Aerodynamics thread

[MiG-29]

Re: J-20... The New Generation Fighter III

Why do you have to look for those studies? Basic aerodynamic theory is good enough for the things we're discussing and repeating them countless times here will be indeed very tedious.

We know why jetfighters use relaxed stability. As to its influence on (degree of) canard deflection, you're the one who said it'll reduce the requirement for pitch control, specifically, by reducing the canards size and its moment arm. We've already argued against this wrong notion and pointed out that increasing the instability will actually increase the requirement for pitch control surface effectiveness.

As for the third, already answered.

you are not answering the questions you are just dodging them, i asked you how does F-22 or J-20 generate forebody lift?

what are the compromises done on stealth fighters?

the even you are not answering why you need relaxed stability.

Chines straight up the forebody vortices at high alpha thus increasing the AoA by reducing premature vortex burst and yaw assymetries, however at cruise flight tell me how J-20 or F-22 generate forebody lift?

Some jets like Gripen or Eurofighter have a pair of strakes behind the canards with the same function of chines; Su-27 does the same with is LERXes.

As remarked previously, the only externally visible “fix” to the airframe are a pair of small strakes behind the canard surfaces. This type of “flow augmentation system”, often serving the purpose of directional and lateral stability enhancement at high AOA, is not uncommon on fighters; suffice to mention the Eurofighter and the Mirage 2000

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[Quickie]

Re: J-20... The New Generation Fighter III

you are not answering the questions you are just dodging them, i asked you how does F-22 or J-20 generate forebody lift?

what are the compromises done on stealth fighters?

the even you are not answering why you need relaxed stability.

Chines straight up the forebody vortices at high alpha thus increasing the AoA by reducing premature vortex burst and yaw assymetries, however at cruise flight tell me how J-20 or F-22 generate forebody lift?

Some jets like Gripen or Eurofighter have a pair of strakes behind the canards with the same function of chines; Su-27 does the same with is LERXes.

As remarked previously, the only externally visible “fix” to the airframe are a pair of small strakes behind the canard surfaces. This type of “flow augmentation system”, often serving the purpose of directional and lateral stability enhancement at high AOA, is not uncommon on fighters; suffice to mention the Eurofighter and the Mirage 2000

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Why would you want to ask such a basic question? Jetfighters use relaxed stability mainly for maneuovrebility. You're the one who refused to answer the many questions I posed to you and I've tried to explain to you too many times.

Why shouldn't the J-20 and F-22 generate forebody lift during cruise flight? The 2 aircrafts will still retain the forebody lifting shape at any onetime. Unless you expect them to change shape suddenly? Vortex generation is used to prevent boundary layer separation during high AOA but the forebody lifting surfaces and the wings are still the main lifting surfaces of the aircrafts during high AOA as well as level flight.

So you still want us to continue pointing all the holes in your argument?

The most famous one must be a negatively deflected canard will still generate lift (i.e. the lift of the canard itself) when the fuselage is at a high AOA.

 

[MiG-29]

Re: J-20... The New Generation Fighter III

Why would you want to ask such a basic question? Jetfighters use relaxed stability mainly for maneuovrebility. You're the one who refused to answer the many questions I posed to you and I've tried to explain to you too many times.

Why shouldn't the J-20 and F-22 generate forebody lift during cruise flight? The 2 aircrafts will still retain the forebody lifting shape at any onetime. Unless you expect them to change shape suddenly? Vortex generation is used to prevent boundary layer separation during high AOA but the forebody lifting surfaces and the wings are still the main lifting surfaces of the aircrafts during high AOA as well as level flight.

So you still want us to continue pointing all the holes in your argument?

The most famous one must be a negatively deflected canard will still generate lift (i.e. the lift of the canard itself) when the fuselage is at a high AOA.

You are still dodging the question for a simple reason, relaxed static stability as the original text i quoted says it reduces canard deflection because the pitch up moment is increased by the center of gravity position, and yes canards deflected negatively at high Alpha increase lift i have three papers that say it, but you have not quoted a single one except your opinion, because your original theory was the J-20 is pushing down the nose in a turn.

And since you have no idea how the F-22 or J-20 generate forebody lift at cruise flight niether why the J-20 is not using flaps to generate the same nose down force you claim the J-20 needs, you dodge the questions.

