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Re: J-20 goes operational

Unread postPosted: 09 Nov 2018, 22:36
by marsavian
ricnunes wrote:
weasel1962 wrote:Weasel's note: The F-35 may be stealthier than a J-20A today but J-20B or J-20C?


It doesn't matter if you're talking about a J-20A, J-20B, J-20C or a J-20D-thru-Z, unless those other post-J-20A aircraft are completely new and differently designed aircraft than they will never be stealthier than the F-35!
Remember, Stealth isn't something that you can simply add to an existing aircraft - you have to design it from the start.

And even if you could "add stealth" (or more precisely reduce RCS) on further J-20 variants like for example a J-20C then how would you compare it against improved F-35s? You are aware that the F-35 will also receive lots of improvements during its lifetime (probably even more than the J-20), no?
If you want to compare the "stealth level" of a tentative J-20C than you should probably "try" to compare it with an also tentative F-35D (or something along those lines)...


You can change the stealth attributes of an aircraft if you are prepared to bear the weight penalty of extra RAM. The Block 3 Super Hornet has apparently improved clean stealth by 10% with more/better applied RAM. You can go much higher than that if you are prepared to take ton hits on weight, the J-20 will eventually have more powerful engines and its prime role is as a long range stalking interceptor so they maybe prepared to take future hits in weight for that stealth purpose.

Re: J-20 goes operational

Unread postPosted: 10 Nov 2018, 00:00
by ricnunes
marsavian wrote:You can change the stealth attributes of an aircraft if you are prepared to bear the weight penalty of extra RAM.


Yes, you can improve a little bit but not by much or again and to be more precise, only a little bit.
This is due to the fact that most of the Stealth comes from the shape itself while a smaller part comes from RAM. Depending on the sources (or perhaps even the aircraft) it is said that the Stealth comes from a ratio of around 70%-to-30% or around 60%-to-40% all in favor of the Shape (over RAM).

marsavian wrote:The Block 3 Super Hornet has apparently improved clean stealth by 10% with more/better applied RAM.


Here you go. This proves all my my previous points :wink:

Re: J-20 goes operational

Unread postPosted: 10 Nov 2018, 00:30
by marsavian
No, you can improve a lot, e.g. halving average RCS and much more in the X-band, if you are prepared to take a significant weight penalty, Boeing is either not on the F-18 or they have already picked the low hanging fruit.

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Re: J-20 goes operational

Unread postPosted: 10 Nov 2018, 05:11
by wrightwing
mixelflick wrote:
knowan wrote:Airshow footage: https://streamable.com/qdw3b

Thoughts?


Rolls much better than I expected. Probably the most sprightly display I've seen yet. I find it telling they don't use thrust vectoring. Probably decided its not worth the cost/weight penalties. Should be something with up rated engines, but being they're behind more than the Russians in that area...

The big question is, how's the stealth? If it's up to par, then coupled with Chinese avionics and weapons... it's going to be quite a threat. Both to US tankers/AWACS as well as our carriers. It will entirely outclass the Super Hornet, and only the F-35C will be able to meet it on an equal footing. Given that platforms lower thrust to weight ratio, I'd have some concerns there too. I do think the F-35's stealth, sensors and SA will be better. How much so and for how long is the real question.

What's the J-20 T/W ratio?

Re: J-20 goes operational

Unread postPosted: 10 Nov 2018, 05:22
by wrightwing
weasel1962 wrote:https://www.defensenews.com/air/2018/11/07/china-showcases-progress-on-stealth-fighter-jet-at-zhuhai-airshow/

Indeed, at the air show, Yang Wei, the chief engineer of the J-20 program, cryptically responded with a cheeky “how do you know we haven’t already done so?” when asked by a local reporter if the J-20 will be similarly fitted with WS-10 engines incorporating thrust vectoring control.


Weasel's note: The F-35 may be stealthier than a J-20A today but J-20B or J-20C?

