Russian Su-57 Aircraft Thread (PAK-FA and IAF FGFA)

[Engineer]

Vortex lift (which only comes into effect at relatively high AoA and causes a lot of drag) increases the subsonic endurance of a Mach 2+ capable aircraft? I rest my case.

If anybody is interested in an aerodynamically sound argument, I'll give more detail on why VG wings help (it's fairly intuitive, unless you've unwisely backed yourself into a corner like a certain somebody).

Vortex lift comes into effect with any positive angle-of-attack, even at "relatively" low angle-of-attack. Of course, the lift contribution wouldn't be as great as in high angle-of-attack. Your talk of drag all by itself is meaningless. What matters is the lift-to-drag ratio. With variable geometry wing, much of the lift in that lift-to-drag ratio is wasted in lifting dead weight, a problem that LERX does not have. All modern fighters use LERX instead of variable geometry wing, which illustrates there is nothing that the latter offers that the former can't do without. I rest my case.

Which is ok, since you don't have any that would prove it to have been an engine fire either (just because you don't have the decency to acknowledge factual uncertainty in your words doesn't make it any better - on the contrary). We're down to interpreting what the photo tells us, and with all due respect, that evidence isn't very consistent with an engine fire. It requires far bigger leaps of logic to believe so than to assume something else caused it.

No disagreement. Why is that not what happened on the Su-57, if we are to believe it was an engine fire? I'm not the guy whose argument requires non-physical behaviour from the fire...

The evidence is actually pretty consistent with an engine fire. No big leap of logic is required, despite it appearing as a big leap for you. You conjure up fictional alternate scenarios with a bunch of weasel words is your problem, not mine. I have no obligation to entertain your fantasies.

There is this meteorological effect called wind: debris and scorching on the ground extend well beyond the airframe on the port side. According to reports the smoke which appeared before the actual blaze broke out came from the starboard side.

You are the one who made the connection that fire in the inlet would spill out and damage the LEVCON as well. I am simply pointing out the obvious.

Sure. That's not what's seen on T-50-5 though, you appear to have a pretty eccentric definition of the word "near".

That is what seen on the fifth prototype though.

Close, but no cigar: "variable geometry inlet" is a proper term, i.e. just one among several - my point all along. Your pretty pictures are nothing more than a smokescreen - they're not wrong, but they don't actually address the issue in question.

You certainly seemed to disagree quite strongly when I said it was not the only one:

So you are finally forced to acknowledge variable geometry inlet is a proper term. Did you use it? The answer is no. I rest my case.

But I get it, terminology only matters with *other* people - "conic intake" (which gets hardly any mentions at all in relevant literature) is perfectly acceptable when it's coming from you. And ordinarily I would indeed be fine with it (I did understand what you meant, after all), I'm merely playing devil's advocate here to show how hypocritical your hair-splitting is.

Just playing it safe with the terminology, as you're such a wordsmith

Uh huh?

Let's get technical though, if you prefer (I sure do!) - what part of my synopsis do you factually disagree with and why?

I once more urge other people to take neither my nor Engineer's word for it. Read up on the subject and judge for yourself if my summary is accurate (and hence whether it's plausible that Engineer knows enough about DSI to make big statements).

I disagree with your claim that DSI belong to a category of streamline traced inlet. The design methodology that you described is for hypersonic inlet, which has its own unique requirements not presence for a Mach 2 inlet. DSI originates from "bump theory" back in 1950 and it is a category of its own. Bringing up conic flow is not factually incorrect but pointless, as it isn't something unique for DSI. Nothing you said about DSI in your explanation is factually incorrect. What you properly not know is how cowling design, even down to thickness of the lip, has a huge impact on performance.

Weasel words, eh? Same, comparable, same again? Give me a break.

If for whatever reason you need higher pressure recovery than DSI can deliver, it isn't able to meet your particular requirements - period. I really don't see why that would even be controversial?!

So, if DSI can deliver the required pressure recovery, then DSI meet those particular requirements and would be used. I'm glad you agree then. The next thing to analyze is whether such scenario exists, and it does. Currently, there are two major powers that use DSI for their top-of-the-line fighters, and their decision proves DSI is better. There is nothing controversial about this. J-10 also has its variable geometry inlet replaced with a DSI, again proving DSI is better.