MiG-29 has vortex generators in the chines at the sides of the nose probe

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and F-5 or F-18 have also forebody vortices at high alpha see

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here you see forebody vortex on F-18

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, but no paper says F-5 or F-18 have forebody lift.

wing-fuselage blending lifting body means the fuselage has some camber, since burnelli`s 1920s aircraft

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to MiG-29

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or F-16, the upper fuselage has camber, the new Boeing blended wing body passenger aircraft has camber by merging the fuselage with the wing

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On combat aircraft, which typically have pointed noses to reduce high-speed drag, the onset of flow
separation occurs further forward on the body. Progressing from the nose of the body aft a vortex is shed
first from one side and then the other. The stable asymmetric vortex system that results downstream
induces a significant lateral force on the nose of the aircraft that can cause un-commanded lateral motion
(nose slice).

The asymmetric behaviour may be removed by symmetrical sharp
(SYA) KN1-6
edges in the nose region of the body, as illustrated in figure 11 which shows the small nose strakes on
Mig-29. Strakes extending from the wing apex or at the nose of the body have been cited as means of controlling
vortex-flow development downstream. Most low-signature aircraft (such as F-22 shown in fig 15) have
sloping sides with a sharp edge or ‘chine’, running along either side of the forebody. This generally has a
similar effect to a strake but, because the chines are very highly swept, vortex flow is produced at low
angles of attack. Thus while chines may be effective in controlling the vortex flow over the wing and
body at positive angles of attack, the effect of the chines also needs to be considered when the aircraft is
flying at negative angles of attack.

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[Quickie]

Re: J-20... The New Generation Fighter III

You are still dodging the question for a simple reason, relaxed static stability as the original text i quoted says it reduces canard deflection because the pitch up moment is increased by the center of gravity position, and yes canards deflected negatively at high Alpha increase lift i have three papers that say it, but you have not quoted a single one except your opinion, because your original theory was the J-20 is pushing down the nose in a turn.

And since you have no idea how the F-22 or J-20 generate forebody lift at cruise flight niether why the J-20 is not using flaps to generate the same nose down force you claim the J-20 needs, you dodge the questions.

I'm going to explain this one last time. As previously explained, the study (the first part of it) is based on a tailless model which they later added the horizontal tail stabilizer. The pitching moment is mostly due to the change in the AC of the wing in relation to the CG of the tailless wind tunnel model. The effect of the canards' arm moment is only just a smaller part of the sum of moments and usually goes counter to model's pitch direction, meaning with a negative sign relative to the model's pitch direction.

As I've explained earlier, they have to add in the tail stabilizer/elevator for pitch control in the final part of the study. For the rafale and gripen, the elevons are used for pitch control. The closed coupled canards are only trimmed to maximize wing's lift but it's not used for pitch control because the moment sum of the canard and wing (which varies with the wing's AC) may go go counter to the required pitch direction. That's why I've argued that you can't simply compare a tailless wind tunnel model (Imagine the Su-33 without its tail control surfaces) to the J-20 which have a very different configuration and is designed to use its long coupled canards for pitch control just like the F-22 uses the elevators for the same function.

niether why the J-20 is not using flaps to generate the same nose down force you claim the J-20 needs, you dodge the questions.

Why should the J-20 use flaps to pitch down? Do the F-22 use flaps for pitch down? No! because the induced drag will shoot off the roof especially at high speed!. It's simply more energy efficient for the aircrafts to use the canards or the elevator.

And since you have no idea how the F-22 or J-20 generate forebody lift at cruise flight niether why the J-20 is not using flaps to generate the same nose down force you claim the J-20 needs, you dodge the questions.

Lol, you can believe whatever you want. Everyone here is free to judge for themselves, and I believe many of them here can see the many holes in your argument. And the best thing is all your argument is still on record in the previous posts, that is of course you haven't tried to delete them already.

 

[Air Force Brat]

Re: J-20... The New Generation Fighter III

You are still dodging the question for a simple reason, relaxed static stability as the original text i quoted says it reduces canard deflection because the pitch up moment is increased by the center of gravity position, and yes canards deflected negatively at high Alpha increase lift i have three papers that say it, but you have not quoted a single one except your opinion, because your original theory was the J-20 is pushing down the nose in a turn.

And since you have no idea how the F-22 or J-20 generate forebody lift at cruise flight niether why the J-20 is not using flaps to generate the same nose down force you claim the J-20 needs, you dodge the questions.

