Aerodynamics thread

[MiG-29]

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

That's correct, I do know better than you, which is why your b.s. doesn't work with me.


In the paper, Dr. Song explained that canards can bring the nose down by providing negative lift, and called the canards "negative load control surfaces". The exact statement is as follow:


Continue on, he explained that canards are advantageous over flaps in pitch control. Specifically, at high AoA the wing would be close to stalling, and extending flaps is equivilent to increasing their AoA, causing them to stall and lose control. Canards simply have to go into negative AoA to force the nose down.






.

When the article you quoted talks about canards, it is referring to fixed canards. Specifically, the article is talking about the Beechcraft Starship, having fixed canards fitted with trailing flaps. This is why the article says "that the canard itself is already flapped (the elevator)" and why it mentioned the canards stalling. A picture of Beechcraft Starship is shown below:

False. Su-27 doesn't "bring its nose down" through active deployment of flaps or deflection of elevators. The Su-27 nose comes down because as the aircraft is flying at over 90 AoA, at which point drag at the tail is not compensated by an equivilent surface at the nose. At such high AoA, the control surfaces of Su-27 are useless. Thus, this little fact of your's doesn't contradict Dr. Song's statement in anyway.


.

Poor of you you missed the fact the starship has hinged canards hahahaha come on next time read more before asserting things, hinged canards also increase lift like the canards of Viggen

and since you only says fallacies i will prove you why Su-27 uses Tailplanes showing you have no idea what Song was talking about in as imple way, he says that in his view and according to the studies they done canards can bring the nose down better than thet tailplane.

however studies done by in the US and footage and Su-27 videos show the tailplane is effective in high angle of Attacks on the page 7 of this study and figure 10 they show and say canard deflection is effective only at low AoA to bring the nose down while the tailplane is still effective at high AoA and the post stall regime.

In Page 9 figure 18-21 they show how taiplane are still effective to bring the nose down during cobra

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from minute 4 you can see how Su-27 uses tailplanes to bring down the Jet after cobra
[video=youtube;emb6er8LOtk]http://www.youtube.com/watch?v=emb6er8LOtk[/video]

here we see a very tight turn and Eurofighter does not need to deflect as much its canards
[video=youtube;keqfMIzwsnY]http://www.youtube.com/watch?v=keqfMIzwsnY[/video]

 

[Engineer]

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

I will disagree just using simple studies of canard deflections in the USA.

Let us start witha simple fact:

Delta wings have low aspect ratio thus they achieve their max lift at higher AoA than higher aspect wings, since J-20 has a delta, it shows how much its struggles with the AoA to achieve lift
see

"Wings with aspect ratios less than 5 typically stall at
higher angles of attack than higher-aspect-ratio wings. The
wing of the model had an aspect ratio of 3. The overall shape
of the CL versus AOA curve is similar to curves for other lowaspect-
ratio wing configurations"

For an aircraft with pure delta wing, such as the LCA, this assessment is true. For J-20, the aircraft indeed uses low aspect wings, but it is made up by the fact that Canards, LERX and body-lift are also employed. The following chart is extracted from Dr. Song's paper. In it, the white bar represents a configuration that doesn't use body-lift, while the black bar represents a configuration that does. From left to right, the first pair of bars refers to a configuration with wing-body blending. The second pair refers to a configuration with both wing-body blending and canard. The last configuration shows wing-body blending, canards, and LERX being used simultaneously.

The result is a 81% increase over traditional configuration, showing J-20 has plenty of lift available for maneuvering at high AoA.

Let us see

"The AOA of
the wing/body was varied from -8 to 50 degrees,and CL varied
from .036 to 1.586. The maximum lift occurred at an AOA of 40
degrees."

Here it is clear the delta wing of the model achieved its max lift at a pretty high AoA

Now
You are claiming the J-20 is flying straight, that is not true it is turning, but why you can explain such as large deflection of the canard?

See the very likely J-20 has not its main engines, therefore it is very likely stil underpowerd.

