J-20 5th Gen Fighter Thread V

[weig2000]

To date, there are only two formal/official documents known to the public related to China's fifth-generation stealth fighter. One is obviously Song Wencong's paper, which laid the design foundation of J-20. Another recently disclosed one is a high-level requirements doc for China's fifth-generation aircraft, authored by Gu Yongfen (with a team) in 2003, former Chief Designer of J-8 and a senior academician of Engineering Academy of China. Here is the first and last page of the document.



In the last page, the document stated that the PLAAF requires the fourth/fifth-generation stealth fighter be competitive with F-22 and clearly superior to F-35 (I understand people may have different opinions regarding whether J-20 can achieve the requirements, but that's not the point here). There are lots of other interesting information in the document, such as range, stealth, supercruising, engine, radar.

We know that CAC chose the canard design for its superiority in achieving supercruising and to compensate for the relatively weaker engine. The trade-off for that design is more complex flight control and some slight sacrifice at stealth (but still meet their design goal in stealth).

So at least from the two documents, China has clear design goals and bench-marked against F-22 and F-35, made their design choices and trade-offs. In a video posted some pages back in this thread, the chief designer of J-20, Yang Wei, was interviewed at the sideline of the Zhuhai Airshow and said that J-20 has been under-work for "twenty years." Song Wencong's paper was published in 2000/2001, which is quite consistent with Yang Wei's statement. We also know CAC had gained a lot of experiences in canard design from their experience with J-10, DSI from FC-1, and had used J-10B/C for experimenting with avionics. Yang Wei made his name with designing the flight control software for J-10, which would be extremely important given J-20 rather complex aerodynamics. The CAC team was very well prepared and confident when they presented their design in competition with SAC for the fifth-generation stealth fighter project. They won the competition in no small part due to that confidence.

 

[superdog]

Ah, I see this is where the rumors came from. Yes, what he said could easily be interpreted as saying that "...now, it is using domestic engines and can satisfy basic combat requirements though it will be much improved with WS-15." However, it is also possible to interpret that statement as, "...now, if it were to use domestic engines, it could satisfy its basic combat requirements but it could be further enhanced by WS-15." In Chinese, the "if" may be implied without directly saying. That leaves room for doubt and cannot be regarded with certitude that it is currently flying on domestic engines. Although he is definitely saying that current domestic options are fully matured for powering J-20 (no actual dependence on foreign engines), so it can be implied that it is not necessity that drove J-20 to use an AL-31 variant but some other circumstance such as convenience or price.

I think he expressed it pretty clearly that the J-20 shown in Zhuhai is using domestic engines.

But you should bear in mind that this guy is a bit like Zhang Zhaozhong, they both are (were) Rear Admirals of the PLAN, but they work as researchers and military theorists with an emphasis in naval warfare, and besides that they appear frequently on media to educate the public about military matters. They are not associated with air force combat units, with the armaments department, or with aircraft research institutes, so they may not be the kind of "insider" or "authority figure" you'd prefer when it comes to the J-20.

If it was someone like He WeiRong (ex-lieutenant general of the PLAAF who disclosed the time schedule of the J-20 project back in 2009), I'd have no problem believing his statements. But when it comes from Yin Zhuo, I will hold on to my doubts for now. What you hear from frequent media guests like Yin Zhuo or Zhang Zhaozhong should NOT be considered an official statement of the PLA. The accuracy of their statement is hardly guaranteed.

 

[tony0989]

To date, there are only two formal/official documents known to the public related to China's fifth-generation stealth fighter. One is obviously Song Wencong's paper, which laid the design foundation of J-20. Another recently disclosed one is a high-level requirements doc for China's fifth-generation aircraft, authored by Gu Yongfen (with a team) in 2003, former Chief Designer of J-8 and a senior academician of Engineering Academy of China. Here is the first and last page of the document.

View attachment 33789 View attachment 33790

In the last page, the document stated that the PLAAF requires the fourth/fifth-generation stealth fighter be competitive with F-22 and clearly superior to F-35 (I understand people may have different opinions regarding whether J-20 can achieve the requirements, but that's not the point here). There are lots of other interesting information in the document, such as range, stealth, supercruising, engine, radar.

We know that CAC chose the canard design for its superiority in achieving supercruising and to compensate for the relatively weaker engine. The trade-off for that design is more complex flight control and some slight sacrifice at stealth (but still meet their design goal in stealth).

So at least from the two documents, China has clear design goals and bench-marked against F-22 and F-35, made their design choices and trade-offs. In a video posted some pages back in this thread, the chief designer of J-20, Yang Wei, was interviewed at the sideline of the Zhuhai Airshow and said that J-20 has been under-work for "twenty years." Song Wencong's paper was published in 2000/2001, which is quite consistent with Yang Wei's statement. We also know CAC had gained a lot of experiences in canard design from their experience with J-10, DSI from FC-1, and had used J-10B/C for experimenting with avionics. Yang Wei made his name with designing the flight control software for J-10, which would be extremely important given J-20 rather complex aerodynamics. The CAC team was very well prepared and confident when they presented their design in competition with SAC for the fifth-generation stealth fighter project. They won the competition in no small part due to that confidence.

