J-20 5th Gen Fighter Thread VI

[latenlazy]

You supposed to know the equation includes wing span, oh! wing span guess what Flanker has longer wing span haha do you know why F-14 has more lift when its wings are less swept? bigger span, one thing is exposed area and another is reference area, do you know what is the reference area of a helo?

...but the J-20 has a much longer midchord length than the Flanker, which is also part of the equation? The point is the J-20 has much greater wing area than the Flanker. You made a verifiable claim, that the J-20's wing area was smaller than the Flankers, and you were wrong (because you tried to use subjective judgements rather than make objective measurements).

The F-14 gets more lift when it's wings are less swept because all else held equal lift coefficient is greater for wings that are less swept with a shorter midchord length. This is not because of wider span though! Yes, it does have something to do with how the airstream interacts with a wing that has a shorter midchord length, but we account for that through experimentally determined lift coefficients because what determines a wing's lifting (and drag) properties is much more than the length of its midchord or its wing sweep! I'm glad you suddenly acknowledge that lift coefficients do matter! That still doesn't mean the Flanker has more wing area though. Whether the Flanker's less swept shorter midchord length wings have a better lift coefficient is a completely unrelated point from whether the Flanker has more wing area than the J-20. Try again. Even if the Flanker did have a wing with better lift coefficient though, the J-20's wings would still have a lot more area for lifting forces to act on, which is why we even factor in wing area in the first place. Either way we wouldn't know which wing has a superior lift/drag curve just by eyeballing, because what determines those coefficients is more than just one or two of a multifactor variable!

Also, a lower swept wing isn't always necessarily superior for a fighter. The tradeoff to less sweep is also greater drag, so you may not come out with a favorable lift to drag ratio. There's a reason why variable sweep designs have been retired for deltas with vortex generators and nearly all 4.5+ designs opted for delta/trapezoidal wings. Nor is wing sweep the only factor to lift coefficient, and the J-20's wing does not fit an all else held equal condition with either the Flanker's or the F-14's, so simply pointing at their sweeps won't tell you how their lift and drag coefficients compare to one another with their different combination of wing sweeps, chords, and other potential lift enhancers.

 

[duncanidaho]

View attachment 42933

Another attempt ... (left my previous try)

... problem is, the J-16 is a bit distorted and the J-20's radome-tip is not exactly visible.

View attachment 42943

The camera seems to be right above the first J20 in the middle in the first picture. As you look closely at the vertical stabilizer of two J20 behind the first one, you can see they are showing more backward than the one in the middle in front of them. The J16s are behind the J20s in the second row, and much further behind the J20 in the middle, so therefore their length are more compressed.

I think it isn't an idea to use this image as measurement for the J20.

 

[Deino]

The camera seems to be right above the first J20 in the middle in the first picture. As you look closely at the vertical stabilizer of two J20 behind the first one, you can see they are showing more backward than the one in the middle in front of them. The J16s are behind the J20s in the second row, and much further behind the J20 in the middle, so therefore their length are more compressed.

I think it isn't an idea to use this image as measurement for the J20.

I can fully understand all concerns and reasons mentioned which cause inaccuracies but that image is the best available so far and therefore still the best opportunity to estimate the dimensions.

Deino

 

[b787]

.The point is the J-20 has much greater wing area than the Flanker.

You do not know what you are saying at all, one thing is exposed wing are and another reference wing area which uses the longitudinal symmetry reference line

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For starters the Flankers like the F-14 has wider wing span why? simply because the engines are widely separated, thus the reference area has wider wing span thus more area and the Su-27 like F-14 has the pancake area which also generates lift.

Same is the F-14, you are dreaming the F-14 at lower speeds has higher lift than J-20, it has much wider area due to longer wing span thus using reference area the Tomcat is designed for lower speeds and will get much higher lift at landing approaching speeds.
F-14 also increases camber when it sweeps to lower angles thus it generates more lift.
You can see easily Deltas are not good naval fighters, but good interceptors

The exposed wing of the J-20 is not big, is the wetted area of the wing the real wing, and is not part of the fuselage, it is the actual wing.

