J-20 5th Gen Fighter Thread VI

[stannislas]

Published publicly.

There is no way any country or military would allow research papers directly related to still top secret serving military projects to be published publicly.

That means that the researchers had to work with massive redacted versions of their original work, and probably had to re-create much of their original work with non-sensitive data models to be published. That takes time.

On top of that you can bet Chinese military intelligence went through their paper multiple times with fine tooth combs to make sure their didn’t inadvertently let anything slip that they shouldn’t, or their work could not be easily used by others to further their own research before they gave the go ahead to publish.

like I repeated many times earlier in this thread, yes, I think the model they built could be just to pass the clearance, but again, that has nothing to do with the paper published time. I mean, I have no doubt, they had enough knowledge, simulations and experiments results on the canards RCS effects when they design the J-20, but this paper should be fairly new, the first draft was received in 2017...

 

[ougoah]

The vertical stabilisers on the F22 are even bigger. Sure isolating factors isn't accurate. I think what they mean is ceteris paribus if j-20 worked with the same design as F35 with all movement and materials not considered, then the RCS will be more or less the same overall with frontal being better on F35 design and sideways being better on j-20. This is just keeping the design and not applying other US stealth efforts that are not as visible.

So essentially they are comparing the j-20's current design with an exact replication of f-35's layout. Details of course are portabt but my guess is with just one section of one paper available here, I feel whoever made the leak is trying to suggest that of CAC went with a conventional layout like su-57, F35, F22, if would work out to be about the same RCS overall with more or less equal tradeoffs. The details aren't available to us even if we can really interpret and understand them. By all means don't agree with the point being made but it's a worthy share.

 

[ougoah]

I always thought the ventral fins would be designed for stealth like the fuselage. I mean the sides of the fuselage on any stealth fighter is far larger as a surface area than a ventral fin. Radars will only be picking up one side of one ventral fin at only very specific angles. I highly doubt vertical stabilisers and ventral fins work against RCS that much otherwise F22 has the biggest RCS of them all with this vertical stabilisers.

When it comes to canards vs ventral fin, I get it, canards are moving and the gaps with the intakes exposed from movement and movement itself will have a higher chance of reflecting more towards energy source. But ventral fins on j-20 also block out the engine petals from many angles and are designed to absorb, dissipate, and reflect away (from source) energy. Similar to f22's verticals. The ventral fins are also gap free unlike the canards.

 

[Air Force Brat]

Very recent (November 25, 2019) publication of "Research on impact of canard to RCS" by 611. The article seems to have been submitted in 2017.
Summary:

1. Comparison of conventional and canard configurations of otherwise the same fuselage, based on F-35.
2. Before improvement on canard configuration, compared to conventional layout, Canard has
   1. Slightly worse RCS return in frontal area from 0 to 30 degrees because:
      1. Canard aft edge reflection is exposed while conventional horizontal stabilizer is blocked by main wing.
      2. Sharp end of aft edge of canard.
      3. The gap between canard and fuselage is another strong contributor, but mostly to high frequency (C band).
   2. Much less RCS return from the side, from 30 to 90 degrees, because conventional horizontal and vertical stabilizer forms a strong reflector while canard does not.
3. Improvement
   1. Use radar absorbent structure (not paint) on all edges, the light grayish green area. It is much better than paint in terms of frequency band and size.
   2. Smooth curvature and seal of the inner edge of canard.
   3. Cut the corner of canard aft edge.
4. After improvement, the conclusion is that canard configuration with proper measures is equal to conventional configuration in RCS.
5. As to the "canard moving increase RCS":
   1. the test shows that within +- 5 degree movement (in cruising), there is both increase and also decrease (-5 degree). Overall neglect-able.
   2. When the canard must be turned more than 5 degrees, the aircraft is in a situation where the whole RCS has drastically increased (close dog fight or violent maneuver) making canard's contribution neglect-able or the whole stealth thing non-existent.

It is interesting to note 2.2 where Canard configuration is inherently better than conventional on the side.
View attachment 55945

In this post you suggest in the first line that the article was submitted in 2017? leading us to believe this is fairly recent research, but now you are suggesting this is pre-J-20??

When the study suggests "Much less RCS" return from the side with the canard? I would suggest they are missing the fact that the addition of the canard to the forward fuselage, would force the main wing far enough aft that the vertical stabs and ventral fins will indeed be creating an RCS spike with the main wing..

this is all rather nebulous, and I would suggest you take my observations in the same vein as the observations in the article, which seems to be making a case for the canard as opposed to the more traditional configuration...

I believe Dr. Song knew what he was doing, the J-20 is a positive reflection on that.

 

[Brumby]

In terms of f-35 in the model, their explanation is using as a baseline for performance evaluation so the effect of the rest of the plane could be neglect. They actually provided a detail description of their fiction aircraft layout, so if you are interesting, you could check and see if the additional parts are matching with j-20.

