Aerodynamics thread

[MiG-29]

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

.

As far as debunking your claim goes, we have went through this already. The cause for crash of the aircraft was pilot error, said so in your own quote:


The picture shows the tailplane rotated downward, which isn't going to generate any pitch-down moment even if the aircraft were not flying at high AoA.

Let us see if the Russians agree with you

При нестационарном обтекании нарушается боковая балансировка самолета и возникает опасность его сваливания на крыло с последующим переходом в штопор

due to turbulent flow, the aircraft experiences lateral instability and the risk of stall and depart into flat spins
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 .



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

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


рулями=tailplanes

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obviously the Gripen is trying to pull down the nose its deflection is negative hahahaha

but the MiG-29 is not flying with a horizontal velocity vector niether a vertical velocity vector but rather diagonal vector gaining altitide and with the tail pitching up thus

"Angle of Attack and tailplane deflection depend very strongly on the flight path angle in the post stall region, and practically do not depend in the below stall region "

ah i see the MiG like the Su do deflect the tailplane according to the flight path gamma angle (velocity vector) and Alpha angle (angle with respect the Gamma angle) ah i see
minute 1:13 mig deploys tailplanes at 110 degrees of AoA haha

[video=youtube;RJ_ds1SgBG0]http://www.youtube.com/watch?v=RJ_ds1SgBG0&feature=player_embedded[/video]

 

[Engineer]

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

Let us see if the Russians agree with you

При нестационарном обтекании нарушается боковая балансировка самолета и возникает опасность его сваливания на крыло с последующим переходом в штопор

due to turbulent flow, the aircraft experiences lateral instability and the risk of stall and depart into flat spins
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 .

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

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

рулями=tailplanes

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In other words, they have to keep the maneuver short precisely because the control surfaces are ineffective in preventing the aircraft from entering into stall or flat spin. Indeed, when one look at this

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, the following statement can be found:

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.

If tailplane is effective at high AoA in the first place, there would be no time limitation, and the aircraft would have been able to perform the same maneuver as an aircraft with TVN, but without actually installing TVN.

In another part of the

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:

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.

The reason for loss of control is because stall has already occurred. This is why maneuvers like the Cobra are referred to as post-stall maneuvers. From

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, a definition for post-stall is given:

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.

This

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goes on explaining that recovery is due to shift of aerodynamic center behind the center-of-gravity, which has nothing to do with active deflection of the tailplane:

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.

obviously the Gripen is trying to pull down the nose its deflection is negative hahahaha

"Angle of Attack and tailplane deflection depend very strongly on the flight path angle in the post stall region, and practically do not depend in the below stall region "

ah i see the MiG like the Su do deflect the tailplane according to the flight path gamma angle and Alpha angle ah i see
minute 1:13 mig deploys tailplanes at 110 degrees of AoA haha

Your quote doesn't claim tailplane is effective in recovery. Quite the opposite, in that

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, it is said that recovery is not dependent on tailplane:

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.

The use of the word "only" excludes other method such as active deflection of the tailplane for generating that pitch-down moment. The paper further explains that tailplane is ineffective at high AoA:

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.

The same fact is pointed out by Dr. Song paper, where he mentioned canard is superior to tailplane for providing pitch-down moment in 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

In other words, they have to keep the maneuver short precisely because the control surfaces are ineffective in preventing the aircraft from entering into stall or flat spin. Indeed, when one look at this [:

here we see an example of your lack of understanding very evident it is short thus it does not stall for such a reason they say


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

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

but what can i expect of a guy who lies to himself and does not understand what is hysteresis niether what is a Gamma angle and a alpha angle on a pitch angle of Cobra

and what they say the Russians about the tailplanes
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 .


hahahah but what can i say of you hahahah you just looks for definitions of fallacy and try to use just your own opinions not reality

and by the way you are wrong, Cobra is a result of high pitch rates, hysteresis, center of pressure shifts and tailplane deflection and trimming, the Russians say it and Yefim Gondon says in his book plublished in Russia hahahahah plust the polish researcher hahahaha

 

[Engineer]

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

here we see an example of your lack of understanding very evident it is short thus it does not stall for such a reason they say


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

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

Wrong. The definition for post-stall is given in

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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.

In

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, the following description is given in regards to post-stall:

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

This is the same definition given by

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for stall:

An aerodynamic stall is defined as a condition in which the wing attains an angle of attack greater than the angle of attack for maximum lift, resulting in a loss of lift and an increase in drag.

Thus, the aircraft is way past the point of stalling, which is why maneuvers like the Cobra are called post-stall maneuvers. Your attempt to redefine the word stall reveals your own desperation, because your claims have been debunked by multiple papers saying the aircraft has stalled, and control surfaces lost effectiveness.

but what can i expect of a guy who lies to himself and does not understand what is hysteresis niether what is a Gamma angle and a alpha angle on a pitch angle of Cobra

and what they say the Russians about the tailplanes
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 maneuver has to be kept short precisely because the control surfaces are ineffective in preventing the aircraft from entering into stall or flat spin. This is asserted by the following

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:

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.

The

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also mentions th 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.

