Chengdu J-20 pictures, analysis and speculation Part II

[Trident]

Yeah, that's a bit of a mystery. Perhaps that RAM patch doesn't actually have a function with the lens in place, but serves to hide the attachment point with as little remedial work as possible when the lens is removed?

 

[overscan (PaulMM)]

Exhaust or intake makes more sense purely on location for the meshes- doubt there's much depth there to store a submerged radar antenna.

The black hexagon appears to be an optical aperture, probably EODAS.

The lack of these items on the earlier prototype would suggest they are avionics items and this prototype has a more representative equipment fit. If the grilles are boundary air exhausts, it would indicate the DSI intake is being tweaked.

 

[Blitzo]

The black hexagon appears to be an optical aperture, probably EODAS.

A photo of the plane's right side shows lack of the small black hexagon -- I think it may rather be for some kind of switch or opening.

I believe the two side looking EODAS ports are instead located on the nose, just behind the radome, similar to F-35.




Found this very handy picture on this particular forum. An excellent reference for speculating where J-20's EODAS locations may also be. Aforementioned is the two side looking nose mounted EODAS mounts, I also suspect J-20's underfuselage "bump" similarly houses the under fuselage forward/rear looking EODAS apertures. Same for the upper nose mounted black window seen on earlier J-20 prototypes, which corresponds to F-35's position, and I suspect it still exists on 2011. Now the question is where the upper fuselage mounted EODAS is...

 

[Deino]

...
The black hexagon appears to be an optical aperture, probably EODAS.
...

IMO and especially since it is marked by an arrow I tend to say it's an emergency / cescue handle to open the canopy or eject the pilot (I'm not sure, but did not the French Mirage have it on the intakes too ?).

Deino

 

[quellish]

Care to explain what You want to say with this statement or Your observation ???

A lot of the things we see on 2011 do not make sense in 3 dimensions. So hypothetically, apertures shaped in such a way that they look aligned to aggregate backscatter into desecrate regions, but in 3 dimensions actually contribute to a (much) larger return. The scattered radiation would meet in such a way as to cause... other problems.

It does seem like they made a lot of progress on certain parts of the canopy. But at the same time, it looks like 2011 may have even more exposed cavities of a concerning size than the earlier aircraft. All of the J-20s are fascinating sets of contradictions. Some of this can be explained by the very different (apparently) methodology of Chinese aircraft design and development. And some of it not so much.

 

[overscan (PaulMM)]

...The black hexagon appears to be an optical aperture, probably EODAS....

IMI and especially since it is marked by an arrow I tend to say it's an emergency / cescue handle to open the canopy or eject the pilot (I'm not sure, but did not the French Mirage have it on the intakes too ?).Deino

Yep, you are correct - I was only briefly looking during lunch at work.


I think the words on the arrow might be the same as this:

 

[Deino]

@ quellish

THANKs a lot !

 

[latenlazy]

Care to explain what You want to say with this statement or Your observation ???

A lot of the things we see on 2011 do not make sense in 3 dimensions. So hypothetically, apertures shaped in such a way that they look aligned to aggregate backscatter into desecrate regions, but in 3 dimensions actually contribute to a (much) larger return. The scattered radiation would meet in such a way as to cause... other problems.

It does seem like they made a lot of progress on certain parts of the canopy. But at the same time, it looks like 2011 may have even more exposed cavities of a concerning size than the earlier aircraft. All of the J-20s are fascinating sets of contradictions. Some of this can be explained by the very different (apparently) methodology of Chinese aircraft design and development. And some of it not so much.

That's pretty interesting. If you don't mind me asking, could you point out the specific areas that seem problematic. I think it might help us all get a better grasp of what you're talking about (I have a very general understanding of your explanation but don't really know how to apply that to specific observations).

EDIT: Unless you're talking mostly about the aft fuselage. There's probably a lot that still needs to be done there, but I suspect they're waiting to install new engines before doing any major redesign, both of which may not occur until there's a B variant.

 

[Mat Parry]

So hypothetically, apertures shaped in such a way that they look aligned to aggregate backscatter into desecrate regions, but in 3 dimensions actually contribute to a (much) larger return. The scattered radiation would meet in such a way as to cause... other problems.

