Russian Su-57 Aircraft Thread (PAK-FA and IAF FGFA)
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I read this thread on a different machine away from home without logging in and so I saw Engineer's responses. I'm primarily replying because of his rather brave LERX claim, but will take the opportunity to address the rest of his... uh, "arguments".
Ok, NOW you have my full attention - I look forward to seeing your explanation on how LERX allows these conflicting requirements to be reconciled better than would be possible with VG wings. I already outlined very briefly why the latter help and pointed out that LERX was an established and well-known concept when NATF and A/F-X were designed.
I see you are still categorically refusing to even entertain any potential causes other than an engine failure (although doing so would mean acknowledging that you originally jumped to a conclusion without evidence, so perhaps I should not be surprised). The issue isn't whether another cause is in any way preferrable (kind of academic when it's a write-off), but your blithe contempt of both etiquette and logic.
Needless to say, there are plenty of things aboard an aircraft which can start a fire other than the engines. Based on the location of the damage to T-50-5 it could have been the ECS or the batteries or really any piece of electrical equipment liable to have a short circuit.
Sure. That's why the bottom of the engine nacelle in that photo is scorched, right?
On T-50-5, why is there a section of pristine composite skin between the metal engine casing and the burn-through area (which in turn is *aft* of the intakes)? According to you, the fire spread forward out of the engine bay but did not damage the composite parts for some distance, before miraculously stopping just short of the inlet (*without* however spilling out of the opening and doing any significant damage to the LEVCON) and burning through the fuselage there. Come on, you don't actually believe this contrived nonsense yourself, do you?
Unless you can finally supply proof, says that an ignition source close to the location of the fire damage fits the observed facts much better than an engine fire.
Hardly, that's even more ridiculous an argument. I suppose by that logic it is perfectly fine to claim the F-22 is an F-15 derivative (good argument, well made there, Ultra!)? Or the F-15 a MiG-25 copy? By giving such weight to superficial similarities in configuration you are just flaunting your ignorance.
Other non-experts believing the same rubbish doesn't make it true.
Ok, if you're certain that "variable geometry inlet" is the ONLY correct term, why don't you give us a source which says so? Must be documented somewhere for you to be this sure of it and the issue would be clarified once and for all. You might want to be careful not to cite one whose knowledge of inlet design is patchy though...
But then, you don't even adhere to your own "rule", sometimes it's a "variable intake" after all
I can only conclude your insistence on splitting hairs is a reflection of your apparent inability to effectively take on my arguments at the technical level. Since I did not start this nit-picking contest about terminology though, we can drop it as far as I'm concerned. Your call.
Meanwhile, we're still waiting for your explanation about the theory behind DSI of course. Here was your chance to demonstrate some technical competence instead of engaging in logomachy - I've been quite courteous by leaving open an avenue for you to save at least *some* face on this point for so long. Have it your own way - the following summary of the basics behind DSI will expose how you would not have mistaken an (entirely appropriate) reference to supersonic conical flow theory for labelling it a "conic intake*" if you actually knew about the concept in some depth.
DSI belongs to the category of so-called "streamline traced" intake designs, inward-turning inlets that are so popular on hypersonic projects recently are another example. What this means is that the geometries of the compression surfaces and cowl lips are created by tracing the streamlines in a suitably chosen (compressive) supersonic parent flow field which pass through appropriate bounding curves. The shock structure generated by a geometry derived in this way (and with corrections for any effects not accounted for in the parent flow field applied, e.g. viscosity) should then closely match the "target" flow field specified initially.
For a DSI, that parent flow field is invariably... wait for it... some form of conical flow (for an inward-turning inlet you'd go with a Busemann inward-turning compression instead): simple cone, double cone or isentropic spike - whatever meets the requirements. Theoretically you're not even limited to cone bodies, but with a 2D wedge the lack of a substantial transverse pressure gradient in the resulting flow field means there would be little if any boundary layer diversion, defeating the purpose of the exercise. Regarding the bounding curve defining the collection of streamlines to be traced, for the DSI bump it would be the intersection line of the aircraft forebody geometry with the conical shock generated by the virtual (because it sits "inside" the outer mold line of the airframe) conical body.
If you're interested in more detail, googling some combination of "diverterless supersonic inlet", "streamline tracing" and "conical" or "cone" will turn up large numbers of research papers and patents, including good illustrations of the concept. That Engineer was apparently confounded by my reference to conical flow theory in connection with DSI shows his knowledge of the subject he was making such bold claims about didn't even extend this far, hence his desperate attempts at deflecting the issue subsequently.
* Want me to pick apart how that's not the "correct terminology"? Pot, kettle, black and so on.
Trouble is, DSI doesn't in fact have the same pressure recovery, according to the USAF (and if one is familiar with the basic concept behind it, that's pretty intuitive from a first principles perspective).
