Someone (TSQ I think) actually did a measurement of the wingspan based on the length of the aircraft. Can't find the thread on CJDBY right now.
J-20... The New Generation Fighter III
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Someone (TSQ I think) actually did a measurement of the wingspan based on the length of the aircraft. Can't find the thread on CJDBY right now.
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Actually, the reason those people assume J-20 as some kind of interceptor is because of their existing prejudices that China is inferior. Treating the J-20 as an interceptor allows them to avoid the situation where they have to accept some form of competence on China's part. Remember how events unfolded when J-20 first appears:
- people claimed the pictures as photoshopped, and gave "evidences" showing how various sections of the J-20 were copied from F-22, F-35 and Mig1.44;
- when clear pictures come out, some claimed it is a static model, while some maintained the entire thing is fake and explained how it is not mechanically possible for the entire tail plane to be movable;
- when pictures and videos showed the aircraft moved, some of those people claimed the aircraft cannot fly and was purely used for ground testings;
- when J-20 took off, the claim was changed to say the aircraft is only a tech-demonstrator and has no weapon bays;
Anyway, what you have pointed out shows that classic aerodynamic theories are not applicable on modern fighter aircraft. That's not to say such theories are totally useless, but the fact is these theories can only give you information about the aircraft performance at cruise condition. Outside of this condition, such as when the aircraft is in a maneuver, analysis needs to be done using CFD and wind tunnel testings.
If you read Dr. Song's paper, you will understand J-20's configuration is meant to provide high-lift. The title of the paper is "一种小展弦比高升力飞机的气动布局研究" or "Research on a low-aspect high-lift aerodynamic configuration", and in it you will see that high lift at high AoA is attained by the use of multiple vortices over the wing. We have seen the vortices described in the paper in photos of J-20 already.
And yes, the configuration is indeed a compromise. It is a resulting of having to attain F-22's maneuverability without equivalent powerful engines. It is doing the same for less, and this reflects the superb aerodynamic performance of the aircraft.
---------- Post added at 01:18 PM ---------- Previous post was at 01:09 PM ----------
The canard does not push down on the nose. Rather, the canard is position that way to have zero-incidence with the oncoming air. By measuring the angle of the canard, you can deduce the angle-of-attack of the aircraft at that moment.
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I noticed that too delft, and also wonder, the cockpit is on a longer moment arm than most conventionally configured fighter aircraft. Aircraft will pitch around the center of gravity? I'm open to instructive criticism, try to be nice, my thought is the pilot might get seasick, think of the pilot of the Concorde, far forward of the center of lift, as he rotates, he finds himself far above the ground before the mains are airborne, this exagerates the sensation of pitch changes, hence he is experiencing much the same effect as a person playing crack the whip. Jumpin to a different vehicle, but staying on topic of J-20 pitch, Honda, Suzuki, Yamaha, and Kawasaki all have 1000 cc sport bikes. They used to have proportionately longer wheel bases, and due to the need for long suspension travel are fairly tall when you sit on them. In order to improve turn in Honda came up with the concept of mass centralization, that is moving heavy stuff, engine, transmission, swing arm and forks, fuel and oil closer together at the center of gravity, this also shortens up the wheelbase making the chassis more active, or twitchy. I believe this is where some of us are thinking the J-20 may be more stable in pitch, whereas a short coupled fighter is more agile. You really can't completely negate the effects of a longer "wheelbase" with aerodynamic fixs, you can mitigate those effects, but you can't completely negate them. Think about what I'm trying to say before you launch that sidewinder, I am "not" criticizing or putting down the Chinese engineers or this brilliant aircraft. Thoughtfully, Brat, considering Delfts addenda,
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Major
Those who think J-20 is stable is just the same bunch who think J-20 is an interceptor. Consider the followings:
- As flight control systems advanced, they enable fighter aircraft to lose stability. The demand for ever more performance in turn pushes aerodynamics and flight control systems to become more sophisticated, and the cycle repeats. This results in a trend where the more modern a fighter aircraft is, the less stable it becomes. Why would J-20 break this trend?