MiG-29 has vortex generators in the chines at the sides of the nose probe

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and F-5 or F-18 have also forebody vortices at high alpha see

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here you see forebody vortex on F-18

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, but no paper says F-5 or F-18 have forebody lift.

wing-fuselage blending lifting body means the fuselage has some camber, since burnelli`s 1920s aircraft

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to MiG-29

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or F-16, the upper fuselage has camber, the new Boeing blended wing body passenger aircraft has camber by merging the fuselage with the wing

Please, Log in or Register to view URLs content!

On combat aircraft, which typically have pointed noses to reduce high-speed drag, the onset of flow
separation occurs further forward on the body. Progressing from the nose of the body aft a vortex is shed
first from one side and then the other. The stable asymmetric vortex system that results downstream
induces a significant lateral force on the nose of the aircraft that can cause un-commanded lateral motion
(nose slice).

The asymmetric behaviour may be removed by symmetrical sharp
(SYA) KN1-6
edges in the nose region of the body, as illustrated in figure 11 which shows the small nose strakes on
Mig-29. Strakes extending from the wing apex or at the nose of the body have been cited as means of controlling
vortex-flow development downstream. Most low-signature aircraft (such as F-22 shown in fig 15) have
sloping sides with a sharp edge or ‘chine’, running along either side of the forebody. This generally has a
similar effect to a strake but, because the chines are very highly swept, vortex flow is produced at low
angles of attack. Thus while chines may be effective in controlling the vortex flow over the wing and
body at positive angles of attack, the effect of the chines also needs to be considered when the aircraft is
flying at negative angles of attack.

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Mig, we started this thread to discuss aerodynamics, you stated you wanted to discuss Dr. Songs paper, good, it is about the Chinese J-xx or J-20, Dr. Song is the foremost authority on J-20 aerodynamics? YES He is the master, I'm just a pilot who cares, you're a student who is studying aerodynamics, IMHO you aren't "seeing" the lift the strakes or chines produce. So lets leave the poor old J-20. Dr. Song says it produces forebody lift, since he gets paid money for his opinion, and hes the fellow who has explained the J-20 to us, he trumps your learned opinion.
As well the Raphael vid of the beginning of the take-off run the elevons are bouncing up and down because the whole aircraft is bobbing fore and aft due to its close couple landing gear, you see this same bobbing and elevon bouncing as he taxies back to the hangar. Thats happening because the pilots hand is bobbing as the aircraft rocks back and forth on the gear. The canard deflects positively upward at rotation as the pilot rotates the aircraft to produce lift on the main wing, in order to lift off. This is in response to his aft movement of the stick, it also occurs as the pilot flares the aircraft to arrest decent on landing!

Finally, and most importantly pay attention to Dr. state the J-20 is distant coupled, not close coupled. Check last Aprils posts in Pugacheve Divers translation of that Paper by Dr. Song! Respectfully Brat

One final thought, on the J-20 the pilot is manipulating the stick, the FBW is flying the plane, the pilot doesn't decide to control High Angle of Attack flight with canards or elevons, the computer does. The computer is flying each end of the plane separately, if the computer pitched the nose down with the elevons, the lift is spoiled the nose will likely "fall through" and break your high aoa attitude and lift, it is a balancing act, lots of thrust, lots of lift, very little forward speed, the computer pitches the canards downward in order to keep the Aircraft from pitching on to its back, maintaining the balancing act, as Dr. Song said this is a very complicated flight control system.

Now can we have a little discussion of Pak-Fa, those vortex generators over the intakes are driving me crazy! Mr. Bax

 

[MiG-29]

Re: J-20... The New Generation Fighter III

I'm going to explain this one last time. As previously explained, the study (the first part of it) is based on a tailless model which they later added the horizontal tail stabilizer. The pitching moment is mostly due to the change in the AC of the wing in relation to the CG of the tailless wind tunnel model. The effect of the canards' arm moment is only just a smaller part of the sum of moments and usually goes counter to model's pitch direction, meaning with a negative sign relative to the model's pitch direction.

look you "explanation" simply is not logic, J-20 as Rafale or any other fighter have flaps and both elevons and canards are pitch control, at take off the canard is on a positive angle pushing the nose up while the elevon deflected up pushing the tail down besides these jets apply flaps they have flaps for a reason.
[video=youtube;gjBoZ345TnU]http://www.youtube.com/watch?v=gjBoZ345TnU[/video]

[video=youtube;ZOuat35zFXo]http://www.youtube.com/watch?v=ZOuat35zFXo[/video]
I can see you can not say how does F-22 generate forebody lift, and no wonder, vortices are shed by the forebody once the aircraft is pitched, at high AoA and many jets generate them too

