Chengdu J-20 5th Generation Aircraft News & Discussions

[gambit]

Professional Chinese aviation engineers have said those horizontal edges along the nose is used to create vortexes to maximize lift and maneuverability. I will take their words over a fanboy's.

I bet you spent a few hrs on the Internet going thru various forums looking for what you want but found none so you just simply made up that answer.

Those ridges are called 'chines'. When I told you 'wrong', it was not because the chines have no influence on aerodynamics. They do. But aerodynamics is not the only factor. You were wrong in relation to radar detection, specifically, a contribution to making the aircraft low radar observable. The most visible example is the SR-71 where the jet's design demands the most 'extreme' of chines possible.

https://en.wikipedia.org/wiki/Chine_(aeronautics)

Blending the chines into both the fuselage and the main wing avoids presenting corner reflectors or vertical sides to radars.

Wikipedia is too general. Not wrong, just too general. Avoidance of corner reflectors, specifically the 90 deg type, is a must anyway. The F-22, F-35, and J-20 do have corner reflectors.

But I will give a more specific explanation.

I gave you and your Chinese friends two clues regarding radar signals behavior:

- Ten lambda
- Conic

Clues I know my trainees a long time ago, before the F-35 and J-20, would not need to understand why.

First... clue is the 10 lambda ( λ ) rule: This rule states that the creeping wave behavior WOULD NOT exist if the physical diameter of the circle is 10 TIMES the operating wavelength ( freq ) of the impinging radar signal.

Lambda ( λ ) is the symbol used to represent wavelength or frequency.

Curvature produces surface wave behavior. As the signal travels on the surface, there are minute amount of radiation call 'leaky waves'.

Just in case you think I made this stuff up...

http://www.sciencedirect.com/science/article/pii/0165212595000139

The coupling coefficient Gl is approximated for the description of the launching and detachment of leaky guided waves on spheres and circular cylinders.

So in designing a low radar observable structure, we DO NOT want the creeping wave behavior. The leaky waves can be minimized, not completely eliminated, with absorbers, so if they are low amplitude enough, they can be lost in background clutter. But the creeping wave behavior must be dealt with and the best way is to enlarge the diameter to ten times the physical wavelength.

Again...Just in case you think I made this stuff up...

Please note the 'INTRODUCTION' paragraph...

When the geometric dimension is large enough (>10λ), the quantity of creeping wave on the backward direction can be neglected.

Note the authors' names. They are not Westerners. Finally, the paper's date: 1997.

Second... clue is the conic or conical shape: The cone is cylindrical but it also has a taper, or a gradual slope towards a smallest point.

In trying to convey the many ideas in radar detection, most visual depictions of the radar signal is an arrow.

But in reality, this is what a radar signal actually looks like...

The radar signal is actually a long cone with many 'petals'. The central structure is called the 'main beam' or 'main lobe', and the many petals are called 'side lobes'. The main lobe is where the bulk of radar detection occurs. The side lobes are weaker in amplitude, more incoherent, and more prone to produce erroneous information, hence, side lobes data are usually discarded.

When we add the two clues together, what else does the chines do besides providing some aerodynamics effects ?

To date, all radomes are roughly conical in shape, which means they have a taper towards a small point, which also means that eventually, the creeping wave behavior will occurs on the radome and the radar signal will return to source direction. For a 'stealth' aircraft, this is undesirable.

But we do not want the radome to be angular as well. A flat surface is an excellent reflecting surface. We want some curvatures. Remember rule 3:

- Control of quantity of radiators
- Control of array of radiators
- Control of modes of radiation

What the chines do is create an edge to break up the creeping wave behavior. The radar signals essentially traverses the curve and finally radiate into space on the other side. The weakest signals that may return to source direction would be at the radome's tip and should be lost in background clutter.

You don't have the laws of physics on your side. Your understanding may be flawed. You are not a professional aviation engineer. You have no working experiences or even superficial knowledges in this field. You don't have extensive measurements and test results to back up and verify your claims. Chinese engineers have vast amount of resources and experiences to minimizes the effect of canard on RCS. This is my point and I stick with it.

Not even you or anyone has claimed that the canard's RCS can not be minimized or reduced drastically. So stop making a fool of your self with your little bit of 'knowledge' or misunderstanding.

Am I a 'fanboy' ? You bet. I have no problems with the label. I am a fanboy of US airpower in specific, and of the US in general. But none of you PDF Chinese fanboys of the Chinese military can produce a credible technical post like this one or like post 6311.

