J-20 5th Gen Fighter Thread VI


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Biscuits

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J-20 main role is to bypass escort fighters and being the stealth spoting eye forward penetrating scout for the J-16 carrying extra long range PL-21 hunt force multipliers like oil tanker and early warning command control once those are gone remaining escort fighters will have no eyes no leg range turning on radar will make it much easier target turning on flashlight in absolute dark night in the vast Pacific ocean no where for emergency landing once the fuel is empty war is not knight joust if you're fighting fair then you are not trying, missiles will always have way more kinematic performance than platforms so over chasing fighter engine performance is a fruitless pursuit
Well, that’s a different type of mission. If those targets present themselves, then J-20 can seal club them quickly. But that scenario would likely only come up later on when a hypothetical enemy’s attack has already been blunted.

Hunting down stealth fighters, stealth bombers and high end 4.5 gen would still be the main activity.
 

Inst

Senior Member
I think the reason you are getting these numbers is because you are selecting the lowest fathomable, not even realistic, numbers for the WS-10X and taking the highest imaginable for the WS-15. Most sources, although none with absolute authority, say that the J-20A uses AL-31FM2, which is a Russian engine with 145kN thrust. If this is replaced by a WS-10 variant, I think it's safe to assume that at the very least, it won't be much worse in wet thrust, but possibly better. So 145kN is more realistic for the J-20A, perhaps higher. Then, the most commonly cited number for WS-15 is 180kN and that is already monstrous; there is absolutely no need to go to 197kN. And this is assuming that the engineers reached their target thrust; if they don't or it's taking too long, it's totally possible to release the engine for use at some 170kN or so (assuming other parameters are acceptable). If the engineers got it up to 180 with acceptable performance factors in other areas, it's ready to go as WS-15A. There is no time to keep tweaking it up further at the expense of holding up J-20B production. So, I'm looking at an increase to 180kN from at least 145kN which is at most a 24% increase. And all these numbers are totally haywire because we don't really know how much thrust WS-10X J-20A has and we really really don't know how much thrust WS-15 J-20B will have. I don't know why we're having this discussion really.
Lowest thrust figures for the J-20 come from AL-31F, i.e, just the stock AL-31F at around 250kN combined. The WS-10 figures range from 132 to 140kN, both of which are relatively low.

If we go by best case to best case figures, it's 197kN vs 140kN, which gets us to roughly 40% thrust boost, which is still a lot.
 
Lowest thrust figures for the J-20 come from AL-31F, i.e, just the stock AL-31F at around 250kN combined. The WS-10 figures range from 132 to 140kN, both of which are relatively low.

If we go by best case to best case figures, it's 197kN vs 140kN, which gets us to roughly 40% thrust boost, which is still a lot.
Yeah, I know how you got those numbers; I'm saying they're not correct. Reread my comment you quoted and you'll see why it's wrong to use stock old/early AL-31F or WS-10X numbers on J-20. To think that J-20 might be powered by a 125kN AL-31F when J-10 uses a 137kN AL-31FN3 is just... not... smart. WS-10X figures might have been usable if it weren't for the AL-31FM2 providing 145kN thrust with the Chinese unlikely to downgrade the engine for its premier fighter just for indigenization (especially at a time when relations with Russia are very warm). That's why I said that the lowest realistic thrust for J-20A is 145kNx2 but it could be a bit higher.

I have seen some unreliable sources talk about a 197kN figure for WS-15; I have also seen some talk about a 220kN figure. They don't make sense to me. Most sources seem to center on 180kN and have previously (in the comment you quoted) outlined why it doesn't make sense to me for them to keep the engine still in prototype phase trying to get numbers that high rather that release it at 180kN (or even 170kN if they're having trouble) and open the bottleneck for J-20B production.

Could you post the sources you have for 197kN so we can better understand why you seem to have such high regard for a number that the rest of us generally view as a fanboy rumor?
 

Air Force Brat

Brigadier
Super Moderator
In the first photo, he is 'standing" on the left rudder, note the high degree of differential in rudder deflection, of the left and right rudder! This gives a clue into the highly sophisticated FCS of the J-20. The high degree of deflection on the left rudder creates a great deal more drag than the more lightly deflected right rudder, increasing drag on the left rudder and pulling the nose through to the left...

and yes, if he was rolling to the right, the right rudder would then have a much higher degree of deflection than the left aileron.

So this is a "very aggressive" maneuver at a relatively low airspeed, you very seldom see such large control deflections on jet aircraft even during heavy maneuvering. I would suggest he is likely around 250Kts, bleeding to around 200Kts as he makes a relatively agreesive pitch up, then begins the roll, which as you can see is very agressive, the right aileron is deflected downward, increasing lift (and drag) on the right wing. The left aileron is deflected upward, decreasing lift (and drag) on the left wing...

Hence the heavy rudder deflection to overcome "adverse aileron yaw", so this aileron deflection, creates a very strong yawing moment to the right, so heay aileron deflection is necessary to overcome adverse aileron yaw.

The greater rudder deflection on the "boot side rudder" is also outboard of the center line, effectively increasing its aerodynamic leverage with a larger "moment arm".
 
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