Constructive interference?

 

[sferrin]

So hypothetically, apertures shaped in such a way that they look aligned to aggregate backscatter into desecrate regions, but in 3 dimensions actually contribute to a (much) larger return. The scattered radiation would meet in such a way as to cause... other problems.

Constructive interference?

X number of little returns combine into a big one.

 

[Deino]

Can anyone explain these shapes and structures ??? ? ???

Interesting theory just posted over at the SDF by "plawolf"

A little late to the party, but I think the hexagon meshes on the side of the intakes covers an intake and an exhaust which are used for boundary layer control inside the intake.

There would be sliding doors, which may or may not also be covered by a similar mesh screen, on the inside wall of the intake.

By opening and closing one or both of those doors, partially or fully, the J20's intake would be able to create pressure fields that push the boundary lay airflow forwards or backwards when it first hit the outside wall of the intake, which would then feed through to affect where and when the shockwaves form inside the intake, which in turn determines at what speed the airflow hits the compressor blades.

Its a pretty ingenious design, which should allow the J20's fixed DSI to achieve similar supersonic performance as traditional variable geometry intakes while retaining all the RCS advantages of the DSI. Its not a perfect solution, because the movable doors and mechanisms needed for them would surrender much of the weight and maintenance savings a basic first gen DSI would have over a variable geometry intake, but I think the supersonic performance gains are viewed as well worth the cost compared to a basic DSI.

Deino

 

[quellish]

X number of little returns combine into a big one.

Not exactly. More like what you see with an untreated cavity. The output can be greater than the sum of the parts. The frequency distribution of the backscatter can be greatly different from the input, while the net energy is (usually) the same or slightly greater.

BOUNCY BOUNCY!

 

[VH]

A lot of the things we see on 2011 do not make sense in 3 dimensions. So hypothetically, apertures shaped in such a way that they look aligned to aggregate backscatter into desecrate regions, but in 3 dimensions actually contribute to a (much) larger return. The scattered radiation would meet in such a way as to cause... other problems.

It does seem like they made a lot of progress on certain parts of the canopy. But at the same time, it looks like 2011 may have even more exposed cavities of a concerning size than the earlier aircraft. All of the J-20s are fascinating sets of contradictions. Some of this can be explained by the very different (apparently) methodology of Chinese aircraft design and development. And some of it not so much.

And it could be that the Chinese are trying to do too much. Using whatever 5th generation aircraft design data they were able to purloin, China appears to be trying to throw everything into a big pot, shake well and see what comes out in the end.


Remember: A camel is a horse designed by committee

 

[latenlazy]

A lot of the things we see on 2011 do not make sense in 3 dimensions. So hypothetically, apertures shaped in such a way that they look aligned to aggregate backscatter into desecrate regions, but in 3 dimensions actually contribute to a (much) larger return. The scattered radiation would meet in such a way as to cause... other problems.

It does seem like they made a lot of progress on certain parts of the canopy. But at the same time, it looks like 2011 may have even more exposed cavities of a concerning size than the earlier aircraft. All of the J-20s are fascinating sets of contradictions. Some of this can be explained by the very different (apparently) methodology of Chinese aircraft design and development. And some of it not so much.

And it could be that the Chinese are trying to do too much. Using whatever 5th generation aircraft design data they were able to purloin, China appears to be trying to throw everything into a big pot, shake well and see what comes out in the end.


Remember: A camel is a horse designed by committee

Are you suggesting that they could they be trying to optimize for too many bands? Because I can kinda see how 2011 might be trying to do that and it could make a lot of sense. There was a rumour that 2011 still hasn't met desired RCS targets a few weeks back that got waved off as just a rumour, but just yesterday a PLA general said to the media that they might make further adjustments and that developing the J-20 is going to be a process.

 

[_Del_]

Camel or no, I don't see why it could not be an effective warplane. I suppose I'm in the minority when i say that I don't find it particularly attractive, but I can't imagine a strike or interceptor aircraft with a relatively low RCS is anything other than a great leap forward for China (even if it is crude, it is bound to have a lower RCS than legacy aircraft, no?). Impressive for a country that was still manufacturing Mig-21's (J-7's) and the Q-5 until very recently.

