Chengdu J-20 5th Generation Aircraft News & Discussions

[houshanghai]

self delete
there is no need

 

[gambit]

sir,ignore these trollers especially a american-vietnamese poor experts and a anti-china racists

Still cannot resist putting that in, can you? Care to explain to the readers what does one's ethnicity has to do with aviation 'stealth'?

 

[Martian2]

sir,ignore these trollers especially a american-vietnamese poor experts and a anti-china racists

Two ways to resolve the problem:

1. Separate the Chinese members who post updated pictures, insights, and articles from the anti-China trolls by creating two distinct threads.

2. Moderators stop the anti-China trolls from posting a ridiculous number of frivolous anti-China comments or irrelevant clutter. Everyone knows Gambit is abusing his privilege as a "professional" to rampantly troll the J-20 thread as he wishes.

Gambit makes 10 posts for every one that I post.

My new post on the J-20 and F-35 comparison, where I contrast the J-20's optimization across "nine radar-frequency bands" and the F-35's optimization across only two radar bands (e.g. X and upper S) and I explain the non-stealthy lumps and bumps on the F-35's underside, has been buried in a landslide of regurgitated Gambit arguments from months ago or his endless discussion about his personal background.

If a solution is not found, either one or two listed above, I will stop posting here soon.

Last time, Amalakas trolled me to death. This time Gambit is doing the same thing. You cannot argue the principle of freedom of speech and let trolls run loose. It's called abuse of member privileges and making sure that my comparison post on the J-20 and F-35 will not be read by guests, who visit the forum once a week.

 

[gambit]

Two ways to resolve the problem:

1. Separate the Chinese members who post updated pictures, insights, and articles from the anti-China trolls by creating two distinct threads.

2. Moderators stop the anti-China trolls from posting a ridiculous number of frivolous anti-China comments.

Gambit makes 10 to 15 posts for every one that I post. My new post on the J-20 and F-35 comparison, where I contrast the J-20's optimization across "nine radar-frequency bands" and the F-35's optimization across only two radar bands (e.g. X and upper S) and I explain the non-stealthy lumps and bumps on the F-35's underside, has been buried in a landslide of regurgitated Gambit posts from months ago or his endless discussion about his personal background.

If a solution is not found, either one or two, I will stop posting here soon.

Challenging the APA's flawed methodology and report is not being anti-China. And if anything, I dare say based upon my postings about the basics of radar detection and 'stealth', my background seems more valid than yours about the subjects.

 

[siegecrossbow]

Still cannot resist putting that in, can you? Care to explain to the readers what does one's ethnicity has to do with aviation 'stealth'?

No more than "Chinese" has to do with physics.

 

[houshanghai]

get back to j20's original point

today. The weather improved in chengdu
J20 replaced the old engine with a new one by the rumor.it made a high-speed taxi testing???

there is only a climb-grass party's pic today and there is nothing in it

 

[siegecrossbow]

Who took this picture. The weather doesn't look too good today. Too foggy.

 

[houshanghai]

Who took this picture. The weather doesn't look too good today. Too foggy.

http://lt.cjdby.net/thread-1183528-1-1.html
dammed recent weather in chengdu!
it influenced j20's trial flight recently

 

[Martian2]

I know Santro is not convinced that "lumps and bumps" are not stealthy. I am posting my response from another forum to explain the issue further.

----------

Fan blockers could reduce RCS by covering up exposed fan blades too. However some damage is done. I am not sure that I agree with Kopp's assertion that the F-35 has a similar RCS to "clean" Fourth gen though.

That's not what Kopp said. He said only from certain angles; especially a ground-radar illuminating the underside of the lumpy F-35. Basically, the lumpy F-35 underside is not that much different from a lumpy F-15 or F-16 underside.

Wouldn't using continuous curvature help reduce RCS with those bumps though?

The more lumps that you have, the less stealthy you become.

If you do a ray trace of a narrow beam impacting on a sphere, like a small beach ball, there would be very few rays bouncing directly back. This is the concept of continuous curvature.

However, if you do a ray trace of a golf ball with many dimples, there would be many more rays bouncing back from those dimples. Technically speaking, the golf dimples are concave surfaces and the F-35 lumps are convex surfaces. However, the effect is the same. This is the best analogy I can think of.

