Chengdu J-20 pictures, analysis and speculation Part I

[hantang]

J20 is in the air with J10 chasing ...

 

[Deino]

J20 is in the air with J10 chasing ...

Congrats to CAC... can't wait to see pictures of it.

Deino

 

[Deino]

;D

EDIT: first picture deleted ... was a psed F-35B

 

[Deino]

;D

 

[PAK FA]

;D

it looks nice and powerful but its planforming is not as thourough as the YF-23, YF-22 and even F-22, F-35 and T-50.

Its canards and wing leading edges are aligned and the same is for the trailing edges, but the LERX leading edge is not alingned with the wing leading edge, niether with the wing and canards cropped tips; and the leading edge of the wing and trailing of the canards are not set in the ideal LO reflecting angle, niether are aligned.
Add to that the different angle of inclination of the V tail with the canard dihedral and that makes for a higher radar deflection than on an F-22, extensive use of RAM most be used to offset such mismatchs with stealth.

 

[rousseau]

one more good angle but worse definition

 

[saintkatanalegacy]

wow!!! it really resembles my drawing B)

 

[Deino]

Here are more ... besides that, the very first picture I posted is once again a PSED F-35B ... but the others are real !

 

[F-14D]

BBC today;

"China's defence minister has sought to play down the country's military build-up, after talks with US counterpart Robert Gates in Beijing."

J20 is in the air with J10 chasing ...

Isn't political theory grand?

 

[dingyibvs]

Its canards and wing leading edges are aligned and the same is for the trailing edges, but the LERX leading edge is not alingned with the wing leading edge, niether with the wing and canards cropped tips; and the leading edge of the wing and trailing of the canards are not set in the ideal LO reflecting angle, niether are aligned.
Add to that the different angle of inclination of the V tail with the canard dihedral and that makes for a higher radar deflection than on an F-22, extensive use of RAM most be used to offset such mismatchs with stealth.

You mentioned a bunch of aircrafts, but why only compare it to the F-22? The LERX seems to be aligned just fine to me. So the trailing edge of the canards and the leading edge of the wings are not aligned...but neither are the T-50 or the F-35's. And what's the ideal LO reflecting angle? Please do tell. At least it doesn't have a giant radar mirror of an underside like the T-50, that thing has zero stealth unless it's meeting the radar head on.

 

[overscan (PaulMM)]

I agree, please lay off the assumptions about its radar cross section unless you are a qualified RCS Engineer...

 

[saintkatanalegacy]

15*,30,45,60,75*±2.5° lobe tolerance

*low frequency

 

[dingyibvs]

15*,30,45,60,75*±2.5° lobe tolerance

*low frequency

Are those optimal LO angles? If so then thanks! BTW, why are they the optimal angles, if you could explain it in more layman's terms please?

In any case, I think it's foolish to think that engineers at CAC or Sukhoi for that matter doesn't understand the concept of planform alignment. Any non stealthy aspect that we can see on the T-50 and the J-20 must be a compromise which they know the risk of or something that they intend to eliminate when final production components(e.g. the engines) are ready. Design flaws will most likely be subtle ones that only careful, thorough, and professional analysis can detect.

 

[dingyibvs]

Video, take off is at about 3:30 mark:

http://www.youtube.com/watch?v=NfPbf3Ob_1M&feature=player_embedded

 

[Deino]

This one is better ...

http://www.56.com/u45/v_NTc3NTI4NTA.html#sm_st=0

 

[saintkatanalegacy]

15*,30,45,60,75*±2.5° lobe tolerance

*low frequency

Are those optimal LO angles? If so then thanks! BTW, why are they the optimal angles, if you could explain it in more layman's terms please?

In any case, I think it's foolish to think that engineers at CAC or Sukhoi for that matter doesn't understand the concept of planform alignment. Any non stealthy aspect that we can see on the T-50 and the J-20 must be a compromise which they know the risk of or something that they intend to eliminate when final production components(e.g. the engines) are ready. Design flaws will most likely be subtle ones that only careful, thorough, and professional analysis can detect.

both companies understand planform alignment

just not worth pursuing to the fullest extent at this time...

