J-20 5th Gen Fighter Thread IV (Closed to posting)

[Inst]

If you look at the PAK-FA on the Kopp simulations, it generally has a -20 to -30 dbsm range in its frontal zone. It's adequately stealthy for the job, which is to avoid getting killed in BVR by stealth aircraft and to kill other stealth aircraft through better maneuverability.

I recall reading up about the J-20 being considered as potentially iconic as the Mitsubishi Zero, but the fat irony is that while the Mitsubishi Zero was designed as a close-range maneuvering fighter, with poor acceleration, climb, and dive, the J-20 seems to be more designed as an accelerationist along the lines of American fighters of the WW2 due to its design for extremely low drag. When fitted with proper engines, the J-20 will probably have better acceleration than the F-22, as well as good supersonic range and high-speed maneuverability. The PAK-FA will have superior maneuverability, the F-22 superior stealth, and the poor F-35 will just be a bomb truck.

 

[by78]

If you look at the PAK-FA on the Kopp simulations, it generally has a -20 to -30 dbsm range in its frontal zone. It's adequately stealthy for the job, which is to avoid getting killed in BVR by stealth aircraft and to kill other stealth aircraft through better maneuverability.

I recall reading up about the J-20 being considered as potentially iconic as the Mitsubishi Zero, but the fat irony is that while the Mitsubishi Zero was designed as a close-range maneuvering fighter, with poor acceleration, climb, and dive, the J-20 seems to be more designed as an accelerationist along the lines of American fighters of the WW2 due to its design for extremely low drag. When fitted with proper engines, the J-20 will probably have better acceleration than the F-22, as well as good supersonic range and high-speed maneuverability. The PAK-FA will have superior maneuverability, the F-22 superior stealth, and the poor F-35 will just be a bomb truck.

Actually, Zero had excellent maneuverability with superior climb and acceleration, so much so that it outclassed all Allied fighters at the start of WWII.

J-20's long fuselage is indicative of good transonic performance, not supersonic maneuverability.

 

[Inst]

The Zero, however, was not very controllable or effective at high speeds, and its much-vaunted maneuverability fell off quickly at high speeds. It also had a limitation where it was unable to dive at high speeds without falling apart, a low never-exceed speed.

Allied pilots countered the Zero by rolling and diving to avoid getting into a close-in dogfight with the Zero, and diving to attack the Zero when given a height advantage. Between that and the Thach Weave, the United States was able to neutralize the Zero's superior maneuverability.

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If you go through the Dr. Song docs that were dumped here, as well as other information, the J-20 was designed to provide good supercruising performance despite the fact that China is behind in engine technology, so that relatively poor engines would be able to provide both supercruise and range to the J-20. Now, assume that WS-15 or equivalent programs meet expectations, and the J-20 goes up in the air with around 200+ kn of thrust without afterburners, and you'd have a J-20 with exceptional supercruising performance.

It's not necessarily a bad thing; consider that one of the few US aircraft that were downed in the First Gulf War was an F-18 downed by a MiG-25 Foxbat doing a run-and-gun mission while using its kinematics to add speed and range to its missiles. That's what I mean by the J-20 being a sort of tactical opposite to the Zero; the J-20 will likely be more optimized for hit-and-run and alpha strike jobs than the PAK-FA or the F-22. It can dogfight, of course, but it'd be roughly comparable to the F-22 at it, and it would be outclassed by the PAK-FA if it were to end up being caught in a close-in encounter.

 

[latenlazy]

That's what I mean by the J-20 being a sort of tactical opposite to the Zero; the J-20 will likely be more optimized for hit-and-run and alpha strike jobs than the PAK-FA or the F-22. It can dogfight, of course, but it'd be roughly comparable to the F-22 at it, and it would be outclassed by the PAK-FA if it were to end up being caught in a close-in encounter.

