J-20 5th Generation Fighter VII

[siegecrossbow]

I have always wondered if it were possible to ID aircraft by the RCS much like the subs do with each other with sonar. Radar isn't sonar by any means. However, if you could, then a chase plane of a known type following an unknown would imply the unknown was something new and, thus, a J-20.

But...

Probably not.

How do they know if the unknown plane isn’t a Y-20?

 

[Xizor]

I think should be noted that the J-20 is not very stealthy from behind, it’s possible that it’s identified when it’s turned around.

What if J20 is stealthy from Behind? Why are the Chinese trying to introduce serrated nozzles to its engines?
Why are the Chinese edge treating the ventral strakes? Edit : In fact, the entire strake seems to be treated/of a RCS reducing material.
Why do the J20 have the vental stakes angled and in a position that hides the Engines...
What materials have the Chinese chose for the rear part of J20?

Simply put, we can't say the J20 is not LO from behind. What we can say is that J20 is probably relatively less stealthy from behind.

But relatively less stealthy doesn't mean Not stealthy. J20 will remain a mystery. It has to. It is a 5G aircraft. That's its whole MOJO.

 

[anzha]

How do they know if the unknown plane isn’t a Y-20?

Until they have a signature to compare against or other intel to support it, they won't. OTOH, China did have a Y-20 fly to Pakistan and intel snooping as it flew there, if possible, would be a normal thing to do and give a signature to compare against.

Then again, this idea is supposition and speculation to start with. It may not work whatsoever.

 

[Inst]

Something that is supposed to be a simple answer. Confuses me even more. Just tell me in layman's term. Did they detect a J 20 deep in China's interior or not? If so, then China and anyone else is wasting their money on Lungberg lens or not.

I think someone here said recently, people without stealth aircraft will always poopoo other people's stealth aircraft, until they get their hands on one themself. That I think it's where this wing commander is right now.

The precise claim is that Su-30MKI radars have picked up J-20s.

This is possible in two ways:

1: the J-20 is using a Luneberg lens so that it can be tracked by civilian and allied military radars.
2: the J-20 exposed a bad angle to the Su-30MKIs (rear angle has poor RCS stealth0.

 

[Inst]

The J-20 has been deployed near Tibet for testing purposes in the past. The ridiculous part is that the Indians assert they have detected the J-20 with Su-30 radar from 300KM away (which I don’t think was reported officially by the Indian military). BARS radar’s maximum detection range against MIG-29 is around that number. This also begs the question : how did the Indians know they detected a J-20from such a long distance without visual identification?

Novel RCS signature; i.e, the RCS doesn't resemble that of any other known Chinese type for that detection range. Moreover, to exclude the possibility of drones, the aircraft had to be maneuvering or otherwise moving at a speed not possible with a subsonic drone.

Main thing is, stealth aircraft aren't undetectable; even Chinese and Venezuelan claims over F-22 detection have to be evaluated for whether the aircraft was wearing a Luneberg lens.

Most likely, given that stealth aircraft flicker (i.e, change orientation so that while they can be detected, they can't be tracked), it was a Luneberg lens.

 

[Zool]

The J-20 has been deployed near Tibet for testing purposes in the past. The ridiculous part is that the Indians assert they have detected the J-20 with Su-30 radar from 300KM away (which I don’t think was reported officially by the Indian military). BARS radar’s maximum detection range against MIG-29 is around that number. This also begs the question : how did the Indians know they detected a J-20from such a long distance without visual identification?

It never made any sense; even if you were to assume J-20 at the time was flying with luneberg lens (almost certainly was), Tibet is a huge region. Those MKI would have to be flying right along the LAC, at altitude above the mountains, with China deciding to run weather and altitude testing equally close to the boarder. None of it seems likely.

From what I remember, it was the Indian Air Marshal asked by media to comment on J-20 and what India's response was, being they have no 5th Gen coming online anytime soon and are in the process of buying 4th Gen aircraft abroad. His response was basically 'don't worry, we can see it, we've seen it, no problem, next question'. It was to pacify any concerned public.