So what happens with drag at high AoA, well it is also very high so the model needs powerful engines to increase Sustained turn rates

"Values in the high angle-of-attack regime from 20 to 40 degrees, where an agile-aircraft might be expected to have an excursion, decrease from about 2.8 to 1.3, indicating the significant thrust levels required for supermaneuverability."

simple let us see the Max lift attained by the model at different AoA and at what Angle of canard deflection

See:

"Figure 14 shows the variation of CL with canard deflection angle at a wing/body AOA of 10 degrees. The maximum CL was 0.698 at 17 degrees."

later it goes

"Figure 16 shows the variation of CL with canard deflection angle for a wing/body AOA of 22 degrees. The maximum CL was 1.422 at a canard angle of 7 degrees"
later

"Figure 18 shows the variation of CL with canard deflection angle for a wing/body AOA of 34 degrees. This angle of attack is in the region midway along the second rise of the baseline configuration lift curve. The maximum CL was 1.642 at a canard angle of -7 degrees."



and later

"Figure 20 shows the variation of CL with canard deflection angle for a wing/body AOA of 40 degrees. This wing/body angle corresponds to the condition of the maximum CL for the baseline configuration. The maximum CL was 1.700 at a canard angle of -15 degrees."

See that if the Jet is trying to achieve higher lift it will need a relatively high negative deflection, and a high AoA if it is underpowered

"CANARD/WING/BODY CONFIGURATION; AOA 48 DEGRZES Figure 22 shows the variation of CL with canard deflection angle for a wing/body AOA of 48 degrees. This wing/body angle is deep in the second post-stall region for the baseline configuration. The maximum CL was 1.649 at -17 degrees."

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So what is a turn? it is basicly a high AoA so the J-20 is in reality deflecting to achieve higher lift and is not using flaps to avoid pitch down the nose like any delta canard jet will do

There are two problems with this analysis of your's.

The first has to do with your statement on engine power. It is true that the current J-20 prototype does not use WS-15 and is underpower. However, the design thrust-to-weight ratio can still be attained at flight, because the aircraft is only a prototype and is not required to carry combat load. In other words, not carrying the full fuel load, or payload, or combination of both is sufficied in achieving the designed sustain turn rate.

The second problem has to do with your interpetation of the paper. The paper does not address pitch moment, and the lift being referred to by the author is the lift generated for the entire aircraft. In other words, the thesis doesn't support your argument that canards are being used to keep the nose up.

There is also a very important statement in that paper, which you conviently missed. It says the following:

It should be noted that the term "canard deflection angle" refers to the incidence angle of the canard relative to the fuselage centerline.

What this means is that when the aircraft has positive AoA say 40 degrees, and the canards have negative deflection angle of 15 degrees, the canards actually have positive AoA of 25 degrees. However, such combination may create significant pitch up moment, which isn't addressed by the thesis at all. The combination may not be achievable in real life, as it could lead to lost of control of the aircraft. Obviously, the J-20 is pretty in control, so it is unlikely that its canards are having such a large positive AoA.

When canards deflect downward during a high AoA manuever, what is actually happening is that the canards are aligned with the oncoming airflow. As explained in this

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:

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, downward deflection of canards has nothing to do with generating lift. The true goal is to keep the control surfaces unstall and usable.

 

[MiG-29]

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

For an aircraft with pure delta wing, such as the LCA, this assessment is true. For J-20, the aircraft indeed uses low aspect wings, but it is made up by the fact that Canards, LERX and body-lift are also employed. The following chart is extracted from Dr. Song's paper. .

Let me see is there another jet in the world that uses LERX, canards and wing fuselage blending?
ah yeah it is in France it is called Rafale, and let me see was that jet tested with wing positioned vertical twin fins in aerodynamic studies? ah yeah it was in France in the 1980s, so why Rafale has only one fin?
Ah i know because the configuration was good enough to requiere a single fin for lateral stability.

and so let me see, has Eurofighter made studies with TVC ah yeah it has, did Germany test TVC nozzles in a real jet and yeah they did in the 1990s named X-31, hold one, so Song`s theories are not new then? yes they are not new at all.


Does J-20 has compromises. yes, first it has a high wing, the ideal for low drag is a mid wing, second the ideal canard for a fighter is close and above wing level, so why it has high wing and canard set at same level with the wing? well they went for stealth.

Simple, will it need TVC nozzles yes, it will.

 

[Engineer]

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

Poor of you you missed the fact the starship has hinged canards hahahaha come on next time read more before asserting things, hinged canards also increase lift like the canards of Viggen

ROFL!

