Official Chengdu J-20 Discussion Thread

[jack412]

is this the cockpit shot you mean ? the one with 'gamers' controls
Welcome to China Defense.com

there is lots of debate on the j-20, i'm just taking everything at face value and not getting into the CGI debate, i couldnt even pick the CGI from terminator

 

[gf0012-aust]

is this the cockpit shot you mean ? the one with 'gamers' controls
Welcome to China Defense.com

i'm just taking everything at face value and not getting into the CGI debate, i couldnt even pick the CGI from terminator

that's some of them, but you at least get the picture of what I'm on about (no pun intended)

 

[Blitzo]

is this the cockpit shot you mean ? the one with 'gamers' controls
Welcome to China Defense.com

i'm just taking everything at face value and not getting into the CGI debate, i couldnt even pick the CGI from terminator

Curiously this is posted by huitong as a possible cockpit layout as well:
http://cnair.top81.cn/fighter/J-20_cockpit1.jpg

With the rate the pictures are coming out hopefully we'll get a picture of the cockpit within a year or so. But even that may change for the production versions, sigh.

 

[dingyibvs]

You need an account to view CDF.

Here's a picture which I think you meant to post:

http://img214.imageshack.us/img214/821/cockpit7.jpg

Though curiously this is posted by huitong as a possible cockpit layout as well:
http://cnair.top81.cn/fighter/J-20_cockpit1.jpg

Umm, the plane outline in huitong's pic looks suspiciously like the real thing. Maybe THAT was the real first leak?

 

[gf0012-aust]

Umm, the plane outline in huitong's pic looks suspiciously like the real thing. Maybe THAT was the real first leak?

No, there were images running around on some of the closed email groups (not forums) approx 1-2 months prior.

I received mine via the china email group I am in via a local chinese defence analyst.

 

[Feanor]

there are two prototypes, chinese philosophy has not been in the past to make identical sisters, superficially they might look the same, but I seriously doubt that they are identical at the fitout level.

IMO the cockpit layout also raises mission questions, and I don't believe that the articles shown are fighters, they are LR strikers and battle managers...

couple this with what we know of chinese developments in the NCW space, I'm pretty sure that they're filling in the spaces for whats termed "purple" operations.

Could you elaborate on the term "purple orientations"? Thanks in advance.

 

[gf0012-aust]

Could you elaborate on the term "purple orientations"? Thanks in advance.

"Purple" events are multi-service/joint co-ordinated activities. Joint Operations. They can be local forces or they can be coalition/allied events.

 

[Feanor]

So the J-20 is geared towards ground-support?

 

[gf0012-aust]

So the J-20 is geared towards ground-support?

Nope, IMO its LR strike (ground) or LR decapitation of air (hoping to pick up Compass, Rivet, Sentry's etc that stray outside of their alert box)

In addition, I see them as the hi assets in the hi-lo package

 

[MiG-23MLD]

Curiously this is posted by huitong as a possible cockpit layout as well:
http://cnair.top81.cn/fighter/J-20_cockpit1.jpg

With the rate the pictures are coming out hopefully we'll get a picture of the cockpit within a year or so. But even that may change for the production versions, sigh.

When i read his assesment of the J-20 saying it will be better for supercruise and agility than the PakFA i could see the assesment was totally biased.
The LEVCON and thrust vectoring of the T-50 makes it a good supercruiser by allowing it to supercruise without deflecting its tailplanes and using thrust vectoring as a pitch control device.
The Canard on the J-20 affects more its stealth and supercruise ability by two simple reasons the canard generates a downwash wake, but the LEVCON does not, so the canard downwash is killing lift of the main wing reducing total lift.
The LEVCON is at the same level of the T-50 wings it is part of the wing, the Canard of the J-20 is not at the same level increasing radar returns.
the F-22 avoided this by Fitting tailplanes

The LEVCON on the T-50 does not affect the intake negatively thus it is ahead of the intake, on the Eurofighter, MiG-1.44 and even the J-10 and IAI Lavi the canards were placed in a position they do not affect the inlet operation, the J-20 positions the canard aft of the intake to avoid disruption in the engine intake operation.
The Agility of these two fighters will depend on the ability to have enuogh thrust and lift at combat weight, but the J-20 has a fuselage that does generate lift as the T-50 and it is totally dependant on a wing and a canard for lift, the canard drag and downwash is higher than the wing levcon configuration.

