Official Chengdu J-20 Discussion Thread
Certainly, most olf the stuff I've seen is mumbo jumbo and has got little association with how signals work.
I've worked in the damn space so I might have a clue. Outside of the DefProfs who work on systems and understand weapons and sensor systems, My2Cents also has a clue. There are a couple of others who are not DefProf tagged but do work in the subject space, but you would have worked out who they are.
quite frankly, a lot of what is claimed about aerodynamics and how sensors work about this article is just rubbish.
I want to see more definitive shots and get input from colleagues I know who are connected before committing myself to more, but from what I see, and I have seen foreign systems at work, I have worked on signals and sensor management - most of this is trite nonsense.
On X-36 the leading edge of the main wing and the trailing edge of the canard are reflections of each other -- they're not aligned.
But the trailing edge of the canard is aligned with the trailing edge of the "lambda" wing while the leading edge of the canard, wing and the "other" trailing edge of the lambda wing are all aligned.
I made a couple of quick drawings with the alignments lined in:
X-36: http://img141.imageshack.us/img141/15/350pxx363viewdrawing.png
possible J-20: http://img401.imageshack.us/img401/903/j20edge.png
(The tails aren't fully aligned in the latter drawing, but I'm demonstrating the canard/wing alignment. I question this picture's accuracy to the real thing anyway, it shows a sort of LEX coming from the main wing to the canard)
Here's another possible lined drawing: http://img26.imageshack.us/img26/5050/j20edgealignment1.jpg
The point I'm trying to make is that right now we don't know if the canards are aligned with the wings or not, but they most likely are, and also that from the picture you linked to (http://paralay.com/TEMP/J20_4.png), it shows the canards aligned to the wings, at least.
If any of these drawings are wrong or my preconceptions are wrong, please do tell.
I see thanks. What about the whole canard stealth/aerodynamic argument, can you any offer any insight into that? Thanks beforehand.
There is, but it starts to get down to the quality and power dlexibility of the engine(s) and primarily of the EMU/ECU.
again, my view is that is a mule/hybrid as its experimenting with disparate technologies which are not mutually sympathetic
I seriously question whether the sister ships are identical, and would assume that article 2 has modified electronics.
the engine is the least of the important capabilities when having a CTD - and IMO, articles 1 and 2 are CTD's.
too many things are obviously not production, too many things are not mutually sympathetic, too many things that you would have for sig management are not in place, so the discussions about sig management are moot.
having seen data on the impact of canards on an aircrafts RCS, you would have to be an incredible optimist to believe that they are managing that assets RCS with canards in place, especially when we already know how much an RCS changes when going off interrogation aspect.
you might as well hold up a big reg flag and send a public announcement
So basically canards are terrible for stealth? Can you elaborate a little further please?
the effectiveness of any aircraft is against the likely threat and in how contested the battlespace is.
unfort most of the arguments you see about how effective an aircraft will be is in contested space where the enemy is not terribly sophisticated.
if that aircraft is not going in as part of a package, where that package is compromised of other system enablers such as AWACs, SBR, waypoint management prior to cimmittment, purple assistance etc.. then you might as well hold up a barn door and use it as a signal reflector.
canards cannot and do not assist in managing an aircrafts RCS, and in actual fact are an embuggerance as they're the fist transmitting tell when the aircraft goes off axis. we know this as we've seen it with Rafale, Typhoon, Nesher, NGrumman commercial test beds.
There's a reason why the US never went down the canard route after 1956. The UK had to have canards on Typhoon as there was no way to adapt other tech sets to the typhoon model, ditto for Rafale. There's a reason why the Russians also supported the US approach from 1956 - albeit 35 years later before it hit a production artifact.
again IMO there are too many disparate technologies on those artifacts, and that seems to me to reinforce that these are CTD's first. Maybe they'd already committed on the main wing design and discovered lift and management probs through various arcs, canards would be an interim solution.
and again, from my experience with signals management, that platform is a series of competing boundary layer managers and will be as dirty as buggery in handling as well as signals management. its a flying billboard and hence IMO is nowhere near final design.
in contested battlespace where the defender is electronically and sensor competent - they are not helping you stay quiet.
as soon as you go off aspect, you are signals dirty. in a low order threat environment thats no big deal, in an environment where the defender owns the signals and sensor space - its not helping you stay alive.