But really, what else was he going to say? We have no counter in the near or medium term and this is a real threat to the viability of our airforce going forward? Not happening. But I found it shocking that some otherwise pretty thorough Indian defense enthusiasts actually believed a MKI tracked a J-20 and ran with that as fact, without questioning how that scenario would be possible. Ego is an incredibly significant factor in China - India relations...

 

[Inst]

It never made any sense; even if you were to assume J-20 at the time was flying with luneberg lens (almost certainly was), Tibet is a huge region. Those MKI would have to be flying right along the LAC, at altitude above the mountains, with China deciding to run weather and altitude testing equally close to the boarder. None of it seems likely.

From what I remember, it was the Indian Air Marshal asked by media to comment on J-20 and what India's response was, being they have no 5th Gen coming online anytime soon and are in the process of buying 4th Gen aircraft abroad. His response was basically 'don't worry, we can see it, we've seen it, no problem, next question'. It was to pacify any concerned public.

But really, what else was he going to say? We have no counter in the near or medium term and this is a real threat to the viability of our airforce going forward? Not happening. But I found it shocking that some otherwise pretty thorough Indian defense enthusiasts actually believed a MKI tracked a J-20 and ran with that as fact, without questioning how that scenario would be possible. Ego is an incredibly significant factor in China - India relations...

You have no idea what the RCS contribution of Luneburg lenses are, and more likely, Luneburgs vary within the category.

The Bars radar is reputed to have a 175 km range vs 0 dBsm / 1 m^2. With 300 km, we can determine that the Luneburg lens on the J-20 boosted the RCS to at least 8.63 m^2, or at least 9.3 dBsm, from the angle it was detected from.

 

[Brumby]

The J-20 has been deployed near Tibet for testing purposes in the past. The ridiculous part is that the Indians assert they have detected the J-20 with Su-30 radar from 300KM away (which I don’t think was reported officially by the Indian military). BARS radar’s maximum detection range against MIG-29 is around that number. This also begs the question : how did the Indians know they detected a J-20from such a long distance without visual identification?

First up,the 300 km detection range of BARS may be factually true but has no truth value pertaining to practical detection in real life. This is because it is based on a narrow search criteria and more importantly it is based on a 50 % probability of detection threshold. In other words. it has no practical value in establishing a track simply based on maths. It is a Russian advertising disinformation to inflate capability.

In terms of being able to ID there are a couple of technological ways I can think of but I am not claiming that the IAF has such capabilities. The first type is to use Non Cooperative Target Recognition (NCTR) technique. The technique itself is classified but essentially it is known to be based on the unique RF signature return from the fan blade engine. It is one of the accepted criteria used by the US for ROE when visual confirmation is not available.

The second type is what I understand is being suggested by the Indian side in a rather opaque manner. The story is that in that mountainous region when the J-20 passes through the valleys the contrast between the plane's vapor and the cold background is magnified. This contrast in IR IMO would suit an IRST detection operating in the LWIR band.

An IR detector with IR imaging can ID a target. As an example, this is taken from FSO IR channel.



Obviously it has to be within range and subject to weather conditions.

 

[Zool]

You have no idea what the RCS contribution of Luneburg lenses are, and more likely, Luneburgs vary within the category.

The Bars radar is reputed to have a 175 km range vs 0 dBsm / 1 m^2. With 300 km, we can determine that the Luneburg lens on the J-20 boosted the RCS to at least 8.63 m^2, or at least 9.3 dBsm, from the angle it was detected from.

It's a pretty simple probability study using info we have posted back in this very thread at the time of the testing + google maps and reasoning.

Have a peek at the area size of Tibet. Then lookup the location of the airfield the J-20s flew from, and the distance of that base to the boarder. We can run with the BARS maximum range. Then decide how brave you want to be about your assumptions on just how close up to the LAC Indian MKI happened to fly from say Tezpur or Chabua, the same day(s) China flew the J-20 in an area around the base. And just what kind of distance do you get?

So did the MKI really detect J-20? Not likely.

 

[Inst]

By the way, quick question. Some people have pointed out that the canards on the J-20 aren't actually coplanar with the opposite wing, and brought up charts to prove it.

From what you see, are the J-20 canards in fact co-planar on the production versions?