Where's that contradiction supposed to be (because I never claimed a variable ramp inlet doesn't have certain drawbacks)? Unlike you, I don't in fact irrationally "love" one particular intake type and so can make a sensible assessment of the respective pros and cons. Which solution is better? Depends[sup]TM[/sup] - if the objective is pressure recovery, the answer is not DSI though.

Which is better? What the most advanced fighters from the most advanced nation are using, because these fighters are the result of work of people with more experience and knowledge than you or I. Currently, that is DSI.

Since the J-20 is a canard while none of the other 5th generation designs are, do you propose that we conclude it isn't actually a 5th generation fighter? Do yourself a favour and pause to think these moronic ideas through before posting! Again: Requirements. Drive. Engineering. Not fashion items.

China isn't the one claiming J-20 has different priorities; Russia is. We can agree to disagree whether canard is a good solution, but China uses canard to meet those requirements that are also found on American 5-th generation fighters. Russia basically justifies their 5-th generation fighter being different by saying they have a different definition of 5-th generation. Like I said, a different 5-th generation fighter wouldn't be a 5-th generation fighter anymore.

Do us both a favor and take your own advice: think before you post anymore of your moronic ideas just for the sake of arguing.

Did you read my link (how convenient for you to omit it from the quote)? Includes examples for the thick-witted of the fallacies which arguing with a single premise can lead you into.

And yes, your argument DOES boil down to a single premise, because it effectively says pressure recovery being at least the same (or comparable or whatever word takes your fancy at that particular junction I suppose) is a prerequisite for the switch. Thereby it fails to account for the possibility that DSI advantages in other respects might be attractive enough to accept a penalty in pressure recovery (depending on - you guessed it - requirements). And the latter HAS happened in real life - I provided examples - so your point is dead in the water.

Yes, I read your link, and no it does not apply to my argument. Also, my argument does NOT boil down to the strawman fallacy which you setup. One premise is that engineering teams from two nations made the decision to use DSI. The other premise is that variable geometry inlet on J-10 got replaced with DSI, which is significant because this is done as part of improvement. The conclusion is that DSI is better, in the overall sense, which already includes pressure recovery and other advantages. It is your argument that is dead in the water.

 

[Engineer]

Not at all: it was just a hypothesis originally, but unlike your assertion it checked out against real world examples. I questioned and tested my assumption before finding it true whereas you're taking yours as a given and desperately trying to back-fit reality to match it (and, predictably, failing).

Quite the opposite. I look at evidences in the real world, then form my conclusion. You however, take your assumption as a given, then just make circular arguments base on it.

How about putting that evidence you mention up for review - I can't see any? Try to convince us with specific, rational arguments rather than evading all the time and invoking superficial aesthetics.

I already did.

 

[Tirdent]

Vortex lift comes into effect with any positive angle-of-attack, even at "relatively" low angle-of-attack. Of course, the lift contribution wouldn't be as great as in high angle-of-attack. Your talk of drag all by itself is meaningless. What matters is the lift-to-drag ratio. With variable geometry wing, much of the lift in that lift-to-drag ratio is wasted in lifting dead weight, a problem that LERX does not have. All modern fighters use LERX instead of variable geometry wing, which illustrates there is nothing that the latter offers that the former can't do without. I rest my case.

Actually, LERX are designed specifically so that little if any vortices develop at cruise/loiter angles of attack (and the Su-57 even has an active control surface - the LEading Edge Vortex CONtroller - to tailor the strength of the vortices). As I said, they're intended primarily to boost maximum lift coefficient at significant AoA and/or g-load. That's because the vortices cause a lot of drag for the lift they contribute, so L/D ratio is in fact pretty damn poor - it's a device for generating more lift in conditions where drag is already very high to begin with. This has NOTHING whatsoever to do with endurance/loiter, which is a completely different part of the envelope!

Modern fighters strongly prefer LERX because roles and development priorities have shifted. Due to weight, VG wings were never very popular on classical fighters (MiG-23 and F-14 are practically the only exceptions, and the Tomcat has a strong air defence bias) and once for cost reasons such types took on the jobs formerly performed by dedicated strike & air defence platforms, they went away altogether. Stealth later added another powerful incentive to prefer fixed wings due planform alignment (nonetheless, the stealthy NATF & A/F-X were designed in the 1990s with VG wings for patrol endurance!) and removed the need for low altitude penetration in the strike role.

