Aerodynamics thread

[Air Force Brat]

Sukhoi produced Su-33, Su-34 and Su-30MKI . These are all unstable fighters with canards . They also had Su-35 prototypes with canards and finally Su-47 . Therefore, like it or not, considering canards technology they are at the top



It is not number of edges, problem with canards is that they do not lay in same plane with the wing . 4.5th gen fighters like Rafale or Typhoon are not even optimized to have canards parallel with the wing (YF-23 was) .

I rather doubt you're going to find a picture of a YF-23 with canards ace, and the Sukhoi's canards are for vortex generation/lift enhancement, not their primary pitch control as is the distant coupled canard on the J-20. The Eng is right, the FBW system for the J-20 is very complex, and changes parameters as the aircraft speed/configuration is changed for different flight regimes, so Chengdu has the corner on the market when it comes to canard solutions. Dr. Song listed it as one of their most daunting challenges, folks should familiarize themselves with the good Drs. philosophy to the J-20, so that they might comment with some in-sight????

 

[thunderchief]

I rather doubt you're going to find a picture of a YF-23 with canards ace,

My bad, I made a mistake, thinking about something else

and the Sukhoi's canards are for vortex generation/lift enhancement, not their primary pitch control as is the distant coupled canard on the J-20. The Eng is right, the FBW system for the J-20 is very complex, and changes parameters as the aircraft speed/configuration is changed for different flight regimes, so Chengdu has the corner on the market when it comes to canard solutions. Dr. Song listed it as one of their most daunting challenges, folks should familiarize themselves with the good Drs. philosophy to the J-20, so that they might comment with some in-sight????

Not necessarily, if you have canards you would use them to stabilize your fighter and for pitch control even if you have a tail . Now, for some reason Chengdu prefers tailless designs, but that makes things even more interesting - canards would have to work as pitch control, increase lift and remain stealthy . That requires very complex algorithms and may delay introduction of J-20 into operational service .


P.S. Here, NATF , YF-23 with canards

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[F-15]

Yes, it is rather clear that F-15 does not understand the difference between pitch authority/control, and lift enhancement, although any device that moves forward or backward on the main wing to enhance lift, will of necessity change pitch TRIM, and necessitate re-trimming to maintain airspeed or attitude???

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American early LEVCON concept

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American Study says Vortex flap improves 20% performance of F-106

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[video=youtube;tLYe6qAxaM4]https://www.youtube.com/watch?v=tLYe6qAxaM4[/video]

Indian Vortex flap (changed terminology to LEVCON)

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Says improvement in landing speed, (less trim due to higher lift) and improved sustained turn rate

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Indian study says that the deflections of LEVCON, slats, and elevon change the pitching moment

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Check source is Chinese.

Now give me the proof that F-106 and LCA have higher trim/drag and lower lift and lower performance

[video=youtube;rnGh_g7xYtw]https://www.youtube.com/watch?v=rnGh_g7xYtw[/video]

Any delta by adding LEVCONs, LEXs or Canards will affect the longitudinal stability, due to a forward lift thrust, however fly by wire will fix that.

Viggen, XB-70 and Kfir were longitudinally stable, thus not very maneouvrable, once Fly By wire was introduce you got F-16, SU-27 and Gripen type aircraft, F-106 will suffer some pitch up destabilization due to higher longitudinal instability , but so it was Gripen or F-16

LCA and Mirage 2000 fix that with fly by wire

 

[F-15]

Clearly, canard is placed that far forward as anything attached to the wing (such as LEVCON) would not have provided enough pitch authority. As you see, my statements are applicable for fighters and non-fighters.

Yeah right all canards are the same

 

[Air Force Brat]

American early LEVCON concept

You sir continue to obfuscate and confuse yourself, at NO POINT did I mention trim drag, I did state that Sukhoi does not use canards for primary pitch control, Chengdu does. In no way, shape or form is the LEVCON a primary pitch control of the PAK FA, LCA, or even the F-106, it is primarily a lift enhancing device, the PAK-FA does use it to expedite/enhance roll rate and low speed controllability however......

