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Unread post22 Feb 2019, 00:39

lbk000 wrote:
I've seen some suggestions that the USAF tacitly sabotaged the A-12 by feeding the USN partial truths about LO so as it wouldn't compete with ATF funding -- effectively vegging it, the line of thinking being that if the A-12 succeeded, the USN would want more funding to buy them, but if the A-12 failed too soon, then the USN would want more funding to find a replacement.


Which makes no sense given that the Air Force intended to acquire the A-12 to replace the F-111;
that gap in capability remains today.
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Unread post22 Feb 2019, 01:12

marauder2048 wrote:Which makes no sense given that the Air Force intended to acquire the A-12 to replace the F-111;
that gap in capability remains today.

You make it sound like the USAF actually had money on the A-12 when it amounted to just a brief "oh that could be cool" flirt. The USAF already had the F-15E slated to replace the F-111 at the time.

What is this capability gap now???
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Unread post22 Feb 2019, 01:47

lbk000 wrote:
marauder2048 wrote:Which makes no sense given that the Air Force intended to acquire the A-12 to replace the F-111;
that gap in capability remains today.

You make it sound like the USAF actually had money on the A-12 when it amounted to just a brief "oh that could be cool" flirt. The USAF already had the F-15E slated to replace the F-111 at the time.

What is this capability gap now???


I make it sound like the Air Force had money on it because they did.

The F-15E was (is) the interim replacement and can't penetrate.
Hence things like J-UCAS and FB-22 etc. which fill the gap between the F-35
and the penetrating strategic bombers.
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crosshairs

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Unread post22 Feb 2019, 02:35

marauder2048 wrote:
lbk000 wrote:
I've seen some suggestions that the USAF tacitly sabotaged the A-12 by feeding the USN partial truths about LO so as it wouldn't compete with ATF funding -- effectively vegging it, the line of thinking being that if the A-12 succeeded, the USN would want more funding to buy them, but if the A-12 failed too soon, then the USN would want more funding to find a replacement.


Which makes no sense given that the Air Force intended to acquire the A-12 to replace the F-111;
that gap in capability remains today.


I read that in a Popular Science magazine 30 years ago. I doubted it then, and I still doubt today that a derivative of the A-12 was going to replace the F-111. A 6000lb payload is a 6000lb payload and no one here can speak to the range of the A-12 because it never flew. If anything it would have replaced the nighthawks plus maybe a hundred or so more. The USAF was just starting the Strike Eagle buys near the end of the A-12.

That gap would not be there today had the USAF been allowed to acquire enough of the B-2. One can also make the case that F-22 could have filled in for a F-111 replacement. Yes it only holds 2 thousand pound munitions, but quantity could have made up for the light load. Unfortunately the F-22 was terminated early. Under Clinton the USAF was allowed to whither and pass up opportunities to upgrade or buy new advanced versions of the eagle and viper and it passed on buying stealth bombers . Bush and Obama rode the USAF hard and put it to bed wet. That's why the USAF is just now starting to claw its way back to modernization.

I love these conspiracies about the USAF sabotaging the A-12. Wild imaginations,
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Unread post22 Feb 2019, 04:21

crosshairs wrote:I read that in a Popular Science magazine 30 years ago. I doubted it then, and I still doubt today that a derivative of the A-12 was going to replace the F-111.


Why? It's all over congressional testimony and plenty of planning documents from that period.
When the A-12 was cancelled, the plans were updated to reflect AX and then AFX and then
when those died F-15E buys were extended.
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