Chengdu J-20 5th Generation Aircraft News & Discussions

[SQ8]

It is not as you think. Despite some who conveniently dismiss canards whenever it suits them, there is no disputing that on a complex body, the greater the amount of reflectors and edge diffraction generators, the greater the odds of detection. On the frontal view, canards as contributors are negligible, but the frontal aspect view is brief in any dynamic air-air engagement. Our resident former F-15 now airline pilot can attest to that rarity. It is the non-frontal aspects that canards as contributors are most suspicious. We can 'treat' them in some ways but their positions and shapes as dictated by aerodynamic demands take preference over RCS control. In the non-frontal aspects the canards can raise the aircraft above a certain level that may be unacceptable to the original intent. In that case, a decision must be made to either redesign the entire aircraft to exclude canards or live with the fact that they are unacceptable to some degrees.

I've already explained edge diffraction in two earlier posts. I'm not explaining them again.

You've already read my earlier posts in the first thread on the J-20 regarding "moving flight control elements." I said many times that the canards have negligible contribution to RCS when the J-20 is flying towards enemy fighters. The canards' RCS becomes noticeable within-visual-range (WVR) as it performs maneuvers. However, when the J-20 is dogfighting WVR, RCS becomes irrelevant.

Why do you keep forcing me to repeat myself?

And your own post contradict you. As far as the readers goes, they have yet to see anything from the Chinese members even half way close to post 333. I have no problems with their intelligence to see through your pseudo-technical blather.

On post 306 I have shown the readers on why physical optics (PO) is an inappropriate and inadequate tool for this project. That inadequacy was known even to the Iranians and no doubt to the Chinese. But here are the reasons why APA had to use PO...

A Preliminary Assessment of Specular Radar Cross Section Performance in the Chengdu J-20 Prototype

In other words, all the necessary information for them to use other tools to make an even more accurate assessment are unavailable. Physical Optics (PO) is best when we want to assess a surface's specular reflection STRAIGHT ON and said specular measurement gets progressively worse when we depart from perpendicular. So even if we are to be generous and grant APA's methodology as valid, the best we can say is that the J-20's RCS aspect RCS values are very good (or very low) in the normal view in all four profiles: top, bottom, front, and rear. But its RCS from angles are unknown. And that alone is enough to disqualify APA's methodology from being anything other than 'preliminary', which they had to admit.

Here is what APA said about canards...


Right...So may be the canards and their movements are not so trivial after all. I wonder how this concession by APA will affect a certain 'Engineer' who loudly proclaimed the F-22's rudder system is 'less advanced' than the J-20's all-movable stabs now that even APA cautioned against the design in light of RCS contributorship.


It is a reasonable assumption or rather -- hope. Nevertheless, even if we grant APA this latitude, the fact that APA does not have the J-20's precise PHYSICAL measurements to 'plug in' into the PO's algorithm, any RCS estimation from the simulation should be considered suspect. This is not being hostile to anyone but in being in line with the standard peer review process. In fact, the peer review process has a great deal of institutional hostility designed to discourage trivial submissions.


That is true. Inlet tunnel construct in terms of ducting and materials are variables unknown to all, not just to APA. Therefore, it was reasonable for APA to default to PEA as baseline. However, this ideal situation would naturally contribute to the preferred conclusion that the J-20 has a VLO body.

So have kind of established that the J-20, will have very low frontal RCS..and even somebody like me who messed up in wave theory at school can get how a flat plate(relatively) sticking out the front isn't going to sit well with its RCS at angles.
Question is.. how do these pro's and con's translate operationally?
We have discussed what its RCS is despite you guys having differences over it.. allowed me to get a picture of where the J-20 stands(and helped my RCS fundamentals)..

Now, head on.. in an interceptor role.. how much will the J-20's canards effect its picture on a
1. Good ol Pulse doppler.
2. AESA

as a start I am assuming the J-20 is flying at 350 at M 1.3 .. heading for a group of F-18's. I am also assuming for the while that the same technique claimed by the Eurofighter guys for their frontal RCS canard management is employed on the J-20.
When does the J-20 go from being something in the RCS range of say a seagull.. to a cessna.. specifically due to the canards?