In conclusion, the principle of continuous curvature does not mean that if you make a surface smooth and curvy then you're stealthy. It is important to understand the limitations of a design principle.

 

[gagaga]

he belittling f-35... i dont believe it neither... yankees has made the most powerful turbofan engine F135... are u sayin that u know something that the yankees dont konw... my layman point of view...

the logic behind the talks about J-20 vs F-22, not vs F-35, i think its because F-35 isnt comparable to f-22 in the mind of yankees netizen... it become metal conditioning to the whole world, and to the Chinese poster here... actually, the EODAS on f-35 give it some kind of advantages when it comes to against another stealth fighter eg. f-22...

about lumps on f-35 affect its stealthiness, isnt b-2 bomber a all round stealth aircraft? its rear side is W shaping... does it affect its stealthiness? its like f-117, i think, according to my layman point of view, its all about avoid the microwave that has arrived the airframe go straightly back to the emitter... the lumps seems to me dont affect much...

 

[gambit]

I know Santro is not convinced that "lumps and bumps" are not stealthy. I am posting my response from another forum to explain the issue further.

----------



That's not what Kopp said. He said only from certain angles; especially a ground-radar illuminating the underside of the lumpy F-35. Basically, the lumpy F-35 underside is not that much different from a lumpy F-15 or F-16 underside.



The more lumps that you have, the less stealthy you become.

If that is truly what Kopp said, then he is an idiot. A flat underside is no less reflective than a 'bumpy' one...

The truth is that no aircraft's underside is truly flat and a 'bumpy' one does not dramatically increase reflectivity IF those 'bumps' are shaped in ways that obey the rules of 'stealth', which is the denial of the seeking radar any reflections.

Further...

Against a bi-static configuration, then it is irrelevant how flat or 'bumpy' any aircraft's underside. The receiver in the bi-static triangle, as illustrated above, will always receive far more reflective signals and the transmitter's position.

You do not know what you are talking about.

If you do a ray trace of a narrow beam impacting on a sphere, like a small beach ball, there would be very few rays bouncing directly back. This is the concept of continuous curvature.

No issues here.

However, if you do a ray trace of a golf ball with many dimples, there would be many more rays bouncing back from those dimples. Technically speaking, the golf dimples are concave surfaces and the F-35 lumps are convex surfaces. However, the effect is the same. This is the best analogy I can think of.

The difference here is that the golf ball's dimples are uniformly arrayed and for a different purpose. At best, this is a partially appropriate analogy.

In conclusion, the principle of continuous curvature does not mean that if you make a surface smooth and curvy then you're stealthy. It is important to understand the limitations of a design principle.

And I will say without reservations that YOU do not have that understanding.

 

[gambit]

From Aviation Week in 2009: If you want to claim the "APA has got their models wrong, it probably wouldn't compromise security to explain why." Don't try to hide behind the argument of secrecy. The Chinese and Russians already have their own radar modeling software. "The worst argument against APA, though, is that of secrecy."

The flaw here is that APA does not have the true physical dimensions of the Russian's or the Chinese's aircrafts. So in criticizing APA's methodology, no state secrets need be revealed. If APA is so confident of their Physical Optics ONLY modeling of the J-20, then why do they not perform the same for all the famous 'stealth' aircrafts currently in the public eye? Then throw in a few 'non-stealth' aircrafts for baseline comparisons?

Since Lockheed or another reputable organization has not published a study to challenge the APA analysis in two years, we can only conclude the APA models are accurate.

No, we cannot. At best, we can only give APA credit for being honest enough to admit that their Physical Optics ONLY modeling has shortcomings. If flawed methodology alone is enough to make APA's result suspect, then there is no need for Lockheed to response with their data.

Aviation Week has implicitly acknowledged the F-35's shortcoming by suggesting the F-35 is "stealthy enough to survive." However, that was two years ago, before the debut of the J-20 Mighty Dragon in 2011.

In no way does that make the J-20 superior to the F-35. There is no logical relationship.