How did you get this stuff, is it from google? Just curious

 

[Engineer]

tell me where is the post stall in any J-20 video? TVC is not only for improving poststall, it improves turns rates, reduces drag and improves stealth and range, tell me why the Japanese Russians and Americans use TCV nozzles and China does not? why the US does not sell the F-22?

Simple.

The J-20 displayed only combat-manoeuvres. Post-stall is more of a suicide-manoeuvre than combat-manoeuvre.

TVC doesn't improve turn-rate, proven with actual dog-fights between F-22 and forth-generation aircraft including Eurofighter, F-15, F-18 and Rafale. When thrust-vectoring kicks in, the aircraft typically used up all the aerodynamics performance already. Thrust-vectoring only causes the aircraft to go post-stall and lose energy quickly. Rather than out-manoeuvring the opponent, the F-22 ended up a sitting duck. That's why China doesn't use thrust-vectoring, even though China could just pay whatever Russia demands for the technology.

Japan doesn't actually have production aircraft with thrust-vectoring. The X-2 is just a tech-demonstrator. Japanese being interested in thrust-vectoring is consistent with their affinity to complicate things, like turning an F-16 into a more expensive and less efficient F-2.

After F-22, Americans don't design their aircraft to use thrust-vectoring control for manoeuvring any more. One might think F-35 is a good candidate of receiving thrust-vectoring since the aircraft is so heavy. Instead, thrust-vectoring is now used exclusively during vertical-takeoff-and-landing, and only on one of the three versions of F-35. Kicking in thrust-vectoring and going into post-stall is actually frowned upon.

The Russians use thrust-vectoring out of pride. They have been claiming thrust-vectoring will make an aircraft invincible for too long, they have no choice but to press on with using thrust-vectoring or risk looking like fools. Thrust-vectoring is also one technology "perfected" by Russia. It is about the only thing that Russians could feel proud of about the state of their aviation industry. Everything else is 30-year-old hand-me-down from Soviet Union. Again, it is a pride thing.

 

[siegecrossbow]

In the last page, the document stated that the PLAAF requires the fourth/fifth-generation stealth fighter be competitive with F-22 and clearly superior to F-35 (I understand people may have different opinions regarding whether J-20 can achieve the requirements, but that's not the point here). There are lots of other interesting information in the document, such as range, stealth, supercruising, engine, radar.

We know that CAC chose the canard design for its superiority in achieving supercruising and to compensate for the relatively weaker engine. The trade-off for that design is more complex flight control and some slight sacrifice at stealth (but still meet their design goal in stealth).

So at least from the two documents, China has clear design goals and bench-marked against F-22 and F-35, made their design choices and trade-offs. In a video posted some pages back in this thread, the chief designer of J-20, Yang Wei, was interviewed at the sideline of the Zhuhai Airshow and said that J-20 has been under-work for "twenty years." Song Wencong's paper was published in 2000/2001, which is quite consistent with Yang Wei's statement. We also know CAC had gained a lot of experiences in canard design from their experience with J-10, DSI from FC-1, and had used J-10B/C for experimenting with avionics. Yang Wei made his name with designing the flight control software for J-10, which would be extremely important given J-20 rather complex aerodynamics. The CAC team was very well prepared and confident when they presented their design in competition with SAC for the fifth-generation stealth fighter project. They won the competition in no small part due to that confidence.

I agree. If they wanted something like a pure interceptor or fighter-bomber then they would've gone with a conventional or tail-less design to further enhance frontal RCS. The fact that they even added canards and LERX meant that they had some consideration for maneuverability.

 

[taxiya]

To date, there are only two formal/official documents known to the public related to China's fifth-generation stealth fighter. One is obviously Song Wencong's paper, which laid the design foundation of J-20. Another recently disclosed one is a high-level requirements doc for China's fifth-generation aircraft, authored by Gu Yongfen (with a team) in 2003, former Chief Designer of J-8 and a senior academician of Engineering Academy of China. Here is the first and last page of the document.

View attachment 33789 View attachment 33790

In the last page, the document stated that the PLAAF requires the fourth/fifth-generation stealth fighter be competitive with F-22 and clearly superior to F-35 (I understand people may have different opinions regarding whether J-20 can achieve the requirements, but that's not the point here). There are lots of other interesting information in the document, such as range, stealth, supercruising, engine, radar.

We know that CAC chose the canard design for its superiority in achieving supercruising and to compensate for the relatively weaker engine. The trade-off for that design is more complex flight control and some slight sacrifice at stealth (but still meet their design goal in stealth).

