Chengdu J-20 pictures, analysis and speculation Part I

[Sundog]

What are those yellow dots on the wings?

Most likely strain gauges.

 

[Deino]

Here's the video showing the open bays ....

http://v.youku.com/v_show/id_XMjk5ODk2MzQw.html

 

[Deino]

 

[TAKHISS]

J-20's cockpit

 

[TAKHISS]

white silk stocking？

 

[TAKHISS]

models from Shenyang Aircraft Corporation

 

[overscan (PaulMM)]

This is again from AVIC-CUP UAV contest so almost all of them bear the AVIC logo. The fuzzy Chinese text and the watermark tell me this is the product of students from Nanjing University of Aeronautics and Astronautics.

http://www.china-defense.com/smf/index.php?topic=5390.100

 

[Deino]

: :-*

 

[Deino]

Once again there's a sometimes "very emotional" discussion going at several forums regarding the actual J-20's length ! While some still want to keep their opinion of a "super-heavy long-range striker" ;D ... others are already sure that the J-20 is by far not that long ... it's only the impression since it it so flat and slender !

Here's an interesting photo-composition made by "J-20 Hotdog" at the Key-Forum that might help ... He transposed the J-10B image over the J-20. Although both were from two different pics (see also below) the background matches each other perfectly! The "only" difference is the airplane, the towing vehicle and the hangar doors since they were opened while all four planes were prepared for the flight.

However the only problem is now that we don't know the exact length of the J-10B. ???

Deino

 

[totoro]

even if we dont know the length of j10b, which we kinda do, we should know the lengths of either: j7e, jf17 or the pl8 under the j10b's wing or pl5e under the jf17's wing. Using pl8, j20 is between 20,38 and 20,04 meters long, depending on whether we use 2,95 or 3 meters for pl8. using pl5e's dimensions we get 20,27 meters for j20.

 

[LowObservable]

All I can say is that a few guys are getting very upset over length measurements. Must be some projection going on.

 

[overscan (PaulMM)]

J-10A is 16.43m in length. J-10B shouldn't be too different and the difference can be computed from overlaying a J-10A and J-10B.

If you calculate J-20 length from J-7 length, J-10B length, JF-17 length, and compare/average, you should get a valid figure out the end. I will do it tonight.

 

[Deino]

J-10A is 16.43m in length. J-10B shouldn't be too different and the difference can be computed from overlaying a J-10A and J-10B.

If you calculate J-20 length from J-7 length, J-10B length, JF-17 length, and compare/average, you should get a valid figure out the end. I will do it tonight.

Yeppp ... but currently the biggest issue sesm to be unsure data for both the FC-1 and J-7E and if the given length is with or without the pitot !

As such this is one calculation from "latenlazy":

After realizing that my own initial estimates were off with the J-7 because I didn't use the vertical tail tip for length (the vertical tail actually extends out more than the tail planes), I decided to redo my own estimates. Furthermore, I decided to use several different measurements to see if we can get a cluster of sizes.

JF-17 assuming a length of 14.97 without pitot we get a length of 21.6 meters
-Note that any estimates without pitot of the JF-17 will be subject to error because it's difficult to figure out where the pitot begins.

JF-17 assuming a length of 14.00 with pitot we get a length of 19.25 meters

JF-17 assuming a length of 14.00 without pitot we get a length of 20.2 meters

JF-17 assuming a length of 14.97 with pitot we get a length of 20.58 meters

J-7 assuming a length of 14.885 with pitot we get a length of 20.466 meters.
-The actual pixel length of the J-7 and JF-17 were about the same, which shouldn't be surprising since a difference of less than .1 meters could easily be missed by a lower resolution picture, and a difference of selecting one or two pixels would account for such a difference. That said, every one of these estimates will have to account for errors in pixel selection.

J-7 assuming a length of 13.95 without pitot, we get a length of 20.67 meters

J-7 assuming a length of 13.46 without pitot we get a length of 19.9 meters (is this screaming outlier to you? it is to me, the 13.95 figure should be the right one).