JSF News 2 - Stealth Questions Raised

JSF News 2 - Stealth Questions Raised
Posted by Bill Sweetman at 1/7/2009 7:30 AM CST

The Air Power Australia team have produced an unprecedented report which asserts that the F-35 Joint Strike Fighter is much less stealthy than the F-22[/B] - and in fact is comparable in radar cross-section (RCS), under some circumstances, to a conventional fighter in clean condition. APA's updated surveys of modern Russian radars - which are most likely to form the basis of the threat systems that it would encounter from the late 2010s onwards - have set the scene for this analysis.

And which is that 'conventional fighter'? Could it be the F-16? A clean F-16 is very difficult to find by other 'conventional' fighters of the same era and technology, including Russian radars, airborne or ground stations. However, assuming we grant this argument that wide a latitude, we must understand that a clean F-35's lethality is much greater than a clean F-16. A visually clean F-35 can be armed or unarmed. A clean F-16 is unarmed. This is a very weak criticism.

The report is unprecedented because it's the first "civilian" use of radar scattering models to take a first-order look at an aircraft's RCS. It was the development of computer-based RCS models that opened the way to the development of stealth in the 1970s: the theory of scattering was well known but was too hard to apply to a 3-D shape without those tools.

It also mean that there are much more powerful computing tools to predict, model, then verify complex bodies than civilians could access. Further, civilians do not have access to the aircraft itself and EM anechoic chambers to verify the true physical dimensions of these complex bodies.

The APA analysis will no doubt be countered by the JSF team in several ways. They'll argue that the APA team has an agenda. They will argue that the analysis is too crude to reflect reality; that anything it does show is not operationally relevant; and that the true picture is much more complex and (of course) secret.

The APA team does have an open agenda (as does the JSF team) but that does not mean that their data is bad.

It also does not mean their data should be taken as gospel, especially when they do not have access to the aircraft's true physical dimensions.

The analysis is crude insofar as it doesn't make any detailed estimates of the effects of radar absorbent material (RAM). On the other hand, the doctrine laid down by Stealth pioneer Denys Overholser still stands: the four most important aspects of stealth are shape, shape, shape and materials.

Fine...Then we can dismiss materials. But that does not mean Overholser's admonition has been violated in any way by the F-35. Shaping to influence radar signal behaviors goes beyond specular reflections but edge diffractions and assort surface wave variables. APA's methodology admitted they do not have the aircraft's true physical dimensions and do not process non-specular signals. If the F-35's various 'bumps and humps' do not raise the aircraft above a certain threshold commonly known as 'stealthy' enough, then the F-35 is true to Overholser's admonition.

On the other hand, the APA analysis is a lot more detailed than the cartoon representations in Lockheed Martin briefings. And more realistic than the claims of total invisibility made on JSF's behalf.

Then APA is free to perform the same flawed Physical Optics ONLY methodology on the F-15, F-16, F-117, F-22, F-35, and the B-2 to benefit the public over Lockheed's cartoons. Why have APA not done so but instead zero in only on the J-20?

The APA team also makes the point that the F-35 doesn't look as much like an F-22 (or the X-35) as you might think. Those two aircraft both reflected a refined version of the F-117 shape - they are basically faceted designs, although they incorporate large radius curves and the lines between facets are smoothed. But the F-35 has acquired some very conventional-airplane-shaped lumps and bumps around its underside, not to mention the hideous wart that covers the gun on the F-35A. It's enough to raise questions.

Then perhaps a more legitimate comparison would be between the F-22 and the J-20? This make no sense. APA performed a flawed measurement/analysis ONLY on the J-20 but not on both the F-22 and F-35. Then despite the absence of comparative data, APA declared that while the J-20 is inferior to the F-22 despite having the same flat underside, it is superior to the F-35 based upon the latter's 'bumps and humps'. How can the J-20 be inferior to the F-22 in the first place? Based upon what comparative data? The moving canards? But then if the all-moving canards made the J-20 inferior to the F-35, is it possible that those same canards make the J-20's RCS the same or higher than the F-35 despite the latter's underside 'bumps and humps'?

Of course, it's possible to argue that the F-35 meets its stealth requirements (which may or not be the same for all F-35s), and that it will be stealthy enough to survive - combined with situational awareness and tactics.

Very seldom do aircrafts go anywhere alone. A pack of F-35, even if we grant that they are as detectable as clean F-16s, with their superior avionics and networking capabilities, they will do more than just survive. They can fight and win. What do we know of the J-20's avionics?