Better for one set of priorities usually means worse for another. If you want to argue that Russia is wrong to have priorities different from the US and China, then we can at least agree to disagree - but what you're saying here is just demonstrably false. You don't have to take *my* word for it either, the USAF believes in the same "falsehood" (and is spending money on it), so I'm in good company there.
Except that your set of (a single) premises is and that caught you out. Your reasoning was sloppy and you're not doing yourself any favours by continuing to defend the indefensible.
Once more, I'm sure DSI is the best solution for the J-20 (never claimed anything to the contrary, believe it or not...), but that doesn't make it the right choice for other aircraft with needs that may be significantly different. Intakes are a means to an end, the decision is not taken according to "established trends" or something (aircraft are designed by people who are capable of thinking independently from "fashions") but by carefully weighing the pros and cons against the requirements. There is no one-size-fits-all answer if the specifications which must be met diverge by a sufficiently wide margin.
Ok, NOW you have my full attention - I look forward to seeing your explanation on how LERX allows these conflicting requirements to be reconciled better than would be possible with VG wings. I already outlined very briefly why the latter help and pointed out that LERX was an established and well-known concept when NATF and A/F-X were designed.
I see you are still categorically refusing to even entertain any potential causes other than an engine failure (although doing so would mean acknowledging that you originally jumped to a conclusion without evidence, so perhaps I should not be surprised). The issue isn't whether another cause is in any way preferrable (kind of academic when it's a write-off), but your blithe contempt of both etiquette and logic.
Needless to say, there are plenty of things aboard an aircraft which can start a fire other than the engines. Based on the location of the damage to T-50-5 it could have been the ECS or the batteries or really any piece of electrical equipment liable to have a short circuit.
Sure. That's why the bottom of the engine nacelle in that photo is scorched, right?
On T-50-5, why is there a section of pristine composite skin between the metal engine casing and the burn-through area (which in turn is *aft* of the intakes)? According to you, the fire spread forward out of the engine bay but did not damage the composite parts for some distance, before miraculously stopping just short of the inlet (*without* however spilling out of the opening and doing any significant damage to the LEVCON) and burning through the fuselage there. Come on, you don't actually believe this contrived nonsense yourself, do you?
Unless you can finally supply proof, says that an ignition source close to the location of the fire damage fits the observed facts much better than an engine fire.
Hardly, that's even more ridiculous an argument. I suppose by that logic it is perfectly fine to claim the F-22 is an F-15 derivative (good argument, well made there, Ultra!)? Or the F-15 a MiG-25 copy? By giving such weight to superficial similarities in configuration you are just flaunting your ignorance.
Other non-experts believing the same rubbish doesn't make it true.
Ok, if you're certain that "variable geometry inlet" is the ONLY correct term, why don't you give us a source which says so? Must be documented somewhere for you to be this sure of it and the issue would be clarified once and for all. You might want to be careful not to cite one whose knowledge of inlet design is patchy though...
But then, you don't even adhere to your own "rule", sometimes it's a "variable intake" after all
I can only conclude your insistence on splitting hairs is a reflection of your apparent inability to effectively take on my arguments at the technical level. Since I did not start this nit-picking contest about terminology though, we can drop it as far as I'm concerned. Your call.Meanwhile, we're still waiting for your explanation about the theory behind DSI of course. Here was your chance to demonstrate some technical competence instead of engaging in logomachy - I've been quite courteous by leaving open an avenue for you to save at least *some* face on this point for so long. Have it your own way - the following summary of the basics behind DSI will expose how you would not have mistaken an (entirely appropriate) reference to supersonic conical flow theory for labelling it a "conic intake*" if you actually knew about the concept in some depth.
DSI belongs to the category of so-called "streamline traced" intake designs, inward-turning inlets that are so popular on hypersonic projects recently are another example. What this means is that the geometries of the compression surfaces and cowl lips are created by tracing the streamlines in a suitably chosen (compressive) supersonic parent flow field which pass through appropriate bounding curves. The shock structure generated by a geometry derived in this way (and with corrections for any effects not accounted for in the parent flow field applied, e.g. viscosity) should then closely match the "target" flow field specified initially.
For a DSI, that parent flow field is invariably... wait for it... some form of conical flow (for an inward-turning inlet you'd go with a Busemann inward-turning compression instead): simple cone, double cone or isentropic spike - whatever meets the requirements. Theoretically you're not even limited to cone bodies, but with a 2D wedge the lack of a substantial transverse pressure gradient in the resulting flow field means there would be little if any boundary layer diversion, defeating the purpose of the exercise. Regarding the bounding curve defining the collection of streamlines to be traced, for the DSI bump it would be the intersection line of the aircraft forebody geometry with the conical shock generated by the virtual (because it sits "inside" the outer mold line of the airframe) conical body.
