Chengdu J-20 5th Generation Aircraft News & Discussions

[siegecrossbow]

Then we should disqualify every Chinese member here since NONE of you even served in the military, let alone yak about technical issues relating to military gear. Like I said, intellectual consistency has never been the Chinese boys' strong suit.

How do you know we don't have Chinese members who never served in the military here? Did you do a back ground check of every Chinese member here???

Programming is not your strong suit either. Doesn't change the fact that you can "yak" about "software errors" just from a single picture of a plane parked on the ground. Perhaps someone needs to get better with the "computer thing" before he gets better at the "internet thing"?

Consistency in general, not just the intellectual part, has never been your strong suit to start with.

 

[siegecrossbow]

They are just jealous and envious of China's massive military strides. While all countries are progressing, China is just progressing quicker than anyone else at the moment.

They are neither jealous nor envious. They are skeptical. To be fair it is completely normal for them to be skeptical since the most advanced fighter that China could produce a mere two decades ago was the J-8II. Just let time be the judge here.

 

[gambit]

How do you know we don't have Chinese members who never served in the military here? Did you do a back ground check of every Chinese member here???

None ever claimed. And if he did, there are certain clues, even in written speech, that both active duty and former military members can pick up, regardless of country of service, that will eventually reveal the truth. I already busted one fraud.

Programming is not your strong suit either. Doesn't change the fact that you can "yak" about "software errors" just from a single picture of a plane parked on the ground. Perhaps someone needs to get better with the "computer thing" before he gets better at the "internet thing"?

Consistency in general, not just the intellectual part, has never been your strong suit to start with.

Much more than you think...I do not need to actually program the flight control laws to understand the architecture involved.

For example...

I do not need to design the mechanical aspects of the FLCS to understand the philosophy behind the above three examples. If I know that a system has a 'force summation' method to actuate a surface, I can reasonably suspect that there might be something amiss just from watching a command symmetrical deflection of the horizontal stabs if one of them does not deflect as quickly and/or to the same degree as its companion. We can do the same for all of them in software and there would be no difference in principle.

The above example is an excellent illustration of FLCS design and implementation. In both mechanical and software.

The 'serial' design will have the command servo convert pilot stick displacement into a 'compensated' or 'corrected' command for the power actuator that will deflect the flight control surface. The design is simple in both physical hardware and flight control laws architecture. The downside is that this architecture have what FLCS engineers call 'large area of vulnerability'. The word 'large' does not mean area but in component counts. The design would give the aircraft at least two points where an externally induced failure, such as being shot at, would create a catastrophic failure of the subsystem.

The 'nested' design is more complex in both hardware and software architecture. Pilot command is compared against actual power actuator position and the comparator output is called an 'error' which then becomes the final command signal to the power actuator. Some engineers prefer 'differential' over 'error'. The advantage of the 'nested' design is that it is ideal for a FBW FLCS in that the command servo is physically housed with the power actuator. This architecture give the aircraft only one count where a catastrophic failure could occur or a 'small area of vulnerability'. With the 'serial' architecture, if either the command servo or the power actuator is damaged, the entire channel collapse. With the 'nested' architecture, it will take greater odds just to create the same catastrophic failure.

I do not have access to the J-20 but am willing to bet my next year's salary that the J-20's FLCS utilizes the 'nested' architecture in all axis and all channels. With the 'nested' architecture, the flight control laws must be written, not just to have gyros, accelerometers, and air data inputs like 'serial' but also to include power actuator position feedbacks. In both, said laws must be flawless. Any FLCS engineer, hardware or software, will immediately see the 'nested' architecture as the one with the highest potential for 'Byzentine failures'.

Byzantine fault tolerance - Wikipedia, the free encyclopedia

A Byzantine fault is an arbitrary fault that occurs during the execution of an algorithm by a distributed system. It encompasses both omission failures (e.g., crash failures, failing to receive a request, or failing to send a response) and commission failures (e.g., processing a request incorrectly, corrupting local state, and/or sending an incorrect or inconsistent response to a request.) When a Byzantine failure has occurred, the system may respond in any unpredictable way, unless it is designed to have Byzantine fault tolerance.

For a FBW FLCS, the area and greatest potential for Byzentine faults are shifted from the hardware to the software.

So yeah...Any FLCS engineer, either process integration or subsystem designer, can watch the ground movements of the FLCS surfaces and can make reasonable assumptions.