The LEVCON also reduces the effects of supersonic shifts of the center of lift but without the added drag a canard generates

The J-20 at this moment has a very conventiol wing canard platform
http://paralay.com/TEMP/J20_4.png
it has not even trailing edge alignment like the T-50, F-35 and F-22

Also i can see fitting a D-30 engine in the J-20 also is to my opinion not practical, Paralay`s webpage has a very good summary of the S-37 history, and he says the S-37 or Su-47 Berkut was designed as a Naval aircraft not a stealth fighter.
The D-30F6 is a big engine, bigger than the AL-31, this engine has a 15.5 tonnes of thrust but is way too large compared to the AL-31F, fitting it to the J-20 could be a possibility but the problem will be the redesign of the J-20 internally which i think is not a practical thing.
http://forum.keypublishing.co.uk/attachment.php?attachmentid=191296&d=1293730218
This engine will reduce internal volume for fuel and weapons bays so it would be inpractical

 

[Blitzo]

When i read his assesment of the J-20 saying it will be better for supercruise and agility than the PakFA i could see the assesment was totally biased.
The LEVCON and thrust vectoring of the T-50 makes it a good supercruiser by allowing it to supercruise without deflecting its tailplanes and using thrust vectoring as a pitch control device.
The Canard on the J-20 affects more its stealth and supercruise ability by two simple reasons the canard generates a downwash wake, but the LEVCON does not, so the canard downwash is killing lift of the main wing reducing total lift.
The LEVCON is at the same level of the T-50 wings it is part of the wing, the Canard of the J-20 is not at the same level increasing radar returns.
the F-22 avoided this by Fitting tailplanes

The LEVCON on the T-50 does not affect the intake negatively thus it is ahead of the intake, on the Eurofighter, MiG-1.44 and even the J-10 and IAI Lavi the canards were placed in a position they do not affect the inlet operation, the J-20 positions the canard aft of the intake to avoid disruption in the engine intake operation.
The Agility of these two fighters will depend on the ability to have enuogh thrust and lift at combat weight, but the J-20 has a fuselage that does generate lift as the T-50 and it is totally dependant on a wing and a canard for lift, the canard drag and downwash is higher than the wing levcon configuration.
The J-20 at this moment has a very conventiol wing canard platform
http://paralay.com/TEMP/J20_4.png
it has not even trailing edge alignment like the T-50, F-35 and F-22

Also i can see fitting a D-30 engine in the J-20 also is to my opinion not practical, Paralay`s webpage has a very good summary of the S-37 history, and he says the S-37 or Su-47 Berkut was designed as a Naval aircraft not a stealth fighter.
The D-30F6 is a big engine, bigger than the AL-31, this engine has a 15.5 tonnes of thrust but is way to large compared to the AL-31F, fitting it to the J-20 could be a possibility but the problem will be the redesign of the J-20 internally which i think is not a practical thing.
http://forum.keypublishing.co.uk/attachment.php?attachmentid=191296&d=1293730218
This engine will reduce internal volume for fuel and weapons bays so it would be inpractical

Huitong usually gets his info from other websites he considers close to the truth ("unofficial" insiders, other BBS's, etc) and some of his entries aren't entirey accurate, such as giving specs and the finer details.

He's not necessarily biased (well actually everyone's biased but that's not the point), but writes what he hears. In this case he must've heard a reliable source predicting the J-20's (future) performance against PAK FA and F-22... Take his things wih a grain of salt but his information usually turns out accurate.

Also I still think it's a bit early to predict the flight performance of J-20 in such detail when we haven't even seen a good picture of it from top or bottom.

But again I am curious as to why you think canards are so bad for stealth?
Can anyone with more experience put in an opinion on this matter? I only know the basics like edge alignment. Assuming the canards are aligned with the rest of the aircraft, how is it any worse for stealth? I mean there must've been a reason PLAAF chose CAC's design with canards instead of going conventional with SAC's proposal.

(Also, why did you mention the Berkut?? That plane is almost irrelevant to what you were saying...)