 

[Sundog]

Can anyone explain these shapes and structures ??? ? ???

Interesting theory just posted over at the SDF by "plawolf"

A little late to the party, but I think the hexagon meshes on the side of the intakes covers an intake and an exhaust which are used for boundary layer control inside the intake.

There would be sliding doors, which may or may not also be covered by a similar mesh screen, on the inside wall of the intake.

By opening and closing one or both of those doors, partially or fully, the J20's intake would be able to create pressure fields that push the boundary lay airflow forwards or backwards when it first hit the outside wall of the intake, which would then feed through to affect where and when the shockwaves form inside the intake, which in turn determines at what speed the airflow hits the compressor blades.

Its a pretty ingenious design, which should allow the J20's fixed DSI to achieve similar supersonic performance as traditional variable geometry intakes while retaining all the RCS advantages of the DSI. Its not a perfect solution, because the movable doors and mechanisms needed for them would surrender much of the weight and maintenance savings a basic first gen DSI would have over a variable geometry intake, but I think the supersonic performance gains are viewed as well worth the cost compared to a basic DSI.

Deino

This isn't new and the U.S. has reportedly been using it for decades. Supposedly the original YF-23 inlet design as flown used it, the F-22 inlet might use similar tech (They don't exactly advertise stuff like this) and the U.S. has looked at using such systems as stealthy flight controls. Whether or not they have tested the flight controls in flight I don't know. We've apparently also used it for passive thrust vectoring, at least in tests.

 

[sferrin]

Can anyone explain these shapes and structures ??? ? ???

Interesting theory just posted over at the SDF by "plawolf"

A little late to the party, but I think the hexagon meshes on the side of the intakes covers an intake and an exhaust which are used for boundary layer control inside the intake.

There would be sliding doors, which may or may not also be covered by a similar mesh screen, on the inside wall of the intake.

By opening and closing one or both of those doors, partially or fully, the J20's intake would be able to create pressure fields that push the boundary lay airflow forwards or backwards when it first hit the outside wall of the intake, which would then feed through to affect where and when the shockwaves form inside the intake, which in turn determines at what speed the airflow hits the compressor blades.

Its a pretty ingenious design, which should allow the J20's fixed DSI to achieve similar supersonic performance as traditional variable geometry intakes while retaining all the RCS advantages of the DSI. Its not a perfect solution, because the movable doors and mechanisms needed for them would surrender much of the weight and maintenance savings a basic first gen DSI would have over a variable geometry intake, but I think the supersonic performance gains are viewed as well worth the cost compared to a basic DSI.

Deino

Seems overly complex. Why not just go the F-22 / XF8U-3 route?

 

[VH]

Are you suggesting that they could they be trying to optimize for too many bands? Because I can kinda see how 2011 might be trying to do that and it could make a lot of sense. There was a rumour that 2011 still hasn't met desired RCS targets a few weeks back that got waved off as just a rumour, but just yesterday a PLA general said to the media that they might make further adjustments and that developing the J-20 is going to be a process.

No I am not. What I am saying is that China with NO experience in designing stealthy aircraft has suddenly tried to jump into the fray with the big boys, America and Russia. And America has been designing stealthy aircraft starting at least with Have Blue and early B2 studies. Russia has understood the value of stealth for at least as long.


To jump from manufacturing copies of Russian aircraft to an indigenous aircraft designed to counter F-22 and T-50 is too big a gap to bridge in one leap.

 

[VH]

Are you suggesting that they could they be trying to optimize for too many bands? Because I can kinda see how 2011 might be trying to do that and it could make a lot of sense. There was a rumour that 2011 still hasn't met desired RCS targets a few weeks back that got waved off as just a rumour, but just yesterday a PLA general said to the media that they might make further adjustments and that developing the J-20 is going to be a process.

And that rumor is probably true. That PLA general is correct. J-20 development is going to take a long time. A very long time.

 

[VH]

Camel or no, I don't see why it could not be an effective warplane. I suppose I'm in the minority when i say that I don't find it particularly attractive, but I can't imagine a strike or interceptor aircraft with a relatively low RCS is anything other than a great leap forward for China (even if it is crude, it is bound to have a lower RCS than legacy aircraft, no?). Impressive for a country that was still manufacturing Mig-21's (J-7's) and the Q-5 until very recently.

