Aerodynamics thread

[Engineer]

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

Well that is up to you.
He does say what he says and his paper says the same that the Russians are saying, so sorry, i do not believe your theory, niether Engineer`s.

I can use a computer but i does not mean i know how many things of my computer work.
You are claiming because you fly an aircraft you know more than a master in aerodynamics, who happens to be a US naval school member.

So i ask you why i have to believe you?

Sorry but i believe him, and the reason is his paper agrees with several other papers i have read about the Cobra plus he was a United States Naval Academy member and a MASTER OF SCIENCE IN AERONAUTICAL ENGINEERING, so now i ask you, have you written a paper of post-stall aerodynamics as he has?
Do you have a paper that has been presented before the academia and the US Naval academy?
Sorry Brat, your explanation of stall goes well for a Cessna but not for a Su-27.

Wrong. The author of the paper

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has this to say with regards to post-stall maneuver:

The post-stall region has been a source of considerable interest and research in the aviation community over the past two decades. It is characterized by separated and reverse flow over the wing, loss of lift, and a steep increase in drag. As can be seen in Figure 3, stall occurs at C[sub]L[sub]max[/sub][/sub]. The AOA range past that point is the post-stall region.

Thus, it is explicitly stated that stall occurs in post-stall maneuver, contradicting your opinion that Su-27 doesn't stall in Cobra. In

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which has gone through a peer-review before it can be published, the following statement is said:

In the post stall regime, lift no longer increases but decreases with the angle of attack.

This definition is synonymous with the definition of stall given in

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:

The classical stall may be defined as a condition in which the airplane wing is subjected to an angle of attack greater than the angle for maximum lift coefficient.

If you do not believe our statements, it just means your belief is incorrect. It does not alter the reality that our statements are still facts supported by multiple sources of yours. Do you have any paper that back-up your theory? No, because no real aerodynamicist agrees with your pseudo-aerodynamic theories. This is reflected in your inability to give direct quote from any of your paper to support your claims and your reliance on creativity. Hence, your claim is not credible.

In Yefim Gondon`s book "Su-27 Flanker Story" in pages 89 to 93 they have a very good explanation of why Cobra happens and they mention Hysteresis, Inertia and what the pilot does to execute it.

Now His book was made in Russia, with direct Sukhoi input, why i have to believe you?
And by the way i have family who made parts for aircraft in Mexico and family in Russia who flew Soviet aircraft.

Do you think they have a master to explain me the Cobra? no they have not in fact they can explain me something but not all.
Why because a real mathematical model of Cobra is too complex, and the guys who have made them like this guy

You say he is wrong that Su-27 is stalled when he says based upon mathematical models post stall aircraft need to maintain some lift and control devices still working.

Sorry but against that evidence i prefer TIME-OPTIMIZATION OF HIGH PERFORMANCE COMBAT MANEUVERS by
Benjamin R. Carter rather than your explanation.

Nope.

Whether lift still exists is irrelevant to stall. Stall in fact occurs at where maximum lift is achieved, and an aircraft with angle-of-attack past the angle of maximum lift is in a post-stall region, as indicated by the following lift-curve:

The graph is extracted from

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. In reference to the graph, the author explicitly states that the aircraft has already stalled during the Cobra.

The post-stall region has been a source of considerable interest and research in the aviation community over the past two decades. It is characterized by separated and reverse flow over the wing, loss of lift, and a steep increase in drag. As can be seen in Figure 3, stall occurs at C[sub]L[sub]max[/sub][/sub]. The AOA range past that point is the post-stall region.

Thus, the paper which you are quoting from debunks your claim that Su-27 doesn't stall during Cobra.

Furthermore, in the

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, control devices that do not rendered ineffective by stall refer to thrust-vectoring controls. As stated in the following statement:

Hence the reason that the post-stall region has only been a fairly recent area of study: T/W ratios needed to increase, C[sub]L[sub]max[/sub][/sub] values needed to increase, and non-aerodynamic controls (such as TV) had to be developed before an aircraft would be capable of controlled flight in this very adverse aerodynamic region.

Two pages later, the author made the following statement:

The dynamic maneuvers possible in the post-stall region, the freedom from purely aerodynamic control surfaces, and the ability to aim the aircraft’s fuselage and weapons independent of the direction of flight combine to make a SF extremely lethal in the short range air combat arena.