 

[Blitzo]

The LEVCON is at the same level of the T-50 wings it is part of the wing, the Canard of the J-20 is not at the same level increasing radar returns.
the F-22 avoided this by Fitting tailplanes

Wait... from frontal pictures the canards of the J-20 are on the same plane as the wings. They're swept slightly upwards but still on the same "level".

The J-20 at this moment has a very conventiol wing canard platform
http://paralay.com/TEMP/J20_4.png
it has not even trailing edge alignment like the T-50, F-35 and F-22

I could be wrong, but the trailing edges of the wings (in that picture) are aligned with the trailing edges of the canard opposite their side. (Trailing edge of left wing is aligned with trailing edge of right canard... Or is that incorrect??)
Regardless we should be waiting for top/bottom pictures of this plane before we fully decide if the wings were aligned with canards or not. (But I predict they will be -- why go to all this trouble with the serrated edges and other planform alignment and leave out the trailing edge of the wing? It'd be stupid)

 

[dingyibvs]

According to a blogger who works/worked at CAC, the J-20 employs an improved DSI which is adjustable and thus would allow better supersonic performance. I don't wish to discuss the blogger's credibility(though all his predictions from back in 2009 that are verifiable have come true thus far), but I'd like to ask how feasible something like that is. He mentions how the DSI bump is fixed, but the intake itself can be adjusted.

 

[MiG-23MLD]

Huitong usually gets his info from other websites he considers close to the truth ("unofficial" insiders, other BBS's, etc) and some of his entries aren't entirey accurate, such as giving specs and the finer details.

He's not necessarily biased (well actually everyone's biased but that's not the point), but writes what he hears. In this case he must've heard a reliable source predicting the J-20's (future) performance against PAK FA and F-22... Take his things wih a grain of salt but his information usually turns out accurate.

Also I still think it's a bit early to predict the flight performance of J-20 in such detail when we haven't even seen a good picture of it from top or bottom.

But again I am curious as to why you think canards are so bad for stealth?
Can anyone with more experience put in an opinion on this matter? I only know the basics like edge alignment. Assuming the canards are aligned with the rest of the aircraft, how is it any worse for stealth? I mean there must've been a reason PLAAF chose CAC's design with canards instead of going conventional with SAC's proposal.

(Also, why did you mention the Berkut?? That plane is almost irrelevant to what you were saying...)

Blitso

In my opinion the Chinese engineers applied stealth mostly to the fuselage and intake, they applied lots of RAM to the canard and are satisfied mostly with frontal and intake-nacelle stealth which the J-20 by using a configuration similar to the F-35 and F-22 achieves it to a very satisfactory level.
In that respect its stealth is good.

Stealth requieres good shaping, 90% of the stealth is achieved by shaping and 10-15% by RAM coating.
Compared to the T-50 and F-22 has a inferior planforming.
Canards requiered shaping that contradicts stealth, what is good for stealth is not good for aerodynamics.
The Americans on the X-36 and JSF studied the effects of canards on stealth, their canards were adapted for stealth, they concluded canards have contradictory needs when comes to stealth and performace.

The Naval LCA is a very complex machine, it also has LEVCONs, the Indians by fitting a LEVCON reduced landing speed without increasing the aircraft length, on the Su-33 the Russians added canards increasing drag but reducing landing speeds.

The J-20 uses a very conventional configuration, the Chinese, Americans and Europeans have not used a more innovative cofiguration than the Indians and Russians, the Chinese were very conservative for the approach, in fact very 1980s, the Indians and Russians were very innovative by using LEVCONs, they avoided drag and a second lifting surface reducing drag and radar emmisions.

If the J-20 will surpass the T-50 will need more thrust, but in terms of lift it is not the better configuration.
When the Russians studied how to make the MiG-1.44 into a really stealth platform, first they added tailplanes and modified the inlet,
ÏÀÊ ÔÀ ÌèÃ

Sukhoi knew canards are good but impose too much constraigns in shape and drag that a different solution was demanded, this meant a droping leading edge on a LERX, AKA LEVCON, LERXes do the same thing canard do, exept pitch control.