Loss of effectiveness of control surfaces mean they cannot be used for generating the pitch-down moment required for recovery. Indeed, the paper has the following to say:

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.

The use of the word "only" means other methods such as active deflection of tailplane cannot contribute to recovery.

hahahah but what can i say of you hahahah you just looks for definitions of fallacy and try to use just your own opinions not reality

and by the way you are wrong, Cobra is a result of high pitch rates, hysteresis, center of pressure shifts and tailplane deflection and trimming, the Russians say it and Yefim Gondon says in his book plublished in Russia hahahahah plust the polish researcher hahahaha

High pitch rate does not equate to tailplane being effective for recovery. The aerodynamic center shifting does not equate to tailplane being effective for recovery. Tailplane deflection does not equate to tailplane being effective for recovery, just as flapping your arms does not make you capable of flying. You cannot even find a single sentence in your Russian source saying "tailplane is effective at high AoA".

Aren't you good with quoting things? If you can quote an expert saying "tailplane is effective high AoA", you would have posted the quote already. Instead, you have to rely on your creativity with diagrams and pictures, as well as fallacies upon fallacies to divert attention from the following points:

• Tailplane is ineffective at high AoA.
• Aircraft has already stalled in post-stall maneuver.

So why can't you provide a direct quote? Simple. No real aerodynamicists agree with your pseudo-aerodynamic theories. It is ironic how you quoted from multiple papers and yet these exact same papers contradict and debunk your theories.

 

[Air Force Brat]

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

Let us see if the Russians agree with you

При нестационарном обтекании нарушается боковая балансировка самолета и возникает опасность его сваливания на крыло с последующим переходом в штопор

due to turbulent flow, the aircraft experiences lateral instability and the risk of stall and depart into flat spins
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 .



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

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


рулями=tailplanes

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obviously the Gripen is trying to pull down the nose its deflection is negative hahahaha

"Angle of Attack and tailplane deflection depend very strongly on the flight path angle in the post stall region, and practically do not depend in the below stall region "

ah i see the MiG like the Su do deflect the tailplane according to the flight path gamma angle and Alpha angle ah i see
minute 1:13 mig deploys tailplanes at 110 degrees of AoA haha

[video=youtube;RJ_ds1SgBG0]http://www.youtube.com/watch?v=RJ_ds1SgBG0&feature=player_embedded[/video]

Mig while the pilot overpitchs the aircraft intentionally, as he approaches the Max aoa of approx 110 degrees, he applys full forward stick, any aircraft capable of performing the cobra, with a tailplane is fully departed or stalled. The aircraft attitude is at least 90 degrees to the relative wind. The leading edge flap increases the camber of the wing increasing lift, it is not an active control surface for aircraft directional control. The simple illustration of an arrow in flight, illustrates the means of aircraft recovery, as an arrow leaves the shelf, it bends around the shelf of the bow, this bending causes the arrow to oscillate or change direction multiple times. The feathers are always on the tail of the arrow, and are in effect tailplanes. This parralax or bending occurs in the vertical and horizontal planes, if we were to imagine the arrow deflecting 90 degrees, nose up to the relative wind, the drag on the feathers or tail will tend to damp out these oscillations, because the positive pressure or lift is greater on the tail or feathers than on the tip or nose. This same positive pressure in conjuntion with the center of lift moving aft on the main wing of the aircraft, bring the aircraft out of this deep stall or post stall condition. Now you've never seen a Raptor do a full cobra, you've never seen a J-20 do a cobra or even stall, Dr. Song has explained the aerodynamics of the J-20, his explanation fits the flight dynamics we "observe" as we watch the J-20, to disagree with the good Dr., because you don't understand is fine, to call your fellow forum members names, and accuse them of dishonesty, is why you don't get the "respect you feel you deserve". These endless posts and accusations spoil the intent of having a forum, I have always treated you with "respect", but you have to give it, in order to get it, I genuinely like all the forum members, and have more in common with them than most of my neighbors. Make your point, use a cogent defense of your point, and a relevant text that supports your point. I like your passion, but resist the temptation to lose your "cool". I would enjoy knowing a little more about Pak Fa, I believe you have a fairly good grasp of the Russian aircraft. I believe that you probably owe the engineer an apology, as this thread is devoted to aerodynamics, and I know we all care about that, lets keep this more postive and factual, some of your sources are highly suspect, basicly propoganda smearing the "other guy", the thing about Dr. Songs paper I find so refreshing is that it is honest and objective. Cheerio, the Brat

 

[MiG-29]

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

Mig while the pilot overpitchs the aircraft intentionally, as he approaches the Max aoa of approx 110 degrees, he applys full forward stick, any aircraft capable of performing the cobra, with a tailplane is fully departed or stalled. The aircraft attitude is at least 90 degrees to the relative wind.

highly suspect, basicly propoganda smearing the "other guy", the thing about Dr. Songs paper I find so refreshing is that it is honest and objective. Cheerio, the Brat

I do not understand your point well.


Let me tell you my opinion.

First my sources are not against any one. First the russian ones say that what they say regardless of what you or i think about them
The american sources i have quoted never mentioned tailplanes stop trimming, niether the Russian ones.