Having a lower RCS than legacy aircraft should not be the goal of the PLAAF. If they want to prevail in the air they will have to have superior airplanes and crews.


The battles in tomorrow's skies will not be measured on how impressive it is to make the attempt to go from J-7s and Q-5s to the J-20 and J-31.


Its either win or go home.

 

[latenlazy]

No I am not. What I am saying is that China with NO experience in designing stealthy aircraft has suddenly tried to jump into the fray with the big boys, America and Russia. And America has been designing stealthy aircraft starting at least with Have Blue and early B2 studies. Russia has understood the value of stealth for at least as long.


To jump from manufacturing copies of Russian aircraft to an indigenous aircraft designed to counter F-22 and T-50 is too big a gap to bridge in one leap.

Sooo...a largely rhetorical point? I was hoping for some insight into the actual engineering of the plane...

And that rumor is probably true. That PLA general is correct. J-20 development is going to take a long time. A very long time.

Depends on what you mean by very long and what he meant by "a process" (I get the impression that you two didn't mean the same things). I remember not long ago when people assumed that China was still a decade away from a prototype. No matter, time will tell.

And that rumor is probably true. That PLA general is correct. J-20 development is going to take a long time. A very long time.Seems overly complex. Why not just go the F-22 / XF8U-3 route?

Hard to say how complex or not it is based on just the description. It might be an easier one to engineer. Perhaps they found this system much more effective or had other benefits (like weight savings). It's just a theory though, but I think a very good one.

 

[BioLuminescentLamprey]

I am very hesitant to believe the PAKFA has any serious RCS advantage over the J-20. The J-20 has a few features that are considered less than optimal for stealth, but the PAKFA does too....perhaps more so. I'm not an expert by any means, but I'd love to hear Quellish or someone who knows their electromag theory better than me compare the 2 prototypes.

 

[latenlazy]

I am very hesitant to believe the PAKFA has any serious RCS advantage over the J-20. The J-20 has a few features that are considered less than optimal for stealth, but the PAKFA does too....perhaps more so. I'm not an expert by any means, but I'd love to hear Quellish or someone who knows their electromag theory better than me compare the 2 prototypes.

I don't know anything more than basic electromagnetic theory myself, so I'm not going to go out there and say for sure which one is better or not, but just based on good principles of observation, those who do have a good grasp of this stuff should probably consider both a conservative and optimistic estimate, since there are things about RCS that don't have to do with geometry, (mostly materials).

 

[quellish]

I don't know anything more than basic electromagnetic theory myself, so I'm not going to go out there and say for sure which one is better or not, but just based on good principles of observation, those who do have a good grasp of this stuff should probably consider both a conservative and optimistic estimate, since there are things about RCS that don't have to do with geometry, (mostly materials).

Shape, shape, shape.... and magical RAM!

 

[latenlazy]

I don't know anything more than basic electromagnetic theory myself, so I'm not going to go out there and say for sure which one is better or not, but just based on good principles of observation, those who do have a good grasp of this stuff should probably consider both a conservative and optimistic estimate, since there are things about RCS that don't have to do with geometry, (mostly materials).

Shape, shape, shape.... and magical RAM!

But I would presume that as computing gets more powerful shape can afford to get more complex, and as materials improve RAM could take a larger share of the burden?

 

[_Del_]

Having a lower RCS than legacy aircraft should not be the goal of the PLAAF. If they want to prevail in the air they will have to have superior airplanes and crews.


The battles in tomorrow's skies will not be measured on how impressive it is to make the attempt to go from J-7s and Q-5s to the J-20 and J-31.


Its either win or go home.

That's sort of short-sighted. First, if it's a win or go home scenario I imagine that prevailing in the air will be helped immensely by both basic geography and IRBM's. I'd imagine that half of the plan would be destroying the enemy on the ground where possible and denying access to forward basing, just as most modern air arms would aim for. Then assuming the US is the adversary, we are forced to tank aircraft just to get into the fight while China throws large numbers of aircraft in the air, and as tovarish Iosif once said, "Quantity has a quality all its own."
Second, the ability to leap from the J-7 to the J-20 or J-31 also means they are able to put together new programs using new information quickly (at least compared to glacial development in the West). That means the lessons learned in the J-20 and J-31 programs will be put to good and immediate use on the next program, which may arrive sooner than we expect.
In the meantime, I cannot see the J-20 as being much inferior to a Super Hornet all considered. Quite possibly better. A good number of aircraft such as the J-20's and J-31 along with the Sukhoi clones stacks up well against an opposing force consisting of a very small number of F-22's and B-2's and a large number of legacy aircraft, imo.