Because that would require an all new airframe. You're got going to get several magnitudes of RCS reduction, making a few changes here and there. The F-35 isn't remaining stagnant, either.

Re: J-20 goes operational

Unread postPosted: 10 Nov 2018, 21:02
by usnvo
marsavian wrote:No, you can improve a lot, e.g. halving average RCS and much more in the X-band, if you are prepared to take a significant weight penalty, Boeing is either not on the F-18 or they have already picked the low hanging fruit.

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You realize that halving the RCS is just a 3dB reduction right?

Re: J-20 goes operational

Unread postPosted: 10 Nov 2018, 21:09
by marsavian
You realize that halving the RCS is just a 3dB reduction right?


Sure but in the X-band (~13 GHz) the effect is more pronounced, about 10dB reduction which actually brings the RCS from around 10 to under 1 sq m from the side according to this modelling.

Re: J-20 goes operational

Unread postPosted: 10 Nov 2018, 23:07
by citanon
J-20 Zhuhai performance in 4K


Re: J-20 goes operational

Unread postPosted: 10 Nov 2018, 23:59
by ricnunes
marsavian wrote:No, you can improve a lot, e.g. halving average RCS and much more in the X-band, if you are prepared to take a significant weight penalty, Boeing is either not on the F-18 or they have already picked the low hanging fruit.


marsavian wrote:
You realize that halving the RCS is just a 3dB reduction right?


Sure but in the X-band (~13 GHz) the effect is more pronounced, about 10dB reduction which actually brings the RCS from around 10 to under 1 sq m from the side according to this modelling.


Are you aware that one thing is to reduce the RCS of an non-stealth aircraft which has a considerably big RCS and another different thing is to reduce it on an already stealthy aircraft?

Using your examples: a 10% reduction due to RAM from an aircraft with 10 square meters brings it to 1 square meter indeed. But regarding Boeing and its Super Hornet and if we assume that its RCS is 0.5 square meters than a 10% reduction will only bring it to a mere 0.45 square meters (almost nothing).

So, No you cannot improve by much the RCS of an already stealthy aircraft by solely relying on RAM materials coating.
For this you need redesign the aircraft's shape and so I stand for that I previously mentioned - The Stealth of an aircraft (a really stealth one) comes more from its Shape than from its RAM coating (note that I'm not saying that RAM isn't important).

Re: J-20 goes operational

Unread postPosted: 11 Nov 2018, 03:50
by charlielima223
I like to use that brick analogy here.

If I take a metallic brick and wrap it up with RAM, it will have a lower radar return than a metallic brick not wrapped in RAM. Yet no matter how much RAM I put on it, it's still a brick.

ricnunes wrote:
So, No you cannot improve by much the RCS of an already stealthy aircraft by solely relying on RAM materials coating.
For this you need redesign the aircraft's shape and so I stand for that I previously mentioned - The Stealth of an aircraft (a really stealth one) comes more from its Shape than from its RAM coating (note that I'm not saying that RAM isn't important).


I wholeheartedly agree with you that shaping and design its more important than material's used. However there has always been speculation and talk as well as research into meta-materials



https://www.youtube.com/watch?v=LFxQEUDIAuk&t=618s

Currently I remain skeptical to most claims but science has done some amazing things.

Re: J-20 goes operational

Unread postPosted: 11 Nov 2018, 04:23
by citanon
Well, if the J20 ever puts on a flying saucer costume, or start wearing 12 inch thick foam padding, we'll know it's not just for Halloween. :D

Re: J-20 goes operational

Unread postPosted: 11 Nov 2018, 05:15
by weasel1962
Image

Pic posted on CDF. Based on dimensions, main weapons bay holds 4 x 3.8m AAMs and side holds the 2 x 2.9m AAMs.