Then, assuming a strike role, in a straight border penetration.. who gets to see the J-20 first?.

A Sa-20 site a 80km from the border..say a few degrees off the J-20's nose?
or a Sa-17 site 90km northeast of it?

Again.. I am assuming that during this time, canard movement is minimal..and the jet is trying to fly a profile that avoids enemy threat circles.

 

[gambit]

So have kind of established that the J-20, will have very low frontal RCS..and even somebody like me who messed up in wave theory at school can get how a flat plate(relatively) sticking out the front isn't going to sit well with its RCS at angles.
Question is.. how do these pro's and con's translate operationally?
We have discussed what its RCS is despite you guys having differences over it.. allowed me to get a picture of where the J-20 stands(and helped my RCS fundamentals)..

Now, head on.. in an interceptor role.. how much will the J-20's canards effect its picture on a
1. Good ol Pulse doppler.
2. AESA

as a start I am assuming the J-20 is flying at 350 at M 1.3 .. heading for a group of F-18's. I am also assuming for the while that the same technique claimed by the Eurofighter guys for their frontal RCS canard management is employed on the J-20.
When does the J-20 go from being something in the RCS range of say a seagull.. to a cessna.. specifically due to the canards?

Then, assuming a strike role, in a straight border penetration.. who gets to see the J-20 first?.

A Sa-20 site a 80km from the border..say a few degrees off the J-20's nose?
or a Sa-17 site 90km northeast of it?

Again.. I am assuming that during this time, canard movement is minimal..and the jet is trying to fly a profile that avoids enemy threat circles.

Presenting a minimum radar return via frontal aspect is not new. We knew about it back in the Vietnam War. The J-20's canards in this situation would be statistically negligible. But the problem, not just for the J-20 but to everyone, is even admitted by APA in that other than frontal aspect, the more generators a body has, the greater the odds of detection.

 

[SQ8]

Presenting a minimum radar return via frontal aspect is not new. We knew about it back in the Vietnam War. The J-20's canards in this situation would be statistically negligible. But the problem, not just for the J-20 but to everyone, is even admitted by APA in that other than frontal aspect, the more generators a body has, the greater the odds of detection.

How does that translate operationally gambit..

P.s.. Im not a big fan of APA and Dr Copp.. so I take his analysis with a pinch of salt.

 

[gambit]

How does that translate operationally gambit..

It is not easy to ALWAYS present your least visible view. That is why we have mission planning where pilots carefully plan out whatever it is that they must do. Avoiding known enemy radar sites is part of that planning. But as far as something as unpredictable as meeting the enemy in the air, with what we know today of the advantages of 'stealth', being as low radar observable as possible and being lower than your enemy is an advantage that must be exploited to the full.

 

[Martian2]

1. In a much earlier post, I quoted a J-20 Chinese test pilot who confirmed the J-20 can supercruise. F-35 cannot.

2. J-20 has a clean design like the F-22. I have already mentioned the two flaws in the J-20 design that makes it currently inferior to the F-22 (e.g. "some curvature of the sides" that need to be re-worked and glaring round engine nozzles). However, the F-35 is far more flawed with its compromised design of "‘hideous lumps, bumps, humps and warts’ [that] have appeared on the JSF to disrupt the shaping imperative."

3. Australia Air Power "Physical Optics simulation across nine radio-frequency bands" has shown the J-20 is optimized for stealth. In contrast, the F-35 design is mostly meant to defeat radars in two bands: "to best defeat radars operating in the X and upper S band."

In conclusion, aside from avionics, the J-20 Mighty Dragon is superior to the F-35 in both supercruise ability and stealth across all "nine radio-frequency bands."

----------

Lockheed Martin F-35 Lightning II - Wikipedia, the free encyclopedia

"In spite of being smaller than the F-22, the F-35 has a larger radar cross section. It is said to be roughly equal to a metal golf ball rather than the F-22's metal marble.[126] The F-22 was designed to be difficult to detect by all types of radars and from all directions.[127] The F-35 on the other hand manifests its lowest radar signature from the frontal aspect because of compromises in design. Its surfaces are shaped to best defeat radars operating in the X and upper S band, which are typically found in fighters, surface-to-air missiles and their tracking radars, although the aircraft would be easier to detect using other radar frequencies.[127] Because the shape of the aircraft is so important to its radar cross section, special care must be taken to maintain the "outer mold line" during production.[128] Ground crews require Repair Verification Radar (RVR) test sets in order to verify the RCS of the aircraft after performing repairs, which was not a concern for previous generations of non-stealth fighters.[129][130]"

F-35 with "‘hideous lumps, bumps, humps and warts’ [that] have appeared on the JSF to disrupt the shaping imperative."

