Aerodynamics thread

[Engineer]

Longer are means also lower vortex interaction so you get a longer arm but you lose lif

Correct, which is why on the J-20, the leading edge extension is used to strengthen vortex interaction. A similar solution is employed on the Eurofighter.

in LCA which is tailless you just need to move the wing forward and add the LEVCON, so pretty much there is no advantage plus the LEVCON generates less drag.

With this listen, it does not mean a fighter is better, canards and LEVCONS are only fixes none is superior, everything depends what the designer wants, at the end of the day is the lighter the fighter it gets, lower wing loading and higher thrust to weight ratio what matters

The LCA uses trailing edge flaps for pitch authority as well. When you look at PAKFA, you see the employment of tailplane to provide pitch authority. Neither plane relies just on LEVCONS, for good reasons.

As to drag, one of the ways to reduce it is by reducing trim-drag through making the aircraft more unstable. However, this requires greater pitch authority which is better achieved by canard, especially during high angle-of-attack situations. I agree with you that thrust-to-weight ratio is important, but wing loading is shown to be a bad metric due to influences of vortex lift.

 

[Engineer]

You are an Idiot, if you want i can tell you where you can find Sampaix, he will disagree with you, specially since he loves Rafale, you are just giving your interpretation to fit your twisted mind regardless if it is true or not

The graph shows canard is generating lift, even at low angle-of-attack, even if the amount generated is not as high as at high angle-of-attack. In short, canard generates lift despite how some people here assume otherwise. Right now, I am merely repeating what the graph shown, so calling me an idiot is no different than calling the author of that graph an idiot.

 

[F-15]

The graph shows canard is generating lift, even at low angle-of-attack, even if the amount generated is not as high as at high angle-of-attack. In short, canard generates lift despite how some people here assume otherwise. Right now, I am merely repeating what the graph shown, so calling me an idiot is no different than calling the author of that graph an idiot.

I know the author personally and i know what is he talking, you are twisting the graph to win an argument

 

[Engineer]

I know the author personally and i know what is he talking, you are twisting the graph to win an argument

I am merely repeating what the graph says. The C[sub]L[/sub] vs. alpha curve is higher with canard than without. Even if this effect is miniscule, that still means canard contributes to lift at low angle-of-attack. There is no need for me to twist the graph.

 

[F-15]

Correct, which is why on the J-20, the leading edge extension is used to strengthen vortex interaction. A similar solution is employed on the Eurofighter.


The LCA uses trailing edge flaps for pitch authority as well. When you look at PAKFA, you see the employment of tailplane to provide pitch authority. Neither plane relies just on LEVCONS, for good reasons.

As to drag, one of the ways to reduce it is by reducing trim-drag through making the aircraft more unstable. However, this requires greater pitch authority which is better achieved by canard, especially during high angle-of-attack situations. I agree with you that thrust-to-weight ratio is important, but wing loading is shown to be a bad metric due to influences of vortex lift.

Sir, LCA is one of the lightest jets ever, no configuration is perfect and none give you only advantages these are just to fix the disadvantages the aircraft has with other elements.

LEX also move the center of pressure forward that proves you do not even know what you are talking about

 

[Engineer]

Sir, LCA is one of the lightest jets ever, no configuration is perfect and none give you only advantages these are just to fix the disadvantages the aircraft has with other elements.

LEX also move the center of pressure forward that proves you do not even know what you are talking about

None of these statements contradict how long-coupled canard enjoy advantages of a long moment-arm when compared to LEVCON. That's not to say your statements are necessary wrong, just that your statements lack logical inferences.

 

[F-15]

None of these statements contradict how long-coupled canard enjoy advantages of a long moment-arm when compared to LEVCON. That's not to say your statements are necessary wrong, just that your statements lack logical inferences.