But that in turn depends on what the requirements are, and what threats it was designed against. (That's why stealth air vehicles are as diverse as they are, from the DarkStar to the AGM-129, while submarines look pretty much the same.) In the design of the F-22, for example, features such as 2-D nozzles, edges swept at 42 degrees, and high-altitude, high-speed flight were required to address that threat set.

Reasonable enough. Then unless we know what the J-20's threat requirements are, the comparison between the J-20 and the F-35 is an invalid one. The F-35's missions are well known. It is to be a jack-of-all-trades with high standards for all of those trades. What do we know of the J-20? Nothing other than we know there are speculations.

More recently, the Northrop Grumman X-47B and Boeing X-45C designs have clearly been aimed at all-aspect, wideband stealth - although that's particularly important for an unmanned vehicle, which may not be as flexible in its response to a pop-up threat.

The worst argument against APA, though, is that of secrecy. Implemented on an experimental airplane 30 years ago, stealth is no longer covered by Arthur C. Clarke's principle that "any sufficiently advanced technology is indistinguishable from magic." Competitors and potential adversaries around the world have assuredly run F-35 models in simulations, in RCS chambers and on open ranges. So if APA has got their models wrong, it probably wouldn't compromise security to explain why.

In simulations, yes. But in EM anechoic chambers? Not likely. Absent precise physical dimensions, any simulated results are suspect.

 

[Martian2]

The original X-35 was a stealthy design. The current F-35 SDD AA-1 is a "much inferior contoured design, clearly intended to accommodate the larger weapon bays."

This is a familiar story. The X-35 was well-designed to meet the original military specifications (e.g. "bomb truck"). The military changed its mind and Lockheed had to drastically alter its design to accommodate the new military specifications (of an air superiority fighter) to carry a larger weapons load. This compromised the F-35 stealth design.

Assessing Joint Strike Fighter Defence Penetration Capabilities

"Assessing Joint Strike Fighter Defence Penetration Capabilities
Air Power Australia Analysis 2009-01
7th January 2009

by Dr Carlo Kopp, SMAIAA, MIEEE, PEng
© 2008, 2009 Carlo Kopp

The evolution of the JSF design from the X-35 demonstrators to the F-35A/B/C SDD configuration has seen significant changes to the aircraft's shaping, critical to its stealth performance. While the design of the inlets was improved, the lower fuselage design is now inferior to the original X-35 configuration. The latter has important implications for the JSF's ability to survive when penetrating modern Integrated Air Defence Systems (Image via Air Force Link).
...
Joint Strike Fighter Stealth Capabilities

The Joint Strike Fighter is an unusual airframe design, since it departs from many of the well established ground rules in stealth shaping, established in other designs such as the F-117A, B-2A, A-12A, YF-23A and F-22A Raptor. Stealth shaping is widely regarded to account for the first hundredfold reduction in aircraft radar signature, compared to non-stealthy designs of similar size, with application of lossy and absorbent materials used to further reduce the signature where feasible.
...
The first major departure from established shaping conventions is the angular or aspect dependency of the Joint Strike Fighter’s radar signature.

Diagram 3.

Diagram 4.

Study of the shaping of the aircraft and comparison with other designs shows that the Joint Strike Fighter can provide genuinely good stealth performance only in a fairly narrow ~29° sector about the aircraft’s nose, where the shaping of the nose, engine inlets, panel edge serrations, and alignment of the leading and trailing edges of the wings and stabilators results in the absence of major lobes or “spikes” in the radar signature. The ±14.5° angular limit is constrained by the principal reflecting lobe of the leading and trailing edges of the wings and stabilators. The signature degrades rapidly due to the influence of the lower centre fuselage as the angle swings past ±45° off the nose, refer Diagram 4.

An important development was that the SDD aircraft saw the original inlet design discarded and replaced with a scaled down inlet arrangement based on the F-22A design. Concurrently the lower fuselage was redesigned.

In the SDD design, the beam/side aspect radar signature is especially problematic, due to the presence of multiple specular reflecting shapes, specifically due to singly and doubly curved lower fuselage surface feature shaping. The Joint Strike Fighter has a complex lower fuselage shape as well as a wing and fuselage lower join shape, unlike any other aircraft designed with stealth in mind, refer preceding images. The result of this design choice is that the beam/side aspect Radar Cross Section will be closer in magnitude to a conventional fighter flown clean than a “classical” stealth aircraft. This is an inevitable result of clustering no less than nine unique convex specular scattering shapes in the lower hemisphere of the aircraft. Diagram 3 illustrates this.