Freedom from purely aerodynamic control surfaces refers to thrust-vectoring control, and thrust-vectoring control is not the tailplane. In other words, the author of

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contradicts your opinion that tailplane is used during post-stall maneuver. Indeed, one simply needs to look at other sources to see many mentioning of tailplane being ineffective at high AoA. The first is 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.

A

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has the following to say:

if the aircraft can fly at angles of attack of 80[SUP]o[/SUP] - 120[SUP]o[/SUP] with the ability to maintain stability in all channels. In this flight regime the ability for conventional control is usually lost.

A

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also mentions lost of effectiveness of tail surface. The exact statement is as follow:

It can be explained by loosing of effectiveness of control surfaces... In the range of AoA up to 35[SUP]o[/SUP] the normal increases approximately linearly, then stabilises and practically the tail surface losses its effectiveness.

So, you are right that the papers are in agreement with one another, but they are in agreement in disagreeing with your claim that Su-27 doesn't stall during Cobra as well as your claim that tailplane is effective at high AoA.

 

[Air Force Brat]

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

Well that is up to you.
He does say what he says and his paper says the same that the Russians are saying, so sorry, i do not believe your theory, niether Engineer`s.

I can use a computer but i does not mean i know how many things of my computer work.
You are claiming because you fly an aircraft you know more than a master in aerodynamics, who happens to be a US naval school member.

So i ask you why i have to believe you?

Sorry but i believe him, and the reason is his paper agrees with several other papers i have read about the Cobra plus he was a United States Naval Academy member and a MASTER OF SCIENCE IN AERONAUTICAL ENGINEERING, so now i ask you, have you written a paper of post-stall aerodynamics as he has?
Do you have a paper that has been presented before the academia and the US Naval academy?
Sorry Brat, your explanation of stall goes well for a Cessna but not for a Su-27.

In Yefim Gondon`s book "Su-27 Flanker Story" in pages 89 to 93 they have a very good explanation of why Cobra happens and they mention Hysteresis, Inertia and what the pilot does to execute it.

Now His book was made in Russia, with direct Sukhoi input, why i have to believe you?
And by the way i have family who made parts for aircraft in Mexico and family in Russia who flew Soviet aircraft.

Do you think they have a master to explain me the Cobra? no they have not in fact they can explain me something but not all.
Why because a real mathematical model of Cobra is too complex, and the guys who have made them like this guy

You say he is wrong that Su-27 is stalled when he says based upon mathematical models post stall aircraft need to maintain some lift and control devices still working.

Sorry but against that evidence i prefer TIME-OPTIMIZATION OF HIGH PERFORMANCE COMBAT MANEUVERS by
Benjamin R. Carter rather than your explanation.

Mig, Mr. Carter would agree with me, the Suchoi guys would agree with me, the Cobra is a post stall manuever, simple physics actually, the Su-27 is in a "deep stall", well beyond being in any kind of a steady state aerodynamically, it is able to recover as quickly as it does due to stored energy, high thrust , and outstanding aerodynamic design. Now, no I don't believe some of the advertizing nonsence in the Suchoi adds, they are airplane salesmen, thats their business, and they are good at it. So for all our benefit, please? In 50 or so words define aerodynamic "stall".

 

[Engineer]

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

So for all our benefit, please? In 50 or so words define aerodynamic "stall".

lol! He won't, because he is afraid of the truth. He will simply respond with

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and

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to divert attention away from his own mistakes. It is actually very predictable.

 

[Air Force Brat]

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

lol! He won't, because he is afraid of the truth. He will simply respond with

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and

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to divert attention away from his own mistakes. It is actually very predictable.

Yes, unfortunately, the more I know, the more obvious my past mistakes become, I believe it might have been an article written by Mr. Carter for a civilian aviation magazine that opened my eyes to AOA, whoever had written it was a Navy pilot. While AOA is taught to civilian pilots, its somewhat nebulous until it clicks. The good ole Air Force Mag had lots of excellent articles as well. When I started learning to fly, my Dad bought me a copy of Stick and Rudder, by Wolfgang Langwiesch.

