J-20 5th Gen Fighter Thread V

[siegecrossbow]

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

The Viggen doesn't use all moving canards though. If the J-20 just needed a slight increase in pitch reaction shouldn't it just use "fixed" canards with moving surfaces in the rear (like in Viggen)? That would probably not compromise the frontal RCS as much since the frontal edges of the canards won't be moving much.

Also, can you rephrase the second part of your reply? Normally I am not a big stickler for spelling and grammar but what you wrote verges on incomprehensibility.

 

[SpicySichuan]

In addition to Yin Zhuo's comments, it is also stated here that the J-20 will use WS-10 or its relatives during trial and initial stages. So I assumed that Yin Zhuo's statement could be 50% accepted.

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.

 

[b787]

The Viggen doesn't use all moving canards though. If the J-20 just needed a slight increase in pitch reaction shouldn't it just use "fixed" canards with moving surfaces in the rear (like in Viggen)? That would probably not compromise the frontal RCS as much since the frontal edges of the canards won't be moving much.

Also, can you rephrase the second part of your reply? Normally I am not a big stickler for spelling and grammar but what you wrote verges on incomprehensibility.

to be more explicit, the J-31 uses aft tails because the advantage you have with canards are not absolute, both configurations have advantages and disadvantages, the main advantage is pitch reaction you will have on a fore tail design, but aircraft are not only for high AoA but for other needs, J-31 designers went for aft tails not because they do not know the advantages of canards or being less capable than Chengdu, but because the flight parameters also pondered the disadvantages canards do have, the advantages you get with canards are marginal, and at the end of the day wing loading and TWR are more important, thus you comment it has canards it must be a fighter, is not true, a fighter in the class of Gripen has a low wing loading of around 350 kg/m, also you have to consider the lift the fuselage generates, these are the true parameters to watch, if Chengdu opted for canards is for the advantages they offer for the needs they had, but the designers of F-22 or J-31 saw the disadvantages of canards and the advantages of aft tails and got other needs prioritized.

In few words the advantages you get with canards are not as high as you think they are in a range of 3%-6% at the most and this can be fixed with some solutions one is TVC nozzles

 

[manqiangrexue]

This video (1:02) says it uses domestic engines, is it reliable?

Oooh, I just watched the whole thing. When asked how J-20 compares to American stealth fighters, he said that J-20 is more maneuverable than F-22 and it's radar capability is on par with F-22, F-35. It possesses BVR capabilities on par with F-22. However, it's supercruise capability lags behind the Raptor due to an insufficiently powerful engines at this phase. He also notes that J-20 is still immature and still being tested/improved even as LRIP is commences.

 

[siegecrossbow]

to be more explicit, the J-31 uses aft tails because the advantage you have with canards are not absolute, both configurations have advantages and disadvantages, the main advantage is pitch reaction you will have on a fore tail design, but aircraft are not only for high AoA but for other needs, J-31 designers went for aft tails not because they do not know the advantages of canards or being less capable than Chengdu, but because the flight parameters also pondered the disadvantages canards do have, the advantages you get with canards are marginal, and at the end of the day wing loading and TWR are more important, thus you comment it has canards it must be a fighter, is not true, a fighter in the class of Gripen has a low wing loading of around 350 kg/m, also you have to consider the lift the fuselage generates, these are the true parameters to watch, if Chengdu opted for canards is for the advantages they offer for the needs they had, but the designers of F-22 or J-31 saw the disadvantages of canards and the advantages of aft tails and got other needs prioritized.

Once again, there is so much rambling within your argument that it's hard for me to decipher your meaning, but I'll try.

You are saying that there are marginal advantages to using canards on the J-20, which implies that the disadvantage outweighs the advantage. My point was that if the designer had no need for maneuverability at all, they would've been better off not adding the canards. Just look at the new sixth generation design by Boeing. After increasing its size (and presumably adding DEW), they removed the canards that they had on a previous iteration since whatever marginal benefits they offered didn't outweigh costs. If the J-20 is designed as a pure interceptor/bomber like the FB-22 or the new Boeing sixth gen, wouldn't it be better to reduce the overall number of control surfaces? After all, it doesn't make sense to risk detection on a pure "shoot and scoot" mission.

