Objective comparison of F-22's and the T-50's aerodynamics?

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firstimpulse

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Unread post03 Mar 2013, 20:24

count_to_10 wrote:
kamenriderblade wrote:Why hasn't somebody made TVC in the full two dimensions yet?

It isn't worth the weight.


It's been done on demonstrators, but not real fighters, probably because of what count said.
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haavarla

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Unread post03 Mar 2013, 23:36

Ironic isn't it.. The Russians develop and produce TVC. But they do not use it them self, well until now they do(Su-35S and Su-30SM).

But yes, TVC nozzles do increase service cost. IMO the jets will have more down time. It cost extra bucks and with increase weight.

With a 3D TVC its even worse..
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wrightwing

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Unread post04 Mar 2013, 04:15

kamenriderblade wrote:Why hasn't somebody made TVC in the full two dimensions yet?


The weight, and the concern for maximum signature reduction.
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neurotech

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Unread post04 Mar 2013, 06:25

haavarla wrote:Ironic isn't it.. The Russians develop and produce TVC. But they do not use it them self, well until now they do(Su-35S and Su-30SM).

But yes, TVC nozzles do increase service cost. IMO the jets will have more down time. It cost extra bucks and with increase weight.

With a 3D TVC its even worse..

F-22 style pitch-only TVC helps with supersonic trim. 3D thrust vectoring doesn't help supersonic cruise the same way. The F-22 can maneuver and turn and bank quite well at M1.0+ compared to earlier aircraft. 3D wouldn't improve supersonic performance, but add weight.
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haavarla

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Unread post04 Mar 2013, 13:57

I beg the different. The TVC in MKI, Su-35S and T-50 works just as well for supersonic trim.
They move in pitch, but at a diffferent angle, \ /. No problem what so ever. The actuall movment for nozzles trim, is very small deflection.
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wrightwing

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Unread post04 Mar 2013, 14:14

haavarla wrote:I beg the different. The TVC in MKI, Su-35S and T-50 works just as well for supersonic trim.
They move in pitch, but at a diffferent angle, \ /. No problem what so ever. The actuall movment for nozzles trim, is very small deflection.


That's not true 3D vectoring though, and their nozzles are far less effective at signature reduction.
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linkomart

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Unread post04 Mar 2013, 14:18

3D wouldn't improve supersonic performance, but add weight.

Not quite that simple, unfortunately. TVC in the yaw axis (wether you call it y or z or...) CAN help you if you got stability problems at high Mach numbers. The yaw stabilizing effect from the fin is often reduced at high mach due to aerolastic effects, and if the structure is weak the reduction can be substantial. This means that the fin needs to be sized to meet high mach stability requirement, adding drag and weight. If you can use TVC to stabilize the aircraft at high mach, the fin might be reduced in size.

That said, it all depends on what design you have, so your conclusions may vary. I have not seen a TVC system worth the effort, but as I said, it's not that simple.

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haavarla

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Unread post04 Mar 2013, 17:57

Yes, It will be very interesting to see how the T-50 design will perform vs the much evolved Flanker design, from which we know is a very stirdy design. The Flanker has large Verticals Stabz and it even has those Ventral smaller fins underside to aid in directional stability. And on top of this we know the Su-35S has good higher mach performance as well, so the compromise with drag vs stability is interesting. Its allways some sort of pros and cons, the lower Verticals on the T-50 and missing Ventral Fins no doubt decrease drag issue.

As for TVC, the Flankers has never had any issues with stability at higher mach, the TVC function as extra control in both slow and high speed regimes.
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neurotech

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Unread post04 Mar 2013, 19:54

linkomart wrote:
3D wouldn't improve supersonic performance, but add weight.

Not quite that simple, unfortunately. TVC in the yaw axis (wether you call it y or z or...) CAN help you if you got stability problems at high Mach numbers. The yaw stabilizing effect from the fin is often reduced at high mach due to aerolastic effects, and if the structure is weak the reduction can be substantial. This means that the fin needs to be sized to meet high mach stability requirement, adding drag and weight. If you can use TVC to stabilize the aircraft at high mach, the fin might be reduced in size.

That said, it all depends on what design you have, so your conclusions may vary. I have not seen a TVC system worth the effort, but as I said, it's not that simple.

my 5 cent

Perhaps the 3D description was inaccurate, the Su-30/Su-35 is 2D TV.

Forgive me for being pedantic, but certain aircraft, most notably the MiG-29, are known for their lack of yaw authority in the event of an engine abnormality. This is for both low-speed (Paris '89 mishap) and in supersonic flight. The Su-27/30 has large tail fins for a reason, and engine-out performance is part of it.