 

[MiG-29]

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

Mig, Mr. Carter would agree with me, the Suchoi guys would agree with me, the Cobra is a post stall manuever, simple physics actually, the Su-27 is in a "deep stall", well beyond being in any kind of a steady state aerodynamically, it is able to recover as quickly as it does due to stored energy, high thrust , and outstanding aerodynamic design. Now, no I don't believe some of the advertizing nonsence in the Suchoi adds, they are airplane salesmen, thats their business, and they are good at it. So for all our benefit, please? In 50 or so words define aerodynamic "stall".

Look i know perfectly whjat is he saying and he is not agreeing with you


first he is claiming this:

"What the previous two observations mean is that an aircraft can still be flyable in
the post-stall region provided that several criteria are met:
1. The aircraft has enough thrust to overcome the huge drag increase.
2. The aircraft has controls that will not be rendered ineffective by separated
flow over the wings and tail.
3. CL remains great enough in post-stall to overcome the aircraft’s weight".



You are claiming the tailplane is of no use
but he claims

2. The aircraft has controls that will not be rendered ineffective by separated
flow over the wings and tail.

what does say the Russian article

"Однако инертность истребителя, небольшая продолжительность "Кобры" (около 10 секунд) и упреждающие действия летчика рулями позволяют избежать этого.
However, the short duration of "Cobra" (about 10 seconds) and the anticipated application of the tailplaness allows the pilot to avoid all that ."
what does say the polish article

"third phase, (recovery from the manoeuvre)
characterised by full deflection of the horizontal
tail for diving with the increasing,
negative pitch rate (at the end of this phase
the pitch rate for diving reaches its maximum,
negative value. The angle of attack
approaches its value of the steady flight, but
aircraft still rotates and further decreases the
angle of attack due to its inertia);"





You are claiming the aircraft is stalled

3. CL remains great enough in post-stall to overcome the aircraft’s weight".


this says everything, lift still still is pushing the aircraft up
what does say the Russian article

"Тем не менее, выполнение "Кобры" показало принципиальную возможность удержать самолет от сваливания на закритических углах атаки

however the execution of the cobra has shown the basic ability to keep the aircraft from stalling at supercritical angles of attack"


ah it says no stalled

So you can try to say Carter or the Russian article agrees with you but they do not.

stall means when the aircraft has not ability to fly and controll it self, at 110 degrees of AoA Su-27 on static condition will stall, but it will not on dynamic pitch up.

hypermanoeuvrability is defined as " if the aircraft can fly at Angles of attack of 80-120 with the ability of maintain stability in all channels"



If you do not believe me check page 2

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[Engineer]

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

Look i know perfectly whjat is he saying and he is not agreeing with you

Wrong. You have no idea what he is saying and are resorting to the fallacy of

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to desperate argue for something that are not true.

first he is claiming this:

"What the previous two observations mean is that an aircraft can still be flyable in
the post-stall region provided that several criteria are met:
1. The aircraft has enough thrust to overcome the huge drag increase.
2. The aircraft has controls that will not be rendered ineffective by separated
flow over the wings and tail.
3. CL remains great enough in post-stall to overcome the aircraft’s weight".



You are claiming the tailplane is of no use
but he claims

2. The aircraft has controls that will not be rendered ineffective by separated
flow over the wings and tail.

No where in that statement did the author refer to tailplane being used. In fact, from

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where you have extracted your quotes from, the author was clearly referring to thrust-vectoring control:

Hence the reason that the post-stall region has only been a fairly recent area of study: T/W ratios needed to increase, C[sub]L[sub]max[/sub][/sub] values needed to increase, and non-aerodynamic controls (such as TV) had to be developed before an aircraft would be capable of controlled flight in this very adverse aerodynamic region.

Tailplane is considered as aerodynamic control, thus "non-aerodynamic controls" means controls other than aerodynamic surfaces are employed for post-stall maneuvers. This excludes the use of tailplane.

---------- Post added at 09:46 PM ---------- Previous post was at 09:42 PM ----------

what does say the Russian article

"Однако инертность истребителя, небольшая продолжительность "Кобры" (около 10 секунд) и упреждающие действия летчика рулями позволяют избежать этого.
However, the short duration of "Cobra" (about 10 seconds) and the anticipated application of the tailplaness allows the pilot to avoid all that ."