- With J-10, Chengdu has already mastered the technique to design and construct fighter aircraft which is unstable. Why would they now go backward and design an aircraft that is more stable than when performance requirements dictate the opposite to happen?
Given that J-10 is unstable, and going by the reasonable expectation that J-20 will be less stable than its predecessors, then we can conclude that J-20 is also unstable.
The claim that J-20 is stable is just another way to claim J-20 as an interceptor. The only people who come up with such claims are those who assume Chinese engineers are all brain damaged or totally incompetent -- that when everybody else has already moved on from the emphasis of speed, the Chinese would still be relentless at trying to make their aircraft fly faster to meet 2nd generation standard. The prejudice is crystal clear.
Anyway, I think what you are trying to get at is that J-20 has higher inertia than a shorter aircraft. This may be the case, but you must also realize that the moment arm for each flight control is also longer. This means the flight controls exert more torque on the aircraft, increasing speed of the response. So, the disadvantage of a higher inertia and the advantage of longer moment arms cancel out one another, meaning the aircraft being longer is a non-issue as far as maneuverability is concerned.
J-20 is described by some to be the first aircraft to combine lifting body with canard design.
A lifting body is a fixed-wing aircraft configuration in which the body itself produces lift. In contrast to a flying wing, which is a wing with minimal or no conventional fuselage, a lifting body can be thought of as a fuselage with little or no conventional wing. Whereas a flying wing seeks to maximize cruise efficiency at subsonic speeds by eliminating non-lifting surfaces, lifting bodies generally minimize the drag and structure of a wing for subsonic, supersonic, and hypersonic flight, or, spacecraft re-entry. All of these flight regimes pose challenges for proper flight stability.
I think not long ago siege put up a translated article on the J-20 that would have laid to rest whether this aircraft is designed as a maneuverable interceptor or a fully competitive 5th-gen air superiority breed. Maybe someone can find the link for it, or I can always repost it again.
A lifting body is a fixed-wing aircraft configuration in which the body itself produces lift. In contrast to a flying wing, which is a wing with minimal or no conventional fuselage, a lifting body can be thought of as a fuselage with little or no conventional wing. Whereas a flying wing seeks to maximize cruise efficiency at subsonic speeds by eliminating non-lifting surfaces, lifting bodies generally minimize the drag and structure of a wing for subsonic, supersonic, and hypersonic flight, or, spacecraft re-entry. All of these flight regimes pose challenges for proper flight stability.
I think not long ago siege put up a translated article on the J-20 that would have laid to rest whether this aircraft is designed as a maneuverable interceptor or a fully competitive 5th-gen air superiority breed. Maybe someone can find the link for it, or I can always repost it again.
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^^ First to blend canard with LERX and lift body, to be exact.
The combination purportedly enhanced lift by almost 50% over conventional lift-body designs.
---------- Post added at 10:43 PM ---------- Previous post was at 10:12 PM ----------
J-20 flew again earlier today. Apparently the plane flew daily since 2-27-12, according to eyewitnesses. Are we about to see 2003 any time soon?
The combination purportedly enhanced lift by almost 50% over conventional lift-body designs.
---------- Post added at 10:43 PM ---------- Previous post was at 10:12 PM ----------
J-20 flew again earlier today. Apparently the plane flew daily since 2-27-12, according to eyewitnesses. Are we about to see 2003 any time soon?
I think it was here
http://www.sinodefenceforum.com/mem...-chinese-military-article-take-look-5679.html
Kinda sad the home thread at chinese defence hasn't had many translated articles in recent months, it was always good and appreciated reading.
Yeah, unlike quesionts such as what engines the J-20 is using, how stealthy or manoverable it is, how many missiles it carries, etc. J-20 being an unstable design never have been questioned among the Chinese fans... And everybody knows about that paper by Dr. Song.
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