Aerodynamics thread

Air Force Brat

Brigadier
Super Moderator
Re: J-20... The New Generation Fighter III

I'll have to think about that, I see your point, but it also increases wing area and camber, and practically lowers the angle of incidence of the wing to the fuselage, increasing visibility over the nose on take off and landing, but then you are the engineer and I'm just the air force Brat. You did make me put my thinking cap on. LOL

---------- Post added at 06:10 PM ---------- Previous post was at 05:43 PM ----------

The canards were tested at several positions
and deflected from -10 to +10 degrees. In addition,
configurations consisting of a horizontal tail and a
canard with horizontal tails are analyzed.
The results of the analysis inidcate that
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DO you understand what the sentence in addition means? it means the study was done also to triplane configuration, not that the study was done only to triplane configurations, also the position was studied, which means they moved aft and forward the canard

---------- Post added at 05:16 PM ---------- Previous post was at 04:48 PM ----------



If you see Figure 1 -Sketch of Models, you can see the studied the horizontal separetion of the canards, which is confirmed in page 11 by this
"The effect of longitudinal canard position on the aerodynamic characteristics
of the 50-degree model had been well established by the time
the transonic wind-tunnel program was run. "

This was done in the previous study true but the position also have horizontal separetion and figure 100 shows it with P1 and P2 having the largest horizontal separation and gap bewteen wing and canard , but here is where the study becomes clearer, if the J-20 has a canard long coupled canard, but the canad position is near the center of gravity, which is detrimental as pitch control, plus the J-20 has not a very large horizontal gap between the wing and the canard, plus J-20 has not a vey large horizontal gap to say the canard has not effect on vortex lift.


Song said the canard was mover forward to increase pitch lever arm, why? simple simple,if you have seen X-36 JAST or any american stealth fighter with canard, you will see they set the canard and wing at the same level, this is detrimental to lift, but benefitial for stealth so what the chinese did is add a LERX.

This is in part confirmed by the paper

"The effect of canard longitudinal position on the incremental pitching
moment is shown in Figure 25. Data are for Mach numbers from 0.6 to 1.10
and the canard positions are P 1 and P As expected, moving the canard
forward increases the incremental pitching moment"


However if you see the distance of X-31`s canard and the wing you see J-20 has not such a large horizontal gap, not even compared to Eurofighter, it only has a large gap compared to Rafale or IAI lavi

He even claims canard and LERXes increase lift at high AoA, which means some vortex lift exists.


And my point was negative deflections do not mean pitch down at high AoA, i do not agree with you because a car and indy car in this case is not flying at high AoA but straight at 0 degrees

Yeah I figured you wouldn't, so you don't believe fluid dynamics as applied to aircraft also applies to Indy cars, but you do agree don't you that the negative pitch on the front spoiler applies down force to keep the body from lifting? Yes Sammo, Sammo, If you further increased the negative pitch on the long coupled canard the nose will go down.........? Yes You also note that the canard may move a lot without affecting pitch, I do slightly agree, the canard is the Primary, pitch control..... Ruddervator is the secondary as well as Elevons on trailing edge. The FBW may be calibrated to allow a large deflections of the canard, before coming in with more generous deflections of Ruddervator and Elevons as stick moves further aft, MY THEORY?
 

MiG-29

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

I'll have to think about that, I see your point, but it also increases wing area and camber, and practically lowers the angle of incidence of the wing to the fuselage, increasing visibility over the nose on take off and landing, but then you are the engineer and I'm just the air force Brat. You did make me put my thinking cap on. LOL

---------- Post added at 06:10 PM ---------- Previous post was at 05:43 PM ----------



Yeah I figured you wouldn't, so you don't believe fluid dynamics as applied to aircraft also applies to Indy cars, but you do agree don't you that the negative pitch on the front spoiler applies down force to keep the body from lifting? Yes Sammo, Sammo, If you further increased the negative pitch on the long coupled canard the nose will go down.........? Yes You also note that the canard may move a lot without affecting pitch, I do slightly agree, the canard is the Primary, pitch control..... Ruddervator is the secondary as well as Elevons on trailing edge. The FBW may be calibrated to allow a large deflections of the canard, before coming in with more generous deflections of Ruddervator and Elevons as stick moves further aft, MY THEORY?
I will be very honest, up to what i know indy cars work more like tailplanes, stable aircraft need a negative lift vector on their tail to keep the nose up indy cards do the same.


