J-20 5th Generation Fighter VII

Sure, we can continue here.
Keep in mind that F-35 might be more stealthy from front, but F-22 is more stealth from rear. How they covered the entire engine is a big part of that.

Compared to J-20, the engine cowling on F-35 seems hug engine closer and have finer sawtooth. It doesn't have the gap between the 2 engines that J-20 has. there is also a little gap between tail boom and engine nozzle on J-20 which you don't see on F-35. None of this is to say J-20 is not stealthy as a platform, but there are definitely concerns at the back. When we are dealing with 0.01 or 0.001 or 0.0001 m^2 RCS, all these little details matter.

Going to move this discussion back to the J-20 thread.

tphuang said:

given how much effort is put into eliminating the tiniest imperfections in stealth aircraft, I would have to disagree with that. Also, I don't think ventral fins are that bad. To me, it's just a smaller vertical tail fin. and it also blocks the nozzle pretty well from the side.

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The same logic you’re applying to the ventral fins also apply to every other edge surface though. If you’re primarily concerned about the canards because of backscatter effects, absorbers in the scatter hotspots, edge treatments, and materials that can control or alter the specular angle of the backscatter should be adequate to greatly reduce if not eliminate that problem. In that sense the canards not being planar to the wing should also help that aspect.

tphuang said:

Sure, we can continue here.
Keep in mind that F-35 might be more stealthy from front, but F-22 is more stealth from rear. How they covered the entire engine is a big part of that.

Compared to J-20, the engine cowling on F-35 seems hug engine closer and have finer sawtooth. It doesn't have the gap between the 2 engines that J-20 has. there is also a little gap between tail boom and engine nozzle on J-20 which you don't see on F-35. None of this is to say J-20 is not stealthy as a platform, but there are definitely concerns at the back. When we are dealing with 0.01 or 0.001 or 0.0001 m^2 RCS, all these little details matter.

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Noted, but the underside of the F-35 looks like a mess to me. I say looks like a mess; I'm sure it's designers know better and all those bumps and bulges don't damage the RCS. I don't think we can just eyeball the J-20 and say that these "deviations" from our simplified layman understanding of RCS minimization are actual problems. Especially since they seem relatively simple to fix; for example, the J-20 engine cowling could certainly have finer serrations and hug the engine closer if that were required. Perhaps it's to do with the fact that the WS-10C is still an interim engine that the cowling isn't optimized for?

Also, how much of these differences are militarily significant? Suppose a radar could detect an F-22/F-35 in certain conditions at a distance of 100km. If that same radar under identical conditions could detect a J-20 at 105km, is that extra 5km really going to make much of a difference?

latenlazy said:

Going to move this discussion back to the J-20 thread.

The same logic you’re applying to the ventral fins also apply to every other edge surface though. If you’re primarily concerned about the canards because of backscatter effects, absorbers in the scatter hotspots, edge treatments, and materials that can control or alter the specular angle of the backscatter should be adequate to greatly reduce if not eliminate that problem. In that sense the canards not being planar to the wing should also help that aspect.

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Even if you can reduce the RCS of canards by 90%, it could still make a real difference on the overall RCS of the aircraft when we are talking about 0.001 m^2. Not being planform aligned with wing is definitely a concern. Also, I think when we are talking about managing the scattering of RF, you are not managing it evenly across all the angles. So with canards, you can manage it really great from the front, but maybe not so good from the back. Which might not be a problem when we consider the other issues from the rear.

ZeEa5KPul said:

Noted, but the underside of the F-35 looks like a mess to me. I say looks like a mess; I'm sure it's designers know better and all those bumps and bulges don't damage the RCS. I don't think we can just eyeball the J-20 and say that these "deviations" from our simplified layman understanding of RCS minimization are actual problems. Especially since they seem relatively simple to fix; for example, the J-20 engine cowling could certainly have finer serrations and hug the engine closer if that were required. Perhaps it's to do with the fact that the WS-10C is still an interim engine that the cowling isn't optimized for?

Also, how much of these differences are militarily significant? Suppose a radar could detect an F-22/F-35 in certain conditions at a distance of 100km. If that same radar under identical conditions could detect a J-20 at 105km, is that extra 5km really going to make much of a difference?

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I don't think that's the right way to look at it. In fact, having higher RCS on the rear might not even be an issue if you can operate it in a way that keeps enemy aircraft in front of you until you are ready to speed away.

Think about it this way. Let's say F-35 is a magnitude better than J-20 in frontal RCS. With same radar technology, the range to track F-35 would be 1/1.78 of J-20. That sounds not good until you think about J-20 having a larger radar/EO tracker and EW suite than F-35, which would eat into some of that advantage. On top of that, these things are all networked. Having more aircraft in theater would give better situation awareness to both J-20/F-35 and also allow them to pick up more RF. China could also have anti-stealth radar in the theater which would point them to the general vicinity of F-35. which would allow J-20 to search a much narrower band and have longer tracking range. These are never like your RCS is x times my and your radar is y times my, so I can always track at this z multiple greater than you can track me. Depends on the tactics, the surrounding aircraft, the missiles, the sensor fusion/networking capabilities. All that is to say don't be concerned even if j-20 is 0.001 m^2 from front and F-35 is 0.0001 m^2 against X band radar. There are a lot of other factors in play.

tphuang said:

I don't think that's the right way to look at it. In fact, having higher RCS on the rear might not even be an issue if you can operate it in a way that keeps enemy aircraft in front of you until you are ready to speed away.