Quite literally NONE of this means variable sweep isn't still the gold standard solution for certain requirements - it's merely that the importance of those capabilities has diminished relative to others.

You are the one who made the connection that fire in the inlet would spill out and damage the LEVCON as well. I am simply pointing out the obvious.

Clearly you have never seen an engine fire. The engine casing made entirely of metal is a pretty good container for fire, but the inlet itself isn't. Flame spills out of the engine's ends and starts burning the front or back first. Here is an example.

Do you really believe anybody reading this thread will have such a short memory?

So you are finally forced to acknowledge variable geometry inlet is a proper term. Did you use it? The answer is no. I rest my case.

Forced to acknowledge? Talk about a straw man argument (to borrow one of your favourite phrases)! I never - ever - claimed "variable geometry intake" was wrong. Stop this pathological lying!

Since we've already established that "variable geometry intake" (while correct) is not the only applicable term, you have no case to rest...

Uh huh?

I didn't say it got no mentions, did I? Now go and compare the number of hits you get for "conic inlet" to "half-cone intake" or "conical shock inlet" or something similar.

BTW, here's a reference for "movable ramp intake":



Now what?

I disagree with your claim that DSI belong to a category of streamline traced inlet. The design methodology that you described is for hypersonic inlet, which has its own unique requirements not presence for a Mach 2 inlet. DSI originates from "bump theory" back in 1950 and it is a category of its own. Bringing up conic flow is not factually incorrect but pointless, as it isn't something unique for DSI. Nothing you said about DSI in your explanation is factually incorrect. What you properly not know is how cowling design, even down to thickness of the lip, has a huge impact on performance.

Ok, since you're basically begging to be exposed as ignorant - here's an (incomplete) list of sources which agree with me:

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As for cowl design, this was never flagged as anything more than a short overview - I'm not going to go into the nitty-gritty details of every aspect. I actually made the effort to provide a text in my own words rather than simply copying some source or other, to show that I actually understand what's going on - if you feel a paragraph on cowling design is in order, why don't YOU contribute one? Let's see you finally add something constructive with insight of your own, rather than nitpicking and debating semantics!

China isn't the one claiming J-20 has different priorities; Russia is. We can agree to disagree whether canard is a good solution, but China uses canard to meet those requirements that are also found on American 5-th generation fighters. Russia basically justifies their 5-th generation fighter being different by saying they have a different definition of 5-th generation. Like I said, a different 5-th generation fighter wouldn't be a 5-th generation fighter anymore.

Do us both a favor and take your own advice: think before you post anymore of your moronic ideas just for the sake of arguing.

Yes, I read your link, and no it does not apply to my argument. Also, my argument does NOT boil down to the strawman fallacy which you setup. One premise is that engineering teams from two nations made the decision to use DSI. The other premise is that variable geometry inlet on J-10 got replaced with DSI, which is significant because this is done as part of improvement. The conclusion is that DSI is better, in the overall sense, which already includes pressure recovery and other advantages. It is your argument that is dead in the water.

Whatever I honestly can't be bothered anymore. As any neutral observer will be able to see, what I've said previously on these points still stands and already addresses your rambling here.

I already did.

Where? That ludicrously incompetent photo comparison which you were so hasty to disclaim authorship of when I tore it apart?

I could make up image comparisons which "prove" all kinds of nonsense - the F-15/F-22 example already mentioned comes to mind - on that basis (except I'm incapable of the intellectual dishonesty required to peddle such tripe).

 

[Tirdent]

Hehe, I *swear* I didn't read this before composing the above response to Engineer's claims on LERX - actually I just came across it looking for the diagram below to illustrate my explanation on why VG wings help reconcile high supersonic dash and long subsonic loiter. It's too good not to post though:



Anyhow - VG wings. The reason why they are extremely effective at combining the above two requirements (far better than LERX could ever be) is that the nature of drag changes between subsonic loiter and supersonic dash flight conditions. In the former case, lift-induced and skin friction drag are the most significant contributors, whereas at high supersonic speed wave drag is dominant.


(from Ray Whitford, Design for Air Combat, p. 19)

Reducing lift-induced (and as a knock-on effect, skin friction) drag requires high wing aspect ratio at moderate sweep, much like an airliner. This directly affects induced drag and, because a high-aspect ratio wing provides better field performance and hence may get away with somewhat smaller wing area, can benefit wetted area too. The latter assumes it is field performance and not some kind of maneuvering point defining wing area for the aircraft in question, of course.