The above quote says nothing about tailplane being used for recovery from post-stall maneuver. Not only this, but the fact that the maneuver needs to be kept as short as possible means the aircraft cannot be controlled at high AoA. In other words, tailplane lost its function at high AoA. Aircraft having traditional configuration fitted with TVN does not need to keep the Cobra maneuver as short as possible.

what does say the polish article
"third phase, (recovery from the manoeuvre) characterised by full deflection of the horizontal tail for diving with the increasing, negative pitch rate (at the end of this phase the pitch rate for diving reaches its maximum, negative value. The angle of attack approaches its value of the steady flight, but aircraft still rotates and further decreases the angle of attack due to its inertia);"

The

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says tailplane is ineffective:

It can be explained by loosing of effectiveness of control surfaces... In the range of AoA up to 35[SUP]o[/SUP] the normal increases approximately linearly, then stabilises and practically the tail surface losses its effectiveness.

Thus, not only does the article disagrees with your claim, it explicitly states that tailplane losses its effectiveness at high AoA. Your claims are therefore debunked.

---------- Post added at 09:57 PM ---------- Previous post was at 09:46 PM ----------

You are claiming the aircraft is stalled

Wrong. You are claiming the aircraft is not stalled. Air Force Brat and I are both pointing out the fact that the aircraft has stalled.

3. CL remains great enough in post-stall to overcome the aircraft’s weight".


this says everything, lift still still is pushing the aircraft up
what does say the Russian article

"Тем не менее, выполнение "Кобры" показало принципиальную возможность удержать самолет от сваливания на закритических углах атаки

however the execution of the cobra has shown the basic ability to keep the aircraft from stalling at supercritical angles of attack"


ah it says no stalled

So you can try to say Carter or the Russian article agrees with you but they do not.

Wrong.

Carter disagrees with you. He has clearly indicated that stall occurs at the angle-of-attack that results in maximum lift, and provided the following graph for clarity:

So lift can still push the aircraft up, but the aircraft can still be in stall. From Carter's thesis,

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, the following statement is made in defining post-stall:

The post-stall region has been a source of considerable interest and research in the aviation community over the past two decades. It is characterized by separated and reverse flow over the wing, loss of lift, and a steep increase in drag. As can be seen in Figure 3, stall occurs at C[sub]L[sub]max[/sub][/sub]. The AOA range past that point is the post-stall region.

Thus, he is saying that an aircraft in post-stall has already stalled. Since Cobra maneuver is a post-stall maneuver, an aircraft in a Cobra maneuver has stalled. Your claim that Carter agrees with you has no basis in reality.

The definition of stall is simply that increase of AoA results in decrease of lift. The

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has the following to say in regard to stall:

The classical stall may be defined as a condition in which the airplane wing is subjected to an angle of attack greater than the angle for maximum lift coefficient.

In other words, there is no requirement that lift must disappear completely for stall to occur, debunking your pseudo-aerodynamic theories.

---------- Post added at 10:08 PM ---------- Previous post was at 09:57 PM ----------

stall means when the aircraft has not ability to fly and controll it self, at 110 degrees of AoA Su-27 on static condition will stall, but it will not on dynamic pitch up.

Wrong again. Stall occurs when maximum lift is reached. From

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:

The post-stall region has been a source of considerable interest and research in the aviation community over the past two decades. It is characterized by separated and reverse flow over the wing, loss of lift, and a steep increase in drag. As can be seen in Figure 3, stall occurs at C[sub]L[sub]max[/sub][/sub]. The AOA range past that point is the post-stall region.

Thus, Carter disagrees with you. Another definition from

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also states that stall occurs when the angle-of-attack is greater than the angle for maximum lift to be generated:

The classical stall may be defined as a condition in which the airplane wing is subjected to an angle of attack greater than the angle for maximum lift coefficient.

Thus, US Naval Test Pilot School disagrees with you. Continuing on, the manual says the following:

Stalls. The stall may be defined by either airflow separation with increasing angle of attack causing loss of lift, control difficulty, or excessive buffet/vibration (see 6.2.2 and 6.2.5)

We can clearly see flow separation occurring while the Su-27 is conducting the Cobra maneuver:

hypermanoeuvrability is defined as " if the aircraft can fly at Angles of attack of 80-120 with the ability of maintain stability in all channels"



If you do not believe me check page 2

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From page 2 of that

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, and in fact the very next sentence:

if the aircraft can fly at angles of attack of 80[SUP]o[/SUP] - 120[SUP]o[/SUP] with the ability to maintain stability in all channels. In this flight regime the ability for conventional control is usually lost.