X-29 is generating forebody vortices here is the picture evern with smoke

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But of course no one says X-29 has extensive forebody lift

 

[no_name]

Re: J-20... The New Generation Fighter III

The J-20's nose follows a similar design approach with some differences as the F-22. It's shaped to reduce radar cross section, but it is also shaped precisely to reduce nose slice and unintended lateral instability. (The hexagonal shape of the J-20's nose, like the F-22's diamond like cross-section, helps with lateral control)

I have read somewhere that the nose of the J-20 itself is also a lifting body and produces positive lift. Why they would design it to be so and then use canards to force nose down I do not know. But maybe it has to do with shifting centre of lift at different airspeeds?

 

[MiG-29]

Re: J-20... The New Generation Fighter III

Mig, we started this thread to discuss aerodynamics, you stated you wanted to discuss Dr. Songs paper, good, it is about the Chinese J-xx or J-20, Dr. Song is the foremost authority on J-20 aerodynamics? YES He is the master, I'm just a pilot who cares, you're a student who is studying aerodynamics, IMHO you aren't "seeing" the lift the strakes or chines produce. So lets leave the poor old J-20. Dr. Song says it produces forebody lift, since he gets paid money for his opinion, and hes the fellow who has explained the J-20 to us, he trumps your learned opinion.
As well the Raphael vid of the beginning of the take-off run the elevons are bouncing up and down because the whole aircraft is bobbing fore and aft due to its close couple landing gear, you see this same bobbing and elevon bouncing as he taxies back to the hangar. Thats happening because the pilots hand is bobbing as the aircraft rocks back and forth on the gear. The canard deflects positively upward at rotation as the pilot rotates the aircraft to produce lift on the main wing, in order to lift off. This is in response to his aft movement of the stick, it also occurs as the pilot flares the aircraft to arrest decent on landing!

Finally, and most importantly pay attention to Dr. state the J-20 is distant coupled, not close coupled. Check last Aprils posts in Pugacheve Divers translation of that Paper by Dr. Song! Respectfully Brat

One final thought, on the J-20 the pilot is manipulating the stick, the FBW is flying the plane, the pilot doesn't decide to control High Angle of Attack flight with canards or elevons, the computer does. The computer is flying each end of the plane separately, if the computer pitched the nose down with the elevons, the lift is spoiled the nose will likely "fall through" and break your high aoa attitude and lift, it is a balancing act, lots of thrust, lots of lift, very little forward speed, the computer pitches the canards downward in order to keep the Aircraft from pitching on to its back, maintaining the balancing act, as Dr. Song said this is a very complicated flight control system. Now can we have a little discussion of Pak-Fa, those vortex generators over the intakes are driving me crazy! Mr. Bax

Brat elevons and flaps are the same thing, the differences is the way they are used and elevon is a flap and a flap an elevon in terms of physics.

Rafale at take off uses the the canard as a pitch control by increasing lift and pushing up the nose and the elevon to push up the nose.
F-18 is the opposite, because it has a tailplane not a foreplane (canard) and the tail has a relative long moment arm
In F-18 even the vertical fin rudders pitch up the nose this is enough to allow the F-18 use the flap deflected down to increase lift
[video=youtube;FkaGW-9dYs8]http://www.youtube.com/watch?v=FkaGW-9dYs8&NR=1&feature=fvwp[/video]
All these jets have flaps, Rafale has a split trailing edge and has elevons and flaps, same is J-20

tell me why? well here is the answer

This configuration is designed to operate till the
maximum lift, without any limitation.
The fly control system, with four digital
independent channels, continuously master the
required stability for each flight phase.
In approach phase, the canard is turning upward
while the pitch control surfaces are down, acting
as flaps .
This configuration adds a strong lift on the
canard and on the pitch control surfaces that
dramatically reduce approach speed on the
carrier.

