J-20 5th Gen Fighter Thread VI


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Brumby

Major
Well, in certain way, I think you misunderstood about what they did and what they trying to achieve.

Let‘s look at the scenario here.

Firstly, I agree the general purpose of this paper may affiliate rcs impact over the j-20 canards, cause f-35 with canards just mean less because there is no such thing. And they might did the experiment on J-20 in the first place.

After they did the experiment and testing, they found, in general, canards with certain improvements could match the rcs performance of a conventional layout. But due to whatever reason, they realize the publish the original data on j-20 is sensitive or they have to through a lot extra efforts in order to do so.

So instead, they build a model for a fictional f-35, and redid the experiments and tests on that, and write a paper about it. Since this particular aircraft is not Chinese, it’s not real, so no secret involved, no clearance needed.

You see, the idea here is to publish the finding and method without specifying the data they use, as long as the conclusion is the same, they could live with the fact, that the real j-20 results may have slight differences, but hi, I don’t think they will disclose those data any time soon, in fact if you ask them, they may as well deny the connection between this paper to j-20.

Overall, the title of this paper is called “Study of canards impacts on rcs”, our guess is based on their background, but as an academic, when publishing a paper, their no.1 job is to get the paper published with the correct conclusion, the rest are all interchangeable.
I understand what their attempt is but the problem is with the choice of the model i.e. F-35. If they had simply used a stealth design "model X" and apply whatever test based on with and without canards, then the conclusion is a much simpler conversation. Once you overlay a specific design onto the conversation, all the specifics then matters especially when the aim is to extend that conclusion unto the J-20 airframe 9by inference). The most fundamental flaw in logic is with the starting point, i.e. the F-35 and J-20 are of different designs. .
 

lgnxz

New Member
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I had the same impression initially and maybe i thought it is some typo error between J-20 and F-35. If the aim is to affirm the use of canards on the J-20, it has the attributes of a strawman logic in approach. I would love to see the study published using the J-20 as the primary platform of interest and not on the F-35 which does not it. That would probably be a one way ticket to the "Gulag"..
Wow what a loaded statement filled with assumptions from both of you. Affirming the use of j-20 canard? This is just your negative assumptions about PLA (or china in general with that even stupider gulag thing at the end) on a rather straight forward research about aircraft RCS based on its wing config. If you really want to know why j-20 use canards (a topic which already been discussed to oblivion), just simply read the translated paper from dr. song.

So from this they draw the conclusion that canards may be inherently better than conventional tails on an F-35, what they ignore is that with the additional lift of canards on the forward fuselage, they would need to move the main wing aft
What makes you thing that they don't do that? Assuming that the design change in research is to just simply move the horizontal tail of the F-35 from back to front with same size and shape, there's simply not enough space in the f-35 body at the front of the main wing. The same goes for converting a j-20, which has its main wing at the back, you ultimately have to move the main wing to the front to put the horizontal wing at the back. Like what's the difference here??? From fuselage alone what make you thing that this design change won't affect exactly the same thing to both f-35 and j-20? Looks to me that fulfilling your wish of redoing it with j-20 will achieve the same result
 

stannislas

Junior Member
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I understand what their attempt is but the problem is with the choice of the model i.e. F-35. If they had simply used a stealth design "model X" and apply whatever test based on with and without canards, then the conclusion is a much simpler conversation. Once you overlay a specific design onto the conversation, all the specifics then matters especially when the aim is to extend that conclusion unto the J-20 airframe 9by inference). The most fundamental flaw in logic is with the starting point, i.e. the F-35 and J-20 are of different designs. .
If you read the paper, it’s actually not a f-35... they just build their model base on it, and if you take a look the canards version looks a lot like a j-20 than a f-35.

but jump back back to what you said, As I mentioned before, I don’t they need to prove j-20 and canard f-35 are similar, because that’s not their study nor their intention. What they published is a paper about their study on the canards impacts on rcs and that’s it, other part of the arrangement has nothing to do with this study what so ever.

Yes, other parts, or general airframe design are different among each plane and the general rcs performance could be a lot different, but in terms of canards specifically, according to their paper, “with certain improvements, it could match the rcs performance of a conventional layout”
 

Brumby

Major
The result I'm getting from the paper is that the Chinese can get the RCS contribution of canards down to -50 dBsm. But their conclusion that properly designed canards impose no penalty isn't a given, as their comparison model is bizarre when compared to actual conventional stealth aircraft (F-22, F-35, although not the Su-57).
-50 dBsm is XVLO territory. Even the F-35 is credited with only -30 dBsm overall. A rivet is probably much lower but that would be highly misleading. LOL. A stealth design has many moving parts and the eventual design would reflect tradeoffs. Isolating the conversation unto a specific variable can be highly misleading.
 