Given that the dimensions of many of these shapes are of the order of metres, the application of absorbent or lossy coatings or laminates will not be sufficient to drive the critical lower hemisphere beam/side aspect signature down to values which qualify as VLO and thus “stealthy”. Refer Annex C.

The aft sector radar signature is also problematic, as a result of the use of an axisymmetric nozzle design. While the aft fuselage and tailboom shaping qualify as “stealthy” across the upper bands, the nozzle presents as a specular reflector in bands where the wavelength is comparable or exceeds the dimensions of the nozzle segments. This is discussed below.

The second major departure from established stealth conventions is that the Joint Strike Fighter is designed to perform in the X-band, and upper portions of the S-band, with little effort expended in optimizing for the lower L-band, UHF-band and VHF-band. This design strategy is consistent with defeating mobile battlefield short range point defence SAM and AAA systems such as the SA-8 Gecko, SA-9 Gaskin, Chapparel, Crotale, Roland, SA-15 Gauntlet, SA-19 Grison and SA-22 “Greyhound”, where limited radar antenna size forces all acquisition and engagement functions into the X-band and upper S-band. Joint Strike Fighter literature refers to this optimization in terms of “breaking the kill chain”, the intent being to deny the effective use of X-band engagement radars and X/Ku-Band missile seekers, but not acquisition radars in lower bands.

Such SAM systems are the category of “residual” threat which a battlefield interdiction aircraft will encounter once the F-22A force has “sanitized” an area by destroying the long range search/acquisition radars and area defence SAM batteries. With limited range and coverage footprint, but high mobility and autonomous capability, battlefield short range point defence SAM and AAA systems can “pop-up” from hidden locations and ambush interdiction aircraft at medium to low altitudes. Significantly, in a “sanitized” environment such air defence weapons are operating without external support from other sensors or the top cover provided by long range area defence SAMs such as the SA-12/23, SA-20 and SA-21.

The engine nozzle presents a good case study of the band dependency of stealth performance in the Joint Strike Fighter design. In the upper X-band and Ku-band, the individual nozzle segments present as flat panels with a serrated trailing edge. The result will be a circular pattern of narrow reflecting lobes which will produce mostly good effect in these bands. However, in the lower bands this arrangement will rapidly degrade in behaviour to that of a truncated conical shape, which is a strong specular reflector. The resulting external shape related signature will be much the same as a conventional exhaust nozzle on a non-stealthy fighter, with an outer skin contribution and rim contribution. While the interior of the nozzle will be coated with broadband lossy materials and a tailpipe blocker used to obscure the turbine face, the signature of the nozzle exterior below the X-band cannot qualify as “stealthy”. Refer Annex C.

X-35 Dev/Val prototype (above) vs F-35 SDD AA-1 (below). The clean wing fuselage join and flat low curvature lower fuselage of the X-35 had the potential to yield quite good beam/side aspect radar signature, but the revised SDD design discarded this arrangement in favour of a much inferior contoured design, clearly intended to accommodate the larger weapon bays. While the F-35 SDD engine inlet arrangement is superior to the X-35 Dev/Val prototype inlet design, the gains in the forward sector cannot overcome the performance losses incurred in the beam/side aspect sectors (Images via Air Force Link).

Diagram 5: Very Low Observable airframe shaping should be optimised to produce best effect, i.e. lowest radar cross section, from those angles from which the aircraft is most likely to be illuminated by a threat system such as an engagement or acquisition radar in a Surface to Air Missile battery. This diagram shows the cardinal depression angles for an aircraft at the tropopause, accounting for the curvature of the earth and atmospheric refractive effects which 'bend' the ray path between the aircraft and threat radar. The specific angles in this diagram are determined using Russian specifications for missile range, the SBF refractive model for short ranges, and an exponential CRPL refractive model for ranges in excess of 100 nautical miles. It is important to observe that in straight and level flight all surface based threats are firmly in the lower hemisphere, putting a premium on low Radar Cross Section in the angular range between 3.7 and 36.5 , as area defence missile systems will illuminate the aircraft within this angular range. Point defence missiles systems and 'trash fire' such as AAA and MANPADS are generally altitude limited to 10 - 15 kft and are a much less critical threat. A smart IADS operator will not radiate until a potential target is close enough to get a steep elevation angle for a shot, a tactic commonly associated with 'shoot and scoot' operations - the cardinal example being Serbian ZRK Kvadrat / SA-6 operations in 1999 (Author).