I think doing it this way gave us a nice set of converging figures that basically tells us we should expect the J-20's length to be roughly 20.5 meters, which is what other estimates using other methods have indicated (except for the one where we tried to match the J-20's nacelles with the Su-27s, but even that yielded a figure below 21 meters, and it was somewhat difficult trying to match the nacelles of the two). I don't trust the JF-17 without pitot measurements for one very good reason. It's difficult figuring out where the pitot starts on the JF-17, so those measurments are bound to be inaccurate.

Another possibility might be the data for the PL-8 on the J-10B or the PL-5E on the FC-1 ... but both are quite small so the error will be quite significant.

CHeers, Deino

 

[overscan (PaulMM)]

Okie dokie.


So, the length of the MiG-21F-3 fuselage from intake lip to engine exhaust is 12.177m from Mikoyan documents.
The length from centrecone tip to tip of tail is 13.46m.


Assumption: J-7E appears to have an unchanged fuselage length over MiG-21F-3.


Using this as my base value I get the following:


J-7E - 13.79m (excl pitot), 14.95m (incl. pitot)


This seems reasonable - thats a little bit longer than the MiG-21F-3 which might be due to the apparently larger nosecone.


Moving to JF-17


JF-17 - 14.1m (excl pitot), 14.86m (incl. pitot)


This again is reasonable - PAF is quoting 49ft (14.94m) but this is obviously a rounded off figure.


Now J-10B


J-10B - 16.95m


Again, seems reasonable - J-10A is 16.43m, and J-10B nosecone looks longer.


J-20 - 20.53m (excluding pitot)


Therefore I agree with J-20 "Hotdog". It's 20.5m in length.

 

[Deino]

;D I would say You did it !!! THANKs a lot. ;D

Deino

 

[overscan (PaulMM)]

If the J-20 is 23m long, then J-10B must be about 19m long. Not likely. So thats definitely the end of that argument

 

[Abraham Gubler]

Yeppp ... but currently the biggest issue sesm to be unsure data for both the FC-1 and J-7E and if the given length is with or without the pitot !

Reminds me of the great FB-111 ‘extended fuselage’ misunderstanding. Because USAF Strategic Air Command measured the length of their F-111 to the end of the pitot and USAF Tactical Air Command measured it on their F-111s to the end of the radome. They all had the same airframe but for some reason various journalists and so on interpreted the difference in quoted aircraft length to mean that the FB-111 had an extended fuselage or nose!

 

[Deino]

:-*
... finally back with some nice photos !!!

 

[AAAdrone]

I still don't see how that thing could be stealthy with canards....

 

[Kryptid]

Some speculation on my part...

If they decide to go with thrust vectoring, might that help alleviate the stealth disadvantages of the canards? In cruise, for example, might we imagine that it could use TVC for trim and freeze the canards in place so as to minimize radar reflections?

Actually, that makes me wonder if that strategy could also help keep the center of lift forward at supersonic speeds as well; if you were to hold the canards in place, they might act as "lifting" canards instead of "control" canards. According to Dr. Raymer's book, the center of lift of an aircraft with lifting canards is a weighted average between the center of lift of the wings and the canards. That may help the tail moment arm remain large.

 

[RyanC]

It doesn't have to be stealthy to the extent that the F-22 is in order to present a vast qualitative advance. Something on the level of F-117 stealthiness is still a pretty big improvement, while keeping costs reasonable.

 

[AAAdrone]

Some speculation on my part...

If they decide to go with thrust vectoring, might that help alleviate the stealth disadvantages of the canards? In cruise, for example, might we imagine that it could use TVC for trim and freeze the canards in place so as to minimize radar reflections?