45 is said to be optimal for area size and "uniformity"... pretty much the reason why the YF-23 is a very clean aircraft

also, nacelles on the T-50 aren't necessarily a bad thing for stealth since they aren't vertically parallel and are subject to creeping waves...

apologize if it's a bit OT

 

[Deino]

The next row of pictures is appearing ... getting a bit more complete !

 

[saintkatanalegacy]

my prediction on the lerx is somewhat right after all. it's well blended with the fuselage instead of a wing

 

[PAK FA]

.
. And what's the ideal LO reflecting angle?

That number is close to 30 degrees, if you watch this video, it says around 30 degrees,

http://video.google.com/videoplay?docid=5291484096194699595#

watch this video, this has the interview with Petr Yakovlevich Ufimtsev, the father of stealth, check minute 13.
Do you understand what means planform alignment? it mean edges will have the same orientation and are going to be parallel, example leading edges, on the F-22 its wings and tailplanes have their leading edges aligned, so the wing has the same sweep angle of the tailplane leading edge
If you watch the whole video Petr Yakovlevich Ufimtsev says non static radars can detect stealth aircraft and at the end the conclusion is stealth aircraft are detectable.
A stealth aircraft just sends away the radar reflection away from the original source.
On the F-117, it has a faceting orienting the radar reflection at more directions than let us says the F-22, however this approach makes the F-117 aerodynamically uneffecient due to high drag, flow separation and non laminar flow.
The ideal wing leading edge for stealth is one serrated and jagged like the main landing gear doors of stealth aircratf, however this is aerodyynamically unefficient, so what most modern aircraft do is sweep the leading edges of the wings in a way they get close to 30 degrees or 60 degrees.

Why do you align leading edges? because you want to give the same direction of reflection to the reflections of both wing and tailplane and inlet, like you can see on the F-22, this allows designers for more freedom when they design a wing.
On the Y/F-23, the designers swept both trailing edge and leading edge at the same angle, giving a wing with a triangular shape, by using a LERX the Y/F-22 has a wing that has different sweep at the trailing edge and leading edges, however all corners where edges meet have the same reflection angle.
On the F-22 and PAK FA they follow that pattern but to make it more aerodynamically speaking efficient they racked the wing tips with the same reflecting angle used all over the aircraft as the F-15 racked wing tip to reduce buffeting.
The J-20 sacrified the LERX alignment for the sake of aerodynamics, the leading edges of the canard and wing are swept at the same angle but not the LERX and the canard has dihedral.
The dihededral of the canards also does not follow the same angle used on the V tail and engine nacelle, so in this aspect i can tell you the J-20 is not so stealthy, but even the F-22 and T-50 raked the wingtips without planform alignment however these three designs do it with the correct angle to reduce radar deflections

 

[dingyibvs]

I know full well what planform alignment is what it's for. Now, please show me how the J-20 isn't planform aligned. The canards, wings, and LERX's all look well aligned to me. Hint: don't just focus on one side of the plane, try comparing the left canard with the right wing for example.

And 30 degrees? Can you show me which wing angle on the F-22 is at 30 degrees? Looks like a bunch of 45 degree angles to me.

 

[flateric]

The next row of pictures is appearing ... getting a bit more complete !

note that birdy takes-off with parachute container opened...door failure precaution measure?

 

[PAK FA]

I know full well what planform alignment is what it's for. Now, please show me how the J-20 isn't planform aligned. The canards, wings, and LERX's all look well aligned to me. Hint: don't just focus on one side of the plane, try comparing the left canard with the right wing for example.

And 30 degrees? Can you show me which wing angle on the F-22 is at 30 degrees? Looks like a bunch of 45 degree angles to me.

No you are not understanding well what i am saying, planform alignment is done to give the same direction of reflection, the leading edges of the wing and tailplane on the F-22 are parallel, so both leading edges send the radar reflection at the same direction, however wherever to corners are made, you will have the same LO reflecting angle.
Any straight edge is not stealthy, that is the reason weapons bays doors on the F-22 are serrated.
The Canard of the J-20 has the leading edge aligned to the wing leading edge right? the trailing edge aligned to the wing trailing edge right? but the LERX has not the same angle, the trailing edge of the canard and the leadinge edge of the LERX form a stealthy angle true where they meet or vertex, but the LERX is not aligned with the leading edges of the canard and wing, that is the reason most aircraft made with stealthy canards have triangular canards to create simplier and more efficient planform alignement

 

[Abraham Gubler]

Petr Yakovlevich Ufimtsev, the father of stealth, check minute 13.