The mechanics of flight are very complex, however my only point was to tell you the negative deflection does not mean necesarily pitch down of the nose, but it is a way to achieve higher lift in some situation read this and later see the video and check the X-31`s canards deflections

"2. Brief Description of the Related Art

Until about 1978, the region beyond stall was considered an unacceptable flight regime frequently characterized by uncontrollable flight in spins and by undesirable deep stalls. Any deep stall condition is characterized by a stable trimmedflight but at a high angle of attack from which return to normal flight may be difficult or impossible. A deep stall may be defined as an out-of-control condition at an angle of attack greater than the angle of attack for maximum lift with nosignificant motion other than a high rate of descent. Conventional airplanes usually stall and lose control effectiveness at angles of attack in the range of 18.degree. to 20.degree..

However, according to U.S. Pat. Nos. 4,261,533 and 4,099,687, it is now possible, through the use of a rotatable horizontal tail on aft-tail configurations or through the use of tiltable engines on the wings, to provide stable and controllableflight at extremely high airplane angles of attack.

Because movement other than a high rate of descent can be controlled by varying thrust levels and all moveable control surfaces with large deflections, the safety and usefulness of flight at extremely high angles of attack are being re-examinedand redefined.

The essence of the longitudinal control concept, as set forth in U.S. Pat. Nos. 4,261,533 and 4,099,687, is to rotate the tail or to deflect large chord elevons to magnitudes of approximately the same order, but of opposite direction, as theairplane angle of attack, so that the effective tail aerodynamic angle of attack is below the tail stall angle and is thus capable of providing both stability and control for the entire aircraft.

Although rotatable canard arrangements are known from U.S. Pat. No. 4,569,493, U.S. Pat. No. 4,281,810, U.S. Pat. No. 4,010,920, and West German Offenlegungsschrift 2421524, such arrangements deal strictly with the stability and control of aircraft and models in level and unstalled low angle of attack regions of flight and do not address the problems of stability and control of aircraft in the high angle of attack regions of flight.

In most cases, the upper limit of normal flight is associated with conditions for maximum lift, beyond which the wing is completely stalled. For some aircraft configurations, however, for example, those employing wings with high leading edgesweep angles or incorporating strakes, i.e. a continuous band of plates on the fuselage, partial flow separation of the wing or control surfaces may induce stability problems below the attack angles for maximum lift and impose lower limits on the normalflight regions.

Solutions of these problems will allow flight above these lower limits. Flight above the normal limits is considered of a supernormal nature."

later see what the say

In piloted supernormal flight of the aircraft of the present invention, the wing of an aircraft, such as a superagile tactical fighter, is either partially or completely stalled, while the longitudinal control surfaces, such as in a rotatablecanard arrangement, are deflected to approximately the same magnitude, but of opposite sign, as the angle of attack of the aircraft, so that the canard arrangement remains effective to control the aircraft through large ranges of angles of attack, pitch,and flight path. Such angles may vary from descending flight to deep stall, i.e. -45.degree., to ascending flight in vertical climb, i.e. +90.degree.



The thrust T, lift L, drag D, velocity V, and various angular attitudes associated with and acting upon the aircraft in piloted supernormal flight are best illustrated in FIG. 2C. In such supernormal flight, the aircraft operates at an attackangle .alpha. much greater than the angle of attack for maximum lift so that the fixed wing 15 is either completely or partially stalled while the canard surfaces 19 are deflected in a negative sense through the deflection angle-.delta..sub.c. The absolute deflection magnitude of the canard surfaces 19 is approximately the same as the attack angle .alpha. for the entire aircraft so that such canard surfaces 19 are nearly aligned with the local air flow and are, therefore, unstalled. Thus , the canard surfaces 19 remain effective as lift surfaces in providing the required forces and moments for controlling the entire aircraft.
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[video=youtube;YA8QXenJzgA]http://www.youtube.com/watch?v=YA8QXenJzgA[/video]


Check the J-20 is not flying with thrust vectoring, niether is close to a stalled wing situation the jet is basicly, executing a shallow turn What song`s paper is trying to address is something similar but he metions TVC nozzles, on that video J-20 does not have thrust vectoring niether flying at high AoA, the jet is just simply deflecting the canards like a heavy loaded Rafale would do in order to increase lift.