Re: J-20 goes operational

Unread postPosted: 11 Nov 2018, 12:04
by marsavian
ricnunes wrote:
marsavian wrote:No, you can improve a lot, e.g. halving average RCS and much more in the X-band, if you are prepared to take a significant weight penalty, Boeing is either not on the F-18 or they have already picked the low hanging fruit.


marsavian wrote:
You realize that halving the RCS is just a 3dB reduction right?


Sure but in the X-band (~13 GHz) the effect is more pronounced, about 10dB reduction which actually brings the RCS from around 10 to under 1 sq m from the side according to this modelling.


Are you aware that one thing is to reduce the RCS of an non-stealth aircraft which has a considerably big RCS and another different thing is to reduce it on an already stealthy aircraft?

Using your examples: a 10% reduction due to RAM from an aircraft with 10 square meters brings it to 1 square meter indeed. But regarding Boeing and its Super Hornet and if we assume that its RCS is 0.5 square meters than a 10% reduction will only bring it to a mere 0.45 square meters (almost nothing).

So, No you cannot improve by much the RCS of an already stealthy aircraft by solely relying on RAM materials coating.
For this you need redesign the aircraft's shape and so I stand for that I previously mentioned - The Stealth of an aircraft (a really stealth one) comes more from its Shape than from its RAM coating (note that I'm not saying that RAM isn't important).


Going from 10 to 1 sq m is a 90% reduction, not 10%, and the modelling was around 50% for all wavebands. It's a question of degree not absolutes. If RAM at its best only gets you 10-50 factor RCS improvement on your starting point that only turns a non stealthy aircraft into a LO aircraft with an RCS around 0.2-1.0 sq m but 4th gen aircraft like F-16C, F-18E and Euro-Canards use this technique to do that. Shaping can improve your RCS starting point by 100-1000 factors so you already start at 0.1-0.01 sq m before RAM is applied. What RAM primarily does on a VLO shaped aircraft is make it VLO from all aspects and really make the frontal reduction even more pronounced. But both methods work to varying degrees but RAM works less effectively and comes with a significant weight penalty which is why shaping is normally the first order of business when it comes to designing a stealth aircraft as extra weight is not good news when it comes to overall kinematic performance.

Re: J-20 goes operational

Unread postPosted: 11 Nov 2018, 14:48
by mixelflick
.[/quote]
What's the J-20 T/W ratio?[/quote]

According to this article https://www.nextbigfuture.com/2017/10/c ... -2019.html, the new engine produces 19 tons of thrust. So that's 38,000lbs per engine, x2 would be 76,000lbs of combined thrust.

According to wiki, it's empty weight is 42,750. Also per wiki, it carries 25,000lbs of fuel, so that brings it up to 68,750. Add in 5,000lbs of internal weapons and we're at 73,750lbs.

So a 1.03 thrust to weight ratio, or thereabouts.

That's considerably better than the F-35 at full internal fuel and weapons (.75), but considerably worse than the Raptor at 1.14. Thrust to weight ratio isn't everything, but I'd expect the J-20 to be a fearsome threat to all but the F-35 and F-22. The F-35 won't dogfight with the J-20, instead it'll rely on its superior stealth and sensors to kill it BVR, or near BVR if it has to get in close. The Raptor outclasses it considerably, but they're building 500 J-20's to our 180 or so F-22's. We best hope we don't lose any to accidents or combat, because every one is a national treasure.

Re: J-20 goes operational

Unread postPosted: 11 Nov 2018, 14:53
by Scorpion1alpha
sprstdlyscottsmn wrote:Right now, I am tentatively impressed by the J-20. It seems like a good first attempt. Those ventral fins need to go though, those are going to be hell on RCS.


It tend to agree. Along with those canards.

From the videos, it seems to turn pretty well for a large and long fighter. That's just the instantaneous one, don't know about the sustained rates. If the motors isn't the definitive ones it'll eventually get, it may be even better.

But I guess that's not stopping it from trying to be Raptor-esque.

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