There is NO way he deserves that title. He is an important contributer to modern stealth technology but is just the guy who worked out the mathematics of wave diffraction. Signature reduction had been underway for decades before his diffraction stuff was published. And there were a few more decades before Ufimtsev even knew that his work had anything to do with reducing radar cross sections. Hardly a father or even a sperm donor.

 

[flateric]

www.top81.cn via =GT

 

[dingyibvs]

I know full well what planform alignment is what it's for. Now, please show me how the J-20 isn't planform aligned. The canards, wings, and LERX's all look well aligned to me. Hint: don't just focus on one side of the plane, try comparing the left canard with the right wing for example.

And 30 degrees? Can you show me which wing angle on the F-22 is at 30 degrees? Looks like a bunch of 45 degree angles to me.

No you are not understanding well what i am saying, planform alignment is done to give trhe same direction of reflection, the leading edges of the wing and tailplane on the F-22 are parallel, so both leading edges send the radar reflection at the same direction, however wherever to corners are made, you will have the same LO reflecting angle.
Any straight edge is not stealthy, that is the reason weapons bays doors on the F-22 are serrated.
The Canard of the J-20 has the leading edge aligned to the wing leading edge right? the trailing edge aligned to the wing trailing edge right? but the LERX has not the same angle, the trailing edge of the canard and the leadinge edge of the LERX form a stealthy angle true where they meet or vertex, but the LERX is not aligned with the leading edges of the canard and wing, that is the reason most aircraft made with stealthy canards have triangular canards to create simplier and more efficient planform alignement

You do realize that the LERX has only one edge on the J-20, right? You also realize that the one edge is swept backward slightly just like the F-22's LERX's lateral edge, right? It seems quite possible to me that the LERX's are aligned with the lateral edges of the canards and/or wings. In any case, it doesn't look any worse than the F-22's LERX's lateral edges.

EDIT: Just saw the new pics, you're right that the LERX's are not aligned, kinda like the F-22. Though it seems that unlike the F-22, the LERX's are actually curved. How that affects stealth is beyond my understanding.

 

[JFC Fuller]

Has anyone seen a weapons bay yet? ???

 

[flateric]

well, some thin lines are there...

 

[fightingirish]

If you brighten up or change the colour on some pictures, do you see any more details like weapons bay and access panels?
Unfortunately I can't do it here at work.

 

[gtg947h]

Anyone else find it odd that the rudder surfaces almost always appear deflected outwards?

 

[Sundog]

Anyone else find it odd that the rudder surfaces almost always appear deflected outwards?

No, it's obviously part of the airbrake system, in much the same sense the U.S. does the same with the rudders and wing trailing edges on their modern designs.

 

[Stargazer]

Can someone explain to me why a Chinese prototype sports Russian red stars? Not being a specialist in Asian aviation at all, I find it a bit hard to understand...

 

[rousseau]

I am later again as usual

 

[rousseau]

Can someone explain to me why a Chinese prototype sports Russian red stars? Not being a specialist in Asian aviation at all, I find it a bit hard to understand...

So their communist party can doing capitalism behind red flag

 

[flateric]

Can someone explain to me why a Chinese prototype sports Russian red stars? Not being a specialist in Asian aviation at all, I find it a bit hard to understand...

http://en.wikipedia.org/wiki/Red_star
Symbol of Socialism and Communism

The five-pointed red star, a pentagram without the inner pentagon, is a symbol of socialism as well as communism. It is sometimes understood to represent the five fingers of the worker's hand, as well as the five continents. It was one of the emblems, symbols, and signals representing the Soviet Union under the rule of the Communist Party, along with the hammer and sickle. In the Soviet heraldry the red star symbolized the Red Army and the military service as opposed to the hammer and sickle which symbolized the peaceful labour.
As the red star spread to communism in the East, it was adapted: while some states kept the star as it was, some used a yellow star, particularly on a red field, with the same symbolism. The Far Eastern Republic used a yellow star on its military uniforms, and the flag of the People's Republic of China has five yellow stars on a red field. In Brazil, however, the red star remained as it was.

http://en.wikipedia.org/wiki/People's_Liberation_Army_Air_Force
The markings of the PLAAF are a red star in front of a red band, it is very similar to the insignia of the Russian Air Force. The Red star contains the Chinese characters for eight and one, representing August 1, 1927, the date of the formation of the PLA. PLAAF aircraft carry these markings on the fins as well.

