Chengdu J-20 5th Generation Aircraft News & Discussions

[Asoka]

a lot of folks here are saying canards increase the rcs and therefore it contributes to the fighter not being stealthy. it is true canards to increase the rcs, thats and fact, and they increase drag too.

people must understand one thing, purpose. what is it designed to do? now my opinion is that its a high endurance front line fighter/interceptor. this makes it perfect for use on the scs.

looking at the image below it is evident that its size would suggest its role in a high endurance interceptor/fighter

now since this is their first fifth gen fighter. this can also be seen as it being a test platform. developing something thats not critical as there are other platform that can do the job like the h-6. where as something like a full on air superiority fighter like the f22 and pak-fa is something that would be in the early stages of development. which i would assume would be fully Chinese including the engines. i suspect they have the ability to manufacture most of the engine components such as the main fan and the lp and hp compressors but the hp and lp turbines would be the problem and running them at cooler temperatures would increase their life but reduce their power. this being a fighter jet they need to be powerful so must run at much hotter temperatures but this greatly reduces the life of the turbines/engine.

The canards at the front are used 1.) to create vortexes to increase the lift, 2.) to balance the airplane to make it level, 3.) and to increase maneuverability when turning.

When placed close to the main wings, the canards do wonder to increase goals #1 and #2, but it also drastically increase drag during transonic and supersonic phase, so it's not good for supersonic flight. And it's also not so good at goal #2, to balance the plane because of the shorter moment arm.

When the canards are placed far away from the main wings, the drag effect is dramatically reduced, but the goal #1 and #3 of having a canard is also greatly weaken, but goal #2 is increased.

Aircraft designers have been bedeviled by this conflicting goals of incorporating the canards for some times. They know about advantages and short coming since the 60's.

Chinese designers solve this dilemma by using Leading Edge Extension between the canards and wings to create vortexes and use the far away placement of the canard to balance the plane.

Thus, it has predicted that J-20 will have excellent supersonic maneuverability because of its far away placed canards, and low speed maneuverability because of its leading edge extension like those of the F-18.

So far, the low speed, post stall maneuvers, made famous by the Flankers and Raptors, have not been demonstrated publicly by J-20.

One of the member of the design team has written a book which revealed one of the requirement of J-20 is that it must have the range to reach the islands of Japan or the first island chain without refueling, and able to reach Tokyo with just one refueling. So long range is a built-in feature like the Mig-31.

 

[Deino]

...
This is where my confidence that having the canards do not affect the RCS of the J-20 much came from.

"why it should be AS stealthy as the F-22 or F-35"
What it takes to make a stealth fighter is deep understanding of the radar principles, simulation software and supercomputer to model the reflection, RCS chamber to test and refine the design, and advanced coating to absorb the signals. China has demonstrated that it has all those elements. Time will tell whether J-20 is on par with F-22 and F-35.

....

Sorry to say so, but that finally disqualifies Yourself from any further discussion in that regard: "I believe, my confidence ... I'm sure Chinese technicians" ... forget it simply.

Chou believe that all but so many evidence simply speak against that and IMO all what has been proved thru the last posts is that You have indeed NO understanding in stealth nor in the stuff You post. It's pure fan-boy posting.

Even more since You are so much focused purely on the canard-issue: Still no word on the round exhausts without any zig-zag edges, still no valid point, why chaff and flare dispensers are fully open visible ???

You surely will tell us know again "I believe, my confidence ... I'm sure Chinese technicians" ... but again simply forget it.

As such back to my advice: stop all Your accusations ... read, learn and argue before You post.

Deino

 

[Blue Marlin]

1. The canards at the front are used to create vortexes to increase the lift, to balance the airplane to make it level, and to increase maneuverability when turning.

2. One of the member of the design has written a book which revealed one of the requirement of J-20 is that it must have the range to reach the islands of Japan or the first island chain without refueling, and able to reach Tokyo with just one refueling. So long range is a built-in feature like the Mig-31.

vortexes dont create lift
educate yourself

2.you have the idea but i wont go to the extreme of saying it has to reach mainland japan and back. it can do that but i doubt it would be used for that.