As I mentioned before, he does have SOME truths, and as far as I know, the canards are indeed detrimental to stealth, whether or not they're aligned with the main wing(though less so when aligned with the main wing). The key is that canards are small surfaces which don't allow creeping waves to be absorbed before they're diffracted when they reach the canards' edges. Having the canards aligned with the main wings allow the root part of the canard(really, not the canard itself but the part of the fuselage that interfaces with the canards) to be continuous with the fuselage, thus reducing its detriment to stealth. Obviously, it would also reduce reflective radar returns from the frontal aspect, but the J-20's canards are canted upwards and I'm not sure if they can be brought down to be in line with the main wings. It would require it to rotate around two axes. Now, it would appear to me that the disadvantages I just listed for canards would also apply to tailplanes, which both the F-22 and the T-50 have, so I don't see their inclusion on the J-20 as particularly unfriendly to stealth when compared to the other two 5th gen fighters.
To sum things up, it seems that canards can combine the actions of LEVCONs and tailplanes into one, is similarly stealthy/unstealthy with regard to diffracted radar returns, BUT is less stealthy than either with regard to reflected radar waves.
Here's a Chinese research paper posted recently on various boards regarding canards and stealth(you're a member of CDF, so you can see it right?):
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It really doesn't have anything groundbreaking, and it focuses entirely on reducing reflective radar returns. It seems to suggest that increasing the leading edge sweptback angle and decreasing its wingspan would help RCS, as well as reducing the canards' deflection angles as much as possible, and lastly that RAM can decrease its RCS by 5 to 10 dB. The latter indicates that the canards on the J-20 are probably indeed covered with RAM.
Sorry, this is just nonsense.
RAM is discretely applied, usually to no more than 20% of a platforms surface area - it is applied to manage signal returns. You don't apply RAM to all of a surface area. In additon you have to manage the resultant signal return onto the next impacted surface area. In the case of 3 different boundary layer generators, that means that all 3 sets of leading edges as well as the skegs would need treatment or management - that is just a nonsense.
seriously, there is too much BS being written to make it sound technically feasible when basic awareness of fluid/aerodynamics, plus an understanding of how signals actually work would raise alarm bells.
you don't apply RAM to modify deflection angles - you would manage the end receiving point as well. RAM is not applied like bondo where you shape the surface to "signal mold" a return.
you could cover the entire plane in RAM and you'd still end up with a flying transducer....
FMD people are talking about RAM like its some magical goo that will fix all signals concerns - it doesn't.
so we now have some clown talking about applying RAM to the canards and ignoring the obvious signal transmitters that are sitting on the rest of the plane and which are independant of the canards as signal transmitters in their own right?
lastly decreasing swept area does not change RCS emission unless the overall design is sympathetic in the first place. hasn't anyone ever seen how big a B2 or even a B1 is? I'd argue that if you killed the single skeg on a B1 and canted twins onto it that you would get a lower RCS than whats on this platform.
HTF can this design be focussed on reducing signals returns and emissions when ist got conflicting management solutions in place?
the mind just boggles.... again, some of the technobabble being used to explain its signals integrity IMO is plain outright abject nonsense.
Well the paper is really short(4 pages) and he really didn't go into specifics on how RAM is applied, I'm just relaying what he seems to mean. Also, I need to clarify that the paper stated that it is ignoring the signal returns from other surfaces of the plane, so I assume(again, the paper didn't go into specifics so I need to make some assumptions) that double+ reflected waves are not considered, although they're certainly very important in managing an entire plane's RCS.
And this is as you say, most likely a very early prototype or tech demo, because of mutually exclusive design features?
In terms of employment, you don't see it as an air superiority bird?
Finally in terms of the hi-lo mix, the J-10 and J-11 would then be the lo end?
King Comm
New Member
Have you seen this?
A map of China's indigenous fighter development:
The top 4 planes on the left are the proposals for the J-13 programme, below them are the J-8 and J-12, the swing wing thingy further down is the Q-6, and at the bottom are the 4 proposals for the J-9 project.
The red planes and arrows is the lineage of J-10, J-9IV evolved into J-9VI-1 which eventually led to the J-10, note that below J-9VI-1 is a huge delta canard twin engine thingy. That's the J-9VI-2, and here's a picture of its wind tunnel model:
a long, twin engine, twin vertical stabliser delta canard fighter.
