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

[Deino]

By how much? The composite components of the air-frame should give some weight-loss. J-20 is smaller, that's more loss. The original Su-27 used old Russian avionics. How does the weight of modern avionics comparable with those? Also, the original AL-31F used to be 122kN (Su-27 being quite agile on those) while the ones on J-20 would be at least 137kN (AL-31FN3 for J-10), possibly up to 145kN, which is a 12-19% power increase. All that plus the reduced drag from internal carrying seems pretty decent to me.

But then again, the F-22 is 62 feet but is quite heavy, 21-22 tons as compared to the 18 ton Su-27SK. Although it was fashioned a long time before where it may have used less composites, that it is way heavier than the older 14-ton, 64 feet F-15 still says that stealth comes at a heavy weight penalty.

First of all Your question includes much too much of pure guesswork: We simply do not know the percentage of the composit structures of the J-20's airframe. Also even if slightly smaller - e.g. not as long - the J-20 is surely more compact and surely has a decent internal volume both for weapons and fuel), even more we don't know how much weight the avionics has. As such I think it will be more or less a good estimation to be roughly similar to a Flanker ... but to conclude anything especialyl in regard to performances will be simply way off.

Additionally there is so far no "AL-31FN3 for J-10". that's a fact and the so far most powerful AL-31FN version is the AL-31FN series III for J-10B, which is however a completely different beast to the projected AL-31F3 - again there is no AL-31FN3 - ... making any assumptions in regard to performances simply useless.

Deino

 

[manqiangrexue]

First of all Your question includes much too much of pure guesswork: We simply do not know the percentage of the composit structures of the J-20's airframe. Also even if slightly smaller - e.g. not as long - the J-20 is surely more compact and surely has a decent internal volume both for weapons and fuel), even more we don't know how much weight the avionics has. As such I think it will be more or less a good estimation to be roughly similar to a Flanker ... but to conclude anything especialyl in regard to performances will be simply way off.

Additionally there is so far no "AL-31FN3 for J-10". that's a fact and the so far most powerful AL-31FN version is the AL-31FN series III for J-10B, which is however a completely different beast to the projected AL-31F3 - again there is no AL-31FN3 - ... making any assumptions in regard to performances simply useless.

Deino

I might have not had the designation right but isn't the series III for the J-10B highly up-rated? Anyway, having a very voluminous weapons bay just means it CAN be filled with lots of weapons (which would weigh the same if you put them on any aircraft and you don't always have to fill your bays to max every time you go out) but it's filled with air for the empty-frame weight analysis. Being close to a Flanker is what I was hoping for and it should mean sufficient thrust even without WS-15. If it were significantly heavier than the F-22, then I'd start to worry and say that AL-31s may not cut it and the WS-15s are invaluable.

 

[no_name]

Being close to flankers is still not enough. Flankers cannot supercruise.

 

[manqiangrexue]

Being close to flankers is still not enough. Flankers cannot supercruise.

I don't think range is a weakness for J-20 and Flankers have enough range for even China's furthest territorial disputes. Still, it would be nice to supercruise to extend the loiter and combat time if needed. However, when we're talking under-powered, that is truly a fatal flaw when it doesn't have the option of maneuvering with its opponents if detected. As long as that problem can be avoided, it's not a huge gaping problem even if it can't super-cruise, in my opinion.

 

[tphuang]

I might have not had the designation right but isn't the series III for the J-10B highly up-rated? Anyway, having a very voluminous weapons bay just means it CAN be filled with lots of weapons (which would weigh the same if you put them on any aircraft and you don't always have to fill your bays to max every time you go out) but it's filled with air for the empty-frame weight analysis. Being close to a Flanker is what I was hoping for and it should mean sufficient thrust even without WS-15. If it were significantly heavier than the F-22, then I'd start to worry and say that AL-31s may not cut it and the WS-15s are invaluable.

Series 3 is 13.5 kg ton in thrust, which makes it quite underpowered for J-20 imo, but that's what they have right now, so they have to use it.

 

[Totoro]

I remember salyut said fn series 3 offered 1000 kgf over predecessor, not specifying what the predecessor was. While it may be regular al31fn, it may also be something else.

Salyut evidently has tight relationship with chinese, making custom and uprated variants for them. some even say m1 modification was initiated and (partly?) Funded by chinese. If true, who is to say that m2 variant is also not initiated and funded by china? It sounds entirely plausible that china can get its hands on m2 engines as soon as they are done testing. 145000 kgf is in class of 117 engines as it is. Plus we have that interview from zhuhai where the guy said current ws10 variant goes up to 140 kn.

So initial j20 variant, active in 2018 or so, is bound to have at least engines of such thrust, be they al31fm2 or some uprated ws10 variant.

 

[manqiangrexue]

Series 3 is 13.5 kg ton in thrust, which makes it quite underpowered for J-20 imo, but that's what they have right now, so they have to use it.

Why? How much do you think J-20 will weigh in comparison to Flanker?