This means tailplane as a conventional control losses effectiveness at such high angle-of-attack. Thus, the recovery in a Cobra maneuver can only be achieved via passive means through aerodynamics, not active deflection of the tailplane. The

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says the following:

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 the center of pressure on main wing back and creating the strong nose-down aerodynamic pitching moment about the center of gravity.

Another one of your own source disagrees with you, again.

Dr. Song has this to say regarding effectiveness of tail aerodynamic surfaces:

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.

In kiddie's term, control surfaces near the tail stall at high AoA and cannot be used to generate pitch-down moment to recovery the aircraft from high AoA.

 

[MiG-29]

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

Wrong. Wrong. You are claiming the aircraft is not stalled. Air Force Brat and I are both pointing out the fact that the aircraft has stalled.




.

At 110 degrees of AoA any jet is deep stalled, with no ability of flying at all on static condition.
Stalled can be consider flow separation thus you claim yes the Su-27 is stalled, and the technicallity is to claim the SU-27 has already stalled.

but at supercrtical AoA there is no way the aircraft will fly.

and the Cobra is a supercritical angle of Attack, beyond the deep stall of the jet when on static conditions the aircraft plummets from the air.

The critical angle of attack of a SU-27 is around 40 degrees of AoA, at that speed flow separation exits however the aircraft is not in deep stall it shows sign of wing rock for example, at 70 degrees of AoA the jet stalls and flat spins and the controls can be rendered ineffective and the jet can crash by falling into deep stall.


However deep stall does not occur at 110 deg of AoA

and does not occur because hypermanoeuvrability is defined as " if the aircraft can fly at Angles of attack of 80-120 with the ability of maintain stability in all channels" and 2. The aircraft has controls that will not be rendered ineffective by separated
flow over the wings and tail.

 

[Engineer]

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

At 110 degrees of AoA any jet is deep stalled, with no ability of flying at all on static condition.
Stalled can be consider flow separation thus you claim yes the Su-27 is stalled, and the technicallity is to claim the SU-27 has already stalled.

but at supercrtical AoA there is no way the aircraft will fly.

and the Cobra is a supercritical angle of Attack, beyond the deep stall of the jet when on static conditions the aircraft plummets from the air.

The critical angle of attack of a SU-27 is around 40 degrees of AoA, at that speed flow separation exits however the aircraft is not in deep stall it shows sign of wing rock for example, at 70 degrees of AoA the jet stalls and flat spins and the controls can be rendered ineffective and the jet can crash by falling into deep stall.


However deep stall does not occur at 110 deg of AoA

Wrong. A stall is a stall. Saying the aircraft is not in deep/fully stall is as silly as claiming you are not wet because you are only half wet. Carter's thesis,

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is quite explicit on what is a stall:

The post-stall region has been a source of considerable interest and research in the aviation community over the past two decades. It is characterized by separated and reverse flow over the wing, loss of lift, and a steep increase in drag. As can be seen in Figure 3, stall occurs at C[sub]L[sub]max[/sub][/sub]. The AOA range past that point is the post-stall region.

Thus, when angle-of-attack passes the angle of maximum lift, the aircraft is in a stall. And on top of defining the word "stall", he points out that post-stall is the region where AoA is greater than the stall angle. An aircraft in a Cobra is in a stall because the Cobra maneuver is a post-stall maneuver.

From

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:

Начнем с того, что при увеличении угла атаки до критического значения возрастают коэффициенты подъемной силы и лобового сопротивления. Увеличивается и проекция силы тяги двигателей на местную вертикаль. При этом уменьшается проекция подъемной силы на местную вертикаль. А при угле атаки, равном 90°, подъемная сила действует в направлении, обратном скорости горизонтального полета, т. е. превращается в силу лобового сопротивления. По мере роста угла атаки более 90° проекция подъемной силы на вертикаль совпадает по направлению с силой тяжести самолета, а вертикальная составляющая силы тяги двигателей удерживает самолет от падения на хвост.