----------

J-20 Mighty Dragon has smooth and flat underside.

The Chengdu J-20: Peace in Our Time?

"This study has therefore established through Physical Optics simulation across nine radio-frequency bands, that no fundamental obstacles exist in the shaping design of the J-20 prototype precluding its development into a genuine Very Low Observable design.

Above: L-band RCS, below X-band RCS head on, both in PCSR format (M.J. Pelosi).

Engineers and Scientists who work in ‘stealth’ (AKA ‘Low Observable&#8217 designs have a way for explaining it to lay people: ‘Stealth’ is achieved by Shaping, Shaping, Shaping and Materials (Denys Overholser).

The F-22A is clearly well shaped for low observability above about 500 MHz, and from all important aspects. The J-20 has observed the ‘Shaping, Shaping, Shaping’ imperative, except for the axisymmetric nozzles, and some curvature of the sides that smears a strong, but very narrow specular return into something of a more observable fan. The X-35 mostly observed the ‘Shaping, Shaping, Shaping’ rule, but since then, to quote a colleague, ‘hideous lumps, bumps, humps and warts’ have appeared on the JSF to disrupt the shaping imperative, forcing excessive reliance on materials, which are at the rear-end of the path to ‘Low Observability’.

While discussing ‘rear-ends’, both the F-35 and the J-20 have large signature contributions from their jet nozzles. However, the difference is much like the proverbial ‘Ham Omelette’: the F-35 Pig is committed, but the J-20 Chicken is a participant. If the Chinese decide that rear sector Low Observability is tactically and strategically important, they are at the design stage where they can copy the F-22A nozzle design for the production configuration of the J-20."

[Note: Thank you to HouShanghai for the J-20 underside picture and Stereospace for the F-35 underside picture.]

 

[gambit]

3. Australia Air Power "Physical Optics simulation across nine radio-frequency bands" has shown the J-20 is optimized for stealth. In contrast, the F-35 design is mostly meant to defeat radars in two bands: "to best defeat radars operating in the X and upper S band."

APA's flawed methodology is explained here => http://www.defence.pk/forums/china-...craft-updates-discussions-23.html#post1934472

"In spite of being smaller than the F-22, the F-35 has a larger radar cross section. It is said to be roughly equal to a metal golf ball rather than the F-22's metal marble.[126] The F-22 was designed to be difficult to detect by all types of radars and from all directions.[127] The F-35 on the other hand manifests its lowest radar signature from the frontal aspect because of compromises in design. Its surfaces are shaped to best defeat radars operating in the X and upper S band, which are typically found in fighters, surface-to-air missiles and their tracking radars, although the aircraft would be easier to detect using other radar frequencies.[127] Because the shape of the aircraft is so important to its radar cross section, special care must be taken to maintain the "outer mold line" during production.[128] Ground crews require Repair Verification Radar (RVR) test sets in order to verify the RCS of the aircraft after performing repairs, which was not a concern for previous generations of non-stealth fighters.[129][130]"

The highlighted is either a gross misconception of how an EM wave behave on a surface or a deliberate deception of the same. In radar detection, the only body that will produce the same behavior of EM radiation of any freq is the sphere, which is the simplest body. So other than the sphere, for any complex body as that of an aircraft, if appearances alone is enough for anyone to declare, with NO RESERVATIONS OR CAVEATS, on what band(s) of the EM spectrum will produces what behaviors, then Kopp should have no problems telling everyone what the B-52, the F-102, the F-111, or the Concord will produces what simply by looking at photographs.

However, the F-35 is far more flawed with its compromised design of "‘hideous lumps, bumps, humps and warts’ [that] have appeared on the JSF to disrupt the shaping imperative."