In my opinion today`s J-20 still is far from being the ideal jet Song`s paper describe because it lacks TVC nozzles and without it the contradictions of stealth and aerodynamics represent a higher performance penalty
 
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Air Force Brat

Brigadier
Super Moderator
Re: J-20... The New Generation Fighter III

I will be very honest, up to what i know indy cars work more like tailplanes, stable aircraft need a negative lift vector on their tail to keep the nose up indy cards do the same.


The mechanics of flight are very complex, however my only point was to tell you the negative deflection does not mean necesarily pitch down of the nose, but it is a way to achieve higher lift in some situation read this and later see the video and check the X-31`s canards deflections

"2. Brief Description of the Related Art

Until about 1978, the region beyond stall was considered an unacceptable flight regime frequently characterized by uncontrollable flight in spins and by undesirable deep stalls. Any deep stall condition is characterized by a stable trimmedflight but at a high angle of attack from which return to normal flight may be difficult or impossible. A deep stall may be defined as an out-of-control condition at an angle of attack greater than the angle of attack for maximum lift with nosignificant motion other than a high rate of descent. Conventional airplanes usually stall and lose control effectiveness at angles of attack in the range of 18.degree. to 20.degree..

However, according to U.S. Pat. Nos. 4,261,533 and 4,099,687, it is now possible, through the use of a rotatable horizontal tail on aft-tail configurations or through the use of tiltable engines on the wings, to provide stable and controllableflight at extremely high airplane angles of attack.

Because movement other than a high rate of descent can be controlled by varying thrust levels and all moveable control surfaces with large deflections, the safety and usefulness of flight at extremely high angles of attack are being re-examinedand redefined.

The essence of the longitudinal control concept, as set forth in U.S. Pat. Nos. 4,261,533 and 4,099,687, is to rotate the tail or to deflect large chord elevons to magnitudes of approximately the same order, but of opposite direction, as theairplane angle of attack, so that the effective tail aerodynamic angle of attack is below the tail stall angle and is thus capable of providing both stability and control for the entire aircraft.

Although rotatable canard arrangements are known from U.S. Pat. No. 4,569,493, U.S. Pat. No. 4,281,810, U.S. Pat. No. 4,010,920, and West German Offenlegungsschrift 2421524, such arrangements deal strictly with the stability and control of aircraft and models in level and unstalled low angle of attack regions of flight and do not address the problems of stability and control of aircraft in the high angle of attack regions of flight.

In most cases, the upper limit of normal flight is associated with conditions for maximum lift, beyond which the wing is completely stalled. For some aircraft configurations, however, for example, those employing wings with high leading edgesweep angles or incorporating strakes, i.e. a continuous band of plates on the fuselage, partial flow separation of the wing or control surfaces may induce stability problems below the attack angles for maximum lift and impose lower limits on the normalflight regions.

Solutions of these problems will allow flight above these lower limits. Flight above the normal limits is considered of a supernormal nature."

later see what the say

In piloted supernormal flight of the aircraft of the present invention, the wing of an aircraft, such as a superagile tactical fighter, is either partially or completely stalled, while the longitudinal control surfaces, such as in a rotatablecanard arrangement, are deflected to approximately the same magnitude, but of opposite sign, as the angle of attack of the aircraft, so that the canard arrangement remains effective to control the aircraft through large ranges of angles of attack, pitch,and flight path. Such angles may vary from descending flight to deep stall, i.e. -45.degree., to ascending flight in vertical climb, i.e. +90.degree.