The wing of the aircraft does not generate any lift, and the aircraft is kept in the air solely because the engines are used to counteract gravity. However, whether the aircraft falls out of the sky or not is irrelevant. The key is that aerodynamic surfaces such as the wing and tailplane have stalled because lift decreases with increasing AoA and flow separation occurs. This stall also renders aerodynamic controls ineffective. The definition of stall and ineffective controls are both stated in

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:

Stalls. The stall may be defined by either airflow separation with increasing angle of attack causing loss of lift, control difficulty, or excessive buffet/vibration (see 6.2.2 and 6.2.5)

Tailplane, being one of those aerodynamic control surfaces, also losses effectiveness. As stated in

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, tailplane losses effectiveness at high AoA:

It can be explained by loosing of effectiveness of control surfaces... In the range of AoA up to 35[SUP]o[/SUP] the normal increases approximately linearly, then stabilises and practically the tail surface losses its effectiveness.

and does not occur because hypermanoeuvrability is defined as " if the aircraft can fly at Angles of attack of 80-120 with the ability of maintain stability in all channels"

Hypermanoeuvrability does not mean stall cannot occur. From the

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which you have quoted from, and in fact in the very next sentence:

if the aircraft can fly at angles of attack of 80[SUP]o[/SUP] - 120[SUP]o[/SUP] with the ability to maintain stability in all channels. In this flight regime the ability for conventional control is usually lost.

Conventional control means the use of aerodynamic surfaces such as ailerons, flaps and tailplanes for control. And the reason they cannot be used is because of stall. This is why aircraft with traditional configuration needs TVC to achieve hypermanoeuvrability, as TVC is not affected by stall.

and 2. The aircraft has controls that will not be rendered ineffective by separated flow over the wings and tail.

No where in that statement did the author say stall cannot occur. Furthermore, no where in that statement did the author claimed tailplane is used for post-stall maneuver. In

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from which you have extracted your quote from, the very next paragraph says the following:

Hence the reason that the post-stall region has only been a fairly recent area of study: T/W ratios needed to increase, C[sub]L[sub]max[/sub][/sub] values needed to increase, and non-aerodynamic controls (such as TV) had to be developed before an aircraft would be capable of controlled flight in this very adverse aerodynamic region.

Non-aerodynamic controls excludes the use of conventional aerodynamic controls, thus excludes the use of tailplane. In other words, this paper disagree with your claim that tailplane is used for control in a Cobra maneuver. Ineffectiveness of the tailplane at high AoA is pretty clear in

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:

A concentration of characteristic curves C[sub]m[/sub] 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.

Thus, as Dr. Song explained, canard is superior to tailplane at high AoA:

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.

 

[MiG-29]

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

Thus, as Dr. Song explained, canard is superior to tailplane at high AoA:

Not according to the americans

Results of the analysis indicate that the canard is effective in
increasing lift and decreasing drag at Mach numbers from subsonic to high
transonic speeds by delaying wing separation. The effectiveness of the
canard is, however, decreased with Increasing Mach number. At supersonic
speeds the canard has little or no favorable effects on lift or drag.
It is further shown that the horizontal tail is a superior trimming
device than the close-coupled canard at low-to-moderate angles of attack and
that a configuration consisting of canard, wing, and horizontal tail is
superior in performance, to either canard or horizontal tail at high angles
of attack.

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[video=youtube;zGnk_IrNSzo]http://www.youtube.com/watch?v=zGnk_IrNSzo&feature=related[/video]

 

[Air Force Brat]

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

It is further shown that the horizontal tail is a superior trimming
device than the close-coupled canard at low-to-moderate angles of attack

Mig you're missing the point, the J-20 has a distant coupled canard, the forward fuselage generates significant lift. When the aircraft designer says these are the qualities we were aiming for, when the finished aircraft exhibits those flight characteristics that are obvious, the aircraft also has an aft mounted delta wing, trust me the distant coupled canard exhibits superior control authority for an aircraft of this configuration, no trust Dr Song. His integrity is obvious as is his expertise, don't let your personal prejudice or preferences cloud yours, we all have our favorites, my personal favorite remains the F-22, simply because at my age airplanes are supposed to look a certain way, but I am able to see the genious and innovation in the J-20!