Actually, that makes me wonder if that strategy could also help keep the center of lift forward at supersonic speeds as well; if you were to hold the canards in place, they might act as "lifting" canards instead of "control" canards. According to Dr. Raymer's book, the center of lift of an aircraft with lifting canards is a weighted average between the center of lift of the wings and the canards. That may help the tail moment arm remain large.

That could work. Applying the appropriate trim should reduce the radar returns from the canards to a minimum but what I don't know is if the Chinese are going this route or are they, like Ryan said, content with something as stealthy as F-117.

 

[Abraham Gubler]

If they decide to go with thrust vectoring, might that help alleviate the stealth disadvantages of the canards? In cruise, for example, might we imagine that it could use TVC for trim and freeze the canards in place so as to minimize radar reflections?

That is a given. The problem is what do you then do with all the radar returns bouncing off the seam line between the canard and the fuselage? You can't tape it over with RAM inflight.
But like Ryan says there is tactically significant stealth and then there is stealth. The Super Hornet is not a stealthy plane. But due to its LO design it has 50% of the radar detection range other the frontal arc compared to other fighter's its size. This provides it with a significant tactical advantage in a range of scenarios.

LO like in a B-2, F-22 and F-35 is much better but if you don’t have the technology for those second, third and fourth significant figures of RCS reduction then that doesn’t mean a single significant figure isn’t worth it.

 

[chuck4]

Why does the seam between the F-22's flaps and its horizontal stabilizer create the same stealth problem as the seam between the canards and wing on the J-20?

 

[ubiquitous08]

I'm no expert but the seams are reflected backwards so any scattering is away from frontal or side arc. Additionally the Raptor has significant treatments around the flap area (note the chisel like detailing of the area) and is blanketed by the wing tips in side profile.

 

[overscan (PaulMM)]

Clearly Northrop thought canards could work with a VLO design for Naval ATF. What would they know about Stealth.... ;D

 

[Abraham Gubler]

Clearly Northrop thought canards could work with a VLO design for Naval ATF. What would they know about Stealth.... ;D

A heck of a lot more than Chengdu! B)

 

[AAAdrone]

Well I'll be...I guess I'm wrong about canards being the anti-christ in terms of VLO features. Although they might have had that "auto-trim" feature in mind too to keep the canards at an angle to reduce frontal RCS in cruising flight.

 

[Deino]

A heck of a lot more than Chengdu! B)

But why does that mean a delta catd from NG is stealthy and one from CAC can't be !???

 

[Grey Havoc]

A heck of a lot more than Chengdu! B)

But why does that mean a delta catd from NG is stealthy and one from CAC can't be !???

I think he meant that since Northrop, who were one of the pioneers in the field of Stealth aircraft, thought that they could successfully use canards in a stealth design, it makes it more likely that CAC were able to successfully integrate the same into their own, 'proper' stealth design.

 

[overscan (PaulMM)]

The NATF above wasn't the only canard configuration from Northrop ATF studies either.

I'm not saying the the canard design on J-20 is certainly VLO optimised, just that a canard design doesn't inherently preclude stealth optimisation.

 

[AAAdrone]

What about the axial symmetric engine exhaust nozzles? I'm pretty sure those aren't very good for masking IR and RF emissions. Will those ever be changed or are the Chinese content with what they have like how we are with the F-35's exhaust nozzle?

 

[Abraham Gubler]

What about the axial symmetric engine exhaust nozzles? I'm pretty sure those aren't very good for masking IR and RF emissions. Will those ever be changed or are the Chinese content with what they have like how we are with the F-35's exhaust nozzle?

An axial nozzle is not inherently unstealthy. The F-35 nozzle is very stealthy. But it requires considerable additional design and feautres. Sticking a bog standard Russian jet engine in your fighter is not going to provide you with that stealth.

 

[LowObservable]

All-aspect stealth on a supersonic, agile fighter is certainly desirable.

That is why the USAF decided that its future fighter would have that combination of characteristics, back in 1985-86.

25 years later, after spending squillions of dollars we have 140 combat-capable aircraft.