You should heed your own advise, and read more before asserting things. Observe what I have actually said:

When the article you quoted talks about canards, it is referring to fixed canards. Specifically, the article is talking about the Beechcraft Starship, having fixed canards fitted with trailing flaps.

The canards on the Starship are still fixed, making them different thus their analysis completely irrelevant to J-20. Having movable trailing flaps doesn't alter this fact.

and since you only says fallacies

False. Pointing out the mistakes in your statements and correcting them not a fallacy. It is arguing with facts and logic; it is the pursue of truth, which is something that you are unable to comprehend.

i will prove you why Su-27 uses Tailplanes showing you have no idea what Song was talking about in as imple way, he says that in his view and according to the studies they done canards can bring the nose down better than thet tailplane.

however studies done by in the US and footage and Su-27 videos show the tailplane is effective in high angle of Attacks on the page 7 of this study and figure 10 they show and say canard deflection is effective only at low AoA to bring the nose down while the tailplane is still effective at high AoA and the post stall regime.

In Page 9 figure 18-21 they show how canard is still effective to bring the nose down during cobra

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from minute 4 you can see how Su-27 uses tailplanes to bring down the Jet after cobra

First, Dr. Song's paper is pretty clear. He unequivocally points out canards are superior to trailing edge control surfaces because the former do not stall at high AoA. There was nothing uncertain in his statements, and he does not need "in my opinion" or "in our view" as people who have an axe to grind with J-20 have done. Here is his statement:

Control surfaces placed in front of the center of mass, like the canards, are negative load control surfaces. Since the main wing's ability to generate lift tends to saturate under high AOA conditions, the positive load control surfaces' pitch down control capabilities tend to saturate under high AOA as well. Therefore it will be wise to employ negative load control surfaces for pitch down control under high AOA conditions. Figure 7 compares the pitch down control capabilities of the canards and horizontal stabilizers. From the high AOA pitch down control stand point, it will be wise to use canards on the future fighter.

Secondly, at no time did I say Su-27 does not use tailplane. Your invention of this ridiculous statement than proceed to argue against it is called making up

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, which is a logical fallacy.

Thirdly, an airfoil orientated perpendicular to oncoming airstream is a stalled aerodynamic surface. A stalled control surface is one that is ineffective in achieving control for the aircraft, regardless of whether that surface is a canard or a tail plane. The paper you have linked to analyze the post-stall situation where all the control surfaces are essentially useless. Specifically, they try to find the trim condition or orientation of control surfaces for a post-stall maneuvers, then from the deflections calculate the velocity of the aircraft. Fig. 10 refers to the canards' ability to influence angle-of-attack for downstream control surfaces thus their deflection angle, and is not an analysis on the control efficiency. In fact, the goal of the study is not to analysis effectiveness of control surfaces at all. Thus, your statement "tailplane is effective in high angle of Attacks... canard deflection is effective only at low AoA..." is solely your own opinion. Once again, you took someone's words and twist them to mean something completely different. Typical.

As for Su-27, its pitch down moment at the end of a Cobra maneuver has nothing to do with deflections or flaps or control surfaces. This makes sense, as the control surfaces have stalled and are useless. The pitch down moment is resulted because the aircraft is flying perpendicular to oncoming airflow, and the drag imposed onto the tail plane producing a torque. The paper which you have linked to says the exact samething:

The recovery from high angles of attack to the classical flight mode in a few seconds only is possible due to moving the center of pressure on main wing back and creating the strong nose-down aerodynamic pitching moment about the center of gravity.

No where does this statement mention anything about using control surfaces for pitch down moment. Your assumption of the opposite being true so you have no knowledge required for this discussion.

What is said in Dr. Song's paper is that to achieve a pitch down moment, tail surfaces must increase their AoA which would result in their stall. Canards on the other hand, reduced their AoA to bring the nose down thus does not run into the same problem.

We can categorize two types of control surfaces based on the relative position of the pitch control surfaces with respect to the aircraft's center of mass: positive load pitch down control surface and negative pitch down control surface. Control surfaces placed behind the center of mass, including the vertical stabilizers and trailing edge flaps, generate pitch down control torque by increasing lift. They are considered positive load control surfaces. Control surfaces placed in front of the center of mass, like the canards, are negative load control surfaces.