You simple do not know the LEVCON is a LEX thus it does generate Vortices, it moves the wing center of pressure forward and does generate less drag, this is not said by me but by Sukhoi
[video=youtube;Li-xPxcA8tg]https://www.youtube.com/watch?v=Li-xPxcA8tg[/video]

So the LEVCON does not need to move forward to reduce drag and keeps the vortex nearer the wing allowing the vortex system to work, moving the canard forward reduces the vortex lift.

While this does not mean a fighter with LEVCON is superior to one with Canards, it only means the LEVCON can allow the designer to reduce drag while maintaining higher lift than if it would had used canards.

In your context, with Thurderchief, the J-20 then needs a small LEX, and now it is shaper to increase the vortex system, since prototype 2001 and 2002 had one blunter, the blunter one has more area, so it generates more lift at low Alpha (AoA) but the newer LEX is better for vortex generation, however it is far too small to really being of great impact.
Thus you can see is something less practical of a solution, Eurofighter uses also the same fix of J-20, it has some strakes too.

I can not tell you which fighter is better, only i can tell you the LEVCON can be used for roll and it does control the vortex system shed by the LEVCON (movable LEX) but a Sharper LEX always is better for vortex generation.

F-18E opted for a larger and blunter LEX for more wing lifting area to upset the higher weight of the new Super Hornet, but lighter F-18C has the better LEX design for vortex generation, but also a shaper LEX generates more drag.

So a LEVCON is a better solution than Canard or LEX if you are looking for some conditions where drag and lift are compromised

 

[latenlazy]

You simple do not know the LEVCON is a LEX thus it does generate Vortices, it moves the wing center of pressure forward and does generate less drag, this is not said by me but by Sukhoi
[video=youtube;Li-xPxcA8tg]https://www.youtube.com/watch?v=Li-xPxcA8tg[/video]

So the LEVCON does not need to move forward to reduce drag and keeps the vortex nearer the wing allowing the vortex system to work, moving the canard forward reduces the vortex lift.

While this does not mean a fighter with LEVCON is superior to one with Canards, it only means the LEVCON can allow the designer to reduce drag while maintaining higher lift than if it would had used canards.

In your context, with Thurderchief, the J-20 then needs a small LEX, and now it is shaper to increase the vortex system, since prototype 2001 and 2002 had one blunter, the blunter one has more area, so it generates more lift at low Alpha (AoA) but the newer LEX is better for vortex generation, however it is far too small to really being of great impact.
Thus you can see is something less practical of a solution, Eurofighter uses also the same fix of J-20, it has some strakes too.

I can not tell you which fighter is better, only i can tell you the LEVCON can be used for roll and it does control the vortex system shed by the LEVCON (movable LEX) but a Sharper LEX always is better for vortex generation.

I think what Engineer is getting at is that the vortices from the LEVCONs on the PAK-FA don't generate enough force (differentials) to do pitch and roll on their own and need tailplanes to assist in the maneuver, while in most cases canard fighters can achieve adequate roll and pitch forces on their own.

 

[F-15]

I think what Engineer is getting at is that the vortices from the LEVCONs on the PAK-FA don't generate enough force to do pitch and roll on their own and need tailplanes to assist in the maneuver, while in most cases canard fighters can achieve adequate roll and pitch forces on their own.

That is not true, LCA is tailless and uses LEVCONs, what he really wants to say i want to win the argument.

Delta wings need long elevons due to the wing swept which reduces their effectiveness, thus they generate lot of drag.

 

[latenlazy]

That is not true, LCA is tailless and uses LEVCONs, what he really wants to say i want to win the argument.

Delta wings need long elevons due to the wing swept which reduces their effectiveness, thus they generate lot of drag.

LCA is also pretty small and of course is a very different design. I explicitly tied the PAK-FA into my sentence for a reason. I'm not saying LEVCONS are always insufficient on their own, just that Engineer seems to be arguing that on the PAK-FA they are. Anyways, I don't have a stake in this particular argument. Just thought trying to clarify what people were trying to say would help move the discussion along.