BTW...The two illustrations above are from my F-16 35mm training slides.

 

[Martian2]

J-20 aileron-control-system stealth enclosure is only about half the size of a wheel

 

[SQ8]

If we may or a moment, step out of the Chinese / American whatever we are having here..

And .. even if as an analogy. look at the LM JAST proposed back in the 90's(which 'surprise surprise' looks a lot like the J-20), one wonders if LM had figured some way out or had a roadmap to figuring out how to keep the RCS down of that concept??
Any ideas? (and forget the J-20,PAK-FA whatever.. I want to know how this could have been made to work).

 

[siegecrossbow]

If we may or a moment, step out of the Chinese / American whatever we are having here..

And .. even if as an analogy. look at the LM JAST proposed back in the 90's(which 'surprise surprise' looks a lot like the J-20), one wonders if LM had figured some way out or had a roadmap to figuring out how to keep the RCS down of that concept??
Any ideas? (and forget the J-20,PAK-FA whatever.. I want to know how this could have been made to work).

Here is a talk on Aviation Week that you may find enlightening. It is in the commentary section:

From JAST To J-20

 

[SQ8]

Ive read it before.. thanks.
My point being, if that was a valid concept( I am sure LM thought it through)..
and LO being a important part of JAST.. then data, concepts must have existed to make it work then.
Why would it not work now?

 

[siegecrossbow]

Ive read it before.. thanks.
My point being, if that was a valid concept( I am sure LM thought it through)..
and LO being a important part of JAST.. then data, concepts must have existed to make it work then.
Why would it not work now?

Judging from this post I don't think LO was the worst issue with the JAST concept:

Harrier wrote:
I attended an aircraft design course where Paul Bevilaqua lectured a few years back. He made the very good point that it is easy to design a STOVL aircraft to hover, or to fly in forward flight, but hard to handle the transition as a designer.

As the lift-fan flow of the JAST/JSF exits from the lower forward fuselage it would mean that in transition, with the lift-fan flow deflected aft, there would be a strong nose-up pitch moment to trim out, and using a canard to do that would have meant using it to push the nose down, which would have meant negative lift from the canard. As transition is when you need maximum lift it is possible the canard, whatever wave drag benefits it gave, was cut for a fundamental STOVL reason.

However comparisons between the JAST and the J-20 have limitations. Just for starters the canards on the JAST appear to be on the same plane as that of the wing whereas those are the J-20, whose dihedral canards and anhedral wings keep them from being coplanar.

I think there is no dispute regarding the fact that canards degrade the RCS. The question is just how big of a contributor canards are to the frontal RCS.

 

[gambit]

Ive read it before.. thanks.
My point being, if that was a valid concept( I am sure LM thought it through)..
and LO being a important part of JAST.. then data, concepts must have existed to make it work then.
Why would it not work now?

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.

 

[Martian2]

Canards involve a small trade-off.

With canards, superior maneuverability can be attained. However, the increased surface area (though minor) does result in a slightly larger radar-cross-section (RCS). The United States possesses the world's most powerful jet engines and canards are unnecessary.

China is still climbing the jet-engine technological ladder and the canards provide increased lift. This results in a larger payload and offsets the weakness of an engine with a lower-than-desired thrust.

In the end, the United States military has demonstrated a strong bias against canards; which is not present in China (e.g. J-10 and J-20) or Europe (e.g. Eurofighter, Rafale, Viggen, etc.). The choice of placing canards on a jet fighter reflects a preference. It only has a small effect on a plane's RCS.

 

[gambit]

Canards involve a small trade-off.

With canards, superior maneuverability can be attained. However, the increased surface area (though minor) does result in a slightly larger radar-cross-section (RCS). The United States possesses the world's most powerful jet engines and canards are unnecessary.

China is still climbing the jet-engine technological ladder and the canards provide increased lift. This results in a larger payload and offsets the weakness of an engine with a lower-than-desired thrust.

In the end, the United States military has demonstrated a strong bias against canards; which is not present in China (e.g. J-10 and J-20) or Europe (e.g. Eurofighter, Rafale, Viggen, etc.). The choice of placing canards on a jet fighter reflects a preference. It has little effect on a plane's RCS.