I don't think we should accept that is the actual cockpit. I think we are too far away from the end production to finalize on what we think it is.
interesting, what would be a contemporary aircraft that you would compare it to in terms to similarity in roles?
From what I know, this is the only official next gen fighter jet program going on in China right now. It would seem to me that they would want to develop something that eventually replaces the flanker's role in PLAAF.
I would definitely not trust huitong's stuff as official. He does seem to have pretty good experience in weeding out the inaccurate stuff though.
Blitzo
Stealth and aerodynamics are not always in agreement, for example, the perfect stealthy wing profile is a sharp wing profile not a rounded wing profile, on a stealthy wing profile the leading edge has to be sharp and with two flat slopes.
The J-20`s canards have diheadral and at a different angle of those of the wing and dorsal vertical fins.
The wing has to have a angle with the nacelles and inlet, on the F-22 the vertical dorsal fins are canted at the same angle of the nacelle wall, the wing keeps a horinzontal level to repeat the caret inlet and nacelle wall angle,
On the X-36 the wing leading edge and canard trailing edge make an angle that also have the same angle seen on the trailing edge of the lamba wing of the X-36, this does not happen on the J-20
Stealth does not mean all the radar radiation is absorbed, but most of it is reflected away from the emitting source by the target, so aircraft are optimized to have stealth in the most likely directions they might be detected, frontal,rear, lateral and stealth is applied in the areas that produce the most of reflection, inlet, forebody engine and so on.
So all stealth aircraft are optimized like that.
It is impossible to an make undetectable aircraft with 100% no reflection and from all points.
Since current radar technology makes airborne carried by fighter still very weak and limits in radar size even more uncapable of detecting stealth aircraft,
The reality stealth is low observebability and thefore the J-20 limits the lateral stealthiness in favour of aerodynamics/
The canard has dihedral that is different to the angle of the canted fins and the canard does not have good lateral LO by having a very conventional shape.
A more stealth canard would be like the one seen on the X-36 or a lamba shaped canard or as the one seen on the SAAB stealth modelhttp://img399.imageshack.us/i/image015du7.jpg/sr=1
http://www.aereo.jor.br/wp-content/uploads/2010/07/KFX-Saab-3-580x435.jpg
Now radar technology means that the F-22 has to find the gaps on the radar network system to increase its undetectability, that is one of the reason the need for a stealth fighter to recieve information from other system to avoid get in to the range detectability of a radar system..
also these pictures show the angles are different see
http://forum.keypublishing.co.uk/attachment.php?attachmentid=191309&d=1293803778
This picture shows different angles at the trailing edge of the canard and wing and this the mostl likely shape canard
http://forum.keypublishing.co.uk/attachment.php?attachmentid=191310&d=1293805166
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what i can see is the dihedral of the J-20 canard does not go well with the angle of the dorsal fins and nacelle walls?
Question why the dorsal fin vertical stabilators have the same angle of the nacelle wall in the J-20 but the canards have another angle?
On the F-22 and J-20 the vertical fins are canted at the same angle of their respective nacelle walls.
The F-22 has the tailplanes hidden by the wing, same is the T-50 and F-35
The only reason is the J-20 needs the canard in that position of dihedral is for anti-flutter needs, aerodynamically is a good solution, but for stealth is not.
Now the canard in the J-20 has not raked tip but the wing seems to be raked for antiflutter needs like the F-15`s wing and J-10`s, so here the angle is not the same from a lateral view.
The wing tips are droped to reduce local angle of attack like the wing of the F-15 while handling high AoA
Also the wing`s trailing edge has a different lower angle than the canard`s trailing edge that is obvious in all the pictures you can see.
from a lateral view, the canard trailing edge and wing leading edge have not the same angle of the trailing edges seen on the canard and wing, that is there reason the X-36 has triangular canards and not Eurofighter types, The J-20 has canard not designed for pure stealth they use RAM to decrease its RCS
http://forums.airforce.ru/attachment.php?attachmentid=28993&d=1293969281
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Haavarla
Active Member
By reports Sukhoi have applied RAM coating to some critical area on the Airframe of the Su-35S.
Which part we don't know.
Still doesn't make the Su-35S any more a stealthy aircraft.
But the question here is how much the RAM coating is reducing the dB signals bouncing of its airframe.
It makes no sense to coat an entire airframe with heavy RAM coating, the aircraft empty weight would be an issue.
But isn't there several degree of tickness on the RAM coating applied to say the F-22?