 

[Blitzo]

Blitso

In my opinion the Chinese engineers applied stealth mostly to the fuselage and intake, they applied lots of RAM to the canard and are satisfied mostly with frontal and intake-nacelle stealth which the J-20 by using a configuration similar to the F-35 and F-22 achieves it to a very satisfactory level.
In that respect its stealth is good.

Lol wut? There is no way you can know where they applied RAM to... O.O

Stealth requieres good shaping, 90% of the stealth is achieved by shaping and 10-15% by RAM coating.

I'm not sure about the numbers, but yes I know shaping is more important to stealth than RAM.

Compared to the T-50 and F-22 has a inferior planforming.

... How can you know that when we haven't even seen a picture of J-20 from top or bottom?? grr

(And by planforming you mean edge alignment, right?)

Canards requiered shaping that contradicts stealth, what is good for stealth is not good for aerodynamics.
The Americans on the X-36 and JSF studied the effects of canards on stealth, their canards were adapted for stealth, they concluded canards have contradictory needs when comes to stealth and performace.

It's not that I don't believe you... but can you link to a source or a copy of their report on canards or something? I find it hard to believe CAC would have their 4th gen adopt canards if it were such a detriment you imply them to be.

The J-20 uses a very conventional configuration, the Chinese, Americans and Europeans have not used a more innovative cofiguration than the Indians and Russians, the Chinese were very conservative for the approach, in fact very 1980s, the Indians and Russians were very innovative by using LEVCONs, they avoided drag and a second lifting surface reducing drag and radar emmisions.

Wait so you're saying because the Russians and Indians use LEVCONs it makes the configuration of naval LCA and PAK FA immediately that much more "innovative"..?
Are you saying the Gripen, Typhoon, Rafale were all bad configurations and should've gone for LEVCONs instead of canards...?

If the J-20 will surpass the T-50 will need more thrust, but in terms of lift it is not the better configuration.

That goes without saying... That's what the WS-15 will be for.

Sukhoi knew canards are good but impose too much constraigns in shape and drag that a different solution was demanded, this meant a droping leading edge on a LERX, AKA LEVCON, LERXes do the same thing canard do, exept pitch control.

Right... can you link me to this decision of Sukhoi or the like?


-------------------
... Alright, but you still haven't really answered my questions:

-Are canards bad for stealth if they are aligned with the rest of the aircraft and on the same "level" (plane) as the main wing, and if so, why?
-In the picture you posted (http://paralay.com/TEMP/J20_4.png --btw the picture probably isn't accurate), in your opinion are the trailing edges of the wings aligned with the trailing edges of the canard opposite them? (The trailing edges of the wings (in that picture) are aligned with the trailing edges of the canard opposite their side. Trailing edge of left wing is aligned with trailing edge of right canard..)

 

[MiG-23MLD]

According to a blogger who works/worked at CAC, the J-20 employs an improved DSI which is adjustable and thus would allow better supersonic performance. I don't wish to discuss the blogger's credibility(though all his predictions from back in 2009 that are verifiable have come true thus far), but I'd like to ask how feasible something like that is. He mentions how the DSI bump is fixed, but the intake itself can be adjusted.

the DSI is basicly a boudary layer spiller, on other aircraft the intake lip is separated from the fuselage by a splitter that gets rid of the boudary layer generated by the fuselage
The advantage is it reduces weight and at speeds below Mach 2 works fine.
However as speeds increases you need another element, you need a a variable geometry intake lip that can reduce the speed the air getting into the inlet duct.
Since these aircraft do not use ramjets, then these aircraft need variable geometry inlets.
Since the DSI has a fixed bump it can not work as a variable geometry ramp or cone as in a central or circular or semi circular intake.
This implies you need to create the shock on the intake lip opposite to the DSI bump. on the F-35 it has a wedge, but still is a fixed geometry intake so the F-35 is limited to speeds below Mach 2.
The F-22 and T-50 use splitters and the same is for most fighters in example F-15, MiG-29, Su-27, Mirage 2000, F-18, LCA, J-10, J-8II.

 

[MiG-23MLD]

Lol wut? There is no way you can know where they applied RAM to... O.O



I'm not sure about the numbers, but yes I know shaping is more important to stealth than RAM.



... How can you know that when we haven't even seen a picture of J-20 from top or bottom?? grr

(And by planforming you mean edge alignment, right?)