The thrust T, lift L, drag D, velocity V, and various angular attitudes associated with and acting upon the aircraft in piloted supernormal flight are best illustrated in FIG. 2C. In such supernormal flight, the aircraft operates at an attackangle .alpha. much greater than the angle of attack for maximum lift so that the fixed wing 15 is either completely or partially stalled while the canard surfaces 19 are deflected in a negative sense through the deflection angle-.delta..sub.c. The absolute deflection magnitude of the canard surfaces 19 is approximately the same as the attack angle .alpha. for the entire aircraft so that such canard surfaces 19 are nearly aligned with the local air flow and are, therefore, unstalled. Thus , the canard surfaces 19 remain effective as lift surfaces in providing the required forces and moments for controlling the entire aircraft.
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[video=youtube;YA8QXenJzgA]http://www.youtube.com/watch?v=YA8QXenJzgA[/video]


Check the J-20 is not flying with thrust vectoring, niether is close to a stalled wing situation the jet is basicly, executing a shallow turn What song`s paper is trying to address is something similar but he metions TVC nozzles, on that video J-20 does not have thrust vectoring niether flying at high AoA, the jet is just simply deflecting the canards like a heavy loaded Rafale would do in order to increase lift.

In my opinion today`s J-20 still is far from being the ideal jet Song`s paper describe because it lacks TVC nozzles and without it the contradictions of stealth and aerodynamics represent a higher performance penalty

You're figuring it out alright, all of us are a lot right and a little bit wrong, The canard and the trailing edge surfaces are uncoupled, that is what has many of us scratching our heads, the forward strakes and the chining leading to the blended wing/fuse are generating more lift than we might expect at the high angles of attack and from a pilot's perspective, although slow the J-20 is at a fairly high angle of attack in these turns, hence the FBW decouples the canards from the trailing edge and ruddervators which are generating a downward force on the tail to bring the J-20 into this relatively high alpha condition, in order to prevent over pitching the aircraft and departure from controlled flight the FBW decouples the canards and commands them to prevent the nose rising. Dr. Song stated that a prime objective was to recover the J-20 to controlled flight , in the event of a TVC failure, the J-20 may have accomplished this, as you have correctly asserted the J-20 has not been extremely slow, nor has it been past mach 1 to our knowledge, so we have to deduct what we know from Dr. Songs paper and the video/photo evidence. Now heres what I suspect, they are gradually expanding the flight envelope, at this stage the TVC would likely complicate that process, and they really don't have a suitable powerplant with thrust vectoring or it would already be installed and flying. This is apparently a very sound airframe, and if they have to, they may be able to get by without TVC. Good work mig and a nice logical defense of your theorys, you are a bright lad, I do appreciatte the papers you provide as sources, if you could pull the lines from your papers that support your positions, and footnote or source them, that would cut down on some of the business of your posts.
 

Quickie

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

The canards were tested at several positions
and deflected from -10 to +10 degrees. In addition,
configurations consisting of a horizontal tail and a
canard with horizontal tails are analyzed.
The results of the analysis inidcate that
Please, Log in or Register to view URLs content!



DO you understand what the sentence in addition means? it means the study was done also to triplane configuration, not that the study was done only to triplane configurations, also the position was studied, which means they moved aft and forward the canard

No matter what, the experimental model without the horizontral tail exists only in the wind tunnel to collect experimental data. No one would be crazy enough to actually built one and fly it. This is why they have to proceed further with the testing of the trisurface configuration as quoted below. So, my point still stands, you can't simply extrapolate the experimental data to a very different design configuration like the J-20.

TRISURFACE CONFIGURATIONS
The canard, if in proper position foi favorable interference, is not
as efficient a trimming device for a stable configuration. This is due in
part to the short moment arm as well aa to the large drag increase caused
by positive canard drflectiona. This increase in drag is particularly
severe at low angles of attack. Due to the above reasons, configurations
consisting of canards, wing, and horizontal tail were evaluated.

Also, the J-20 may not need to be dependent on thrust vectoring as it has tail control surfaces for pitch control in addition to its canards. We always see both of them in action during landing. With additional control surfaces for pitch control, the J-20 can afford to have a shorter canards moment arm if required in its overall design.