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On minute 3:11 you can see the very slightly deflected flaps on Rafale M
[video=youtube;P4N36-reDQI]http://www.youtube.com/watch?v=P4N36-reDQI&feature=fvwrel[/video]

here is the picture of Rafale using flaps down and canards up

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LEVCONs are no more than vortex flaps they were tried on the F-106, however the vortex flap of F-106 is just on the delta, the LEVCON only applies to the wing root and LERX on T-50


Abstract : Surface and off-surface flow visualization techniques were used to visualize the three-dimensional vortex flows on the F-106 aircraft with vortex flaps installed. Results at angles of attack between 9 degrees and 18 degrees and Mach numbers from 0.3 to 0.9 are presented. A smoke flow vapor screen technique was used to document leading-edge vortex paths and sizes, while an oil flow technique was employed to provide detailed information on reattachment and separation line locations and other flow details. Results were obtained for two vortex flap deflection angles, 30 degrees and 40 degrees. Flow visualization revealed the existence of a multiple vortex system that had not previously been seen in subscale tests or predicted for this configuration. The vortex flap generated a leading-edge vortex system that reattached near the flap hinge over a wide angle-of-attack range. In addition to the primary vortex, flow visualization revealed the presence of several distinct vortices that traced a path from the vortex flap and then over the wing. (47 figures, 14 refs.)

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[Air Force Brat]

Re: J-20... The New Generation Fighter III

Brat elevons and flaps are the same thing, the differences is the way they are used and elevon is a flap and a flap an elevon in terms of physics.

Actually not sir, flaps are lift generating devices attached to the trailing or leading edge of the wing, they deflect downward to increase the wings camber, flaperons are trailing edge devices, usually inboard toward the fuse, for take offs and landings they lower the stalling speed of the aircraft, and functionally lower the angle of incidence of the wing to the fuselage, when deflected for landing or takeoff, they do operate differentially to create a rolling moment of the aircraft. If you roll left, the left flaperon will deflect upward decreasing lift, while the right flaperon will deflect downward increasing lift, thereby rolling the aircraft to the left, follow me so far? good- now for the elevon, which is a composite control also, it functions differently as it is a combination of the ailerons and elevators, hence the term elevons, when operating in unison as elevators aft stick deflects trailing edge upward, pushing tail down and nose up, when stick is pushed forward, trailing edge is deflected downward, pushing tail up and nose down, when the stick is moved left aircraft rolls to left, when the stick is moved right aircraft rolls to the right, this surface is on the outboard trailing edge of the wing. Elevons and Flaperons may operate in unison depending on the FBW configuration. They are however, two distinct surfaces, please look up the terms.

---------- Post added at 11:03 PM ---------- Previous post was at 10:48 PM ----------

The J-20's nose follows a similar design approach with some differences as the F-22. It's shaped to reduce radar cross section, but it is also shaped precisely to reduce nose slice and unintended lateral instability. (The hexagonal shape of the J-20's nose, like the F-22's diamond like cross-section, helps with lateral control)

I have read somewhere that the nose of the J-20 itself is also a lifting body and produces positive lift. Why they would design it to be so and then use canards to force nose down I do not know. But maybe it has to do with shifting centre of lift at different airspeeds?

That is indeed the case, because the main wing of the J-bird is aft as are the cg and cl, since the J-20 has been designed as an air superiority fighter, vortex generators are place ahead of and behind the distant coupled canard to provide additional lift for the forward fuselage to minimize trim drag and to combat the phenomena known as mach tuck. This also has the beneficial effect of providing additional forward fuse lift to rotate the aircraft, to climb position, decreasing the takeoff roll.

---------- Post added at 11:12 PM ---------- Previous post was at 11:03 PM ----------

Brat elevons and flaps are the same thing, the differences is the way they are used and elevon is a flap and a flap an elevon in terms of physics.

Rafale at take off uses the the canard as a pitch control by increasing lift and pushing up the nose and the elevon to push up the nose.
F-18 is the opposite, because it has a tailplane not a foreplane (canard) and the tail has a relative long moment arm
In F-18 even the vertical fin rudders pitch up the nose this is enough to allow the F-18 use the flap deflected down to increase lift
[video=youtube;FkaGW-9dYs8]http://www.youtube.com/watch?v=FkaGW-9dYs8&NR=1&feature=fvwp[/video]
All these jets have flaps, Rafale has a split trailing edge and has elevons and flaps, same is J-20

tell me why? well here is the answer

This configuration is designed to operate till the
maximum lift, without any limitation.
The fly control system, with four digital
independent channels, continuously master the
required stability for each flight phase.
In approach phase, the canard is turning upward
while the pitch control surfaces are down, acting
as flaps .
This configuration adds a strong lift on the
canard and on the pitch control surfaces that
dramatically reduce approach speed on the
carrier.

