J-20... The New Generation Fighter II

[Blitzo]

Responding to comments on J-20's poor manoeuvrability huzigeng said that "if the J-20 were a fighter bomber then the YF-23 is not only a fighter bomber but a fighter bomber with pathetic manoeuvrability".

Oh snap

 

[Engineer]

note the position of the LCA landing gear

LCA isn't even a canard-delta, so it has no relevance in this discussion.

now look at the viggen and J-20`s

Again, you have no information on the aerodynamic center of either plane. Position of the landing gears only gives you a hint on where the center-of-gravity might be, but provide absolutely no information on the aerodynamic center.

 

[Engineer]

at cruise having a highly loaded canard and a wing quit aft of the main landing gear will give it lots of canard deflection once center of lift moves backward at supersonic speeds

No. Center-of-lift moving backward means length of moment arm of the canards increase, so greater pitching moment can be provided using smaller deflection.

 

[siegecrossbow]

Oh snap

I think the whole issue of judging an aircraft purely from the shape is flawed. Western analysts first believed that the MIG-25 was a all around super fighter since they thought that the large vertical stabilizers were a sign of good manoeuvrability. Little did they know that the actual fighter is a stainless steel behemoth whose large stabilizers are necessary for maintaining stability at high speeds and altitudes. The same professional experts also made the mistake of comparing the Su-24 Fencer, a ground attacking aircraft, to the F-14 Tomcat due to an overestimation of the engines used. My point is if trained professional analysts could make huge mistakes judging a plane's performance purely from it's shape (lacking information regarding the material and engines), what about us amateurs? Are you sure that analysts are not underestimating China's ability?

 

[MiG-29]

A more accurate description is that you are seeing only what you want to see. What determines the longitudinal stability is the aerodynamic center for the aircraft. The aerodynamic center for the wings by itself means absolutely nothing. And the reason I say you are seeing only what you want to see is because you are cherry picking the wing's aerodynamic center as the sole influence on stability while completely ignoring the effects of canards on the position of the aerodynamic center.


This is not a support for your conclusion that the aerodynamic center is aft of the landing gears. Rather, it's just a reworded version of your original statement in disguise, which still has no proof to back it up.


No. The canards themselves provide lift, unlike traditional tails that receive downwashed from the main wing which kills some of the lift. There is no indication that canard increases drag. Canards allow the vortices going over the wings to be controlled, thus enhancing controllability of the entire system.


Canards do not have to be as big as the wings if the moment arm of the canards are longer. Stability in the longitudinal axis is determined by the overall aerodynamic center for the aircraft, and as long as it is ahead of the center-of-gravity, the plane is unstable.


Pitch control on the J-20 is provided by both canards and V-tail, as evident from the pictures.

To start not all aircraft with canards are unstable, the Viggen is stable, the Kfir is stable, the B-70 is stable,, the concordinsky T-144 and Sukhoi T-4 are stable.

Second canards kill lift because their turbulance down washes the wing common myth is that canards increase lift at at level flight, no they do not and there is evidence well documented they only increase lift at high AoA.

Canards can be used of course as pitch control but their position have compromises, if you set the canard as a pitch control device farther from the center of gravity means their vortices have less ability to re-energize the wing at high AoA.

The Rafale canards are set for vortex re-energization while the Eurofighter`s for pitch control

 

[MiG-29]

No. Center-of-lift moving backward means length of moment arm of the canards increase, so greater pitching moment can be provided using smaller deflection.

incorrect the center of gravity remain the same unless you use artificial stability like in the Su-27, also canard are swiveling on a fixed point that is the real fulcrum of the lever arm so you are just claiming irrealities

 

[siegecrossbow]

To start not all aircraft with canards are unstable, the Viggen is stable, the Kfir is stable, the B-70 is stable,, the concord is table.

Second canards kill lift because their turbulance down washes the wing common myth is that canards increase lift at at level flight, no they do not and there is evidence well documented they only increase lift at high AoA.

Canards can be used of course as pitch control but their position have compromises, if you set the canard as a pitch control device farther from the center of gravity means their vortices have less ability to re-energize the wing at high AoA.

The Rafale canards are set for vortex re-energization while the Eurofighter`s for pitch control

What exactly are stable and unstable canards? Did you mean control canards and lifting canards?

Of the examples of "stable" canards you've lifted which one is capable of the same deflection featured on the J-20. If the canards on the J-20 are simply used to provide lift why not fix them and use control rudders, as in the case of the Viggen?

 

[MiG-29]

I think the whole issue of judging an aircraft purely from the shape is flawed. Western analysts first believed that the MIG-25 was a all around super fighter since they thought that the large vertical stabilizers were a sign of good manoeuvrability. Little did they know that the actual fighter is a stainless steel behemoth whose large stabilizers are necessary for maintaining stability at high speeds and altitudes. The same professional experts also made the mistake of comparing the Su-24 Fencer, a ground attacking aircraft, to the F-14 Tomcat due to an overestimation of the engines used. My point is if trained professional analysts could make huge mistakes judging a plane's performance purely from it's shape (lacking information regarding the material and engines), what about us amateurs? Are you sure that analysts are not underestimating China's ability?

You are correct but remember the aerodynamic shape of an aircraft can be studied easily what they can not study is engines thrust, or construction materials, they assumed the MiG-25 was agile upon the view the MiG-25 was lighter and had better engines and probably better avionics, with the J-20 is the same they say if the J-20 gets better engines than the F119 and good avionics then it will be a F-22 killer, but without all western analysis are not flawed

 

[MiG-29]

What exactly are stable and unstable canards? Did you mean control canards and lifting canards?

Of the examples of "stable" canards you've lifted which one is capable of the same deflection featured on the J-20. If the canards on the J-20 are simply used to provide lift why not fix them and use control rudders, as in the case of the Viggen?

The Viggen canards are not fixed they have hinges or flaps in other words, the use of foreplanes is not a synonim of relaxed stability, there are not stable or unstable canards just relaxed stability aircraft

 

[Engineer]

To start not all aircraft with canards are unstable, the Viggen is stable, the Kfir is stable, the B-70 is stable,, the concord is table.

No one claims that all aircraft with canards are unstable. I am questioning your claim that J-20 is stable. Also, Concorde does not have canards.

Second canards kill lift because their turbulance down washes the wing common myth is that canards increase lift at at level flight, no they do not and there is evidence well documented they only increase lift at high AoA.

In level flight, canards can provide lift by simply deflecting upward.

Canards can be used of course as pitch control but their position have compromises, if you set the canard as a pitch control device farther from the center of gravity means their vortices have less ability to re-energize the wing at high AoA.

The Rafale canards are set for vortex re-energization while the Eurofighter`s for pitch control

Nice try at confusing the issues. Distance between canards and center-of-gravity has no relationship with the vortices' ability to re-energizing the airflow above the wing. That is affected by the distance between the canards and the wings.