 

[quellish]

But I would presume that as computing gets more powerful shape can afford to get more complex, and as materials improve RAM could take a larger share of the burden?

Nope.

 

[latenlazy]

But I would presume that as computing gets more powerful shape can afford to get more complex, and as materials improve RAM could take a larger share of the burden?

Nope.

Hmm. Alright. Still curious about the exact aspects of the J-20's design that seem contradictory to you though. I think you mentioned something about the aft section of the plane, but not sure if your follow up comment to Deino also referred to that, or to other things.

 

[VH]

Sooo...a largely rhetorical point? I was hoping for some insight into the actual engineering of the plane...

Insight into the actual engineering of J-20 is not possible at this time due to the closed nature of China. Anything being said about the performance of J-20 is at best conjecture and speculation.

 

[latenlazy]

Sooo...a largely rhetorical point? I was hoping for some insight into the actual engineering of the plane...

Insight into the actual engineering of J-20 is not possible at this time due to the closed nature of China. Anything being said about the performance of J-20 is at best conjecture and speculation.

Yeah, but the HOPE is that the conjecture and speculation can be educated.

 

[VH]

That's sort of short-sighted. First, if it's a win or go home scenario I imagine that prevailing in the air will be helped immensely by both basic geography and IRBM's. I'd imagine that half of the plan would be destroying the enemy on the ground where possible and denying access to forward basing, just as most modern air arms would aim for. Then assuming the US is the adversary, we are forced to tank aircraft just to get into the fight while China throws large numbers of aircraft in the air, and as tovarish Iosif once said, "Quantity has a quality all its own."
Second, the ability to leap from the J-7 to the J-20 or J-31 also means they are able to put together new programs using new information quickly (at least compared to glacial development in the West). That means the lessons learned in the J-20 and J-31 programs will be put to good and immediate use on the next program, which may arrive sooner than we expect.
In the meantime, I cannot see the J-20 as being much inferior to a Super Hornet all considered. Quite possibly better. A good number of aircraft such as the J-20's and J-31 along with the Sukhoi clones stacks up well against an opposing force consisting of a very small number of F-22's and B-2's and a large number of legacy aircraft, imo.

1. I am talking about aircrew quality, tactics and aircraft design. If you want to consider the US as the adversary you should remember that the Chinese airforce has not fought an air battle since Korea. Plus China seldom if ever goes outside of their sphere of influence to train against other nations. The US has the edge of experience and training.


2. Whatever new information the Chinese have gathered to design J-20 and J-31 has largely been obtained from US aircraft designs. Visual inspection of both Chinese aircraft prototypes confirms evidence of that. I believe if you take a sober look at things it is difficult to believe that a xerox of a thing would be stronger than the original.


I would be interested in hearing your comments on what 'lessons learned' you think will be derived from the J-20 and J-31 and applied to the next generation of Chinese aircraft design.


Don't forget there are already discussions in Chinese media that the J-20 design is not meeting its RCS targets. Meanwhile don't forget that the American designs are mature and discussions are underway for a 6th generation aircraft design and its supporting systems.

 

[VH]

Yeah, but the HOPE is that the conjecture and speculation can be educated.

I would hope that too. A close examination of the J-20 would be nice to see. Many questions would be answered

 

[_Del_]

1. I am talking about aircrew quality, tactics and aircraft design. If you want to consider the US as the adversary you should remember that the Chinese airforce has not fought an air battle since Korea. Plus China seldom if ever goes outside of their sphere of influence to train against other nations. The US has the edge of experience and training.

I have no doubt that the US kill ratio in the air would be impressive. I don't know how the introduction of the latest Chinese fighters would raise that, do you? In that regard it's a step in the right direction (if you're Chinese).