I think it is fundamentally flaw to stick a pair of canards onto an existing design and assume it does not have a cascading effect on the rest of the design. A pair of canards on a F-35 is no longer an F-35, merely an imagination. The F-35 evolved through its design process and initially in fact had canards. Attached is a pictorial presentation of its evolution. I also super imposed the pseudo design from the Chinese research paper onto the the F-35 evolution for comparison. A point of note is that the original F-35 with canards is very different to its final form. In other words you don't stick a pair of canards onto a design and expect that there is no cascading effect.

 

[latenlazy]

I think it is fundamentally flaw to stick a pair of canards onto an existing design and assume it does not have a cascading effect on the rest of the design. A pair of canards on a F-35 is no longer an F-35, merely an imagination. The F-35 evolved through its design process and initially in fact had canards. Attached is a pictorial presentation of its evolution. I also super imposed the pseudo design from the Chinese research paper onto the the F-35 evolution for comparison. A point of note is that the original F-35 with canards is very different to its final form. In other words you don't stick a pair of canards onto a design and expect that there is no cascading effect.

View attachment 55959

You don’t stick a tail or a wing into a design and not expect any cascading effect either. The only design where you don’t deal with cascading effects is a design that is made of nothing. Any feature will add their own cascading effects. That does not mean those cascading effects can’t be designed away.

 

[stannislas]

In this post you suggest in the first line that the article was submitted in 2017? leading us to believe this is fairly recent research, but now you are suggesting this is pre-J-20??

When the study suggests "Much less RCS" return from the side with the canard? I would suggest they are missing the fact that the addition of the canard to the forward fuselage, would force the main wing far enough aft that the vertical stabs and ventral fins will indeed be creating an RCS spike with the main wing..

this is all rather nebulous, and I would suggest you take my observations in the same vein as the observations in the article, which seems to be making a case for the canard as opposed to the more traditional configuration...

I believe Dr. Song knew what he was doing, the J-20 is a positive reflection on that.

A 2017 paper does not necessarily mean this is a recent study... in fact, I'm a bit surprised that they even publish a paper openly, as far as I know, CAC is not an academic institute, so paper weight pretty low in their work.

My guess is that the paper is used for answering funding program (National Science Fund? and Aero Science fund? most likely), which may require a regular paper submission.

 

[stannislas]

I think it is fundamentally flaw to stick a pair of canards onto an existing design and assume it does not have a cascading effect on the rest of the design. A pair of canards on a F-35 is no longer an F-35, merely an imagination. The F-35 evolved through its design process and initially in fact had canards. Attached is a pictorial presentation of its evolution. I also super imposed the pseudo design from the Chinese research paper onto the the F-35 evolution for comparison. A point of note is that the original F-35 with canards is very different to its final form. In other words you don't stick a pair of canards onto a design and expect that there is no cascading effect.

View attachment 55959

emm, you seem to have a problem understanding of modeller design in engineering, they did a very, very standard research practice in academic in almost all scientific/engineering areas all over the world (I don't know how to stress this stronger), eliminating all the other factors, and focus on the topic of this paper "Research on impact of canard to RCS"

 

[TK3600]

Very recent (November 25, 2019) publication of "Research on impact of canard to RCS" by 611. The article seems to have been submitted in 2017.
Summary:

1. Comparison of conventional and canard configurations of otherwise the same fuselage, based on F-35.
2. Before improvement on canard configuration, compared to conventional layout, Canard has
   1. Slightly worse RCS return in frontal area from 0 to 30 degrees because:
      1. Canard aft edge reflection is exposed while conventional horizontal stabilizer is blocked by main wing.
      2. Sharp end of aft edge of canard.
      3. The gap between canard and fuselage is another strong contributor, but mostly to high frequency (C band).
   2. Much less RCS return from the side, from 30 to 90 degrees, because conventional horizontal and vertical stabilizer forms a strong reflector while canard does not.
3. Improvement
   1. Use radar absorbent structure (not paint) on all edges, the light grayish green area. It is much better than paint in terms of frequency band and size.
   2. Smooth curvature and seal of the inner edge of canard.
   3. Cut the corner of canard aft edge.
4. After improvement, the conclusion is that canard configuration with proper measures is equal to conventional configuration in RCS.
5. As to the "canard moving increase RCS":
   1. the test shows that within +- 5 degree movement (in cruising), there is both increase and also decrease (-5 degree). Overall neglect-able.
   2. When the canard must be turned more than 5 degrees, the aircraft is in a situation where the whole RCS has drastically increased (close dog fight or violent maneuver) making canard's contribution neglect-able or the whole stealth thing non-existent.

It is interesting to note 2.2 where Canard configuration is inherently better than conventional on the side.
View attachment 55945

Link to article?

 

[stannislas]

Link to article?

I still recall somewhere that there was a source stating that the J-20 canards were radar transparent to -30 dBsm, i.e, limiting the airframe to that dBsm rating. Unfortunately, I haven't been able to find it, and I was hoping this paper would give corroborating evidence of the stealth level.

In other news, I don't think the direct link was included, so...

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