J-20 is designed for higher cruising speeds than Flanker, you can see Su-57 also has more swept wings, but F-14, Su-27 and Su-57 have widely separated engines, F-14 did not use canards at landing or take off but Su-27 needed them during approach the landing speeds thus they made the Su-33.

J-20 uses bigger canards than Su-33, however Deltas lost lift in wing tip vortex generation.


This affects lift when they turn so deltas use canards to recover lift using the vortex of the canard to reinforce lift in the main wing.
Su-35 has high yield engines lower swept and TVC nozzles, the fighter will be superb at sustained turn rates, but is not that good as Rafale as instantaneous turn rates due to higher wing loading.


J-20 uses fuselage lift and the canards to compensate for the small wetted area and smaller wing span, with TVC will achieve STOL capability improving landing and take off speeds

 

[Figaro]

no it is a dogfighter so your macho pride does not hurt happy?

You are clearly mistaken here. The J-20 has maneuverability as one of its 4S criterion according to a CAC academic journal. If I'm not mistaken, CAC won over SAC's prototype due to the former's superior AOA. Subsonic, transonic, and supersonic maneuverability were key parameters for the J-20 ... now tell me how it's not a dogfighter?

my friend you lose your time there is a saying to a fool never answer if i am one do not answer me

So in this case, I presume you're the fool?

 

[Engineer]

There are definite advantages for TVC. I would say Russians pursuing it back in the 80s and 90s was a wise move. China may even (if not already) benefit from those Russian efforts. Certainly worthy of closer investigation and developing this technology may yield better results in the future when new materials etc can overcome the challenges of excessive weight, wear, sacrificing some thrust... just some of the drawbacks we're aware of. Fighters today have gone to the edge of human ability. In many cases, the thrusts produced and g forces are already too much. The smarter move for China and Russia is to try and match the US in drone and UCAVs. Unmanned and remotely controlled fighters offers so much potential. Both countries do have some pretty advanced drone programs though they lag the US a little.

TVC advantages are limited to last-ditch scenarios, such as retaining control when the aircraft stalls and all the control surfaces become useless.

Marketing gimmicks like "adding TVC makes the aircraft more manoeuvrable" and "using TVC creates less drag since control surface deflect less" are no different than claiming "making something out of nothing" -- pure nonsense.

Energy is required to move an aircraft out of equilibrium flight condition. That is, it takes energy to prevent the aircraft from flying straight. Post-stall manoeuvres like those in airshow continuously take huge amount of energy, because the aircraft is so far from equilibrium flight condition. Since energy must be conserved, and thrust-vectoring doesn't produce extra thrust, the energy must come from forward kinetic energy of the aircraft. That is why aircraft loses speed so quickly when using TVC.

In actual dog fight exercises, aircraft using TVC get more easily defeated. This has been proven many times.

Is WS-15 set to get TVC options? Is it really necessary for the loss of thrust and increased weight and maintenance problems? I mean J-20 doesn't even have a gun installed in current models. They don't want to be using such a high end and expensive fighter for these things. There are plenty of capable WVR fighters in PLAAF. VLO is reserved for taking out strategic targets and matching US and Japanese F-35 and F-22s. Why bother with TVC when you just want to take long and medium range shots. Maybe have two PL-10s in case things get close. Develop TVC and learn from Russian tech (if not done already) by all means, but does J-20 really need or even want to have it? Supercruise is far more useful. Agility and manuevrability beyond a certain point is close to useless most of the time.

It is doubtful WS-15 will come with thrust-vectoring.

Look at all Chinese military programs, and there is one single trait between them: getting something usable out the door as quickly as possible, rather than getting all the bells and whistles.

China has enough trouble engineering a 15-ton engine. Last thing China would do is purposely sabotage its own engine program by adding complex thrust vectoring.

You also brought up a good point, that is manoeuvrability of fighters is already at maximal structure and human tolerance. There isn't going to be more manoeuvrability on top of existing manoeuvrability.