I am a USAF veteran on two jets, F-111 ( Cold War ) and F-16 ( Desert Storm ). After the military, I worked as a field engineer for a company that shall remain unnamed in designing open environment radar detection testing for 'unmanned autonomous flight vehicles', aka 'drones'. I changed industry for family related reasons and am currently in semiconductor, specifically in Probe engineering.

When I said I am %99.999 confident that I am correct about the radomes based upon looks alone, that does not mean I am truly correct. It just mean I am that confident of my guess. I can say that I am %100 confident that Marvin the Martian will be the next UN Secretary General and I will be wrong. But regarding the radomes ? I doubt I am wrong as to why they are shaped that way.

Which leads up to the canards. My point is that in the INITIAL assessment specifically to being a low radar observable design, based upon the three rules that I have repeated posted on this forum over the yrs, the canards are immediately suspect. I do have the laws of physics on my side on this. Whether or not they are treated in some ways to minimize their contribution to RCS, we do not know. At best, we can guess with %99.999 confidence that their leading and trailing edges are treated with absorbers to control edge diffraction. We can see this treatment from various photos.

But that does not eliminate all signals that will come off the canards. I do not care how many times you cry 'vast resources' for the Chinese engineers. Nothing is perfect, not even the Chinese, no matter how much you want to believe of yourselves. Some radiated signals will come off the canards and interacts with signals from nearby structures. This is where I said we should be generous and do not make definitive statements in the absence of hard measurement data.

You PDF Chinese do not like it and would make the definitive statement that the canards do not matter. How can you make that statement in the absence of measurement data, the same demand that you made of me ? Faith is what you have. When I said I am %99.999 confidence of my opinion, it came from knowledge, experience, and logical thinking processes. Faith is that tiny %.001. In your case, faith is %100.

 

[Asoka]

Asok ... again especially since You are new here. PLESAE argue instead of pure accusations.
Do You know gambit's background? Are You sure that he is none of the things You claim he's not ... ??

And in return do You have a degree in aeronautical engineering ??

By the way I still miss YOUR explanation, why the J-20's nozzle should be as stealthy as the F-35 ones, why are fully open chaff-and-flare dispensers are as stealthy as enclosed systems

Again; give an argument and a contra-argument and then it's fine so everyone can make his own mind or otherwise You are in exactly the same position: So stop making a fool of your self with your little bit of 'knowledge' or misunderstanding !

.. and aren't most of us fan-boys in the one or the other way?

Deino

Deino, I respect your role as a unbiased moderator here. And I am new here.

"why the J-20's nozzle should be as stealthy as the F-35 ones"

Here is what I came across.

So basically, you are saying you have only faith that the J-20's engineers did 'something' to minimize or even render the canards statistically insignificant.

I have the laws of physics on my side to put the canards under professional suspicions. Not just me but so do many outside of this forum. You have only faith that the problem is fixed.

Yes, absolutely, that Chinese engineers have the resources and know how to render the RCS contribution of the canards statistically insignificant. They had known the canards adds RCS but they had done studies on how to render them statistically insignificant. The top Chinese engineer said that.

I really don't get where your belief that Chinese engineers can't do it or no one can do it. That's beyond silly to me. You have absolutely no conclusive measurements that the canards still contribute significantly to the RCS.

 

[gambit]

Yes, absolutely, that Chinese engineers have the resources and know how to render the RCS contribution of the canards statistically insignificant. They had known the canards adds RCS but they had done studies on how to render them statistically insignificant. The top Chinese engineer said that.

What else do you expect him to say ? That: "Despite our best efforts, the J-20's canards continues to be problematic and all our tests revealed they are large contributors to RCS." ?

You expect him to say something like that ?

I really don't get where your belief that Chinese engineers can't do it or no one can do it. That's beyond silly to me. You have absolutely no conclusive measurements that the canards still contribute significantly to the RCS.

Sorry, there are plenty things that 'no one can do'. If we have no conclusive measurement data that says one way, we should not place any faith on the other way.

 

[Asoka]

I have read everything from page 250 onward on this J-20 thread. Based on what I have read on your posts on PDF, I takes extreme amount of salt of your claims "I am a USAF veteran on two jets, F-111 ( Cold War ) and F-16 ( Desert Storm ). After the military, I worked as a field engineer for a company that shall remain unnamed in designing open environment radar detection testing for 'unmanned autonomous flight vehicles', aka 'drones'. I changed industry for family related reasons and am currently in semiconductor, specifically in Probe engineering."