That's why I still stand by what I've commented and, it's okay for you to stand by yours, which I know is mistakened, like the one in your reply to Air force Brat, that is,

And my point was negative deflections do not mean pitch down at high AoA, i do not agree with you because a car and indy car in this case is not flying at high AoA but straight at 0 degrees
:confused:
 
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MiG-29

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

You're figuring it out alright, all of us are a lot right and a little bit wrong, The canard and the trailing edge surfaces are uncoupled, that is what has many of us scratching our heads, the forward strakes and the chining leading to the blended wing/fuse are generating more lift than we might expect at the high angles of attack and from a pilot's perspective, although slow the J-20 is at a fairly high angle of attack in these turns, hence the FBW decouples the canards from the trailing edge and ruddervators which are generating a downward force on the tail to bring the J-20 into this relatively high alpha condition, in order to prevent over pitching the aircraft and departure from controlled flight the FBW decouples the canards and commands them to prevent the nose rising. Dr. Song stated that a prime objective was to recover the J-20 to controlled flight , in the event of a TVC failure, the J-20 may have accomplished this, as you have correctly asserted the J-20 has not been extremely slow, nor has it been past mach 1 to our knowledge, so we have to deduct what we know from Dr. Songs paper and the video/photo evidence. Now heres what I suspect, they are gradually expanding the flight envelope, at this stage the TVC would likely complicate that process, and they really don't have a suitable powerplant with thrust vectoring or it would already be installed and flying. This is apparently a very sound airframe, and if they have to, they may be able to get by without TVC. Good work mig and a nice logical defense of your theorys, you are a bright lad, I do appreciatte the papers you provide as sources, if you could pull the lines from your papers that support your positions, and footnote or source them, that would cut down on some of the business of your posts.

I will tell you why i do not believe that theory, i have presented you two reasons why canards are deflected negatively, one is because at high AoA the lift and pitch moment is increased, two because at very high AoA canards are used to regain control of a stalled wing.

If the J-20 needs a strong nose down moment, it only needs to deploy flaps why?

The other drawback with the aft-set wing is that it is difficult to use flaps. Flaps almost double the lift produced by the wing, but on a lifting canard this would produce such a strong nose-down pitching moment that only a very large foreplane could overcome it. Consequently, flap size and effectiveness become factors in the thorny issue of canard sizing.

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However you see the J-20 not deploying flaps, but deploying wing leading edge flaps to increase lift and donward deflection of canards to increase lift.

Rafale does not use too much its canards because trailing edge flaps and relaxed stability are balanced while turning or doing vertical turns

[video=youtube;9_6CsvxMjdc]http://www.youtube.com/watch?v=9_6CsvxMjdc[/video]


from minute 0:55 you can see the Gripen flying high AoA and the canards with negative deflection

the aircraft operates at an attackangle .alpha. much greater than the angle of attack for maximum lift so that the fixed wing 15 is either completely or partially stalled while the canard surfaces 19 are deflected in a negative sense through the deflection angle-.delta..sub.c. The absolute deflection magnitude of the canard surfaces 19 is approximately the same as the attack angle .alpha. for the entire aircraft so that such canard surfaces 19 are nearly aligned with the local air flow and are, therefore, unstalled .
[video=youtube;bea4TnOX8Ns]http://www.youtube.com/watch?v=bea4TnOX8Ns&feature=related[/video]
 
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Air Force Brat

Brigadier
Super Moderator
Re: J-20... The New Generation Fighter III

I will tell you why i do not believe that theory, i have presented you two reasons why canards are deflected negatively, one is because at high AoA the lift and pitch moment is increased, two because at very high AoA canards are used to regain control of a stalled wing.

1.Reason 1 high A0A, the ruddervators are deflected to increase pitch, the elevons are deflected to increase pitch, forward body strakes are increasing lift raising the nose, I believe the engineer stated in one of his posts that the forward fuselage vortex generators or strakes account for 17.5 percent of the J-20s overall lift, FBW, "decouples" the canard to spoil some of the lift generated by deflecting the "distant coupled" canard downward, "preventing overpitching" and maintaining the main wing in a high lift, unstalled condition.