 

[Figaro]

Lada lada lada. We know quite well that the J-20 has been reported to have subsonic maneuverability mostly on par with Chinese 3/4th gens like the J-11 and J-10. Moreover, stop insisting that the J-20 isn't designed for TVC, since we know that the WS-15 will come out with TVC nozzles. It's intended to be serviceable with canards alone, but it's not really maneuverable without TVC additions.

The J-20 was specifically designed to have excellent maneuverability even without very high thrust engines or TVC. CAC designers were prudent enough to believe that China wouldn't have a suitable engine when the J-20 initially came out and hence designed it to compensate for such shortcomings. In no way did they envision the J-20 would need to depend on TVC for maneuverability ... and there have been no reliable reports of the WS-15 boasting TVC.

That said, it's somewhat disappointing to realize the J-20 is limited in wing area (73m^2 vs 78m^2 on the comparably-sized F-22); it strongly suggests it will be closer to the interceptor side of the fighter-interceptor combo.

I really hope you're not as ignorant as you sound right now ...

 

[RadDisconnect]

You do not know what you are saying at all, one thing is exposed wing are and another reference wing area which uses the longitudinal symmetry reference line

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For starters the Flankers like the F-14 has wider wing span why? simply because the engines are widely separated, thus the reference area has wider wing span thus more area and the Su-27 like F-14 has the pancake area which also generates lift.

Same is the F-14, you are dreaming the F-14 at lower speeds has higher lift than J-20, it has much wider area due to longer wing span thus using reference area the Tomcat is designed for lower speeds and will get much higher lift at landing approaching speeds.
F-14 also increases camber when it sweeps to lower angles thus it generates more lift.
You can see easily Deltas are not good naval fighters, but good interceptors

The exposed wing of the J-20 is not big, is the wetted area of the wing the real wing, and is not part of the fuselage, it is the actual wing.

J-20 is designed for higher cruising speeds than Flanker, you can see Su-57 also has more swept wings, but F-14, Su-27 and Su-57 have widely separated engines, F-14 did not use canards at landing or take off but Su-27 needed them during approach the landing speeds thus they made the Su-33.

J-20 uses bigger canards than Su-33, however Deltas lost lift in wing tip vortex generation.


This affects lift when they turn so deltas use canards to recover lift using the vortex of the canard to reinforce lift in the main wing.
Su-35 has high yield engines lower swept and TVC nozzles, the fighter will be superb at sustained turn rates, but is not that good as Rafale as instantaneous turn rates due to higher wing loading.


J-20 uses fuselage lift and the canards to compensate for the small wetted area and smaller wing span, with TVC will achieve STOL capability improving landing and take off speeds

Wing loading calculations are done using reference wing area. If you want to talk about reference wing area, why don't you look at your Su-57?

As for all this "tunnel" creating lift on the F-14, etc, it pays for it with more wetted area and parasitic drag.

 

[b787]

Wing loading calculations are done using reference wing area. If you want to talk about reference wing area, why don't you look at your Su-57?

As for all this "tunnel" creating lift on the F-14, etc, it pays for it with more wetted area and parasitic drag.

why Airliners use high aspect ratio and gliders use high aspect ratio and VG wings increase wing span, well it shows you do know not what you are saying when F-14 has more lift with fully swept wing or lower swept wings?

Deltas are for high speeds only that, canards are enhancers for low speed handling of delta wings.

Anyway enjoy your questions

 

[latenlazy]

why Airliners use high aspect ratio and gliders use high aspect ratio and VG wings increase wing span, well it shows you do know not what you are saying when F-14 has more lift with fully swept wing or lower swept wings?

Deltas are for high speeds only that, canards are enhancers for low speed handling of delta wings.

Anyway enjoy your questions

I didn't know fighters were supposed to be optimized for low speed . There is a reason why pointing to one lift coefficient value tells us nothing about performance. You need to look at the *whole* lift curve.

I take it that, since you deflected from raddisconnect's actual point (that wingloading is calculated using reference area), you acknowledge that you were wrong?