 

[gambit]

If you're as smart, or experienced as you claim yourself to be. Don't act dumb. You know exactly what I meant.

I do not care if you believe what I said about myself or do not believe. I am not here to make friends, receive praise, or earn respect. On an anonymous Internet forum, only the CONTENTS of your posts that matters, specifically, contents that are DIRECTLY related to the target subject.

So here we go, again...

When you design a car, you NEED wheels. Not want, but need. How else can your car move, correct ?

Likewise in aviation, if you design an aircraft where you want improved re-orientation, or improved aspect angle change, then you have several options.

- Large stabilators
- Increased stabilator response speed and rate of change
- Engine thrust redirection aka 'vectoring'
- Canards

While each is an option, as in not required for your jet to fly, the moment you specified a performance want, any of those became a need. Or to put it another way, remove the want so you do not have a need. Ultimately, if you remove the want to fly, then you have removed the need for an airplane. Am not trying to be facetious, just trying to illustrate an idea.

Each of those options have its own needs, advantages, disadvantages, and limitations.

For example...

If you chose to install larger sized horizontal stabilators to put higher aerodynamic forces upon them, you need a higher capacity and stronger hydraulic actuator.

If you want to keep the original size of the horizontal stabilators, but increase their range of motion and rate of response so you can reorient faster, then you need to alter the flight control programming, specifically, the algorithms that uses gyroscopes and accelerometers responses, and the air data inputs.

If you chose thrust vectoring, of course you must have an engine that can do that. Then you must somehow incorporate that ability into commands, whether those commands are automated or from pilot inputs.

If you chose canards, then you have select an additional flight control surface feature, which mean its physical features will be dictated by aerodynamics, not by what you want. Everything about the canard, from size to shape to location, will be dictated by aerodynamic considerations, not by what you want.

So when you look at the J-20's canards, note the shape, dimensions, location, and dihedral ( upsweep ). Changes to any of those elements will affect the jet's ability to reorient. A change too much in one element may render the canard dangerous to stable flight, forcing you to return that element to wherever it was prior to change. You will find the ranges of possible changes in your testing. Then once you are satisfied of the canard's design that it does what you want and do it safely, you lock in the canard's design. No more alteration allowed. The jet will fly with the canards as designed.

Now comes the controversial issue of RCS contribution.

The laws of physics says that the canards' contribution to RCS is inevitable. Those laws also says that if you change any of the canard's elements, such as size, that change will affect the level of its contribution. You want a lower level of contribution. But if you reduce the size you will end up affecting the canard's ability to reorient the aircraft, perhaps negatively affecting.

So in trying to satisfy one customer demand, low radar observability, you may end up negatively another customer demand, rapid reorientation. When it comes to flight controls and its parts, aerodynamic considerations take center stage and is primacy over everything else. Look at the canards as they are on the jet, you can be absolutely confident: That is the final determination by the Aerodynamics Section and it is non-negotiable in terms of stable and safe flight.

This is the argument: " After all these yrs and all the money spent the canards' higher contribution to RCS must have been fixed "

That argument does not fly, pardon the pun. That is an argument of assumption, of hope, and of faith. In a discussion that is supposed to have at least the basics of technical information, the readers have nothing as to how the canards' contribution have been reduced.

Are the canards treated with absorbers ? We can see from various public photos that they are, at least on the leading and trailing edges. But that does not mean their contributions have been rendered statistically insignificant. For all we know, treating the edges reduced some, but not enough.

My point was, and still is, is that in the absence of measurement data, which most likely will never be public, in the interest of intellectual honesty, we have to at least keep the canards under suspicions. It is a fair argument.

Then came the cheap tactic of accusation of racism if Chinese claims are disputed.

 

[Asoka]

vortexes dont create lift
educate yourself

2.you have the idea but i wont go to the extreme of saying it has to reach mainland japan and back. it can do that but i doubt it would be used for that.

Well google this, Blue Marlin, "Lift Enhancement Using Close-Coupled Canard/Wing Vortex Interaction" I am not allow to post a link on PDF yet.