 

[b787]

Oooh, I just watched the whole thing. When asked how J-20 compares to American stealth fighters, he said that J-20 is more maneuverable than F-22 and it's radar technology is superior to F-22, on par with F-35. It possesses BVR capabilities on par with F-22. However, it's supercruise capability is lacking compared to the Raptor due to an insufficiently powerful engines at this phase. He also notes that J-20 is still immature and still being tested/improved even as LRIP is commences.

that is propaganda, without TVC nozzles and without evident proof it supercruises the jet is 100% underpowered, F-22 has supercruise capability because it has excess power at military power how it will surpass the F-22 in maneuvrability if it can not supercruise faster or at least as fast?

 

[b787]

Once again, there is so much rambling within your argument that it's hard for me to decipher your meaning, but I'll try.

You are saying that there are marginal advantages to using canards on the J-20, which implies that the disadvantage outweighs the advantage. My point was that if the designer had no need for maneuverability at all, they would've been better off not adding the canards. Just look at the new sixth generation design by Boeing. After increasing its size (and presumably adding DEW), they removed the canards that they had on a previous iteration since whatever marginal benefits they offered didn't outweigh costs. If the J-20 is designed as a pure interceptor/bomber like the FB-22 or the new Boeing sixth gen, wouldn't it be better to reduce the overall number of control surfaces? After all, it doesn't make sense to risk detection on a pure "shoot and scoot" mission.

look you do not understand agility, agility is not because it has canards or not, it is because you have more lift at higher AoA and you have more thrust at higher banking angle, canards are aids to delta wings, because deltas bleed lift.
The TVC nozzles are also aids because the jets are heavier and lift is hard to get with smaller wings.

F-22 also is heavy, So TCV is helping the jet, Su-35 has a very high wing loading too, so is Su-30MKI, they need TVC nozzles to achieve higher maneuverability, but the lift capability is related to the wing loading, lower wing loading better fighter, Rafale or Eurofighter have wing loadings in the range of 300 kg/m, that is the reason they are so good, not the canard it self

 

[manqiangrexue]

that is propaganda, without TVC nozzles and without evident proof it supercruises they jet is 100% underpowered, F-22 has supercruise capability because it has excess power at military power how it will surpass the F-22 in maneuvrability if it can not supercruise faster or at least as fast?

How is MIG-25 so much faster, with more powerful engine than F-15 but not as maneuverable? Lots of things, "how"s that you don't know about in this world. Don't even pretend like you can figure out the performance of classified fighters with high school math, rudimentary questions. Anyway, I'm just translating. General Goldmouth can talk, Yin Zhuo can talk too.

 

[siegecrossbow]

look you do not understand agility, agility is not because it has canards or not, it is because you have more lift at higher AoA and you have more thrust at higher banking angle, canards are aids to delta wings, because deltas bleed lift.
The TVC nozzles are also aids because the jets are heavier and lift is hard to get with smaller wings.

F-22 also is heavy, So TCV is helping the jet, Su-35 has a very high wing loading too, so is Su-30MKI, they need TVC nozzles to achieve higher maneuverability, but the lift capability is related to the wing loading, lower wing loading better fighter, Rafale or Eurofighter have wing loadings in the range of 300 kg/m, that is the reason they are so good, not the canard it self

Why do you need more lift at higher AOA if you don't intend to maneuver? Many of the newer bomber/interceptor designs place their intakes on the back precisely because there isn't a requirement for high AOA flight.

As for the actual wing loading... We don't know precisely how much the J-20 weighs. Your argument is based on conjecture.

 

[b787]

How is MIG-25 so much faster, with more powerful engine than F-15 but not as maneuverable? Lots of things, "how"s that you don't know about in this world. Don't even pretend like you can figure out the performance of classified fighters with high school math, rudimentary questions. Anyway, I'm just translating. General Goldmouth can talk, Yin Zhuo can talk too.

let me laugh about the non sense you wrote MiG-25 has lower TWR and higher wing loading than the F-15, when you get higher thrust to weight ratio F-15 near 1:1.3, MiG-25 1:0.7 you can see the MiG-25 was not a dogfighter, F-22 supercruises because it has excess power and very low SFC, J-20 without being able to supercruise is a joke it will out manuevre the F-22, specially f the F-22 uses TVC nozzles on a 1:1 combat, the only chance for the J-20 will be have a better HMS and a very advance missile like AIM-9X and the avionics of F-35