J-20 5th Gen Fighter Thread VI

[latenlazy]

Ougoah: I'd think the maintenance was the main reason the Eurofighter skipped TVC. It's very wonky to work with, and while Western engines have exceptional MTBO, TVC means you'll have to do frequent maintenance with the TVC system. It also gives you more points of failure: a TVC system can lock up on you, leaving you with only one engine to work with.

Regarding measurements, if you do wingtip to wingtip, ignoring the pylons, you get 134 pixels. That gives you about 13.1 or 13.2 meters on the J-20's wingspan, but it does give you 21.5 to 21.83 meters on the J-20's length. On the plus side, we get a radome diameter of 1.3 meters, giving us either a 1 m^2 radar aperture based on 25% diameter reduction or a 1.2 m^2 aperture based on 10% diameter reduction.

For wing area, assuming it's 96 pixels from the front apex of the wing to the back apex, then adding 18 pixels for the trapezoidal area, then scaling by 14.7 * 14.7 / 134^2, we get about 77.8 square meters.

So yes, the J-20 is actually pretty large, on the scale of the Flankers. This implies that it has a larger volume than previously estimated, about 1% larger by area. But it also has a robust wing area to compensate.

I think it might be useful for all of us to post what our wingspan to length ratios are, because clearly we're getting different results...

 

[Inst]

The first thing to mention is that there's perspective distortion in the picture. If you look at other pictures of the J-20, the tailfins should not end beyond the attaching pylons, so some of us have lengths slightly too long. From rear probes to radome tip, the left upper J-20 is 195 pixels long, the right upper J-20 is 196 pixels long, and the lower J-20 is 196 pixels long. The wingspan of the lower J-20 is about 119 pixels long, the wingspan of the upper left J-20 is about 121 pixels long, and the wingspan of the upper right J-20 is 120 pixels long.

This gives us aspect ratios of 1.61, and on later calculation actually gives about 21.2 meters length. Using the left-most and using the tailfin distance, I can get 21.94 meters length, but using the rear probe distance I get 21.28 length.

 

[Inst]

For the perspective distortion, see this:

 

[Blitzo]

The first thing to mention is that there's perspective distortion in the picture. If you look at other pictures of the J-20, the tailfins should not end beyond the attaching pylons, so some of us have lengths slightly too long. From rear probes to radome tip, the left upper J-20 is 195 pixels long, the right upper J-20 is 196 pixels long, and the lower J-20 is 196 pixels long. The wingspan of the lower J-20 is about 119 pixels long, the wingspan of the upper left J-20 is about 121 pixels long, and the wingspan of the upper right J-20 is 120 pixels long.

This gives us aspect ratios of 1.61, and on later calculation actually gives about 21.2 meters length. Using the left-most and using the tailfin distance, I can get 21.94 meters length, but using the rear probe distance I get 21.28 length.

How are you calaculating the aircraft's length? What is the known quantity you are comparing the aircraft's pixel length to?

 

[Figaro]

@Figaro: we redid the numbers and it looks definitely like 73 m^2 wing area. We could be even more condescending: on stable aircraft, which as we understand the J-20 is not, canards add lift while canards subtract from lift. On unstable aircraft canards subtract lift while tails add lift.

Moreover, if you go about twenty to thirty pages back, we went over Chinese pilots using simulators of the J-20B. They were headily discussing the TVC on the J-20B. Most of this TVC bashing by Engineer and others is because China did not possess TVC technology, and now with the Su-35 and WS-15, China does possess TVC.

You have to remember, the J-20 will be the first operational canard aircraft with TVC, but the J-20 is not the first to have tested the paradigm. The Eurofighter experimented with TVC, but the project was ultimately shelved due to weight, maintenance, and cost issues. The X-36 aircraft by the Americans found that a tailfinless canard delta utilizing TVC had significant stealth, maneuverability, and drag advantages over conventional aircraft. This is where the J-20 is heading to, it's just that development is too delayed to seriously attempt the tailfinless variant.

Once again, everybody is getting different results here in terms of wingspan, wing-area, and even aircraft length. So the 73 m^2 number is not conclusive at all ... especially given the photographic distortions. Regarding TVC, no where did the pilot mention that it was a simulator for the J-20B ... he only said a TVC simulation. Just because there's a simulator does not automatically imply the WS-15 will incorporate it. If anything, very few reliable rumors have said that the WS-15 will have TVC ... which would complicate the already complex FCS even more. Anyways, earlier you said that the J-20 would depend on future TVC for maneuverability. But as the CAC academic paper suggests, the aerodynamic features/designs were all made in order to compensate for a possible lack of suitable engine when the J-20 first arrived. Hence, most of the super-maneuverability features are already present in the current J-20 ... TVC wouldn't significantly improve upon it.

 

[Inst]

The problem is, we've had no evidence that the J-20 is maneuverable at all. It's definitely made reasonably fast turns in the videos we've been shown, but it hasn't impressed in the same way the F-22 or Su-57 has.

The reason the Eurofighter considered TVC, while the Rafale did not, was because the Eurofighter was a long-coupled canard fighter while the Rafale was short-coupled. The Eurofighter made maneuverability compromises compared to the Rafale, which TVC helped it to recover. The J-20, like the Eurofighter, is also a long-coupled canard fighter. You can do the math.

 

[Richard Santos]

Where did you get the idea that Long coupled canard represents an aerodynamic maneuverability compromise? The long couple canard is often considered more effective aerodynamically for enhancing maneuverability, but creates more serious challenge for the flight control system. Hence most canard fighters have opted for the easier to implement close coupled canard.

 

[latenlazy]

The first thing to mention is that there's perspective distortion in the picture. If you look at other pictures of the J-20, the tailfins should not end beyond the attaching pylons, so some of us have lengths slightly too long. From rear probes to radome tip, the left upper J-20 is 195 pixels long, the right upper J-20 is 196 pixels long, and the lower J-20 is 196 pixels long. The wingspan of the lower J-20 is about 119 pixels long, the wingspan of the upper left J-20 is about 121 pixels long, and the wingspan of the upper right J-20 is 120 pixels long.

This gives us aspect ratios of 1.61, and on later calculation actually gives about 21.2 meters length. Using the left-most and using the tailfin distance, I can get 21.94 meters length, but using the rear probe distance I get 21.28 length.

I noted the distortion problems too. My personal opinion is the best way to mitigate such problems is to use the Flanker and J-20 in the center of the image, since the closer you get to the center the less severe the distortion, generally speaking....

 

[Lethe]

Ougoah: I'd think the maintenance was the main r Ieason the Eurofighter skipped TVC.

I'd guess that lack of funds to do more than the absolute minimum necessary to keep the project alive had more to do with it than anything else.

 

[Richard Santos]

I noted the distortion problems too. My personal opinion is the best way to mitigate such problems is to use the Flanker and J-20 in the center of the image, since the closer you get to the center the less severe the distortion, generally speaking....

Placing the image closer to the center may reduce lens distortion. But very few modern telephoto lenses have enough distortion as to matter for our purposes. The distortion that really creates problems is perspective distortion. That can only be cured by finding images where both the pitch and roll axis of the plane are as close to the image plane of the lens, or as perpendicular to the line of sight to the plane as possible.