 

[Blue Marlin]

Well google this, Blue Marlin, "Lift Enhancement Using Close-Coupled Canard/Wing Vortex Interaction" I am not allow to post a link on PDF yet.

im not gonna attempt to read a journal, not to prove a point.
canard's aka wing do provide lift and i would suggest its to the limit of being classed as a close coupled canard layout. any further out and your under the cockpit.

@gambit what do you think is the j20 a close coupled or long armed in respects to canard configuration ?

 

[Asoka]

Sorry to say so, but that finally disqualifies Yourself from any further discussion in that regard: "I believe, my confidence ... I'm sure Chinese technicians" ... forget it simply.

Chou believe that all but so many evidence simply speak against that and IMO all what has been proved thru the last posts is that You have indeed NO understanding in stealth nor in the stuff You post. It's pure fan-boy posting.

Even more since You are so much focused purely on the canard-issue: Still no word on the round exhausts without any zig-zag edges, still no valid point, why chaff and flare dispensers are fully open visible ???

You surely will tell us know again "I believe, my confidence ... I'm sure Chinese technicians" ... but again simply forget it.

As such back to my advice: stop all Your accusations ... read, learn and argue before You post.

Deino

"Sorry to say so, but that finally disqualifies Yourself from any further discussion in that regard: "I believe, my confidence ... I'm sure Chinese technicians" ... forget it simply."

Well, gee, since I am not an aviation expert, I can only tell only what I have read, not on what I have experienced. My confidence that the Chinese have solved the canard RCS issue is based on this paper written by a Chinese engineer back in 2010. Google these Chinese words for the paper. I can't post a link yet.

"鸭翼电磁散射特性分析与RCS减缩方法研究"

In this paper he examined the characteristics of the canard RCS and determined that a coating the canard with a radar absorption material could drastically reduce the RCS. He also created a mathematical model to minimize the RCS when turning the canards. I am in no position to translate this technical paper. Hope someone else in this forum could do it.

Another paper published in 1994 also shows China has done extensive researches on Canard RCS before J-20 was designed and know measures to reduce the RCS. This paper is about canard RCS on drones.

"低RCS无人驾驶飞行器(包括鸭翼)的外形设计与实验研究"

 

[aliaselin]

"Sorry to say so, but that finally disqualifies Yourself from any further discussion in that regard: "I believe, my confidence ... I'm sure Chinese technicians" ... forget it simply."

Well, gee, since I am not an aviation expert, I can only tell only what I have read, not on what I have experienced. My confidence that the Chinese have solved the canard RCS issue is based on this paper written by a Chinese engineer back in 2010. Google these Chinese words for the paper. I can't post a link yet.

"鸭翼电磁散射特性分析与RCS减缩方法研究"

In this paper he examined the characteristics of the canard RCS and determined that a coating the canard with a radar absorption material could drastically reduce the RCS. He also created a mathematical model to minimize the RCS when turning the canards. I am in no position to translate this technical paper. Hope someone else in this forum could do it.

Another paper published in 1994 also shows China has done extensive researches on Canard RCS before J-20 was designed and know measures to reduce the RCS. This paper is about canard RCS on drones.

"低RCS无人驾驶飞行器(包括鸭翼)的外形设计与实验研究"

I think these have been posted here for several times, but you know here is a forum and little people have enough scientific logic training. So just calm down and no need to waste your time

 

[Asoka]

I think these have been posted here for several times, but you know here is a forum and little people have enough scientific logic training. So just calm down and no need to waste your time

Thanks! I should calm down. I am new here.

Deino said: "Still no word on the round exhausts without any zig-zag edges, still no valid point, why chaff and flare dispensers are fully open visible ???"

From the exhause nozzles, there could be three sources of RCS, 1.) the external petals, 2.) inside of the nozzle. 3.) from the round edge the nozzle.

The F-35 already employed the saw tooth edge method to take care of the round edge. I expect the J-20 and other stealth plane will do the same in the future.

A Chinese engineer has invented a panel to attach to the external petals to absorb the radar signal. I couldn't find the paper. I highly suspect that white shiny petals on some J-20 nozzles could be this radar signal panel. Some people have suggested these white petals are for thermal shielding to reduce IR signature. But I doubt it, since the outside of the nozzle is shielded by the internal petals, the outside is actually cool enough to be touch by human hands, so there is no need for additional shielding.