The shaping changes to the inlet area and lower fuselage are prominent on these images of F-35A SDD prototype AA-1 (Images via Air Force Link).

Diagram 4 summarises the qualitative comparisons of Joint Strike Fighter shaping aspect and band dependency, with green denoting performance which qualifies as Very Low Observable, yellow as Low Observable, and red as order of magnitude closest to conventional reduced signature aircraft designs. The aircraft performs best in the X-band, and Ku-band, with performance declining through the S-band with increasing wavelength. In the L-band the axisymmetric nozzle design no longer produces useful effect, and the length of the inlet edges sits in resonant mode scattering rather than clean optical scattering, degrading performance. In the VHF band (~2 metres) Joint Strike Fighter airframe shaping has become largely ineffective.

The aircraft will have a credible ability to defeat S-band search/acquisition radars, X-band engagement radars and X/Ku/K/Ka-band missile seekers only in the narrow ±14.5° angular sector under the nose. As the angle relative to the threat radars increases, the unfortunate lower fuselage shaping features will produce an increasingly strong effect with a cluster of “flare spot” peaks around 90° where the longitudinal panel and door edge joins produce effect.

In the narrow ±14.5° angular sector under the tail, the design will produce best effect against X/Ku/K/Ka-band missile seekers, but less useful effect against X-band engagement radars due to their higher power-aperture performance. At S-band the nozzle exterior signature will become increasingly prominent, leading to loss of effect in the vicinity of the L-band.

It is clear that these design choices were intentional and no accident. By confining proper stealth shaping technique only to the forward fuselage and inlet geometry, the designers avoided incurring the development, and to a lesser extent, the associated manufacturing costs of a fully stealthy design, with the YF-23A and F-22A presenting good comparisons.

This is an acceptable optimization if the intent is only to defeat an isolated individual low power aperture pop-up short/medium range mobile battlefield air defence system in the category of the SA-6 Gainful, SA-8 Gecko, SA-9 Gaskin, Chapparel, Crotale, Roland, SA-11 Gadfly, SA-15 Gauntlet, SA-19 Grison or SA-22 “Greyhound”. It is a completely unsuitable optimization for a wide range of other threat types which are in service, and the associated characteristic engagement geometries. It is also a problematic optimisation where short/medium range battlefield air defence systems are deployed in a coordinated manner.

The most generous description of the stealth design used in the Joint Strike Fighter is that it is 25% VLO, in the nose sector, 25% LO in the tail sector, and 50% “reduced observable” in the beam sectors, with a strong threat operating frequency and angular aspect dependency in stealth performance. It is clearly not a stealth design in the same sense as the F-117A Nighthawk, B-2A Spirit, YF-23A and F-22A Raptor, and to label it a “VLO design” is at best a “quarter-truth”, quite indifferent to the physical realities of the design and the threat systems it will need to defeat in future conflicts."

 

[lawxx]

According to reliable sources: J-20 of which a prototype has changed WS-15 engine

 

[laowai]

false flag and you arenot a real chinese

Or how about you get banned for being a false flagging suicide troll.

so now i'm not chinese for not agreeing with martian's nonsense, just shows how far you guys are being deluded in def.pk

my father and mother is chinese, i'm proud to be chinese, and i don't have anything to prove, check my flag if you wish, and you will get a hint

i tell you a thing, there are two kinds of forums where you won't raise a voice and be a lurker

one is where you are not up to the caliber of people in it that you don't dare to raise your voice
the other one is where posting is waste of time, and you read it just for the lulz

nevertheless i still respect defence.pk

think about it, are gambit's posts or martian's posts the ones that educating you? use your brain

gambit have been toying with the lot of you, when people earned their professional tag in a forum, it's not just for show

i'm posting this for you people's sake