I really doubt you have any aviation experience or field engineer experience on radar testing. Your poor judgments exhibited on J-20 and lack of solid engineering knowledge really casted serious doubt on my mind. I don't think I am the one on PDF who has this doubt.

 

[gambit]

I really doubt you have any aviation experience or field engineer experience on radar testing. Your poor judgments exhibited on J-20 and lack of solid engineering knowledge really casted serious doubt on my mind. I don't think I am the one on PDF who has this doubt.

If it make you happy: I was a janitor and everything I posted here I took out of the engineers' garbage cans from work.

I do not care if no one believe my account of my life. I am not here to please you or anyone else. Least of all to make friends. Your respect is shit to me. To date, no one have ever used the keywords I provided and returned to this forum and proved beyond any reasonable doubt that I gave wrong information. That is more than we have seen for the PDF Chinese.

 

[Asoka]

What else do you expect him to say ? That: "Despite our best efforts, the J-20's canards continues to be problematic and all our tests revealed they are large contributors to RCS." ?

Sorry, there are plenty things that 'no one can do'. If we have no conclusive measurement data that says one way, we should not place any faith on the other way.

If the chief Chinese engineer can not solve the canard RCS problem, there is no way he can lie about it or hide it. Since it will show up on radars and in the RCS/Radar chamber. His head will roll, if he let J-20 out of the door with this problem.

Your attitude regarding this canard RCS issue is not just bashing the ability of the Chinese, but bordering outright racist.

Several papers you have quoted are written by Chinese engineers in China, so Chinese ability is not lacking the funds required for the project is lacking. So I don't understand your claim that the RCS of the canard is still a problem.

 

[gambit]

Your attitude regarding this canard RCS issue is not just bashing the ability of the Chinese, but bordering outright racist.

Once again, another PDF Chinese proved to be consistent: That criticisms, even technically legitimate ones, are racist in origin.

No need to continue the debate with you.

Readers should take caution.

 

[Asoka]

Once again, another PDF Chinese proved to be consistent: That criticisms, not even technically legitimate ones, are racist in origin.

No need to continue the debate with you.

Readers should take caution.

You claim that China, which has designed and engineered a 5th generation fighter plane like J-20, cannot solve the canard's RCS problem.

The J-20 started in 1996, and first flew on 2011, you claim that after 20 years the Chinese still haven't solved the canard's RCS problem, and probably never will.

If this is not racist motivated, then I don't know what is.

Since the RCS of J-20 or F-22 will probably be never revealed in our life time. The readers on PDF will either have to believe Gambit's claim that J-20's canard still contribute significant RCS and will probably be never be reduced by the Chinese, or the readers can choose to believe it's not difficult to reduce canard's RCS and it is already done so, and J-20 has achieved LO status, at least the frontal aspect.

Take your pick, PDF members.

 

[grey boy 2]

 

[S10]

You claim that China, which has designed and engineered a 5th generation fighter plane like J-20, cannot solve the canard's RCS problem.

The J-20 started in 1996, and first flew on 2011, you claim that after 20 years the Chinese still haven't solved the canard's RCS problem, and probably never will.

If this is not racist motivated, then I don't know what is.

Since the RCS of J-20 or F-22 will probably be never revealed in our life time. The readers on PDF will either have to believe Gambit's claim that J-20's canard still contribute significant RCS and will probably be never be reduced by the Chinese, or the readers can choose to believe it's not difficult to reduce canard's RCS and it is already done so, and J-20 has achieved LO status, at least the frontal aspect.

Take your pick, PDF members.

I don't think you got gambit's meaning. He's not saying canard delta designs can't be low observable, but the canards contribute to a higher RCS return than non canard designs.

Being "stealthy" doesn't mean being invisible to radar, but rather of matter of detection range. The presence of canard may push past the detection threshold a bit sooner. No one is disputing J-20 is a low observable design. There are measures that can be taken to negate some of the increased RCS from the canards, but you can't eliminate their influence completely. Regardless of whether J-20 is on par with F-22/F-35 in terms of signal management, it's already miles ahead of any legacy 4th generation fighters.

Canard designs have been proposed in the past, so they can be compatible with a low observable profile. However, none have materialized into service.

 

[Asoka]

I don't think you got gambit's meaning. He's not saying canard delta designs can't be low observable, but the canards contribute to a higher RCS return than non canard designs.

Being "stealthy" doesn't mean being invisible to radar, but rather of matter of detection range. The presence of canard may push past the detection threshold a bit sooner. No one is disputing J-20 is a low observable design. There are measures that can be taken to negate some of the increased RCS from the canards, but you can't eliminate their influence completely. Regardless of whether J-20 is on par with F-22/F-35 in terms of signal management, it's already miles ahead of any legacy 4th generation fighters.