You cannot have it any ways you like. Either canards as edge diffraction generators are significant overall. Or they are not significant overall. On the one hand, you made great efforts at pointing out similar treatments on the J-20 as the F-22: saw-toothed panels, canted twin vertical stabs, or curvatures. All are great efforts at controlling reflectors and edge diffraction generators. But when you found out that decades of experiences and studies proved what you emotionally invested in APA's flawed measurement methodology on the J-20, all of a sudden, canards as edge diffraction generators are nothing to worry about. Panel gaps are far less power generators than moving flight controls elements.

 

[Martian2]

You cannot have it any ways you like. Either canards as edge diffraction generators are significant overall. Or they are not significant overall. On the one hand, you made great efforts at pointing out similar treatments on the J-20 as the F-22: saw-toothed panels, canted twin vertical stabs, or curvatures. All are great efforts at controlling reflectors and edge diffraction generators. But when you found out that decades of experiences and studies proved what you emotionally invested in APA's flawed measurement methodology on the J-20, all of a sudden, canards as edge diffraction generators are nothing to worry about. Panel gaps are far less power generators than moving flight controls elements.

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?

 

[gambit]

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

And you were wrong then...And I have no problems explaining again why. I will put my posts about this subject against yours any day.

 

[Martian2]

And you were wrong then...And I have no problems explaining again why. I will put my posts about this subject against yours any day.

I don't think you understand how this works. You don't decide. The reader makes the decision in who they want to believe. I think they'll select me over you and your walls of text.

Gambit fails to understand the importance of Australia Air Power's "Physics Optics" simulation. They informed you that all of the potential errors are mitigated or reduced by a list of factors. He is making a mountain out of a molehill to try and discredit the J-20 Mighty Dragon's superlative design.

He is making the classical argument: "Are you going to believe me or your lying eyes?" I'll trust my eyes over his misleading verbiage any day. Let's look at an example.

2- The simulator at this time does not model backscatter from surface travelling wave effects. In the forward and aft hemispheres these can be dominant scattering sources where specular contributions are low. The magnitude of these RCS contributions is reduced by edge treatments, lossy surface coatings, gap treatments, and panel serrations;

"Backscatter from surface travelling wave effects" sounds important, right? No. Mr. Goon told you that "edge treatments, lossy surface coatings, gap treatments, and panel serrations" can take care of the problem.

Your eyes have seen the saw-toothed "panel serrations" on the landing and weapon bay panels. Your eyes can see the "lossy surface coatings" or radar-absorbent material on the F-22 and J-20.

Your eyes can also see the gap treatments on the F-22 and J-20. Both have smooth underside surfaces. The Russian Pak-Fa/T-50 is the one that has little or no gap treatments. Your eyes can see the mess on the underside of the Pak-Fa/T-50.

J-20 underside is smooth and clutter-free from vents, gaps, and stuff jutting out.

With regard to edge treatment, I have already covered part of this topic in my video. If you haven't watched it yet, make sure to do so and bring yourself up-to-date on stealth fighter design.

Edge treatment occurs in the following ways: "edge alignment , improved inlet , wing shaping and some nozzle edge treatment." On the J-20 Mighty Dragon, edge alignment is obvious from the "planform alignment" shown in my video. Improved inlet is the J-20 DSI bump. J-20 wing shaping has been modeled and tested on supercomputers and in wind tunnels. J-20 nozzle edge treatment is obvious from the saw-toothed engine nozzles and saw-toothed integration with the fuselage, which are shown in a picture below.

J-20 advanced inlet with DSI technology is readily apparent.

J-20 has saw-toothed engine nozzles and saw-toothed integration with the fuselage.

Gambit is determined to downplay the J-20 Mighty Dragon's excellent stealth design. He's anti-China. On the other hand, I'm objective.

He will keep posting an endless wall of text without discussing their relevance. His obfuscating tactic is to say or imply: "Look at this mountain of text. There must be a problem in here." However, I try to explain ideas to make them easily understandable to allow you to make an informed judgment.

My J-20 video has over 74,000 views. After you watch it, you will be a more knowledgeable person about stealth design. Gambit cannot point to a video that he has made on stealth design that is helpful to the public.

In my opinion, the disclaimer on backscatter point #2 (discussed above) has a minor effect on the results of Australia Air Power's "Physics Optics" simulation. Similarly, all of the disclaimed factors have a minor effect. Mr. Goon tells you that everything is "mitigated" or "reduced."