Engineers and Scientists who work in ‘stealth’ (AKA ‘Low Observable&#8217 designs have a way for explaining it to lay people: ‘Stealth’ is achieved by Shaping, Shaping, Shaping and Materials (Denys Overholser).

If aesthetics has any influence on an EM wave's behavior on a complex body, then the F-117, which is quite the ugliest thing flying, would be all over the radar scope for everyone to see. Angled facetings definitively falls under Overholser's admonition, after all, he was the one who exploited Ufimtsev's work to create the F-117. When Overholser spoke about shaping, he was not referring to angled facetings alone. Angled faceting is just one of the many techniques for 'stealth' for complex bodies and for the 1970s computational technology at that time, angled faceting was the only technique Lockheed could exploit. Overholser said nothing about curvatures, of which 'lumps, bumps, and humps' are quite evident, are detrimental in designing a 'stealthy' complex body.

APA's and Kopp's hostility to the F-35 is known but has taken to an absurd level.

 

[SQ8]

Kopp has big issues with anything less than the F-22 from the west( due to his own personal history).
So to make his point.. he glorifies and bloats/gloats on all hardware from Russian and Chinese sources.
Bringing in all sorts of exaggerated figures from "reliable" sources to somehow show his main idea that if the RAAF purchase the f-35 they are screwed.

 

[gambit]

Kopp has big issues with anything less than the F-22 from the west( due to his own personal history).
So to make his point.. he glorifies and bloats/gloats on all hardware from Russian and Chinese sources.
Bringing in all sorts of exaggerated figures from "reliable" sources to somehow show his main idea that if the RAAF purchase the f-35 they are screwed.

And with this supposedly 'analysis' APA did really expose their dishonesty. If the J20's edge diffractions are irrelevant, then why are the F-35's assorted 'lumps, bumps, humps and warts' so relevant to place it below the J-20? Has APA performed the same flawed Physical Optics (PO) analysis on the F-16, F-117, F-22, F-35, and B-2 for the readers to see the comparisons? We are talking quite diverse planforms and shapings here. The F-16 would make an ideal 'non-stealth' baseline for these comparisons. A major part of any peer review process and the FIRST thing the reviewers will do is to analyze the methodology involved. APA had to admit that they used an inadequate tool for the job. That alone should be reason enough to disqualify.

 

[Martian2]

1. In a much earlier post, I quoted a J-20 Chinese test pilot who confirmed the J-20 can supercruise. F-35 cannot.

2. J-20 has a clean design like the F-22. I have already mentioned the two flaws in the J-20 design that makes it currently inferior to the F-22 (e.g. "some curvature of the sides" that need to be re-worked and glaring round engine nozzles). However, the F-35 is far more flawed with its compromised design of "‘hideous lumps, bumps, humps and warts’ [that] have appeared on the JSF to disrupt the shaping imperative."

3. Australia Air Power "Physical Optics simulation across nine radio-frequency bands" has shown the J-20 is optimized for stealth. In contrast, the F-35 design is mostly meant to defeat radars in two bands: "to best defeat radars operating in the X and upper S band."

In conclusion, aside from avionics, the J-20 Mighty Dragon is superior to the F-35 in both supercruise ability and stealth across all "nine radio-frequency bands."

----------

Lockheed Martin F-35 Lightning II - Wikipedia, the free encyclopedia

"In spite of being smaller than the F-22, the F-35 has a larger radar cross section. It is said to be roughly equal to a metal golf ball rather than the F-22's metal marble.[126] The F-22 was designed to be difficult to detect by all types of radars and from all directions.[127] The F-35 on the other hand manifests its lowest radar signature from the frontal aspect because of compromises in design. Its surfaces are shaped to best defeat radars operating in the X and upper S band, which are typically found in fighters, surface-to-air missiles and their tracking radars, although the aircraft would be easier to detect using other radar frequencies.[127] Because the shape of the aircraft is so important to its radar cross section, special care must be taken to maintain the "outer mold line" during production.[128] Ground crews require Repair Verification Radar (RVR) test sets in order to verify the RCS of the aircraft after performing repairs, which was not a concern for previous generations of non-stealth fighters.[129][130]"

F-35 with "‘hideous lumps, bumps, humps and warts’ [that] have appeared on the JSF to disrupt the shaping imperative."