 

[InvisibleDefender]

new photos from centurychina

 

[Matej]

Has anyone seen a weapons bay yet? ???

Till the new images will come, this is the estimation.

 

[Stargazer]

Can someone explain to me why a Chinese prototype sports Russian red stars? Not being a specialist in Asian aviation at all, I find it a bit hard to understand...

http://en.wikipedia.org/wiki/Red_star
Symbol of Socialism and Communism

The five-pointed red star, a pentagram without the inner pentagon, is a symbol of socialism as well as communism. It is sometimes understood to represent the five fingers of the worker's hand, as well as the five continents. It was one of the emblems, symbols, and signals representing the Soviet Union under the rule of the Communist Party, along with the hammer and sickle. In the Soviet heraldry the red star symbolized the Red Army and the military service as opposed to the hammer and sickle which symbolized the peaceful labour.
As the red star spread to communism in the East, it was adapted: while some states kept the star as it was, some used a yellow star, particularly on a red field, with the same symbolism. The Far Eastern Republic used a yellow star on its military uniforms, and the flag of the People's Republic of China has five yellow stars on a red field. In Brazil, however, the red star remained as it was.

http://en.wikipedia.org/wiki/People's_Liberation_Army_Air_Force
The markings of the PLAAF are a red star in front of a red band, it is very similar to the insignia of the Russian Air Force. The Red star contains the Chinese characters for eight and one, representing August 1, 1927, the date of the formation of the PLA. PLAAF aircraft carry these markings on the fins as well.

Thank you very much flateric for taking the time to explain this in detail. You see, my question stemmed from the first few pictures. These didn't show the top or bottom (with the red band on each side of the star) but only the side, and from that view, all I could see was the sole red star on the fins... and to me this looked exactly the same as a Soviet/Russian aircraft. Now of course with all the other pictures it's easier to see: the whole star+band on the wings, and only the star on the tail fins... Thanks again!

 

[JFC Fuller]

Matej,

Thank you for posting the picture, there does appear to be some light lines there.

 

[Matej]

Yes, between the center and outer line. They may be related to the opening mechanism, but I think that the much interesting in this case is the outer shape of the bomb bay doors.

 

[Mike Pryce]

Very good pics. Thanks to all.

A very interesting layout. The widely spaced 'tandem wing' of canard and mainplane does seem to rely on the canard for a lot of lift at take-off and landing, unlike, say a Typhoon, where the main wing would lift the nose even with the canard removed. I reckon this is not hugely unstable then, at least in test flight trim. And with the wheels retracting forward that will shift the cg even further forward relative to the centre of lift.

Regarding the 'LERX', they may have a similar function to the strakes on an F-15 (http://history.nasa.gov/SP-468/p338b.jpg), which IIRC help make the area rule curve smoother, rather than have a 'step' in it where the wing joins the fuselage. They seem very strange as aerodynamic surfaces, right behind the canard - up and down washes from the latter would likely burst any vortices from the LERX. But as it appears the big u/c doors retract their top part into the bottom of the LERX, I don't think they are an aerodynamic feature beyond the area rule function. Curious that they are curved though, not aligned edges.

The fuselage looks very big, for lots of fuel and stores presumably. A relatively stable/moderately unstable characteristic, as the widely spaced tandem wing seems to give, will allow a big cg variation for heavy stores. I still reckon this is a strike/interceptor, a big Viggen. But without the off-base abilities - those hanging u/c doors are kept down in flight it turns out, the need to align the zig-zag 'chevrons' of the main doors with those on the aft door over the u/c leg presumably preventing retraction.