RAM is one way to reduce its RCS dB, but the airframe material and design shape is the most critical area when it comes to 'stealth'.
Which part we don't know.
Still doesn't make the Su-35S any more a stealthy aircraft.
But the question here is how much the RAM coating is reducing the dB signals bouncing of its airframe.
It makes no sense to coat an entire airframe with heavy RAM coating, the aircraft empty weight would be an issue.
But isn't there several degree of tickness on the RAM coating applied to say the F-22?
RAM is one way to reduce its RCS dB, but the airframe material and design shape is the most critical area when it comes to 'stealth'.
that is incorrect. in the first instance we don't refer to it as stealth. its about signals management. signals are reflected, refracted and or redirected.
it is also clearly incorrect to state that its (RAM) applied in the areas of most reflection. Its applied to areas where you want to cause a refraction or "sinking" of said signal. signals don[t "bounce" once. they impact all over the aircraft because its an all aspect problem. I've worked on systems where it was applied to an area that would not even raise an eyebrow. Its managed against the likely threat area thats being entered. Its not a man for all seasons. Even the SR-71 had active management in place to deal with specific soviet/chinese systems. they were activated when needed against specific geographical locs.
They are NOT. Please don't make claims which are clearly incorrect.
Its got very little to do with brute power of the radar system. in fact pole tests using ground based very very powerful systems can struggle to detect an actively managed aircraft.
Its got nothing to do with making the aircraft invisible, it can also be about spoofing the signal, or even to dislocate the return enough to cause disruption .
and for the last time, we don't call it stealth, its called stealth in the open press because they don't understand the concept and its sound bited down to give them something easier to digest.
and those canards are moving relfectors which are impact across multiple other boundary generators, as well as hard surface elements that aren't handling tools.
you can't have a canard and be LO. once you enter all aspect sensor country that canard is a transducer - esp when its got the winged surface area of a small plane in its own right.
again, this is nonsense. VLO assets use waypoint management as one tool in strike map. the aircraft is part of a package - the package is what contributes to VLO - its not about the asset.
you need to exercise more restraint in making claims about capabilities that you're obviously unfamiliar about - its misrepresenting things to those who make think that you're accurate in your descriptions when some of them are very very wrong.
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exactly correct. in fact I can tell you point blank that it is not applied to an entire aircraft, that is just internet nonsense.
RAM is a materials science issue - not just a "coating" or applique. There is no such thing as increasing coating thickness to change a management outcome
its also about onboard systems - the design and shape is a percentile of the process. if you have canards then you've just limited the capability to add critical sensors to the sig management toolbox. from that point on the addition of these other sensors means physical architectural changes to the platform which start to become self evident and raise questions.
weasel1962
New Member
Re:
Common sense SOP is that aeronautical engineers will do a computer-generated RCS map first to identify which are the areas that can be achieved by shaping and apply RAM to further reduce areas which afford greater reduction from a specified angle.
Accordingly, as every aircraft type has a differing shape, I would think the areas of application of RAM may not be similar for a J-XX compared to say, a F-35.
And since a computer generated image may not actually result in a predicted RCS, the actual prototype will probably go through some more RCS mapping on the ground and in the air before production. Hence my guess is these may not be the only prototypes (unless the chinese engineers are satisfied with the actual RCS). If we see more prototypes, that could be one reason.
As LM has stated so many times, achieving all aspect stealth is not comparable to simply applying stealth to a 3rd gen plane. The failure to achieve stealth to a single aspect will render an avenue for any aircraft including 3rd gen to exploit.
Common sense SOP is that aeronautical engineers will do a computer-generated RCS map first to identify which are the areas that can be achieved by shaping and apply RAM to further reduce areas which afford greater reduction from a specified angle.
Accordingly, as every aircraft type has a differing shape, I would think the areas of application of RAM may not be similar for a J-XX compared to say, a F-35.
And since a computer generated image may not actually result in a predicted RCS, the actual prototype will probably go through some more RCS mapping on the ground and in the air before production. Hence my guess is these may not be the only prototypes (unless the chinese engineers are satisfied with the actual RCS). If we see more prototypes, that could be one reason.
As LM has stated so many times, achieving all aspect stealth is not comparable to simply applying stealth to a 3rd gen plane. The failure to achieve stealth to a single aspect will render an avenue for any aircraft including 3rd gen to exploit.