This is why the canards are deflected downward while the J-20 is turning.

here we see a very tight turn and Eurofighter does not need to deflect as much its canards

And here are photos of Eurofighter undergoing high-G maneuver, showing downward deflection of the canards:

We know that the Eurofighter has relaxed stability, where the aerodynamic center is infront of the center of gravity. Thus, the Eurofighter is not nose-heavy and does not need to use canards to keep its nose up. From the above pictures, we see Eurofighter's canards also deflect downward during a turn. Since the Eurofighter has no requirment of lifting its nose up during a turn, the purpose of canards deflecting downward is clearly not to enhance lift at the nose, thus completely debunk your ridiculous pseudo-aerodynamic theories.

There is an additional reason why the J-20 requires significant downward deflection in the canards. The reason is unstability, and is explained by Dr. Song in his paper:

Further relaxing the longitudinal instability could not only enhance trans-sonic lift to drag characteristics but also improve super sonic lift to drag capabilities, increase take-off and landing characteristics, and maximize low-speed lift characteristics. This is akin to killing three birds with a single stone. Yet a increase in longitudinal instability will also increase the burden on high AOA pitch down control and subsequently increase flight control complexities.

In kiddie's terms, the more unstable aircraft is, the more pitch-down capability the aircraft requires.

Since canards provide that pitch-down capability, it is natural to see more downward deflection from them for a more unstable aircraft. In other words, J-20 requires more canard deflection simply means the aircraft is more unstable than fighter aircraft that are currently in service.

 

[tch1972]

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

I will disagree just using simple studies of canard deflections in the USA.

So what is a turn? it is basicly a high AoA so the J-20 is in reality deflecting to achieve higher lift and is not using flaps to avoid pitch down the nose like any delta canard jet will do

Any aircraft with partial slat/flap deploy,the canard/elevator deflected more than when the wing is clean. As for the degree of canard deflection, slow flying and large canard deflection doesn't indicate engine under power. Engine power can't be tested when the aircraft is flying slow. Base on what I studied, canard deflection downward shows the J20 wings is producing lot of lift at that slat setting and if the canard isn't deflected at that angle to counteract , the tendency is the aircraft will start gaining altitude.

---------- Post added at 02:57 PM ---------- Previous post was at 02:54 PM ----------

And here are photos of Eurofighter undergoing high-G maneuver, showing downward deflection of the canards:

Notice the slat is also lowered in this case.

 

[Engineer]

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

Let me see is there another jet in the world that uses LERX, canards and wing fuselage blending?
ah yeah it is in France it is called Rafale, and let me see was that jet tested with wing positioned vertical twin fins in aerodynamic studies? ah yeah it was in France in the 1980s, so why Rafale has only one fin?
Ah i know because the configuration was good enough to requiere a single fin for lateral stability.

and so let me see, has Eurofighter made studies with TVC ah yeah it has, did Germany test TVC nozzles in a real jet and yeah they did in the 1990s named X-31, hold one, so Song`s theories are not new then? yes they are not new at all.

I see you have no proof showing that has problems with lift as you claimed, so you now try to distract by claiming Dr. Song's theories are not new. This is a fallacy known as

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. How typical of you.

What configuration other aircraft has, and what configurations their design team looked into, is completely irrelevant to J-20 aerodynamics. Whether ideas presented in Dr. Song's paper are new is also irrelevant, because these ideas being new or not does not degrade the present aerodynamics of the J-20.

Does J-20 has compromises. yes, first it has a high wing, the ideal for low drag is a mid wing, second the ideal canard for a fighter is close and above wing level, so why it has high wing and canard set at same level with the wing? well they went for stealth.

Of course compromises have been made in the design of J-20. However, Dr. Song and his team also incoporate many features to eliminate the disadvantages of those compromises. In some cases, the compromises end up being enhancements. Case in point, the most obvious compromise is the use of low-aspect ratio wing to reduce drag. The disadvantage of low-aspect ratio wing is low lift. Using a combination of body-lift, canard, chines and LERX, the total lift is increased to 181% than using a traditional configuration alone. Compare to using canard-delta configuratin with wing-body blending, there is a 118% increase in lift. This is shown in the following chart extracted from his paper:

Another example, because of the presence of LERX, the canards have their root placed at the same level as the wingroot. However, through a combination of diheral-anhedral canard-wing setup, they were able to retain the simplicity at the wingroot while achieving a high-canard setup. This is an elgant solution to the original conflicting problem.