----------

J-20 Mighty Dragon has smooth and flat underside.

The Chengdu J-20: Peace in Our Time?

"This study has therefore established through Physical Optics simulation across nine radio-frequency bands, that no fundamental obstacles exist in the shaping design of the J-20 prototype precluding its development into a genuine Very Low Observable design.

Above: L-band RCS, below X-band RCS head on, both in PCSR format (M.J. Pelosi).

Engineers and Scientists who work in ‘stealth’ (AKA ‘Low Observable&#8217 designs have a way for explaining it to lay people: ‘Stealth’ is achieved by Shaping, Shaping, Shaping and Materials (Denys Overholser).

The F-22A is clearly well shaped for low observability above about 500 MHz, and from all important aspects. The J-20 has observed the ‘Shaping, Shaping, Shaping’ imperative, except for the axisymmetric nozzles, and some curvature of the sides that smears a strong, but very narrow specular return into something of a more observable fan. The X-35 mostly observed the ‘Shaping, Shaping, Shaping’ rule, but since then, to quote a colleague, ‘hideous lumps, bumps, humps and warts’ have appeared on the JSF to disrupt the shaping imperative, forcing excessive reliance on materials, which are at the rear-end of the path to ‘Low Observability’.

While discussing ‘rear-ends’, both the F-35 and the J-20 have large signature contributions from their jet nozzles. However, the difference is much like the proverbial ‘Ham Omelette’: the F-35 Pig is committed, but the J-20 Chicken is a participant. If the Chinese decide that rear sector Low Observability is tactically and strategically important, they are at the design stage where they can copy the F-22A nozzle design for the production configuration of the J-20."

[Note: Thank you to HouShanghai for the J-20 underside picture and Stereospace for the F-35 underside picture.]

To be thorough, I should mention the F-35 has two "lumps" on the topside (above the air inlets) as well.

 

[gambit]

To be thorough, I should mention the F-35 has two "lumps" on the topside (above the air inlets) as well.

Are you really that 'thorough'? Because if you are, you would have withdrawn just about everything you posted from APA...

 

[houshanghai]

BEIJING 207 institute had done total RCS test on J-20 not long ago and the result of j20 rcs test is very amazing.they were satisfied with j20's rcs

j20's bottom is very smooth like F22,not like F35.

 

[houshanghai]

 

[gambit]

BEIJING 207 institute had done total RCS test on J-20 not long ago and the result of j20 rcs test is very amazing.they were satisfied with j20's rcs

Being 'satisfied' really does not mean much. They may be satisfied with the J-20's RCS being higher than what is speculated for the F-35 despite all the work done on it.

j20's bottom is very smooth like F22,not like F35.

The correct word is 'underside', and how do you know that the F-35's underside is somehow a negative? Because China said so?

 

[Martian2]

BEIJING 207 institute had done total RCS test on J-20 not long ago and the result of j20 rcs test is very amazing.they were satisfied with j20's rcs

j20's bottom is very smooth like F22,not like F35.

If I were you, I would ignore the troll. He repeats the same things over and over again, despite being presented with new evidence. He only posts after I put up a comprehensive analysis. Indians used to do it to me all the time.

They rehash the same old arguments from months ago to clutter the thread. This way no one will see my exhaustive analysis after I've spent hours collecting the information and presenting it in a streamlined manner. You'll notice that I am ignoring his taunts and him.

It's a standard trick to keep arguing with you; then the quality of the thread deteriorates, which is what he wants. Please ignore him or he'll clutter this thread again. Thank you.

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The important thing is that people all over the internet recognize the importance of my analyses:

[quote='khh' date='Jul 12 2011, 01:56 PM' (from another forum)]
Nice info about the J20, F-35 and F-22 stealthy features...... [/quote]

 

[siegecrossbow]

The correct word is 'underside', and how do you know that the F-35's underside is somehow a negative? Because China said so?

Stop putting words in people's mouth.

Houshanghai did not compare J-20's RCS with that of the F-35 in his post. All he did was state the fact that the 207 institute was satisfied with the RCS readings and that the J-20's underside is smooth and similar to that of the F-22 in that respect. Where did he say that the F-35's underside was a negative and how did China figure into this?