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Author Topic: General Dynamics ATF  (Read 15922 times)

Offline Nils_D

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Re: General Dynamics ATF
« Reply #30 on: November 25, 2012, 01:05:16 pm »
Well, I did some remodelling and test-fitting and came up with this. The wheels are at the same distance from CG as before but the tires are somewhat smaller to fit into smaller bays which themselves have been moved back to make place for the Sidewinder bays.

Offline Nils_D

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Re: General Dynamics ATF
« Reply #31 on: December 30, 2012, 06:23:11 pm »
Blahblahblah progress blahblah

Offline lantinian

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Re: General Dynamics ATF
« Reply #32 on: February 21, 2013, 09:04:12 am »
This model is turning out great. I really enjoy seeing it coming together like that. Nils_D, you should consider contacting one of those game studios making combat sims for mobile devices. I am sure they will be interested in making this model available for gameplay.


On another note, the vertical tails seams like completely out of place with the rest of the design. I wish I coud read some trade studies about why GD thought single tail is better than say no tail with & two larger winglets option. I can't see any benefit than say better roll performance.
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Offline PaulMM (Overscan)

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Re: General Dynamics ATF
« Reply #33 on: February 21, 2013, 09:12:48 am »
It is well documented :

Quote
The wing planform and airfoil design were chosen to minimize weight while providing the maximum turn capability and supersonic cruise. The single vertical tail, however, presented problems in achieving a totally stealthy design. General Dynamics ran many wind tunnel tests to find a location and shape for twin canted vertical tails on the T configuration. The vortex flow off the forebody and delta wing produced unstable pitching moments when it interacted with twin tails. Without horizontal tails, the aircraft did not have enough pitch authority to counteract these moments. A single vertical tail and no horizontal tails was finally identified as the best overall approach to the design despite the degradation of radar cross section in the side sector. The proposal configuration was designated T-330.
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Offline lantinian

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Re: General Dynamics ATF
« Reply #34 on: February 21, 2013, 01:20:51 pm »
Yes Paul, I clearly remember that passage  ;) , which is why I asked specifically why single tail was chosen over no tail with winglets, not two tails. I personally think the passage you mentioned referred to this configuration a the same one but with the tail canted inward.



While I was referring to the following configuration with winglets which as least I don't consider vertical tails.



IMHO the vortices generated by the forebody and the the delta wing would have passed on the inside of the winglets roughly over the center of the wing in a similar way the ones on the F-22 do appear here



So since both of those two configurations would have had greater range and lower side RCS, not to mention being sexier, I think the 3D model wil be much better of if it looked like the last one but that's just me.
« Last Edit: February 21, 2013, 04:18:54 pm by lantinian »
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Offline Kryptid

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Re: General Dynamics ATF
« Reply #35 on: February 21, 2013, 06:14:47 pm »
There may have been a weight penalty for using such winglets/wingtip-mounted tails, as the wings may have needed to be reinforced to translate the loads from them to fuselage.
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Online sferrin

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Re: General Dynamics ATF
« Reply #36 on: February 21, 2013, 06:46:34 pm »
Yes Paul, I clearly remember that passage  ;) , which is why I asked specifically why single tail was chosen over no tail with winglets, not two tails. I personally think the passage you mentioned referred to this configuration a the same one but with the tail canted inward.





I don't suppose you have a high rez version of that somewhere do you?  (Nice pic.)
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Offline lantinian

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Re: General Dynamics ATF
« Reply #37 on: February 23, 2013, 05:04:31 am »


Quote
I don't suppose you have a high rez version of that somewhere do you?  (Nice pic.)


Sorry. I double checked with Google, but these are the highest res it could find

http://dailyairforce.com/post_image/1098.jpg
http://i.imgur.com/WFlO6h.jpg

« Last Edit: February 23, 2013, 09:20:13 am by lantinian »
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Offline ScrutorAudax

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Re: General Dynamics ATF
« Reply #38 on: Yesterday at 07:42:53 pm »
I know this is from a long time ago, but other advantages of a large single tail are spin properties. 
 
Also, at moderately high alpha (30 deg) a single tail will typically see cleaner airflow as it lies along the right/left mirroring plane.  The vortices from the leading edge extensions also add a vertical component at the wing tips and subtract a vertical component at the fuselage center.  This sucks the air down towards the central vertical stabilizer, adding to the velocity across the vertical stabilizer because the plane is at an upwards angle. 
 
You can see that the flow at (1) across the tail is straighter than the flow at (2).  The twin vertical tails on the GD ATF would increase pressure at the rear because of the lateral flow (2) and would cause a diverging pitch-up moment. 
 
Putting rudders at the wingtips of a delta is generally not an aerodynamically good idea due to the strong spanwise flow at the tips.
 
Although the pictures I included below are not of the GD ATF (I would be happy to perform some CFD on it), it helps give a visual of the flow field of an aircraft with a strong LEX or delta configuration.  The model shown is of the Fairchild F-X.

Offline Sundog

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Re: General Dynamics ATF
« Reply #39 on: Yesterday at 10:11:18 pm »
Actually, twin tails usually have better spin resistance, since when the aircraft is in spin, one of the vertical tails will be in good airflow coming between the wing and the horizontal tail, whereas a single tail has tendency to be blanked out by most of the fuselage.

Offline ScrutorAudax

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Re: General Dynamics ATF
« Reply #40 on: Today at 02:45:02 pm »
In the case of a delta, twin tails will be shielded by the wing regardless.  In addition to the shielding by the wing, one of the twin tails will be shielded by the other.

Online sferrin

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Re: General Dynamics ATF
« Reply #41 on: Today at 04:17:33 pm »
In the case of a delta, twin tails will be shielded by the wing regardless.  In addition to the shielding by the wing, one of the twin tails will be shielded by the other.

Not that it would help with stealth but how about ventrals like the F8U-3?  Is a vertical tail with two ventral tails as effective as one big vertical or two smaller verticals?
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Offline ScrutorAudax

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Re: General Dynamics ATF
« Reply #42 on: Today at 04:38:02 pm »
Quote
Not that it would help with stealth but how about ventrals like the F8U-3?
 
 
The main issue with that is clearance on takeoff.  The XF8-U3 had folding ventrals (same with the North American-Rockwell FX). 
 
Quote
Is a vertical tail with two ventral tails as effective as one big vertical or two smaller verticals?
 
 
Yes, but they are all design compromises.  It depends on the aerodynamic layout of the plane and its design objectives.  For stealth it's a bad idea because you would have three radiators instead of two or one, and the ventral fins would make it even worse because of the increased tolerance for the folding mechanism.  For high-alpha properties it could possibly be better.

Offline ScrutorAudax

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Re: General Dynamics ATF
« Reply #43 on: Today at 04:42:50 pm »
I found a bunch of pictures of the GD ATF rendering.  I couldn't tell if they were from Nils_D's model or not.  They look very good.

Offline ScrutorAudax

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Re: General Dynamics ATF
« Reply #44 on: Today at 04:44:57 pm »
Here's some more.