There are more examples, but the above illustrate the difference between world-class designer, and certain armchair aerodynamicist whose only knowledge is twisting people words so that he can claim everything on the J-20 as a bug or design fault. Inability to employ logic and think critically will doom the latter to failure.

Simple, will it need TVC nozzles yes, it will.

TVN might be beneficial. However, is it a requirement? The answer is clear in Dr. Song's paper:

Although it is possible to solve the problem of post-stall controllability through the use of thrust vectoring nozzles, the aerodynamic configuration itself must provide enough pitch down control capability to guarantee the aircraft to safely recover from post-stall AOA should the thrust vectoring mechanism malfunction. As a result, it is vitally important to study unconventional aerodynamic control mechanisms for high AOA flights.

So, the answer is no.

I think your insistence that J-20 must have TVN is based on the observation that PAKFA needs TVN to meet the design criterias of a 4th generation fighter. I don't think the strategy employed by a team that simply takes and stealthied a Su-27 could be generalized as an approach that must taken by others.

 

[MiG-29]

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

ROFL!


The canards on the Starship are still fixed, making them different thus their analysis completely irrelevant to J-20. Having movable trailing flaps doesn't alter this fact.






Secondly, at no time did I say Su-27 does not use tailplane. .

Figure 2 of the paper says something you did not mention, and that is why you are only not wrong but bluntly lying, figure 2 of page 3 explains something that you can not even grasp, it says in order for the tailplane to be effective you need the aircraft to be unstable at low AoA and stable at post stall, so there is a nose down force and the tailplanes become effective




The Su-27 is recovered by tailplane deflection and that is evident


watching this video you see the F-22 does post stall but contrary to your fallacies F-22 moves the tailplanes all the time, it is doing post stall, and exactly as the paper says the effectiveness of the F-22 is done by TVC nozzles and tailplane deflection on Su-27 tailplane deflection alone can bring the nose down



[video=youtube;YmKbPnjwibA]http://www.youtube.com/watch?v=YmKbPnjwibA&feature=autoplay&list=HL1332656782&lf=mh_lolz&playnext=1[/video]

 

[Engineer]

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

Figure 2 of the paper says something you did not mention, and that is why you are only not wrong but bluntly lying,

Quite clearly, you are

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your own attributes, thoughts, and emotions on to me. An example of lying is your claim that the paper made the statement "tailplane is effective in high angle of Attacks... canard deflection is effective only at low AoA..." when the paper hasn't done so.

figure 2 of page 3 explains something that you can not even grasp, it says in order for the tailplane to be effective you need the aircraft to be unstable at low AoA and stable at post stall, so there is a nose down force and the tailplanes become effective

The Su-27 is recovered by tailplane deflection and that is evident

In Cobra Maneuver, recovery from high AoA has nothing to do with tailplane deflection. This is already mentioned in the paper:

The recovery from high angles of attack to the classical flight mode in a few seconds only is possible due to moving the center of pressure on main wing back and creating the strong nose-down aerodynamic pitching moment about the center of gravity.

Deliberate misinterpetation of the author's words, as you are doing now, and as you have typically done, isn't going to help you.

A control surface that has stalled is not effective in providing control. To bring the nose down, trailing edge control surfaces must increase the AoA, thus entering a stall if the AoA of the aircraft is high to begin with. Canards are superior for pitch control in comparison to flaps, because canards decrease AoA to bring the nose down and remains effective at high AoA. This is why J-20 doesn't deploy flaps while turning. This is explained in Dr. Song's paper:

Control surfaces placed in front of the center of mass, like the canards, are negative load control surfaces. Since the main wing's ability to generate lift tends to saturate under high AOA conditions, the positive load control surfaces' pitch down control capabilities tend to saturate under high AOA as well. Therefore it will be wise to employ negative load control surfaces for pitch down control under high AOA conditions. Figure 7 compares the pitch down control capabilities of the canards and horizontal stabilizers. From the high AOA pitch down control stand point, it will be wise to use canards on the future fighter.

watching this video you see the F-22 does post stall but contrary to your fallacies F-22 moves the tailplanes all the time, it is doing post stall, and exactly as the paper says the effectiveness of the F-22 is done by TVC nozzles and tailplane deflection on Su-27 tailplane deflection alone can bring the nose down

If you flap your arms wildly, can you fly? The answer is no, because your arms moving rapidly has no connection as to whether it is effective in generating lift. The same applies to control surfaces.

