J-20... The New Generation Fighter II

delft said:

During dog fighting in the '60's the air speed of the fighter aircraft rapidly decreased to some 400 km/h. At that speed thrust vectoring is very important. I can't remember reading about any more recent experience.
My expectation is that in the next 6 years J-20 will be fitted with stronger engines with thrust vectoring, but I'm not really a competent judge of the matter.

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During the last red flag, Indian MKIs made themselves into sitting ducks when they engaged their thrust vectoring during mock dogfights because the extreme directional change from using tvc to it's full meant a fighter bled off airspeed like crazy.

In modern air combat, speed and energy states are key. That is why fourth gen eurocanards and the J10 has put a lot of emphasis on transonic agility and the J20 seems to be designed as an extension of that philosophy.

TVC will no doubt add to a plane's agility, however, it's true importance may be to limit control surface movement and so help a plane better retain speed and energy during turns instead of making air show stunts that are of limited use in actual
combat.

If TVC is used to limit control surface movement, then it will only add a marginal improvement in agility and it's omission would by no means be a critical shortcoming. Besides, full operational deployment is still nearly a decade away. Plenty of time to add TVC to the WS15 if it was really deemed necessary.

This is what I expected. Pilots should have no direct control over TVC. The optimal use must be computed by the fly-by-wire system. And it is a nice exercise for the designer to determine, whether the extra weight and cost and the increase in maintenance is a reasonable price to pay for the slight (?) increase in manouvrability to be achieved.

In my amateur opinion, I'm thinking that the J-20 is designed aerodynamically to exploit primarily lift enhancement and drag reduction, but less for roll rates. So if they decide to put 3D thrust vectoring in the aircraft they may likely to be independently adjustable (maybe automatically by flight laws) for exactly that purpose. Thus once engine and TVC issues are solved you will eventually have a fighter that:

generates good lift without increasing AoA too much to bleed energy.
low drag for good supercruise performance and generally faster acceleration.
thrust vectoring mainly used to aid rolling abilities

This should IMHO, creates a potentially very maneuverable plane.

picture what the internal weapon bay going to look like.

challenge said:

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picture what the internal weapon bay going to look like.

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Whoa, let's step back a bit first. Look at the position of the canards relative to the fuselage. That's not consistent with the J-20s configuration. There's no LERX either. I think these pictures are old wind tunnel or computer images of weapons bay possibilities for either the CAC or SAC proposal for the J-XX. Based on the current view there is I'm leaning towards the SAC one, which was basically an F-22 with canards and a double delta style wing, which would fit in with that picture.

Yeah it may be the tri-plane design.

edit like this one:

no_name said:

Yeah it may be the tri-plane design.

edit like this one:

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This design was supposedly abandoned since the final plane was too long/overweight and was more complicated than CAC's design.

Yes I think it competed with an early version of the J-20 and lost out. It was the most aerodynamical, but has the most drag and most unstealthy of the design.

Quickie said:

Actually I'm not so convinced the acrobatic-like type of thrust-vectoring maneuvers would be really useful in a dogfight. What's more important is the extent of improvement in turn rates that thrust vectoring could possibly provide, something which I think depends largely on the design of the aircraft itself.

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Ofcourse it is useful. Thrust vectoring improves turn rate on ALL directions - something very desirable in the super agility criteria in the 5th generation fighter.

Pitch


Roll


Remember, that J-20's canards only improve the pitch and roll part (see the picture above) - they don't offer any improvement with yaw. J-20 completely relies on its all-moving tailfins (vertical stablizers) to do the yaw. With thrust vectoring, it will hugely improve combat turn rate along the yaw axis (see below).

Yaw



The "super maneuverability/agility" criteria stems from the hypothesis that, if no fighter size long range "anti-stealth" radar is operational in near future, and as stealth technologies improve - it means stealth fighters of opposing sides would fly into each other "blind" until visual range - and thus the need for close range dog fighting capabilities for 5th generation aircrafts.

But your acrobatic maneuvers are still limited by two factors:
* the ability of the pilot to remain functioning. He or she is well supported, but there are still limits
* the speed loss of the aircraft during the maneuver. If your aircraft loses too much speed your still lost.