2.Reason 2 although the wing is at a high angle of attack, it is kept there to maintain the tight turning radius observed in the video by the elevons, ruddervators, and forward fuselage lift, in addition the leading edge flaps have increased the lift of the main wing, by increasing their camber, as evidenced by the aircrafts 70+ degree bank angle, and the slow speed tight turn radius. The Pilot increases thrust as he pulls the stick aft to hold the approx 40 degree angle of attack, if allowed to the Aircraft would continue to "overpitch", so the FBW decouples the canard from the positive pitch input the pilot is applying, and "balances" the lift of the forward fuselage with negative pitch of the canard, thats why DR. Song talks about the divergent characteristics required by transonic and supersonic flight!

[Thats why I choose an Indy or F1 car as an illustration the rear spoiler applies down pressure to load the tires and maintain tire adhesion, without a front spoiler applying a similar down pressure on the front end, the front would lift. It does cause drag, but a little drag keeps the whole car planted and safe, just like the downward deflected canard on the J-20. 2. I don't deny that a high mounted, close coupled canard creates lift by vortex generation, even with a slight negative pitch, 3 The J-20 has a distant coupled, low mounted canard, the primary function of which is pitch control, the FBW is applying positive pitch with the trailing edge surfaces and ruddervators and negative pitch in the front, just like the front spoiler on the car, to prevent over pitching and lose of control. The aircraft is in balance flight, and like a submarine has to be in trim, fore and aft. "As a certain Radio Host is want to say, "Don't Doubt Me"". Just a joke mig, Tianlong and Dr. Song hold the key, thats why I have stated that this is a very smart airplane, as Dr. Song states, complicated, confusing, but smart.
 

MiG-29

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

"As a certain Radio Host is want to say, "Don't Doubt Me"". Just a joke mig, Tianlong and Dr. Song hold the key, thats why I have stated that this is a very smart airplane, as Dr. Song states, complicated, confusing, but smart.

I do not think that is the case, and i will tell you why, the J-20 by applying flaps will generate a nose down movement simply like that, tailess fighters like Mirage 2000 or LCA is what they do when they over pitch.

Song`s paper talks about using canards at very high alpha, near poststall, and like the paper or X-31 video i posted you, canards are deflected at the same Angle but with opposite sign of the AoA at post stall, the chinese theory is similar to the European in that they want to use delta wings so they added Lerx, and canard and some wing-fuselage blending, but is not like you are thinking, Song`s paper is anything but new or revolutionary, looking at the Rafale or even Gripen you can find similar aerodynamics, it is nothing new, X-31 is similar in TVC nozzles application at high AoA and coupling with canards deflection, something that both Germans and Americans have already tested in test flights not in theoretical work and tested his theories since the 1990s.

In fact JAST JSF were with similar solutions, what really has surprised western analysts is the possibility that China has made advances in avionics and materials and adapted western technologies into an original concept.

Watch this video and see that LCA can control the jet with pure wing trailing flaps and elevons, J-20 can do that, but they do not apply flaps simply because flaps mean a pitch down force, so they do not apply flaps otherwise the nose will go down

[video=youtube;vSYgVRe61F8]http://www.youtube.com/watch?v=vSYgVRe61F8[/video]
 
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Quickie

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

I do not think that is the case, and i will tell you why, the J-20 by applying flaps will generate a nose down movement simply like that, tailess fighters like Mirage 2000 or LCA is what they do when they over pitch.

Song`s paper talks about using canards at very high alpha, near poststall, and like the paper or X-31 video i posted you, canards are deflected at the same Angle but with opposite sign of the AoA at post stall, the chinese theory is similar to the European in that they want to use delta wings so they added Lerx, and canard and some wing-fuselage blending, but is not like you are think, Song`s paper is anything but new or revolutionary, looking at the Rafale or even Gripen you can find similar aerodynamics, it is nothing new, X-31 is similar in TVC nozzles, something that both Germans and Americans have already tested in test flights not theoretical work his theories since the 1990s.