I'm less certain of that assessment than I used to be. At subsonic speeds I suspect that the F-22 might be able to out-turn both the PAK-FA and J-20 due to the way it generates powerful vortices at high angles of attack, even if either one would probably be more agile in terms of nose pointing. While digging through Chinese aerodynamics threads I found a post by someone who seemed to know a few things about the field that showed a CFD of the vortices each design generated and a graph with L/D ratios of each design. The graph showed the F-35 had better L/D ratios at subsonic speeds than the T-50 and the claim was that the F-22's L/D ratio was even better than the F-35s. I could not determine whether he had found that information elsewhere or generated it himself, and could not find any other graphics like this, but it seemed to preliminarily confirm some arguments about how the aerodynamics of the LockMart 5th gens worked relative to the T-50 and J-20. That said actual performance information on these designs is suspect, but it was a sharp reminder that how these designs work at different flight regimes are not obvious just by visual appearance, especially given how unique both the J-20 and T-50s designs are. I will say though the PAK-FA may not look it because of its pancake fuselage, but it might have better area ruling than the F-22 and therefore might be more optimized for supersonic regimes like the J-20.

 

[Inst]

On the other hand, the J-20 has a better fineness ratio than the Su-50, at about ~1.53 (20.4/13.3) vs ~1.41. The canard delta set-up also has its own benefits for area ruling, so...

needs more information, doesn't it?

 

[latenlazy]

On the other hand, the J-20 has a better fineness ratio than the Su-50, at about ~1.53 (20.4/13.3) vs ~1.41. The canard delta set-up also has its own benefits for area ruling, so...

needs more information, doesn't it?

Where'd you get the fineness ratio figures? If you're simply doing a length to width calculation, I'd have to warn that that only applies to 2 dimensional objects. For three dimensional objects the fineness ratio is length to cross sectional area, not length to width.

 

[siegecrossbow]

I wonder if they missed a decimal point. Even the Typhoon is often quoted to have an RCS or 0.05-0.1m^2.

For the PAKFA - a fifth gen contender, to have an RCS 5-10 times as high is really really poor if true.

Even at 0.05m^2, that RCS figure is unacceptable for a 5th IMO.

I think that depends on whether the RCS figure is frontal or if they somehow averaged the all aspect RCS. In the latter case it probably isn't too bad.

 

[Inst]

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Well, the fineness ratio is defined as length divided by width, so...

Paralay probably has his own frontal cross section estimates as well, so you also could go from there. He estimates that the T-50 has a frontal cross section of 9.47m^2, while the F-22 has a frontal cross section of 9.25m^2, and the J-20 has a frontal cross section of 8.9m^2. It's old data, though, from 2013; his figures may have since been updated.

Tell me if this works, I don't have excel installed.

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[latenlazy]

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Well, the fineness ratio is defined as length divided by width, so...

Paralay probably has his own frontal cross section estimates as well, so you also could go from there. He estimates that the T-50 has a frontal cross section of 9.47m^2, while the F-22 has a frontal cross section of 9.25m^2, and the J-20 has a frontal cross section of 8.9m^2. It's old data, though, from 2013; his figures may have since been updated.

Tell me if this works, I don't have excel installed.

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Perhaps I misused the terminology. What it comes down to is that it's ultimately about how well the body conforms to the area rule, and the length to width comparison is a shorthand for that. But it's really the change in cross sectional area over length. I think I might've been wrong to suggest that it's length to cross sectional area, but what I was trying to communicate was that supersonic drag isn't so straightforward that that information is readily available, so I was surprised when you came out with such a definitive comparison.

 

[davidwangqi]

Interestingly, J20 which has canards has better frontal RCS (<20 degree) (~5-10 times smaller for high frequencies) than T50 according to Kopp's simulations.

If you look at the PAK-FA on the Kopp simulations, it generally has a -20 to -30 dbsm range in its frontal zone. It's adequately stealthy for the job, which is to avoid getting killed in BVR by stealth aircraft and to kill other stealth aircraft through better maneuverability.