Trouble is, high aspect ratio is a good way to have prohibitive levels of wave drag at supersonic speeds, as this drag component is strongly linked to longitudinal distribution of cross sectional area (what's often known as the area rule). Wing thickness to chord ratio also needs to be low ("thin" wing) and strongly sweeping the wing back provides marked improvements on both counts. Cross sectional area contribution of the wing is much more favourable because it gets distributed smoothly along the length of the airframe rather than being lumped into a narrow sector, and while maximum thickness of the wing remains the same, the stream-wise chord length increases to effectively lower t/c ratio of the airfoil.

So please don't rely on Engineer on such subjects - at least not when he's backed himself into a corner from which he can't emerge without losing face (I'm pretty sure he actually knows enough to realize full well he's messed up a couple of times here). Hell, you don't have to take my word either - but cross-check his claims.

 

[Engineer]

Actually, LERX are designed specifically so that little if any vortices develop at cruise/loiter angles of attack (and the Su-57 even has an active control surface - the LEading Edge Vortex CONtroller - to tailor the strength of the vortices). As I said, they're intended primarily to boost maximum lift coefficient at significant AoA and/or g-load. That's because the vortices cause a lot of drag for the lift they contribute, so L/D ratio is in fact pretty damn poor - it's a device for generating more lift in conditions where drag is already very high to begin with. This has NOTHING whatsoever to do with endurance/loiter, which is a completely different part of the envelope!

Modern fighters strongly prefer LERX because roles and development priorities have shifted. Due to weight, VG wings were never very popular on classical fighters (MiG-23 and F-14 are practically the only exceptions, and the Tomcat has a strong air defence bias) and once for cost reasons such types took on the jobs formerly performed by dedicated strike & air defence platforms, they went away altogether. Stealth later added another powerful incentive to prefer fixed wings due planform alignment (nonetheless, the stealthy NATF & A/F-X were designed in the 1990s with VG wings for patrol endurance!) and removed the need for low altitude penetration in the strike role.

Quite literally NONE of this means variable sweep isn't still the gold standard solution for certain requirements - it's merely that the importance of those capabilities has diminished relative to others.

LOL! You keep conjuring up with "certain requirement" which only exists within your imagination. Have you considered the "certain requirement" where variable geometry wing doesn't apply at all? That's "certain requirement" is reality at the moment. Modern fighters use LERX as opposed to variable geometry wing, that's what matter. Whether you believe variable wing should be a gold standard does not. Simple as that.

Flame spills out of the engine's ends and starts burning the front or back first.

Do you really believe anybody reading this thread will have such a short memory?

That's not only what I said though:

LOL! I wonder why you have to resort to

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. Perhaps I was clearly distinguishing the difference between engine and inlet, and that doesn't suit the strawman that you are trying to setup?

Forced to acknowledge? Talk about a straw man argument (to borrow one of your favourite phrases)! I never - ever - claimed "variable geometry intake" was wrong. Stop this pathological lying!

Since we've already established that "variable geometry intake" (while correct) is not the only applicable term, you have no case to rest...

BTW, here's a reference for "movable ramp intake":

View attachment 44889

Now what?

Strawman again. I didn't say "movable ramp inlet" isn't an "applicable term", did I? I did say variable geometry inlet is the technical term, which launched you into a frenzy. Now that we have established variable geometry inlet is a technical term, I rest my case.

I didn't say it got no mentions, did I? Now go and compare the number of hits you get for "conic inlet" to "half-cone intake" or "conical shock inlet" or something similar.

I showed you it does appear in your so called "relevant literature". How else does one differentiate one shape of variable geometry inlet from another? And relevant according to whom? Apparently it must receive Tirdent's seal of approval. Just like the phrase "certain requirement", it is whatever Tirdent feels like at that moment. LOL!

Ok, since you're basically begging to be exposed as ignorant - here's an (incomplete) list of sources which agree with me:

View attachment 44888

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View attachment 44886

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View attachment 44887

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View attachment 44885

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Which of these says DSI 'belongs to a category of "streamline traced" inlet design'? LOL! And how does this refute my argument that DSI being used on the top-of-the-line fighter is a proof that DSI is better?