In fact JAST JSF were with similar solutions, what really has surprised western analyst is the possibility that China has made advances in avionics and materials and adapted wester technologies into an original concept.

Watch this video and see that LCA can control the jet with pure wing trailing flaps and elevons, J-20 can do that, but they do not apply flaps simply because flaps mean a pitch down force, so they do not apply flaps otherwise the nose will go down

[video=youtube;vSYgVRe61F8]http://www.youtube.com/watch?v=vSYgVRe61F8[/video]

You made it seem like not deflecting down the flaps is a problem for J-20. By your logic, the Rafale and Gripen (and LCA and Mirage 2000 too) have a more serious problem since they are destined to be not able to deflect the flaps down during a climb or landing because the aircrafts use them as elevons. On the contrary, the J-20 may still be able to deflect its flaps down by increasing the deflection of the canards and its tail control surfaces at a higher than usual degree.
 
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MiG-29

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

You made it seem like not deflecting down the flaps is a problem for J-20. By your logic, the Rafale and Gripen (and LCA and Mirage 2000 too) have a more serious problem since they are destined to be not able to deflect the flaps down during a climb or landing because the aircrafts use them as elevons. On the contrary, the J-20 may still be able to deflect its flaps down by increasing the deflection of the canards and its tail control surfaces at a higher than usual degree.

LCA and Mirage 2000 are definitively limited by the use of flaps, but they use a trick, and it is called low wing loading, and high relaxed stability, other fighters with canards like IAI Lavi, Rafale, Gripen or Eurofighter can use the canard to pitch up.

J-20 is not using flaps simply because by using them a strong nose down pitch will be generated, the canard is just having a lower AoA with respect the air flow and it is aligned with it.


If the theory it needs a down force was true, then deploying flaps is a smarter idea, why? by deploying flaps the J-20 achieves higher lift, thus better turn rates are achieveable, however the reality is the J-20 is not deploying them simply because the jet is using the canards to lift up the nose.

At minute 4:00 you can see the Gripen with negative canards deflection, that is just to align the flow with the canards and reduce their AoA

[video=youtube;v55JwuWDctU]http://www.youtube.com/watch?v=v55JwuWDctU&feature=BFa&list=HL1332077632&lf=mh_lolz[/video]
 
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Quickie

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

LCA and Mirage 2000 are definitively limited by the use of flaps, but they use a trick, and it is called low wing loading, and high relaxed stability, other fighters with canards like IAI Lavi, Rafale, Gripen or Eurofighter can use the canard to pitch up.

J-20 is not using flaps simply because by using them a strong nose down pitch will be generated, the canard is just having a lower AoA with respect the air flow and it is aligned with it.


If the theory it needs a down force was true, then deploying flaps is a smarter idea, why? by deploying flaps the J-20 achieves higher lift, thus better turn rates are achieveable, however the reality is the J-20 is not deploying them simply because the jet is using the canards to lift up the nose.

At minute 4:00 you can see the Gripen with negative canards deflection, that is just to align the flow with the canards and reduce their AoA


We tried to explain to you the how the J-20 generate lifts, especially body lifts, to shift the aircraft's AC but you choose to ignore it.


We have evidence of the J-20 using its canards to control aircraft pitch (through the effect of canards' moment of arm), but not so much for the other aircrafts that you mentioned, especially the Rafale and Gripen because these 2 aircrafts use the elevons for pitch control during those maneuovres.

You said the J-20 will pitch down if it were to deflect down its flap. I explained earlier why this is not necessary true for the J-20 but definitely true for Rafale and Gripen. In fact the elevons have to be deflected up for pitch up for these 2 aircrafts. (Their deflection, partly because of their large surface area, is not as noticeable as the canards or tail elevators).

If you're so convinced that these 2 aircrafts can in fact deflect the flaps down during landing (aircraft at a positive AOA) or climbing or better still, during a turn maneuovre. Show us the proof.

If you can't, then don't continue derailing this thread with your pseudo aerodynamic theory.
 
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