Please ignore Gambit. He will try to confuse you to pursue his anti-China political agenda. I've been straight with all of you from "day one." Six months ago, I said the J-20 was inferior to the F-22 and superior to the F-35. Now, Australia Air Power has confirmed my analysis.

 

[gambit]

I don't think you understand how this works. You don't decide. The reader makes the decision in who they want to believe. I think they'll select me over you.

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...

http://www.ausairpower.net/APA-2011-03.html

The assessment cannot be more than preliminary for a number of good reasons:

1. The final airframe shaping remains unknown, and changes may arise through the development cycle, to improve aerodynamic performance, operational characteristics, and LO/VLO performance;

2. The state of Chinese Radar Absorbent Materials (RAM), Radar Absorbent Structures (RAS) and radar absorbent coatings technology is not well understood in the West;

3. The state of Chinese technologies for sensor aperture (radar, EO, passive RF) structural mode RCS reduction is not well understood in the West;

4. The state of Chinese technologies for RCS flare spot reduction, in areas such as navigation/communications antennas, seals, panel joins, drain apertures, cooling vents, and fasteners is not well understood in the West.

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...

The choice of all moving slab stabilators and canards will impact RCS at deflection angles away from the neutral position. If large control deflections are produced in flight regimes other than close combat manoeuvring, the specular RCS of the all moving slab controls would need to be considered.

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.

At this time the simulator does not implement surface travelling wave modelling and associated edge or gap backscatter modelling, or edge diffraction scattering effect modelling. As the backscatter from these, in real aircraft, depends upon leading and trailing edge absorbent treatments, it is a reasonable assumption that in a production design these RCS contributions would be strongly suppressed as a result of effective treatments, and thus the magnitude of these RCS contributions would be smaller than specular returns, from angles other than the peak mainlobes.

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.

The engine inlet tunnels were modelled as Perfect Electrical Absorbers (PEA; Refer Annex E). Given the absence of any useful data on the internal configuration of the inlets and tunnels, a more elaborate model would again be entirely speculative. This is consistent with an ideal S-bend inlet tunnel clad with ideal RAM on its interior walls, and the use of an ideal engine face blocker. This is an optimistic assumption given historically observed difficulties in inlet tunnel signature reduction, as in many designs the inlet tunnel cavity RCS is a dominant wideband contributor in the forward aspect.

The exhaust tailpipe RCS contributions were also modelled as Perfect Electrical Absorbers (PEA). Given the absence of any useful data on the internal configuration of the tailpipes, a more elaborate model would be as before entirely speculative. The PEA model is consistent with an ideal tailpipe internally clad with ideal heat resistant RAM, and the use of an ideal turbine face and afterburner fuel spraybar blocker. This is an inherently optimistic assumption, as can be shown by employing an approximate model for an untreated tailpipe cavity, accounting for the reduction in projected nozzle area. This is detailed in Annex C.

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.

The photographic imagery of the J-20 prototypes was not of sufficient quality to incorporate any useful detail of panel join boundaries, door boundaries, and other surface features which produce RCS contributions due to surface travelling waves coupled to the aircraft skin. Even were such detail available, there is no guarantee production aircraft would retain the prototype configuration, reducing the value of any such results.

Further admission that APA had no choice but to use an inadequate tool for this project.

The position of the canards, delta wing leading and trailing edge surfaces, and fully moving tail surfaces was set to neutral, reflecting an optimal cruise configuration at nominal supercruise altitudes and airspeeds. Large deflections by these control surfaces in flight would produce large but transient increases in specular backscatter.

In a life-or-death situation, this would be turned around as 'transient but large'. Against an AESA equipped opponent, as long as these transients are localized or 'clustered' against a neutral background, the J-20 can be accurately tracked.

As the simulation technique is confined to the Physical Optics method, care must be taken in the interpretation of results, as at grazing or shallow angles of incidence the method will usually underestimate the magnitude of the RCS. In the most critical nose and tail aspect angular sectors, a good design will have no major scattering sources producing specular returns captured by the simulation, and the RCS will be dominated by nonspecular mechanisms, primarily diffraction and surface travelling waves, engine inlet and exhaust backscatter, as well as the structural mode RCS of antennas, panel join gaps, or other electrical apertures35.

The highlighted is the clincher that APA had to concede: That the PO method has serious shortcomings and that the results will be skewed towards underestimation or to a certain preferred view.