It's not that I don't believe you... but can you link to a source or a copy of their report on canards or something? I find it hard to believe CAC would have their 4th gen adopt canards if it were such a detriment you imply them to be.




Wait so you're saying because the Russians and Indians use LEVCONs it makes the configuration of naval LCA and PAK FA immediately that much more "innovative"..?
Are you saying the Gripen, Typhoon, Rafale were all bad configurations and should've gone for LEVCONs instead of canards...?



That goes without saying... That's what the WS-15 will be for.



Right... can you link me to this decision of Sukhoi or the like?


-------------------
... Alright, but you still haven't really answered my questions:

-Are canards bad for stealth if they are aligned with the rest of the aircraft and on the same "level" (plane) as the main wing, and if so, why?
-In the picture you posted (http://paralay.com/TEMP/J20_4.png --btw the picture probably isn't accurate), in your opinion are the trailing edges of the wings aligned with the trailing edges of the canard opposite them? (The trailing edges of the wings (in that picture) are aligned with the trailing edges of the canard opposite their side. Trailing edge of left wing is aligned with trailing edge of right canard..)

Look to prove you this is very easy just compare the differences between the X-36 and the J-20.
On the X-36, the leading edge of the main wing and the trailing edge of the canard have the same angle that the intake walls have, however on the J-20 you have the leading edge of the wing and the trailing edge of the canard at a different angle.
The J-20 has the same type of canard as the J-10 and Eurofighter.
Planforming means a specific angle is kept when two edges meet, the J-20 does not meet that requierement on its wings and canard

The canard also to have the same angle as the nacelle wall and dorsal fin has would need to be at the same angle of the dorsal fin. but it has not that angle

 

[gf0012-aust]

He mentions how the DSI bump is fixed, but the intake itself can be adjusted.

Its a shock ramp. They've used it before when trying to determine inlet construction. It's a compromise solution when you don't want to go out an rebuild the inlets, and when the EMU/ECU can't compromise enough

I suggest that you exercise some caution when reading what some of the "so-called experts" are saying

a lot of it is abject nonsense. all the pseudo technical terms in the world don't alter fluid and aerodynamics fundamental principles....

Let me give you a hint, and I have worked on signal management. If that plane shifts one degree off axis it will radiate differently, any assumptions about returns go out the door.

There is nothing and I repeat NOTHING on that article that shows distributed arrays and the potential for active management through the entire turn axis of that aircraft.

 

[dingyibvs]

Bltzio, I'm no aerodynamic or radar expert, but based on Mr. Mig's discussions on topics that I do know something about, it appears that he puts forth a good amount of good info, but also a good number of inaccuracies and semi-truths. I'd suggest getting a second opinion and compare and contrast the info before taking it in as legitimate.

 

[dingyibvs]

the DSI is basicly a boudary layer spiller, on other aircraft the intake lip is separated from the fuselage by a splitter that gets rid of the boudary layer generated by the fuselage
The advantage is it reduces weight and at speeds below Mach 2 works fine.
However as speeds increases you need another element, you need a a variable geometry intake lip that can reduce the speed the air getting into the inlet duct.
Since these aircraft do not use ramjets, then these aircraft need variable geometry inlets.
Since the DSI has a fixed bump it can not work as a variable geometry ramp or cone as in a central or circular or semi circular intake.
This implies you need to create the shock on the intake lip opposite to the DSI bump. on the F-35 it has a wedge, but still is a fixed geometry intake so the F-35 is limited to speeds below Mach 2.
The F-22 and T-50 use splitters and the same is for most fighters in example F-15, MiG-29, Su-27, Mirage 2000, F-18, LCA, J-10, J-8II.

Its a shock ramp. They've used it before when trying to determine inlet construction. It's a compromise solution when you don't want to go out an rebuild the inlets, and when the EMU/ECU can't compromise enough

I suggest that you exercise some caution when reading what some of the "so-called experts" are saying

a lot of it is abject nonsense. all the pseudo technical terms in the world don't alter fluid and aerodynamics fundamental principles....

Yes...I understand the purpose of DSI, I was just wondering if there's a way to retain the DSI's stealth advantages while avoiding its(and all other fixed inlet designs') "optimal speed" limitations.