Look at your first source, and check out the patent filing date. The patent was filed in 2006, whereas DSI first flew in December 1996. DSI exists long before your so called "category" does.

Also, look at your own source to see what is a streamline. Streamline is basically the path traced by a particle. That sounds just like CFD.

So according to Tirdent, anything that involves analysis of streamline falls under a category of "streamline traced design". Modern automobile — streamline traced automobile category. Modern buildings — streamline traced building category. LOL!

As for cowl design, this was never flagged as anything more than a short overview - I'm not going to go into the nitty-gritty details of every aspect. I actually made the effort to provide a text in my own words rather than simply copying some source or other, to show that I actually understand what's going on - if you feel a paragraph on cowling design is in order, why don't YOU contribute one? Let's see you finally add something constructive with insight of your own, rather than nitpicking and debating semantics!

Oh, I just assumed that's something you might be interested in since you said you preferred to be technical. I'm not surprise you don't want to go into details, since I know that was never your intention to begin with. By the way, DSI is being used by two countries on their top-of-the-line fighters, contrary to your view variable geometry inlet has higher performance than DSI.

Whatever I honestly can't be bothered anymore. As any neutral observer will be able to see, what I've said previously on these points still stands and already addresses your rambling here.

You have no argument to begin with. I rest my case.

Where? That ludicrously incompetent photo comparison which you were so hasty to disclaim authorship of when I tore it apart?

I could make up image comparisons which "prove" all kinds of nonsense - the F-15/F-22 example already mentioned comes to mind - on that basis (except I'm incapable of the intellectual dishonesty required to peddle such tripe).

Clearly, evidence has been presented. Whether you think the evidence is "ludicrous" or "superficial" is your own problem, not mine. You have yet to present any valid argument to explain the high degree of similarities between Flanker and Su-57, because you have none that suits your assumption. By the way, said image can be traced back to a

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back in 2012, so it is clearly not I who authored it for this discussion. What this also shows, is that similarities between the two aircraft is obvious to everyone who is not blinded or unwilling to see.

 

[Engineer]

Hehe, I *swear* I didn't read this before composing the above response to Engineer's claims on LERX - actually I just came across it looking for the diagram below to illustrate my explanation on why VG wings help reconcile high supersonic dash and long subsonic loiter. It's too good not to post though:

View attachment 44894

Anyhow - VG wings. The reason why they are extremely effective at combining the above two requirements (far better than LERX could ever be) is that the nature of drag changes between subsonic loiter and supersonic dash flight conditions. In the former case, lift-induced and skin friction drag are the most significant contributors, whereas at high supersonic speed wave drag is dominant.

View attachment 44893
(from Ray Whitford, Design for Air Combat, p. 19)

Reducing lift-induced (and as a knock-on effect, skin friction) drag requires high wing aspect ratio at moderate sweep, much like an airliner. This directly affects induced drag and, because a high-aspect ratio wing provides better field performance and hence may get away with somewhat smaller wing area, can benefit wetted area too. The latter assumes it is field performance and not some kind of maneuvering point defining wing area for the aircraft in question, of course.

Trouble is, high aspect ratio is a good way to have prohibitive levels of wave drag at supersonic speeds, as this drag component is strongly linked to longitudinal distribution of cross sectional area (what's often known as the area rule). Wing thickness to chord ratio also needs to be low ("thin" wing) and strongly sweeping the wing back provides marked improvements on both counts. Cross sectional area contribution of the wing is much more favourable because it gets distributed smoothly along the length of the airframe rather than being lumped into a narrow sector, and while maximum thickness of the wing remains the same, the stream-wise chord length increases to effectively lower t/c ratio of the airfoil.

So please don't rely on Engineer on such subjects - at least not when he's backed himself into a corner from which he can't emerge without losing face (I'm pretty sure he actually knows enough to realize full well he's messed up a couple of times here). Hell, you don't have to take my word either - but cross-check his claims.

I assume you know this already? Apparently not, since you act like you have discovered a new continent or something. The conflicts between subsonic and supersonic cruise has been addressed by relaxed stability and vortex lift. This is the basis for J-20's aerodynamics layout, as described in

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So, given Tirdent doesn't even know requirement conflicts exist between subsonic and supersonc flight, Tirdent is clearly not reliable for aerodynamics knowledge.