Saying that Chinese planners and engineers don't know what they're doing is, at best, more than a little smug.

 

[Abraham Gubler]

All-aspect stealth on a supersonic, agile fighter is certainly desirable.

That is why the USAF decided that its future fighter would have that combination of characteristics, back in 1985-86.

25 years later, after spending squillions of dollars we have 140 combat-capable aircraft.

Ahh you have heard of the JSF project have you? Lamenting the lack of return on investment in stealth on the eve of the mass production program to replace almost all TACAIR with an all aspect VLO fighter is a bit premature or intentionally blinkered.

Saying that Chinese planners and engineers don't know what they're doing is, at best, more than a little smug.

Well apart from no one actually having said that (in the last few pages of this thread at least) it is also a bit rich to in one breath mention 25 years of development and squillions of dollars of investment needed for VLO and then assume (apparently) that the Chinese don’t need this. 25 years ago they were still building MiG-19s and despite purchasing parity differences have not invested anywhere near what the USA has over 60 years on VLO technology.

I’m sure the Chinese engineers know exactly what they are doing and like all good engineers everywhere are working with the actual technology they have at hand rather than what some observers wish they had in order to validate their long standing criticisms of other projects. They have a lot of benchmarks to tick off before they are building a VLO tactical aircraft. Hard chines on the nose and a coat of dark grey paint are not on that list.

 

[latenlazy]

I’m sure the Chinese engineers know exactly what they are doing and like all good engineers everywhere are working with the actual technology they have at hand rather than what some observers wish they had in order to validate their long standing criticisms of other projects. They have a lot of benchmarks to tick off before they are building a VLO tactical aircraft. Hard chines on the nose and a coat of dark grey paint are not on that list.

On the other hand, computing has come a long way since the 70s, and computing was one of the primary advantages that allowed the US to come up with advanced stealth designs. I think the basics of the field in terms of shaping are what they are. The rest is really left to a question of materials.

 

[sferrin]

I’m sure the Chinese engineers know exactly what they are doing and like all good engineers everywhere are working with the actual technology they have at hand rather than what some observers wish they had in order to validate their long standing criticisms of other projects. They have a lot of benchmarks to tick off before they are building a VLO tactical aircraft. Hard chines on the nose and a coat of dark grey paint are not on that list.

On the other hand, computing has come a long way since the 70s, and computing was one of the primary advantages that allowed the US to come up with advanced stealth designs. I think the basics of the field in terms of shaping are what they are. The rest is really left to a question of materials.

GIGO

 

[latenlazy]

GIGO

Hah. Even garbage code can spit out the right results, granted that it doesn't crash first

 

[sferrin]

GIGO

Hah. Even garbage code can spit out the right results, granted that it doesn't crash first

How can incorrect input give you correct output, and how would you know?

 

[latenlazy]

GIGO

Hah. Even garbage code can spit out the right results, granted that it doesn't crash first

How can incorrect input give you correct output, and how would you know?

Because I program, and garbage code often refers to how inefficient and badly implemented the code is as opposed to the accuracy of the actual input and output parameters. For example, windows is a lot of bad coding. It is a poorly thought out GUI design, can be inefficient, and crashes often, but no one's going to dispute that it fudges the actual inputs and outputs.

As a programmer you already know what input and output to expect because everything you do with the computer you can theoretically do by hand. It would just be far more tedious. With more advanced simulation programs, especially simulations that can be tested in the real world, a real world test would be matched with the input and output parameters to verify that the program is doing what it's supposed to and not fudging the results.

This is the most basic aspect of computer science (so basic that this is the first thing you're expected to learn in high school CS), and people in China with PhD degrees in this stuff (way more qualified than I am) wouldn't miss this, even if they suck at programming. The baseline requirement in CS is being able to get the intended result. Garbage code refers to how you got there.

A lot of the best PhDs in China (and not just in CS) are also probably trained in foreign institutions, particularly the US. The guys working on these planes are engineers, not cavemen.