If you're interested in more detail, googling some combination of "diverterless supersonic inlet", "streamline tracing" and "conical" or "cone" will turn up large numbers of research papers and patents, including good illustrations of the concept. That Engineer was apparently confounded by my reference to conical flow theory in connection with DSI shows his knowledge of the subject he was making such bold claims about didn't even extend this far, hence his desperate attempts at deflecting the issue subsequently.
* Want me to pick apart how that's not the "correct terminology"? Pot, kettle, black and so on.
Trouble is, DSI doesn't in fact have the same pressure recovery, according to the USAF (and if one is familiar with the basic concept behind it, that's pretty intuitive from a first principles perspective).
Better for one set of priorities usually means worse for another. If you want to argue that Russia is wrong to have priorities different from the US and China, then we can at least agree to disagree - but what you're saying here is just demonstrably false. You don't have to take *my* word for it either, the USAF believes in the same "falsehood" (and is spending money on it), so I'm in good company there.
Except that your set of (a single) premises is and that caught you out. Your reasoning was sloppy and you're not doing yourself any favours by continuing to defend the indefensible.
Once more, I'm sure DSI is the best solution for the J-20 (never claimed anything to the contrary, believe it or not...), but that doesn't make it the right choice for other aircraft with needs that may be significantly different. Intakes are a means to an end, the decision is not taken according to "established trends" or something (aircraft are designed by people who are capable of thinking independently from "fashions") but by carefully weighing the pros and cons against the requirements. There is no one-size-fits-all answer if the specifications which must be met diverge by a sufficiently wide margin.
Putting the cart before the horse again in terms of logic. You are assuming the assertion about the Su-57 (which is what's being questioned) to simply be a given without first having proven it - circular logic at its finest. Ultra is perfectly right: the F-15 and F-22 comparison invalidates your argument by .
If you prefer, you could also look at it the other way round, i.e. based on *knowing* that the F-22 (despite the undeniably high degree of similarity in configuration) is NOT a F-15 derivative, examine whether the claim about the Flanker and PAK-FA stands to reason. Which it doesn't, because the example shows that even demonstrably unrelated designs by totally separate manufacturers can display the same degree of similarity due to having been designed for requirements that are, though not identical, similar in important respects. So without further proof to bolster your position (which of course you don't have, because it doesn't exist...) you're championing a .
Since you've already demonstrated you can't wrap your mind round how requirements drive engineering decisions in the DSI debate, it is hardly surprising that you would allow yourself to be blinded by superficial aesthetics with respect to overall configuration though. Go on, try to expound on your theory based on functional similarities and technical characteristics - how is the Su-57 closer to the Su-27 than the F-22 to the F-15 in actual engineering terms rather than just looks?
Engineer
Major
You are projecting. You are assuming the Su-57 is not derived from the Flanker then using it to conclude Su-57 is not a derivative. Just because you are using circular logic, doesn't other does. Nothing Ultra said invalidates my argument, because Ultra statement itself is and not a valid argument to begin with. He might as well use "Earth is round" as a premise. Nothing you said invalidates my argument either, because you don't even have an argument. Meanwhile, we already see evidences supporting existence of derivation between Flanker and Su-57. Similarities between the two go far beyond superficial and are down to specific details.
Engineer
Major
LERX generates vortex system which increases strength with increase of angle-of-attack. Angle-of-attack is larger at lower speed, and is very large during combat maneuvering. In these situations, LERX provides more lift. LERX achieves the same objectives as variable-geometry wing without moving parts, by providing lift when lift is needed the most.
"Could have been", "If", "likely", "potential"... with use of so many weasel words, you clearly don't have any evidence to refute engine problem as cause of the fire. On the other hand, we have already seen flameout, on a prototype that gets pampered for an airshow. I am not interested in your potential causes, because my point is that Russia is reckless, with putting an experimental engine on an experimental airframe then ended up with multiple incidents as example.
You do know that fire gives off heat omnidirectionally, right?
According to me, the fire actually occurs on the port side rather than the starboard side that Sukhoi has claimed, because the LEVCON on the other side does appear to have significant damage. I am already being generous by going with what Sukhoi says. So you are right in a sense, as I don't actually believe in the contrived nonsense that Russian put out.
Occam's razor says an engine fire fits the observation of a fire near the engine.
Simliarities between Flanker and Su-57 go beyond superficial. This isn't "the two aircraft have wing so one is a copy of another".
My reply will continue in the next post due to character limit.