So at least from the two documents, China has clear design goals and bench-marked against F-22 and F-35, made their design choices and trade-offs. In a video posted some pages back in this thread, the chief designer of J-20, Yang Wei, was interviewed at the sideline of the Zhuhai Airshow and said that J-20 has been under-work for "twenty years." Song Wencong's paper was published in 2000/2001, which is quite consistent with Yang Wei's statement. We also know CAC had gained a lot of experiences in canard design from their experience with J-10, DSI from FC-1, and had used J-10B/C for experimenting with avionics. Yang Wei made his name with designing the flight control software for J-10, which would be extremely important given J-20 rather complex aerodynamics. The CAC team was very well prepared and confident when they presented their design in competition with SAC for the fifth-generation stealth fighter project. They won the competition in no small part due to that confidence.

Just to translate part of the article regarding engine for J-20.

The should be two phases for J-20. Initially J-20 is to be equipped with Taihang or its improved variant to verify the flight characteristics. The second step is to equip it with an engine of T/W ratio of 10.

As this is the plan by the pre-study report, not a execution report afterwards, we can not be sure Taihang is actually installed on J-20. But a 14.5 tone thrust Taihang variant was disclosed a year?? ago, it is not a wild imagination that some Taihang variant is used by J-20.

Backed by this article (if it is genuine) discrediting Yin Zhuo's notion of J-20 using domestic engine is premature.

 

[taxiya]

How did you get this stuff, is it from google? Just curious

I guess this report being a pre-study product produced decade ago is not highly classified. After all it is a "wish-list", not real specifics and parameters that are useful in defeating the aircraft. Similar things have happened to other former secret projects, less than J-20 maybe. There are documentary TV programs detailing development of 052C and Type-99 tanks, KJ-2000 etc. You can find them in Youtube.

 

[Richard Santos]

tell me where is the post stall in any J-20 video? TVC is not only for improving poststall, it improves turns rates, reduces drag and improves stealth and range, tell me why the Japanese Russians and Americans use TCV nozzles and China does not? why the US does not sell the F-22?

TVC improves pitch Rate, and by vectoring the two nuzzles in different directions, the roll Rate. This improves the aircraft's agility, but not maneuverability. The two concepts are different. Maneuverability is useful in vast majority of air combat situations, agility is useful in a much more limited range of combat situations. TVC only reduce drag in a badly trimmed aircraft. But It imposes a severe weight penalty, at least in the f-22.

TVC does afford some additional pitch control to an aircraft in the post stall regime. However, aircraft without TVC has managed post stall maneuver just fine. The bigger problem in post stall maneuver is not pitch control, but yaw control. J-20 seem to me to have undoubtedly been designed for post stall maneuver, which is probably the main reason why the designers accepted the compromise of adding ventral fins, rather than adopt larger dorsal fins that would have been superior from stealth perspective. Ventral fins become ineffective in poststall regime because it would be masked from smooth airflow by the pitched up fuselage. But ventral fins would remain effective and aid in the aircraft's yaw control.

 

[b787]

TVC improves pitch Rate, and by vectoring the two nuzzles in different directions, the roll Rate. This improves the aircraft's agility, but not maneuverability. The two concepts are different. Maneuverability is useful in vast majority of air combat situations, agility is useful in a much more limited range of combat situations. TVC only reduce drag in a badly trimmed aircraft. But It imposes a severe weight penalty, at least in the f-22.

TVC does afford some additional pitch control to an aircraft in the post stall regime. However, aircraft without TVC has managed post stall maneuver just fine. The bigger problem in post stall maneuver is not pitch control, but yaw control. J-20 seem to me to have undoubtedly been designed for post stall maneuver, which is probably the main reason why the designers accepted the compromise of adding ventral fins, rather than adopt larger dorsal fins that would have been superior from stealth perspective. Ventral fins become ineffective in poststall regime because it would be masked from smooth airflow by the pitched up fuselage. But ventral fins would remain effective and aid in the aircraft's yaw control.

true post stall control is only achieved by TVC nozzles, high AoA below 70 or even 80 deg has achieved briefly by some aircraft, but true poststall ike you see on F-22 or Su-35 is only achieved with TVC nozzles.Agility is improved, basically turn rates, but the most important is drag reduction.

PAKFA has those small fins thanks to TVC nozzles, F-22 uses it more for stealth, but it has only pitch control, so still uses big vertical fins.

the J-20 has no hinges or rudders in the ventral fins like MiG-1.44, so its usefulness at high AoA, is not as you claim specially since it they are canted for stealth.

When you show me the J-20 doing all the repertoire the Su-35 or F-22 can do in an airshow, you can say to me it has good post stall, at this moment it just turns like any regular jet and its flight routines in airshow or videos are basic turns a Panavia Tornado or a MiG-21 will do.

 

[b787]

I agree. If they wanted something like a pure interceptor or fighter-bomber then they would've gone with a conventional or tail-less design to further enhance frontal RCS. The fact that they even added canards and LERX meant that they had some consideration for maneuverability.

Viggen is an interceptor, the use of canards is because Canards have a slight edge in pitch reaction under some special conditions.
but those advantages have disadvantages too, the advantages usellualy is no more tha 2%-5% improvements.

If you think J-31 will fly worse than J-20 is only in ranges of 3%-5% but still J-31 will have advantages and as in the case of F-22 add TVC nozzles and you eliminate any advantage the canard configuration might have