The F-22 (& presumably Su-30MK series) are quite stable throughout most of the supersonic envelope without TV being active. If the jet needs TV for cruise stability above M1.0 then chances are there is also high-speed flutter or other majorly undesirable aerodynamic effects on the structure of the jet.

Part of the justification for the Su-30/35 tailfin size is the aerodynamics at high-alpha. The T-50 fins are further separated, so the smaller vertical stabilizer would stay effective at high alpha. The F/A-18 & MiG-29 have LERX vortex generators that also assist in vertical stabilizer effectiveness. That said, I'm not an expert at aerodynamics, as I was on the avionics side of things.
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disconnectedradical

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Unread post06 Mar 2013, 22:39

Do we have accurate dimensions of the T-50? Anyone has a good estimate of the T-50's frontal area compared to the F-22?
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johnwill

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Unread post07 Mar 2013, 07:43

neurotech wrote:Part of the justification for the Su-30/35 tailfin size is the aerodynamics at high-alpha. The T-50 fins are further separated, so the smaller vertical stabilizer would stay effective at high alpha. The F/A-18 & MiG-29 have LERX vortex generators that also assist in vertical stabilizer effectiveness. That said, I'm not an expert at aerodynamics, as I was on the avionics side of things.


You probably know more about aerodynamics and aeroelasticity than I do about avionics, however.......

The T-50 verticals are farther separated, but the fuselage is also wider, tending to continue blanking the tails at high alpha. The LERX does little to assist the vertical effectiveness, as the primary use is to generate vortex lift from the wings. In fact, LERX are the cause of severe buffeting on twin verticals, leading to early durability failures on F/A-18 and others.

Just an opinion, but I suspect the T-50 verticals maintain effectiveness (high alpha and supersonic) due to their all-moving design. Consider that all-moving horizontal tails, which all fighters (except deltas) use, do not suffer the aeroelastic loss of effectiveness that plagues all rudders and ailerons. The T-50 makes use of that capability in its verticals, as did the SR-71.
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linkomart

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Unread post07 Mar 2013, 08:36

@neurotech
Should have said that my reasoning were purely theoretical, to my knowledge there are no aircrafts that have used TVC for stability purpose, exept some small experimantal ones (Aurora technologies as an example). In my humble experience when you start to balance the pros and cons in a design the pro for TVC are less than the con.

@johnwill Agree with what you say, and it is also possible that the all moving tail has less drag than a fixed one. Probably heavier, but less drag.
(I say probably because an all moving tail can be made smaller thus lighter, but the attachment are almost certain to be heavier, pro and con, pro and con. )

my 5 cent
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haavarla

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Unread post07 Mar 2013, 13:29

There is also the canted Engines design to consider on the T-50. It probably makes it easier to control on one engines, but it could also have some IR-reduction Pros as well.
Anyway, consider the MKI have used TVC(AL-31FP) for quite some years, all the major hurdles to maintain and service such TVS nozzles should be less of a problem for the T-50, sinse its the same thing.
And final, there is the flight safty aspect with using TVC. You can recover the aircraft much faster, than without TVC.
Also in the case of some Hydraulic failure the TVC can help control the jet.
In case of bird strike/engine blow out, the TVC can help control the jet.
In case of combat damage, the TVC can help control the jet.

So i challange your "more Cons, less Pros"..
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linkomart

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Unread post07 Mar 2013, 13:50

So i challange your "more Cons, less Pros"..

I won't argue, my experience is as stated. Yours may differ. IMHO It's not as easy as to just line up pro's and con's, you have to look at your requirements and goals.
When you design an Aircraft you almost always design it against a set of requirements, one of the toughest is often the hardest to control, the cost.
If you are not careful you will end up with a B1-R for a light weight fighter.

But if you feel that TVC is the best thing since sliced bread, by all means, design your airplane with TVC.

my 5 cent
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exorcet

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Unread post07 Mar 2013, 15:28

ericchase88 wrote:Those little protrusions are very small compared to T-50 LEVCON. It won't help F-22 generate nearly as much helpful vortex and lift as T-50.


Larger vortex might mean lower pressure yes, but also more drag. Partially from that pressure and partially from energy lost in the vortex.

If you want to make an instantaneous turn, make the vortex as big as you can get it.

If you want a sustained turn, just make the vortex big enough to pull the surrounding air with it over the wing/fuselage.

Aerodynamically, it's not clear which plane is superior, but if one is superior to the other I don't think the difference between them would be enormous.


EDIT

You also asked about wing sweep and lift. It's the cosine of the sweep that matters for the lift slope. The lack of lift and increased drag comes from stronger vortex formation. The wing basically mixes air more than it transfers downward momentum into it.
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