 

[MiG-29]

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

Quite clearly, An example of lying is your claim that the paper made the statement "tailplane is effective in high angle of Attacks... canard deflection is effective only at low AoA..." when the paper hasn't done so.




In Cobra Maneuver, recovery from high AoA has nothing to do with tailplane deflection. This is already mentioned in the paper:


:

On Fig 16 they show you the relation tailplane deflection with respect the Angle of Attack of the Su-27.

Fig 17 shows you the tailplane deflection and even goes to -12 degrees of deflection and returns after several seconds.


Fig 18 shows you the gain in altitude and Su-27 AoA.

However in Fig 10 they show the trim is effective of the tailplane at post stall while the canard is not.

The little factor you want to forget is the Su-27 is deflecting the tailplane and the tailplane remains effective due to the nose down force of the static stability that has become positive.

In few words, canards stall first due to their deflection and tendency to stall before the wing and X-31 uses TVC nozzles to do for a back tail

 

[Engineer]

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

On Fig 16 they show you the relation tailplane deflection with respect the Angle of Attack of the Su-27.

Fig 17 shows you the tailplane deflection and even goes to -12 degrees of deflection and returns after several seconds.


Fig 18 shows you the gain in altitude and Su-27 AoA.

However in Fig 10 they show the trim is effective of the tailplane at post stall while the canard is not.

The little factor you want to forget is the Su-27 is deflecting the tailplane and the tailplane remains effective due to the nose down force of the static stability that has become positive.

False. You are drawing conclusion that the paper hasn't made. Large and rapid movement of tailplane has no correlation with the effectiveness of the tailplane, similar to how wildly flapping your arms doesn't allow you to fly. The

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says the following:

A concentration of characteristic curves Cm for the tailplane setting angle φ[SUB]t[/SUB] being varied at post-critical AoA (i.e. very low sensitivity of pitch moment with respect to the tailplane setting angle) reflects the loss of effectiveness of a horizontal tail at higher AoA.

Nose down moment toward the end of Cobra maneuver is not caused by active deflection of control surfaces, but a passive aerodynamics phenomenon. That is, the aircraft will naturally returns to equilibrium flight without control inputs. This is explained in the paper:

For super manoeuvre aircraft the return back from the high AoA to the initial flight condition should be possible independently of the effectiveness of the tail control surfaces.

That same paper also explained the mechanism for returning the nose to horizontal. No where in this statement is there any mentioning about deflection of control surfaces:

The recovery from high angles of attack to the classical flight mode in a few seconds only is possible due to moving the center of pressure on main wing back and creating the strong nose-down aerodynamic pitching moment about the center of gravity.

Notice the use of the word "only", which unequivocally excludes deflection of tailplane as a contributor.

In few words, canards stall first due to their deflection and tendency to stall before the wing and X-31 uses TVC nozzles to do for a back tail

False. Canards that stall are fixed canards because their AoA cannot be controlled. For fully articulating canards, stalling is entirely avoidable. As explained in this

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, the canards are kept at zero AoA:

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.

Canards are superior to trailing edge control surfaces for pitch-down moment, precisely because the former do not stall. To bring the nose down from high AoA the canards deflect downward into negative AoA instead of upward. For trailing edge control surfaces, their AoA have to be increased to bring the aircraft's nose down. When the aircraft already has high AoA, this leads to stall of the control surfaces, rendering them ineffective. Here is a statement from Dr. Song's paper:

Control surfaces placed in front of the center of mass, like the canards, are negative load control surfaces. Since the main wing's ability to generate lift tends to saturate under high AOA conditions, the positive load control surfaces' pitch down control capabilities tend to saturate under high AOA as well. Therefore it will be wise to employ negative load control surfaces for pitch down control under high AOA conditions. Figure 7 compares the pitch down control capabilities of the canards and horizontal stabilizers. From the high AOA pitch down control stand point, it will be wise to use canards on the future fighter.