This all goes back to your initial "loaded" question regarding PAK FA, many moons ago, which I answered accurately and succinctly, just as the Eng continues to answer your questions, and you continue to question his answers... I can give you my utmost assurances that he has a far greater grasp of this topic than you have given him credit for, his real knowledge far eclipsing my own, and most certainly yours, a little respect is due, and would go a long way to reduce your abrasiveness.

Operationally pilots refer to pitching moment as "pitch trim", and I already explained that the application of ANY leading or trailing edge device would change pitch trim, and the aircraft is then retrimmed to either airspeed, attitude, or angle of attack.

 

[F-15]

You sir continue to obfuscate and confuse yourself, at NO POINT did I mention trim drag.

Sir, there are aircraft tailess like LCA and Mirage 2000 that use fly by wire, on the naval LCA the LEVCON will increase lift ahead of the CG thus making it longitudinally unstable, that will be variable since the LEVCON also deflects; on F-106 tests the aircraft had pitch sensitivities.
The addition of vortex flap on F-106 meant it had increased elevon moment arm and this translated into increased pitch-control effectiveness.

Your assertion only is valid since the F-106 had more sensitivity and it was difficult to control pitch attitude, on the LCA, the low speed handling has been achieved because in India the Vortex flap has been improved, the LCA is a tailess.

The US indeed created LEVCONs, but it was in India that the LEVCON terminolgy was created, but they are Vortex flaps

read

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[latenlazy]

My bad, I made a mistake, thinking about something else



Not necessarily, if you have canards you would use them to stabilize your fighter and for pitch control even if you have a tail . Now, for some reason Chengdu prefers tailless designs, but that makes things even more interesting - canards would have to work as pitch control, increase lift and remain stealthy . That requires very complex algorithms and may delay introduction of J-20 into operational service .


P.S. Here, NATF , YF-23 with canards

Those canards aren't sitting on the same plane .

Yano, I actually suspect that the canards on the J-20 perform different functions for different AoA. At low AoA they probably operate as vortex controllers/generators, but at higher AoA they primarily perform pitch authority. Just a theory of course.

 

[F-15]

Those canards aren't sitting on the same plane .

Yano, I actually suspect that the canards on the J-20 perform different functions for different AoA. At low AoA they probably operate as vortex controllers/generators, but at higher AoA they primarily perform pitch authority. Just a theory of course.

Correct, the canards have a huge advantage over LEX or elevators and back tailed aircraft, the canard control the vortex, on Su-33 and Su-37, the canards were added to control the flow of the vortex system the LEX generate.

The Su-33 solution was not to reduced the swept of the LEX neither increase its area, but to add canards that increased forward lift.
On Su-37, the canards controlled the vortex system, thus increasing lift, however this aircraft is quiet complex since still uses tailplanes.

Canards in that regard are very effective.

The LEVCON does the same.

LEVCONs are like a seesaw; they control the amount of lift ahead and behind the CG, in the same way canards do

 

[F-15]

Sukhoi produced Su-33, Su-34 and Su-30MKI . These are all unstable fighters with canards . They also had Su-35 prototypes with canards and finally Su-47 . Therefore, like it or not, considering canards technology they are at the top



It is not number of edges, problem with canards is that they do not lay in same plane with the wing . 4.5th gen fighters like Rafale or Typhoon are not even optimized to have canards parallel with the wing (YF-23 was) . Therefore, EM wave could at certain angles (mostly from the side) bounce back from canards down to the wings and back like in waveguide. I will try to find picture to explain better .

Correct

The Su-37 used canards to control the vortex system, LEX are fixed, you can imagine them like a delta wing without leading edge slats, the original solution was set canards right away behind the LEX on Su-33 and Su-37, but as you have said it has disadvantages, so the LEVCON was developed from the Vortex flap, a slat on a LEX, controlling the vortex the LEX generates, this allows planform alignment and avoids the disadvantages you mentioned

 

[latenlazy]

Correct

The Su-37 used canards to control the vortex system, LEX are fixed, you can imagine them like a delta wing without leading edge slats, the original solution was set canards right away behind the LEX on Su-33 and Su-37, but as you have said it has disadvantages, so the LEVCON was developed from the Vortex flap, a slat on a LEX, controlling the vortex the LEX generates, this allows planform alignment and avoids the disadvantages you mentioned

But I imagine that solution trades off some pitch authority.