Brumby

Major
If you read the paper, it’s actually not a f-35... they just build their model base on it, and if you take a look the canards version looks a lot like a j-20 than a f-35.
So the thing is - it is not a F-35 but let's call it a F-35 any way? That leads to the unavoidable question - why?

but jump back back to what you said, As I mentioned before, I don’t they need to prove j-20 and canard f-35 are similar, because that’s not their study nor their intention. What they published is a paper about their study on the canards impacts on rcs and that’s it, other part of the arrangement has nothing to do with this study what so ever.
My original comments was based on what was posted by "Taxiya" and item 1 said "Comparison of conventional and canard configurations of otherwise the same fuselage, based on F-35".
 

taxiya

Major
Registered Member
Interesting that we are promoting a study of canards and conventional tail RCS based on the F-35 fuselage, showing that (a)RCS is better from the side with the canard because of the strong reflector created by the horizontal and vertical fin junctures.....in order to affirm the use of canards on the J-20

So from this they draw the conclusion that canards may be inherently better than conventional tails on an F-35, what they (2)ignore is that with the additional lift of canards on the forward fuselage, they would need to move the main wing aft in order to maintain the center of lift near the center of gravity, and doing this they would likely create a similar reflector of the main wing and vertical stabilizers?

IMHO this ignores the even stronger RCS reflector created by the vertical tails and ventral fins with the main wing on the J-20??

I would suggest that the F-35 has less of an RCS spike aft with the verts and horizontal stabilizer, than the J-20 does with the verticals and ventral fins??

the study does accurately conclude that angles and sharply angled tips do indeed spike RCS return
F-35 fuselage being used in simulation was only to give a fair comparison of two configurations, NOT because F-35 is anything special. For the same purpose, they could have used F-22. Also remember, this is the research to verify the feasibility of J-20, probably during the competition with conventional layout, there was NO better base fuselage to start with, J-20 was still on paper at that time. For this reason, they were not "beating F-35 to affirm J-20", they were "beating SAC proposal to affirm J-20". Both had fair chance in radio dark room, and Canard were equally good. Note, the author said "equally good overall", nothing else.

(1) If you read my post again, you will see that the article only claimed better side RCS from 30 to 90 degrees.

(2). They did not ignore that. In their modified "F-35" they moved both main wing and vertical stabilizer together with the absence of horizontal stabilizer. so the reflector effect is gone. You can see that in J-20 where the vertical stabilizer half way out of main wing but lacking the horizontal stabilizer.

J-20's vertical tails are much smaller than F-35 or F-22. The total area (adding ventral fins) are probably comparable. More than that, the angel between the fin and vert are much larger than the vert and horizontal stabilizer of F-35 and F-22. Meaning much less angular reflection effect. Overall, in this area, J-20 is no worse than F-35.

At the end, they are engineers who did both calculation and radio dark room tests and drew their conclusion based on hard data. If LM researchers had published something like this, I would not question it either.;)
 

taxiya

Major
Registered Member
A suggestion. The article is in Chinese with lots of measurements and conclusions from them. There is no meaning for any of us to go into detailed debate without reading the whole article and I don't have the time to fully translate it except their conclusions. So take it as what you want but keep in mind that they are are the professionals.
 

stannislas

Junior Member
Registered Member
So the thing is - it is not a F-35 but let's call it a F-35 any way? That leads to the unavoidable question - why?


My original comments was based on what was posted by "Taxiya" and item 1 said "Comparison of conventional and canard configurations of otherwise the same fuselage, based on F-35".
fair enough, that indeed was a summary over the model they use, but if they want to conclude further into the details, that's not enough.

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.

But in terms of why I would be surprised when they got the paper out, their supervisor asked them to redid the data on an unclassified aircraft
 

stannislas

Junior Member
Registered Member
Also remember, this is the research to verify the feasibility of J-20, probably during the competition with conventional layout, there was NO better base fuselage to start with, J-20 was still on paper at that time.
This paper is published on Nov 25, 2019...
 

plawolf

Brigadier
This paper is published on Nov 25, 2019...
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.
 
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