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On minute 3:11 you can see the very slightly deflected flaps on Rafale M
[video=youtube;P4N36-reDQI]http://www.youtube.com/watch?v=P4N36-reDQI&feature=fvwrel[/video]

here is the picture of Rafale using flaps down and canards up

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LEVCONs are no more than vortex flaps they were tried on the F-106, however the vortex flap of F-106 is just on the delta, the LEVCON only applies to the wing root and LERX on T-50


Abstract : Surface and off-surface flow visualization techniques were used to visualize the three-dimensional vortex flows on the F-106 aircraft with vortex flaps installed.
While the Study may have called them vortex flaps, they are very simple fixed leading edge flaps for the purpose of this study on highly swept wings, did they produce vortexes, yes, but the correct term is leading edge flap or slat, not slot, slats or leading edge flaps. Changing terminology thru the years has made our discussions more difficult, you say Lexcon, I say Strakes, sameoh piece of leading edge extension. Nothing in this study particularly relevant to our J-20 aero discussion.

 

[MiG-29]

Re: J-20... The New Generation Fighter III

Actually not sir, flaps are lift generating devices attached to the trailing or leading edge of the wing, they deflect downward to increase the wings camber, flaperons are trailing edge devices, usually inboard toward the fuse, for take offs and landings they lower the stalling speed of the aircraft, and functionally lower the angle of incidence of the wing to the fuselage, when deflected for landing or takeoff, they do operate differentially to create a rolling moment of the aircraft.


While the Study may have called them vortex flaps, they are very simple fixed leading edge flaps for the purpose of this study on highly swept wings, did they produce vortexes, yes, but the correct term is leading edge flag or slat, not slot, slats or leading edge flaps. Changing terminology thru the years has made out discussions more difficult, you say Lexcon, I say Strakes, sameoh piece of leading edge extension. Nothing in this study particularly relevant to our J-20 aero discussion.

Elevons as flaps change the camber, but of course the use is different, but okay returning to LEVCONs AKA vortex flap


I will explain you the russian philosophy of LEVCONs


Russia studied on Su-37, Su-35 and Su-33 the triplane configuration, this jets use both canards and LERXes (strakes).
The Russians added canards to their naval Su-27 for the following reason. to reduce approaching speed, so an extra vortex was added and the canard is a foreplane so it also controls the vortex incidence (like the vortex flap on F-106) and generates extra lift ahead of the center of gravity allowing for a heavier nose and lower trim drag

Now why they did not go for canards?

Answer:canards as they have advantages they have cons, one is added drag in the form of downwash at cruise flight, this kills lift on the main wing; plus on Su-33 added extra parasite drag, so for the russians it was a contradiction, they wanted the controlability of a canard at high AoA as on Su-37 or S-37(Su-47) but not the added drag and difficulty of adding canards in terms of stealth, why difficulty? simple, the ideal canard is not like on J-20 but as on Rafale, because the ideal high AoA lift increase is achieved on a canard set high and close to the wing.

MiG-1.44 had a Rafale type canard with several dogtooth vortex generators to do for the lack of a Lerx.

So the LEVCON sits on the place where the vortex it is generated, the LEVCON as you have said it is a slat, or leading edge flap but for a LERX but this slat controls the vortex and reattaches it to the wing at high AoA, what are the advantages?

Increased lift with respect a LERX, no downwash on the main wing, and since it is part of the wing no need for align or planform as a canard needs, because it does not need to be above wing level

JAST as well as F-22 sit the wing at the level of the tail, foretail in JAST and aft tail in F-22, this is a stealth meassure to reduce reflecting surfaces, a Su-27 for example has its tailplane below wing level adding an extra surface reflection F-22 hides its tailplane frontally with its wing

why vortex flap is not a regular slat? simple delta wings generate vortices at high AoA, and here we are not talking about a slat of a straight wing but of a wing that generates a strong vortex like a delta wing, thus the denomination vortex flap, but you are right it is a slat

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3.3 Sustained Turn Rate Improvement using Levcon
Leading Edge Controller (Levcon) is an secondary
control surface located at the leading edge of the wing
and the fuselage. The Levcon is initially planned in LCA
Navy for the low landing speed capability and other cruise
performance. An important requirement of a fighter aircraft
is the Sustained Turn Rate (STR). The fighter variant of
Tejas is not meeting the STR requirement of ASR. The STR
is a strong function of the aerodynamic efficiency. From
the wind tunnel results it was found that the Levcon produce
higher L/D (Fig. 17). A detailed study to implement Levcon
in fighter and identification of other design constraints is
under progress.

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further read about levcons

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