I believe if you take a sober look at things it is difficult to believe that a xerox of a thing would be stronger than the original.

I do not recall saying that they would be superior to the F-35 or the F-22. I said they would be at worst comparable to legacy aircraft in performance with a lower RCS. Again a marked improvement in a very short period of time. I also don't see how you can compare the J-20 to a xerox of anything currently manufactured by the west. The J-31 obviously bears some resemblance and owes something to LockMart products.

I would be interested in hearing your comments on what 'lessons learned' .. Don't forget there are already discussions in Chinese media that the J-20 design is not meeting its RCS targets.

Isn't that already an example of lessons learned? And specifically I meant in material technology and the manufacturing involved, as well as RCS in practice vs theory. Tactics using LO and practical aspects of the use of advanced sensors would obviously be a part of that. The point was not that they were as good as the F-22 or F-35, but that with an impressive jump in design from the MiG-21 to the J-20, it seems reasonable that the jump from the J-31 to the F-35 is not insurmountable given a period of time and experience in the J-31 program.

 

[latenlazy]

1. I am talking about aircrew quality, tactics and aircraft design. If you want to consider the US as the adversary you should remember that the Chinese airforce has not fought an air battle since Korea. Plus China seldom if ever goes outside of their sphere of influence to train against other nations. The US has the edge of experience and training.

The same could have been said for the Japanese Air Force in WWII. And the US probably hasn't had an air battle with a technological peer in a while, which is what China's looking to become. Old experiences can only count so much for new conflicts though, so it's best not to extrapolate too much.

2. Whatever new information the Chinese have gathered to design J-20 and J-31 has largely been obtained from US aircraft designs. Visual inspection of both Chinese aircraft prototypes confirms evidence of that. I believe if you take a sober look at things it is difficult to believe that a xerox of a thing would be stronger than the original.

While I don't doubt that China has probably obtained a lot of information on US aircraft designs, it might be an overreach to suggest that that has been their primary source of information for R&D. For one, while the engineering techniques are classified, the theories and concepts are not. The physics is the same for everyone. Secondly, with increasing computation power (as well as poaching of USSR/Russian engineers and Chinese expatriates educated abroad) it's much easier make leaps when testing and developing new technologies, so it's not unfeasible for China to get this far on their own given that they have better tools than what the US had in the 70s and 80s. After all, technological development is not a linear process. Third, the general belief is that China got a lot of technical assistance on the development and testing of stealth concepts from Russia, and if China has gotten any foreign assistance on their stealth program, it's far more likely that more of that came from Russia than the US.

It's an even bigger stretch to suggest that China has "copied" off US designs. The start of China's program (and in fact computer simulations and wind tunnel models of the J-20) precede by many years the reported cyber espionage of the F-35 and F-22's designs, which themselves happened far too closely to the J-20's first flight date to reasonably expect wholesale aspects of those designs ended up on the J-20. If they were stealing data for more than developing countermeasures (which is actually the far more dangerous aspect of technological espionage), it's unlikely that they would simply "copy" a design, but learn the general techniques and principles behind one, and then apply it for their own needs.

Off tangent, but just on the accuracy of the analogy, the xerox may not be as good as the original, but there have been many instances in engineering where a copy of a design has actually been better than the original. How effective your copying abilitie are are dependent on your scientific and engineering foundation, and not on whether the design is original or not.

Don't forget there are already discussions in Chinese media that the J-20 design is not meeting its RCS targets. Meanwhile don't forget that the American designs are mature and discussions are underway for a 6th generation aircraft design and its supporting systems.

Careful, I said that there was a rumour that the J-20 didn't meet RCS targets. That bit was NOT reported in the media, but came up in the online rumour mill where we get most of our information from, but which requires A LOT of parsing and fact checking. The PLA general's comments to the media was only that the J-20's design may undergo further revisions. There's a case to be made that you can two and two together, but it's far from certain that those two things are related. Furthermore, one cannot extrapolate too much from the J-20 undergoing further revisions. After all, it is still in development, and revisions are only natural. That the design undergoes revisions does not necessarily have any bearings on how quickly or slowly they are able to develop the design, or how close or far they are from achieving their target performance.