 

[Gloire_bb]

China isn't the one claiming J-20 has different priorities;

Generation isn't about priorities, it's about qualities. Very approximate ones.
If you're finding too much in common between light strike fighter and air superiority platform - one of them does something horribly wrong.

 

[FORBIN]

Somebody know the power of the new/futur Saturn izdeliye 30 i see here 17.7 tons seems a lot i have posted a report with IIRC 16 tons ?

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And for climb rate i have i think with this futur engines 330 m/sec eventualy 350
For F-22 i have 330 m/sec
Same for STR and ITR eventualy

 

[Air Force Brat]

Generation isn't about priorities, it's about qualities. Very approximate ones.
If you're finding too much in common between light strike fighter and air superiority platform - one of them does something horribly wrong.

and here's where history may mislead you, the SU-57 like the F-22 is primarily an A2A platform, but nothing in those A2A requirement really take away from the fact that with a few tweaks, each will haul a very nicely load, and delivery it very precisely.. the F-22 has a little larger bays, probably even larger bays than the J-20, although it will not carry internally all that the F-35 will.. but each is capable of carrying a bunch of ordinance on hard points after "first day" air ops are accomplished??

Yes, I know it will very likely take more than 1 day to neutralize the threats, and likely everyone will limit themselves to L/O operations until that happens.

and the F-35, while named the JSF, turns out to have all the F-22 aerodynamic tweaks, which allow it to be flown to 73 degrees Angle of Attack, post stall and recovered with NO drama or ugly, nasty behavior, (actually its been flown to 105 degrees angle of attack) without OVT to "fix the problems",,, think F-14 when pushed outside of its envelope, flat spin? anyone? I'll let you ride in back??

So the SU-57 while having outstanding super maneuverability, is also capable of A2G with a few tweaks, and NO that doesn't mean that there are any compromises air to air?? (other than being much less L/O? than you would desire for a pure A2A platform)

 

[FORBIN]

Somebody know the power of the new/futur Saturn izdeliye 30 i see here 17.7 tons seems a lot i have posted a report with IIRC 16 tons ?

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And for climb rate i have i think with this futur engines 330 m/sec eventualy 350
For F-22 i have 330 m/sec
Same for STR and ITR eventualy

I find 16 -17 tons better blogger speak Russian but other is not a military cheerleader

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For the nozzle the new is more oriented about stealth or reduce IR emissions or both ? ceramic maybe as have F-135 i have see

The first photos available already show some things about Izd.30;
Reduced nozzle length
The presence of a nozzle worked with "notched" edges
The "notching" of the nozzles is one of the means used to reduce the thermal signature of the device

and here's where history may mislead you, the SU-57 like the F-22 is primarily an A2A platform, but nothing in those A2A requirement really take away from the fact that with a few tweaks, each will haul a very nicely load, and delivery it very precisely.. the F-22 has a little larger bays, probably even larger bays than the J-20, although it will not carry internally all that the F-35 will.. but each is capable of carrying a bunch of ordinance on hard points after "first day" air ops are accomplished??

Yes, I know it will very likely take more than 1 day to neutralize the threats, and likely everyone will limit themselves to L/O operations until that happens.

and the F-35, while named the JSF, turns out to have all the F-22 aerodynamic tweaks, which allow it to be flown to 73 degrees Angle of Attack, post stall and recovered with NO drama or ugly, nasty behavior, (actually its been flown to 105 degrees angle of attack) without OVT to "fix the problems",,, think F-14 when pushed outside of its envelope, flat spin? anyone? I'll let you ride in back??

So the SU-57 while having outstanding super maneuverability, is also capable of A2G with a few tweaks, and NO that doesn't mean that there are any compromises air to air?? (other than being much less L/O? than you would desire for a pure A2A platform)

And others F-35 ofc but also J-20 are different according what i have read and actualy watchers say J-20 agile as a J-11/Su-27 and turn radius data i have actualy even with a more powerful engine he can't reach both you mention but remains secondary ofc they are fighters mainly for BVR combat.
In addition agility even with a combat with IR missiles remains limited missiles capable 40 - 50 G fighters 9 eventualy few seconds 10 - 11 ... but remains lure fortunately !

I think the more important is to get the first shot look the bandit in first it is an advantage.
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