2 of these series IIIs make 27 tons thrust. 8 Pl-12 is 1.6 tons (for the sake of simplicity, as usually, you'd carry 6 like the PL-10 and 2 like the smaller PL-8). Let's say aircraft is 20 tons empty. That leaves 5.4 tons of fuel (max load for Flanker is 10 tons) for 1:1 TWR. If the conflict is close, it could take off with light fuel load. If it is far; it could take off with a lot of fuel, but by the time it got there, a lot would have burned off.

If a Flanker were loaded like that, it would be 18 tons of aircraft + 1.6 tons of missile + 5.4 tons of fuel = 25 tons with 25 tons thrust (AL-31F = 12.5 tons each) so 1:1 TWR also. Compared to conventional fighters, J-20 doesn't suffer from external load drag.

F-22 is 22 tons. 8 AMRAAMs are about 1.4 tons. From 2 x 156kN engines, it has 31 tons of thrust [although I'm not sure if constricted thrust-vectoring stealth nozzles further reduce this by some amount (I've heard 15% = 26.5 tons)]. Assuming it's 31 tons, add 5.4 tons of fuel and that's 31 tons of thrust for 28.8 tons of load = 1.076 TWR. But if there is a stealth nozzle reduction that is unaccounted for in the 31 ton figure, then the TWR could go as low as 0.92.

I know that the 3 jets use fuel with varying levels of efficacy but if I'm not mistaken, J-20 was designed to make optimal range out of its fuel.

From this, it looks to me like even if 13.5 tons is a bit lacking due to increasing standards, it's not far off. A 14.5-15 ton engine would work quite nicely and a 15.5-16 ton engine would be fantastic. But it doesn't even come close to needing the 18+ tons of the WS-15. Of course, this assumes that J-20 is 20 tons empty, not 25 LOL

 

[tphuang]

Having underpowered engine doesn't allow the flight tests to cover full suite of situations that the design calls for. Ideally, you would want to test it to see its max supercruise speed or if it can supercruise under different operational scenarios. Or testing the turn rates, climb rates and rest of the flight envelope under different payload and altittude.

Again, I'm saying this based on the assumption that they are using standard AL-31FN series 3 engines on the recent prototypes. They could be tuning up the thrust level since they probably don't care if these engines die out faster than the ones they normally use for J-10B. And yes, I'm basing the 13.5 ton on Series 1 AL-31FN's thrust of 12.5 ton + 1 ton increase. It could be that Series 2 had slight increase in thrust. I believe the service life was better, but not sure if the thrust was higher or not.

99M series was at least partially funded by China and it's behind schedule. The upgraded variant of Taihang will hopefully be ready soon, but who knows at this point. On a side note, it's interesitng to see down the line if the progress of this upgraded Taihang is holding back J-15/16 production. Anyhow, I think they have to be producing production configured J-20 for FTTC by 2016 so FTTC can start evaluating, testing and developing tactics before the first regiment gets formed. That doesn't leave much time for this upgraded AL-31FN or Taihang to be in mass production.

 

[manqiangrexue]

Having underpowered engine doesn't allow the flight tests to cover full suite of situations that the design calls for. Ideally, you would want to test it to see its max supercruise speed or if it can supercruise under different operational scenarios. Or testing the turn rates, climb rates and rest of the flight envelope under different payload and altittude.

Again, I'm saying this based on the assumption that they are using standard AL-31FN series 3 engines on the recent prototypes. They could be tuning up the thrust level since they probably don't care if these engines die out faster than the ones they normally use for J-10B. And yes, I'm basing the 13.5 ton on Series 1 AL-31FN's thrust of 12.5 ton + 1 ton increase. It could be that Series 2 had slight increase in thrust. I believe the service life was better, but not sure if the thrust was higher or not.

99M series was at least partially funded by China and it's behind schedule. The upgraded variant of Taihang will hopefully be ready soon, but who knows at this point. On a side note, it's interesitng to see down the line if the progress of this upgraded Taihang is holding back J-15/16 production. Anyhow, I think they have to be producing production configured J-20 for FTTC by 2016 so FTTC can start evaluating, testing and developing tactics before the first regiment gets formed. That doesn't leave much time for this upgraded AL-31FN or Taihang to be in mass production.

Ah, you mean that testing is hindered due to the fact that they are using an interim engine, underpowered compared to the intended WS-15. Yes, of course. I was wondering how good the J-20 would be just with the AL-31FN series III, if WS-15 didn't exist and that were the final engine (although that's an underestimation since they would at least get AL-41 rather than settle for the series III). I was wondering if the J-20 with AL-31FN series III would be underpowered compared to other prominent jets, not compared to J-20 with WS-15.

 

[no_name]

I don't think range is a weakness for J-20 and Flankers have enough range for even China's furthest territorial disputes. Still, it would be nice to supercruise to extend the loiter and combat time if needed. However, when we're talking under-powered, that is truly a fatal flaw when it doesn't have the option of maneuvering with its opponents if detected. As long as that problem can be avoided, it's not a huge gaping problem even if it can't super-cruise, in my opinion.

It's not just about range. And being able to do something that your opponent can't is always an advantage.

If you compare with flankers, then maybe it's not bad or even superior. But J-20 was originally designed partly with F-22 in mind (or mainly?) so I don't think they will settle for AL-31FN even if it was otherwise similar to flankers in performance.