And yes the US is also developing their 6th generation platform, but keep in mind that so is China. China is VERY serious about catching up to the US, and that intention, with the resources backing it, cannot be underestimated. For example, they're pursuing parallel R&D of their 10 and 15 T:W ratio engines. Right after they completed the core for the 10 T:W ratio engine, they began to mature and realize their research so that they could build a core for the 15 T:W ratio engine (which is, supposedly, supposed to begin testing in 2016). Things are moving fast, and while being conservative is always good, being too conservative might be under selling what China's capable of.

 

[Deino]

Just another idea / theory regarding these strange hexagonal structures .... posted by "Jō Asakura" at the Key-Forum:

The first bleed vent (L) serves to strengthen the initial oblique shockwave, the second (R) is to deal with residual boundary layer separation due to the intensity of the initial shock wave (and ingested BL) downstream of the compression bump surface. The problem arises in the supersonic regime when total pressure flow is degraded due to the interaction of the bleed system and shock waves. However, as these two vents increase the bleed flow rate, then the severity of these low pressure gradients is reduced.

The F-35 also suffered from similar problems but LM instigated (at least one) redesign of the duct itself. Even so it is probable that the duct design will still, to some extent, inhibit the F-35's performance. If Mr. PLAwolf is trying to sell these J-20 duct modifications as some sort of highly evolved hybrid of the DSI, he's most welcome to- but his assertions would be wrong. After all the whole idea of the DSI is a simple, elegant high pressure shock solution devoid of mechanisms and gizmos.

The passive porous elements (above) employed on the JF-17 are almost certainly due to address the flow separation imparted from the forward fuselage, remember the DSI was retrofitted. One would need very accurate dimensional data on the J-20 before one can confirm the root cause of it's DSI problems, but I would suggest they are for similar reasons- namely in the absence of a 'conventional' splitter plate and BL cavity, the design and dimensions of the fuselage forebody are not conducive to a pressure gradient that efficiently deals with flow separation, not only trans & supersonic, but @ various AoA.

To admit all this is way off my technical understandings :-[ ... but maybe someone else understands what he tells...

Deino

 

[VH]

Careful, I said that there was a rumour that the J-20 didn't meet RCS targets. That bit was NOT reported in the media, but came up in the online rumour mill where we get most of our information from, but which requires A LOT of parsing and fact checking. The PLA general's comments to the media was only that the J-20's design may undergo further revisions. There's a case to be made that you can two and two together, but it's far from certain that those two things are related. Furthermore, one cannot extrapolate too much from the J-20 undergoing further revisions. After all, it is still in development, and revisions are only natural. That the design undergoes revisions does not necessarily have any bearings on how quickly or slowly they are able to develop the design, or how close or far they are from achieving their target performance.

And yes the US is also developing their 6th generation platform, but keep in mind that so is China. China is VERY serious about catching up to the US, and that intention, with the resources backing it, cannot be underestimated. For example, they're pursuing parallel R&D of their 10 and 15 T:W ratio engines. Right after they completed the core for the 10 T:W ratio engine, they began to mature and realize their research so that they could build a core for the 15 T:W ratio engine (which is, supposedly, supposed to begin testing in 2016). Things are moving fast, and while being conservative is always good, being too conservative might be under selling what China's capable of.

Your source is not the only source claiming that China is having difficulty meeting RCS goals for the J-20. What revisions they undertake are still a matter for debate and will only show up when these revisions are finally revealed.


Secondly, although China maybe serious about catching the United States in aircraft design especially stealth aircraft it should be understood that the US is just as serious about not being overtaken by China or anyone else. While China maybe developing a 6th generation aircraft it is trying to hit a moving target. And the United States is determined to keep the lead.


For what it is worth my humble advice to China would be to field a fully developed 5th generation fighter that includes engines of indigenous design and the associated systems before talking about 6th generation aircraft.


Finally modern air combat is today a heady mixture of aircraft design, materials, air crew quality and tactics. It is a system. I have not seen any Chinese breakthroughs in any of those areas that would allow China to claim that they are surging into the lead.


But if you have better information that supports China achieving breakthroughs in those areas please share it with us all.


I stand ready to learn.

 

[VH]

.... Again a marked improvement in a very short period of time. I also don't see how you can compare the J-20 to a xerox of anything currently manufactured by the west. The J-31 obviously bears some resemblance and owes something to LockMart products.