Think about it this way. Let's say F-35 is a magnitude better than J-20 in frontal RCS. With same radar technology, the range to track F-35 would be 1/1.78 of J-20. That sounds not good until you think about J-20 having a larger radar/EO tracker and EW suite than F-35, which would eat into some of that advantage. On top of that, these things are all networked. Having more aircraft in theater would give better situation awareness to both J-20/F-35 and also allow them to pick up more RF. China could also have anti-stealth radar in the theater which would point them to the general vicinity of F-35. which would allow J-20 to search a much narrower band and have longer tracking range. These are never like your RCS is x times my and your radar is y times my, so I can always track at this z multiple greater than you can track me. Depends on the tactics, the surrounding aircraft, the missiles, the sensor fusion/networking capabilities. All that is to say don't be concerned even if j-20 is 0.001 m^2 from front and F-35 is 0.0001 m^2 against X band radar. There are a lot of other factors in play.

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You're looking at things from a "system of systems" approach and that certainly has its place. Sure, if the tactical circumstances are favourable, like a fight near the mainland where China has a higher number of J-20s on station and they're backed by long wave radar, the battle is likely to resolve in China's favour. But the J-20 should also be able to survive and prevail in circumstances that aren't as permissive. This is essential if China is to be a true peer competitor of the US.

Moreover, I feel that this approach overlooks comparing assets one-to-one at the unit level, which I feel has a lot of merit. After all, "systems of systems" are built out of individual units, and the stronger they are individually the more capable they are unison. You can mitigate weaknesses with creative tactics, but why go for that approach if you don't have to? China certainly has the experience to correct the defects with the J-20's rear RCS (if they exist). I expect any remaining shortcomings to be fixed with the WS-15.

tphuang said:

Even if you can reduce the RCS of canards by 90%, it could still make a real difference on the overall RCS of the aircraft when we are talking about 0.001 m^2. Not being planform aligned with wing is definitely a concern. Also, I think when we are talking about managing the scattering of RF, you are not managing it evenly across all the angles. So with canards, you can manage it really great from the front, but maybe not so good from the back. Which might not be a problem when we consider the other issues from the rear.

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The frontal canard sweeps are planform aligned to the frontal wing sweep. The rear canard sweeps are aligned to the rear sweep of the opposite wing. If you’re instead referring to coplanarity, I don’t know if the canards sitting on the main wing actually helps with RCS because now you have traveling surface waves directly interacting with the wing and LERXes behind it as backscatter. Needless to say there’s a lot of complex interactions involved here that don’t make heuristic based judgments obvious, but I think this is also true for any number of other surface features that aren’t just control or wing surfaces.

ZeEa5KPul said:

You're looking at things from a "system of systems" approach and that certainly has its place. Sure, if the tactical circumstances are favourable, like a fight near the mainland where China has a higher number of J-20s on station and they're backed by long wave radar, the battle is likely to resolve in China's favour. But the J-20 should also be able to survive and prevail in circumstances that aren't as permissive. This is essential if China is to be a true peer competitor of the US.

Moreover, I feel that this approach overlooks comparing assets one-to-one at the unit level, which I feel has a lot of merit. After all, "systems of systems" are built out of individual units, and the stronger they are individually the more capable they are unison. You can mitigate weaknesses with creative tactics, but why go for that approach if you don't have to? China certainly has the experience to correct the defects with the J-20's rear RCS (if they exist). I expect any remaining shortcomings to be fixed with the WS-15.

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Aside from pride, why is it so important which aircraft might be better 1 to 1 on paper?

J20 with ws15 will still be less stealthy than f35. Among other things, it's production quality is not as good. Fixing up all the issues in the rear would require more than just a new engine.

tphuang said:

Aside from pride, why is it so important which aircraft might be better 1 to 1 on paper?

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I want to say that the pride bit is quite important. Who ever competed for silver? Second place is just first loser.

Practically, the more capable your aircraft is individually, the more missions it can perform successfully, and the more effective it is when working collectively. This accumulation of advantage is what decides wars.

tphuang said:

J20 with ws15 will still be less stealthy than f35. Among other things, it's production quality is not as good. Fixing up all the issues in the rear would require more than just a new engine.

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I expect the J-20 with WS-15s to feature more changes to the airframe than just a new engine. I don't expect anything radical, but certainly extensive corrections to whatever problems remain with the rear. I also don't agree that your claim (if I understood it correctly) that the J-20's quality is inferior to the F-35 when it comes to things like fit and finish - problems with the housing of the WS-10C aside.

Comparing aircraft one on one is nonsensical. As has been pointed out many times in this thread and others, this is not how military operations are conducted. It's always about having the right systems and logistics in place. Only insecure fanboys demand their preferred plane be superior in every single aspect.

tphuang said:

Aside from pride, why is it so important which aircraft might be better 1 to 1 on paper?

J20 with ws15 will still be less stealthy than f35. Among other things, it's production quality is not as good. Fixing up all the issues in the rear would require more than just a new engine.

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There has been a clear trend in post-Vietnam aerial combat that the side with superior aircraft not only win the battle, but do so with minimum losses in a lopsided victory. Even in the Eritean-Ethiopian war, the marginally superior Su-27 shot down 4 MiG-29s without loss. So being better 1 on 1 is important.