General Dynamics ATS, pre-ATF and ATF designs

Sundog said:
The F-22's wing is a modified delta. A delta wing basically means it has a triangular shape in planform, it's just the trailing edge is slightly swept forward on the F-22. It doesn't have anything to do with whether or not the aircraft has a horizontal tail. The MiG-21 is one of the most famous delta winged aircraft around and it had a horizontal tail. But, I understand that most people think of tailless designs when they think of delta wings.
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Right, the F-22 wing planform and aspect ratio aligns pretty well with a delta wing, I was simply highlighting the similarities between the GD ATF and the F-22 after the summer 1987 “fire drill” which saw the configuration change from swept trapezoidal wings to diamond-like delta.

red admiral said:
Massively as the various materials (e.g. CodeOne magazine) make clear.
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Well not necessarily; reading the article from Code One as well as Sherm Mullin’s account, a variety of configurations were explored when the swept trapezoidal wing design became untenable due to weight. The articles didn’t explicitly state that the chosen configuration was based on GD’s proposal, only that substantial weight savings while maintaining roughly comparable aerodynamics to the trapezoidal wings was the driving factor. That said, I wouldn’t be surprised if it did use a lot of work from GD’s submission.
 
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Sherm's account emphasizes how much of a team effort it was, so trying to isolate specific features to specific companies might be fruitless.
 
a question about the tail..
I think it was mentioned earlier that GD had some issues with the single tail.. were there any other alternative designs for the tail or planform?
 
helmutkohl said:
a question about the tail..
I think it was mentioned earlier that GD had some issues with the single tail.. were there any other alternative designs for the tail or planform?
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Yes there's lots of wind tunnel models where they tried lots of different things with the tail.
 
Moved posts to correct topic for General Dynamics ATF projects - original topic was a user artwork topic.
 
Oh the subject of the difficulties that GD had with twin vertical stabilizers in their ATF proposal, the F-22 would also end up encountering problems with vibrations and buffeting in the vertical tails at certain Mach numbers and g conditions, due to the vortex impingement at those specific conditions. This was reported back in 2000.

www.flightglobal.com

Buffeting problem may mean airframe changes for F-22

www.flightglobal.com www.flightglobal.com

According to Jay Miller’s book on the F-22, this issue was eventually resolved with some strengthening of the vertical tails and flight control software changes.

Still, this makes me a bit curious on why GD abandoned twin canted vertical stabilizers. Perhaps there wasn’t enough time for them to fine-tune a satisfactory configuration before the RFP submission? Along with the inlet, vertical tails took among the longest time in wind tunnel testing for the Lockheed/Boeing/General Dynamics team, and even then, there ended up being buffeting from flow impingement that modeling had failed to predict.
 
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I have an old Air Combat magazine with the design shown at the top of page 21 in it. I remember trying to model it out of sheets of basswood when I was a teenager.
 
Some very familiar planforms
 

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Looking at the General Dynamics ATF again, was there ever a rationale given for the "messy" trailing wedge shaping? While the angles would match the leading edge, having this many edge discontinuities seems to be even worse.
 
Worse compared to what? Apparently edge alignment was a major moving factor here.
 
Moved to correct topic.

I think this diagram gives a hint:

atf_evol_part1_11_1267828237_1659-jpg.107799

The central thrust of General Dynamics ATF development prior to the "stealth reset" was a tailless delta. I imagine the 'serrated' edge approach was to align the trailing edge to the leading edges for decreased RCS reasons without departing too greatly from the existing wing geometry.
 
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overscan (PaulMM) said:
Moved to correct topic.

I think this diagram gives a hint:

atf_evol_part1_11_1267828237_1659-jpg.107799

The central thrust of General Dynamics ATF development prior to the "stealth reset" was a tailless delta. I imagine the 'serrated' edge approach was to align the trailing edge to the leading edges for decreased RCS reasons without departing too greatly from the existing wing geometry.
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Drifting off topic, but would this approach have worked with the GD / MDD A-12 ?

cheers,
Robin.
 
flateric said:
Worse compared to what? Apparently edge alignment was a major moving factor here.
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I get that the numerous serrations were meant to align the trailing edge with the leading edge, but with so many discontinuities, I wonder if it would have been better if the trailing edge was just straight and at a less swept angle that doesn't match the leading edge (not perpendicular to the front, obviously).

However, based on the chart that overscan posted, it appears that a straight trailing edge had been considered but was dropped in favor of the serrated one. However, neither Lockheed's nor Boeing's submissions used this approach, and in the end the F-22 didn't either and went with a trailing edge that was at a less swept angle, although that could also be due to the integration of horizontal tails.
 
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Goes back to requirements, requirements, requirements. And then tradeoffs. And edumacating the customer where needed. And where politically possible.
 

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