As for internal RCS from the nozzle, when the enemy is right behind you ready to shoot, you better violently maneuver to get out of the way, so internal of nozzle will not be constantly exposed to return radar signal. Plus, if he already close to you, it is better to use heat seeking missile and his gun.

"why chaff and flare dispensers are fully open visible ???"

I am not sure those are flare dispensers. They could be mesh openings for Plasma stealth. Several hexagonal meshes are found on the left and right side of the body, which has no equivalent on the F-22, F-35, and T-50.

Dr Carlo Kopp of Air Power Australia has shown in his simulation that the long and slender side of the J-20 has the strongest signal return. Having plasma stealth for the laterals could be a nifty solution.

"Plasma stealth is a proposed process to use ionized gas (plasma) to reduce the radar cross-section (RCS) of an aircraft. Interactions between electromagnetic radiation and ionized gas have been extensively studied for many purposes, including concealing aircraft from radar as stealth technology. Various methods might plausibly be able to form a layer or cloud of plasma around a vehicle to deflect or absorb radar, from simpler electrostatic or radio frequency (RF) discharges to more complex laser discharges.[1] It is theoretically possible to reduce RCS in this way, but it may be very difficult to do so in practice." --Wikipedia.

 

[Asoka]

vortexes dont create lift
educate yourself

2.you have the idea but i wont go to the extreme of saying it has to reach mainland japan and back. it can do that but i doubt it would be used for that.

Many parts of Japan is actually quite close to the Asian mainland, well within the combat range of the Flankers. It's actually the idea of using airplanes to attack foreign country that is shockingly radical to the Chinese. Until recently Chinese military planes do not venture outside the first island chain.

 

[yusheng]

the canard RCS problems have been discussed before, don't understand why they put it again and agian with the outdated theories.

one main reason that these canard are not made up by matel but ceramic and carbon fiber reinforced plastics, its RCS has totally different nature, but no one discuss these features.

 

[Asoka]

the canard RCS problems have been discussed before, don't understand why they put it again and agian with the outdated theories.

one main reason that these canard are not made up by matel but ceramic and carbon fiber reinforced plastics, its RCS has totally different nature, but no one discuss these features.
View attachment 346417 View attachment 346418 View attachment 346419 View attachment 346420 View attachment 346421 View attachment 346422

"the canard RCS problems have been discussed before, don't understand why they put it again and agian with the outdated theories.

Good post. I bet Gambit's inviolable physics laws do not take into account that airplane structures and surfaces could be made of radar absorbent materials.

Because most of the fanboys can't read the original technical papers written in Chinese so they must rely on the B.S. written by journalists and think tankers who also spur out B.S.

Chinese researches on stealth are astonishingly open, many technical paper are not classified and freely available on the internet. Probably the Chinese authority think the Chinese are late comers to Stealth and the Westerners have no need to learn from them.

 

[ohmrlobalobayeh]

If you're as smart, or experienced as you claim yourself to be. Don't act dumb. You know exactly what I meant.

The psyche behind Gambit's postings could be read like an open book with 1 look

 

[l0ngl0ng]

Gamb*t-desired RCS

 

[Deino]

...
"why chaff and flare dispensers are fully open visible ???"

I am not sure those are flare dispensers. They could be mesh openings for Plasma stealth. Several hexagonal meshes are found on the left and right side of the body, which has no equivalent on the F-22, F-35, and T-50.....

Again "could be" "I think" I believe" ... they are chaff and flare dispensers, just look ... or are they vents from the warp-drive or a cloaking device ??

Dr Carlo Kopp of Air Power Australia has shown in his simulation that the long and slender side of the J-20 has the strongest signal return. Having plasma stealth for the laterals could be a nifty solution.
....

Come on !
Especially since he has RCS facilities available and a full-scale model of a J-20 to test it !??
Dr Karlo Kopp is an idiot with only one desire: To persuade the Australian military to purchase the F-22 (which is impossible) and additionally to spread the fear in the face of "incoming hordes of Chinese" !

He is a joke.

Deino