Maybe you missed this when it was discussed before but the first third of the J-20 bears a marked resemblance to the F22. Check out the view of the F-22 and J-20 from headon


More than distant relatives I would say. How about you?

 

[sferrin]

If I were Uncle Sam I'd be crawling all over the F-22's canopy manufacturer with a microscope and cattle prod.

 

[_Del_]

Maybe you missed this when it was discussed before but the first third of the J-20 bears a marked resemblance to the F22.

Aside from the canopy they are not that similar at all. The forward fuselage, like that of the J31, is more similar to the F-35 if anything. It's hardly a xerox and certainly not one of the F-22.

 

[latenlazy]

Your source is not the only source claiming that China is having difficulty meeting RCS goals for the J-20. What revisions they undertake are still a matter for debate and will only show up when these revisions are finally revealed.

I'm curious what your other sources are? But anyways, I agree. There will be more revisions. Still I anticipate that these further revisions are already built into expect IOC date. The PLA general's comments do not in any way imply the J-20 is behind of schedule, and was more than likely directed at the stirrings in the public that the J-20 was ahead of schedule.

Secondly, although China maybe serious about catching the United States in aircraft design especially stealth aircraft it should be understood that the US is just as serious about not being overtaken by China or anyone else. While China maybe developing a 6th generation aircraft it is trying to hit a moving target. And the United States is determined to keep the lead.

Really? I feel like we dropped the ball on the F-35 and tied our hands with it a bit. I also think that our budgetary outlook is going to put pressure on our military, and we end up not being able to iterate quickly enough. I think there's no doubt that the target is always moving, but that's why we don't look at place but pace, and China's going at a terribly fast clip and seeming to do pretty good all the while. It's not about whether the target is moving, but who is moving faster.

For what it is worth my humble advice to China would be to field a fully developed 5th generation fighter that includes engines of indigenous design and the associated systems before talking about 6th generation aircraft.

Well, I don't think they plan on building a 6th generation prototype for a while, but that doesn't mean they aren't doing the R&D for it and looking at designs already. My estimate is that, if the 2016 date for the 15 T:W ratio engine is right, that engine is probably going to be ready by about 2030, which may also be when they settle on a design and start building a prototype. It sounds optimistic, but using the J-20's development as a reference timeline things seem to square rather well. Even if the US starts their 6th generation program in 2020, that's a significant gap that China has managed to close.

Finally modern air combat is today a heady mixture of aircraft design, materials, air crew quality and tactics. It is a system. I have not seen any Chinese breakthroughs in any of those areas that would allow China to claim that they are surging into the lead.

I agree with you, but I suspect that given what we're seeing with the PLAAF's procurement practices and other developments that's clearly the direction they're headed. I wouldn't say that they're surging ahead, but I do think they're beginning to reach parity.

If you haven't seen breakthroughs in technology you might not have been paying attention. China's fielding a lot of different UAV designs that clearly have specialized purposes, and they seem to have caught up (or begun to at least) in the radar game (KJ-2000, J-16 and J-10B's AESAs, the Type 052D's sensor suite). We're also seeing some interesting technologies being put onto the J-20. It's been documented that China has gotten pretty good at electric engineering.

They've changed how they train their pilots too and the number of hours each pilot gets in a plane. If I'm remembering correctly they've slowly downsized their pilot count so that the pilots they have can get more hours. Since their J-10 and J-11 fleets have gotten large enough they've been conducting war games and aggressor exercises (look up the Red Sword/Blue Sword competition). I wouldn't say they're there yet but they're clearly headed in the right direction.

One thing we should not overlook is how far looking the PLA really is. These guys aren't just groping around in the dark or imagining national revival with little understanding of what they're doing. They're deadly serious and have done a lot of studying and thinking. We even helped them along with understanding contemporary military combat, operations, training, doctrine, etc in the 1980s when relations were still good, and they didn't just stand still afterwards.

I agree with the overall point that the PLA remains untested, but I think some depend on it too much and stretch its implications too far. It could well be that by the time there is a conflict (god forbid) the nature of combat will have evolved enough that even those with more experience don't hold a unique advantage.