Canard designs have been proposed in the past, so they can be compatible with a low observable profile. However, none have materialized into service.

It seems you are the one who doesn't get Gambit's drift. He is saying precisely 'canards contribute to a higher RCS return than non canard designs' and that can not be changed because his physics laws and the J-20 is not LO because of that.

"There are measures that can be taken to negate some of the increased RCS from the canards," Gambit is denying there are measures the Chinese can take to reduce them, and has done so.

"but you can't eliminate their influence completely. " Of course not, but they can be reduced significantly into the level of negligible.

"Canard designs have been proposed in the past, so they can be compatible with a low observable profile. However, none have materialized into service." The J-20 can be the first plane with LO into service. Nothing wrong with that. The reason F-22 did not used canards is probably because it has vector thrust already, so it doesn't need the canards to complicate the controls.

"The presence of canard may push past the detection threshold a bit sooner." How soon? I don't know but I bet the Chinese has minimized the effect that it hardly makes a difference.

"Regardless of whether J-20 is on par with F-22/F-35 in terms of signal management" That agreed. Because China is a late comer it could liberally borrow from F-35 and F-22 and B-2's stealthy features and refined them with their supercomputer and RCS chamber. China has the time, money, and talents.

 

[Deino]

Has this video already shown?

https://twitter.com/x/status/790854350977458176

 

[星海军事]

Has this video already shown?

https://twitter.com/x/status/790854350977458176

I made the post-production today.

 

[gambit]

Readers,

In post 6368, Mr. Asok said this...

If this is not racist motivated, then I don't know what is.

Let us take examine the absurdity of that argument.

In designing a low radar observable, aka 'stealth', body, three rules are in play...

- Control of quantity of radiators
- Control of array of radiators
- Control of modes of radiation

In designing a low radar observable body, the corner reflector is definitely UNDESIRABLE.

The corner reflector as a complex structure falls under rule 2: Control of ARRAY of radiators.

In the event that the corner reflector is unavoidable, such as the array between the vertical and horizontal stabs, another rule says to avoid the 90 deg type. This is why 'stealth' fighters have twin canted vertical stabs. The corner reflectors created are not 90 deg, reducing, but not completely eliminating, the dreaded 'double bounce' signal behavior. These are the laws of physics.

Regarding the J-20's canards, Mr. Asok asserted that since the J-20's chief designer said the signal contribution from the canards have been minimized to be statistically insignificant. Unfortunately, there are no measurement data to back up that claim.

What if the Chinese claimed they solved the corner reflector problem and still provide no measurement data or even a paper in professional organization like IEEE ? According to Mr. Asok, we MUST take the Chinese at their words because the Chinese have 'vast resources' and plenty of time to work on the problem. If we challenge the Chinese claim based upon the laws of physics, we are racists in doing so. We are saying that despite talents, money, and time, the Chinese people are too stupid to solve problems.

It is telling that for the Americans on this forum, we do not toss out the charge of racism every time someone challenge US claims about our hardware. If we are able, we will seek out credible technical sources to back up the claims. If not possible, we will admit we do not have supporting documentation, but we do not call the skeptics racists. Some believe US and many do not, but we do not call the doubters racists.

But the charge of racism is typical of the PDF Chinese whenever they are unable to support their arguments. Racism is an odious idea, so charging someone as a racist immediately make you a victim and put you in a morally superior position. You can also safely avoid any more questions, even if the questions are technically legitimate.

 

[Pepsi Cola]

Lol this guy. For all honesty, I couldn't care less of your argument of whether it is more stealthy or not when compared to F22 or F35. Every country has its own requirement for its jet. Just because a fighter is allegedly less stealthy doesn't mean it's inferior in any way. Judging by how the PLAF doesn't even want the FC31, even though its design language is very similar to the F35 (Supposed wet dream of a jet), means that China has the resources to "do it like Americans" but they simply see the J20 as a better choice.

Gambit, I don't know if you're racist or not, but you sure like to target Chinese products and love to talk down on them. If you have also brought up some good points about them just to be fair, no one would have accused you of anything. Accusing other for being PDF Chinese is nothing better than them calling you a racist American. You accuse them for being factless, but you do realize that you are also factless when it comes to J20. Maybe the Chinese engineers really did make the J20 stealthy enough to be "statistically insignificant", maybe not. The fact is no one knows. Another fact is that China chose J20's design over other proposed designs, and there was a reason for it.​