Engineer
Major
Is "variable-geometry inlet" the proper term? Yes. Did I say it is the "only" term? Nope. Quit your strawman. You made up a terminology, showing your knowledge of inlet design is patchy.Ok, if you're certain that "variable geometry inlet" is the ONLY correct term, why don't you give us a source which says so? Must be documented somewhere for you to be this sure of it and the issue would be clarified once and for all. You might want to be careful not to cite one whose knowledge of inlet design is patchy though...
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But then, you don't even adhere to your own "rule", sometimes it's a "variable intake" after all
LOL! You got shown that your knowledge of inlet design is patchy, so now you fill your posts with as many terminologies as possible. Argument by verbosity doesn't refute the fact that DSI was chosen and being used on top-of-the-line fighters in both US and China. Decision of two engineering teams vis-a-vis irrelevant opinion of an unknown person on the Internet, the formers obviously have more weight. The fact that DSI got selected and not your beloved variable geometry inlet shows DSI is more suitable in actual applications, hence better.
Trouble for you is that DSI does not need to have the same pressure recovery, just comparable pressure recovery. Being able to achieve the same objectives while being lighter and more stealthy is what makes DSI superior. J-10A's three-shock variable geometry inlet got replaced by DSI is a testament to that.
You contradicted yourself because "better for one set of priorities usually means worse for another" applies to your beloved variable geometry inlet as well. You have no proof that this is "usually" the case when it comes to DSI and you have no proof that this is "usually" the case in general. What's more, as science and technologies improve, what you said is actually less likely to be the case. Claiming Russia has different priorities is an excuse. After all, an aircraft with drastic differences to other 5-th generation fighters wouldn't technically be a 5-th generation fighter.
Except there is no requirement that an argument must consist of more than one premise, and even if there were, there are more than one premise to support my conclusion. Stop projecting your inability to apply logic on to me.
We are talking about fighter aircraft, constrained by the same physics as other fighter aircraft. There isn't "significant different" in needs. However, there is significant differences in what each country can accomplish with available resource. DSI is just one but not the only alternative to variable geometry inlet. US and China both demonstrated they can achieve and apply those alternatives, Russia hasn't demonstrated so. That's all there is to it.
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Is "variable-geometry inlet" the proper term? Yes. Did I say it is the "only" term? Nope. Quit your strawman. You made up a terminology, showing your knowledge of inlet design is patchy.
LOL! You got shown that your knowledge of inlet design is patchy, so now you fill your posts with as many terminologies as possible. Argument by verbosity doesn't refute the fact that DSI was chosen and being used on top-of-the-line fighters in both US and China. Decision of two engineering teams vis-a-vis irrelevant opinion of an unknown person on the Internet, the formers obviously have more weight. The fact that DSI got selected and not your beloved variable geometry inlet shows DSI is more suitable in actual applications, hence better.
Trouble for you is that DSI does not need to have the same pressure recovery, just comparable pressure recovery. Being able to achieve the same objectives while being lighter and more stealthy is what makes DSI superior. J-10A's three-shock variable geometry inlet got replaced by DSI is a testament to that.
You contradicted yourself because "better for one set of priorities usually means worse for another" applies to your beloved variable geometry inlet as well. You have no proof that this is "usually" the case when it comes to DSI and you have no proof that this is "usually" the case in general. What's more, as science and technologies improve, what you said is actually less likely to be the case. Claiming Russia has different priorities is an excuse. After all, an aircraft with drastic differences to other 5-th generation fighters wouldn't technically be a 5-th generation fighter.
Except there is no requirement that an argument must consist of more than one premise, and even if there were, there are more than one premise to support my conclusion. Stop projecting your inability to apply logic on to me.
We are talking about fighter aircraft, constrained by the same physics as other fighter aircraft. There isn't "significant different" in needs. However, there is significant differences in what each country can accomplish with available resource. DSI is just one but not the only alternative to variable geometry inlet. US and China both demonstrated they can achieve and apply those alternatives, Russia hasn't demonstrated so. That's all there is to it.
OK GENTs, can we chill here?? inlets, LERX,, hey you know I love all that kool stuff and Eng, nobody on SDF has more respect for you Brother than I, and Trident, welcome to SDF Brother, and I'm very thankful to have you both on SDF,,,,,
Trident you're the new, and here you are both right,,, there a lots of ways to do inlets,, and there are lots of ways to do leading edge devices and canards, but we've all got the point.
our Mod crew has worked very hard to re-establish the accuracy and civility that has defined SDF
this is the PAK-FA, T-50, SU-57 thread?? yes??? and Trident, there is NO denying the SU-57 has deep genetic roots in the Flanker,, remember, a "Flanker, is a Flanker, is a Flanker!".. yeah that's "trademarked" and that MY line...
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).
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...
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.
Sure. That's not what's seen on T-50-5 though, you appear to have a pretty eccentric definition of the word "near".
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:
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
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).
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?!
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.
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.
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.
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).
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.