I understand very well what is hysteresis and why the americans have studied hysteresis to understand the Cobra.


The articles say this and this is what happens.


Hysteresis means the vortex does not burst inmediatedly as it should on static conditions.

So why you need to pitch up very fast? answer to create hysteresis, this delays the vortex burst and stall of the wing.

The tailplanes loss of effectiveness does not mean they do no affect the pitch angle , what it means is the tailplanes still have a pitch moment normal, this normal is not enough to bring the aircraft from post stall without hysteresis working on.

So here is where the hysteresis plays its part, by pitching very fast the jet goes to 110 degrees of AoA.

if the jet stalls then it will fall to earth simply like that, however lift is acting as drag why?
well lift at 90 degrees of AoA is horizontal while thrust is vertical and for moment is acting as lift however the Cobra can not go beyond 120 degrees why? simple because thrust can not overwhelm the aerodynamic components acting on the jet and so the jet runs the risk of vortex burst and flat spin.

Do you know what is going to happen if the vortices burst? simply yaw assymetries will spin the jet and the jet will fall into a flat spin.

Now you are thinking the MiG-29 has a horizontal or vertical trajectory, but it does not it is actually climbing on a diagonal which resembles more a curve, so it has a gamma angle with respect the horizon and it is the velocity vector of the flight path and a Alpha angle with respect the gamma angle because the aircraft is pitching down its tail.

That is what the author calls pitch angle

The author says lift becomes zero at 90 degrees but how come it has a pressure center?

that is contradictory, so what is what is tilting the Su-27? simple lift is horizontal at 90 degrees so it is acting as drag but as thrust goes to 110 degrees its ability to lift the jet decreases with the cosine of the angle of atack

Now during cobra the jet does not fly beyond 110 because that drag that is behind the center of gravity and the inertia of the jet will create a pitch down moment.

The tailplanes are contrary to your assertion that are stalled, are in reality are deflected with respect the angle of attack so they not create an over pitching and the limited pitching force they have will not disturb the pitch down force of the jet.

Why i know the jet has tailplane pitching force?

first this


"Angle of Attack and tailplane deflection depend very strongly on the flight path angle in the post stall region, and practically do not depend in the below stall region "


all your theory that the tailplane is stalled makes no sense for a simple reason

why you have to deflect the tailplane depending in the angle of pitch if it is stalled?

if it has no force?

the other source is even more clear


" 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); quoting "

and this does go well with


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

later you are claiming the jet is stalled? really?

To start the Su-27 will stall at 70 degrees of static pitch up AoA, at 40deg of AoA already it starts to have wing rock instabilities, at 70 degrees of AoA it stalls and flat spins, that is real stall of a Su-27.

However the jet does not stall otherwise it will depart

The russian source is clear why it does not stall

due to turbulent flow, the aircraft experiences lateral instability and the risk of stall and depart into flat spins
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 .



and they go and say the Su-27 does not stall during the Cobra

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

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


рулями=tailplanes


this goes perfectly with

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


So you can say to me the same theory Engineer says, but you are wrong because the Su-27 does not stall, you are free as he is to believe what ever you want, but i do not agree and i understand well the papers, i know perfectly all these papers say what they say

 

[Quickie]

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

This Wikipedia article explains how drag forces are at play during post stall in a cobra maneouvre, which are different from the aerodynamic forces that are at play when the aircraft are unstall.

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When the elevator is centered, the drag at the rear of the plane causes torque, thus making the aircraft pitch forward. At that time the pilot adds power to compensate for the lift loss.

 

[Engineer]

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

I do not understand your point well.


Let me tell you my opinion.

First my sources are not against any one. First the russian ones say that what they say regardless of what you or i think about them
The american sources i have quoted never mentioned tailplanes stop trimming, niether the Russian ones.

Actually, not a single source said tailplane is used in trimming at post-stall, so your above statement is entirely your own opinion. The core of the issue is that none of the source says tailplane is effective in generating pitch-down moment for recovery. In fact, they said the opposite.

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for example, the following statement is made:

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.

In another part of that paper, the authors go on saying:

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.

Another

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mentions lost of effectiveness of tail surface, contradicting your pseudo-aerodynamic theories on the tailplane. 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.

Simply put, deflection of tailplane does not mean it is effective at high AoA.

---------- Post added at 12:02 PM ---------- Previous post was at 11:55 AM ----------

I understand very well what is hysteresis and why the americans have studied hysteresis to understand the Cobra.


The articles say this and this is what happens.


Hysteresis means the vortex does not burst inmediatedly as it should on static conditions.

So why you need to pitch up very fast? answer to create hysteresis, this delays the vortex burst and stall of the wing.

The tailplanes loss of effectiveness does not mean they do no affect the pitch angle , what it means is the tailplanes still have a pitch moment normal, this normal is not enough to bring the aircraft from post stall without hysteresis working on.

Actually, you very last statement shows you know nothing about hysteresis. Hysteresis means the current state of the system is dependent on the history of the state. For the Cobra maneuver, this simply refers to the fact that dynamic of the aircraft throughout the maneuver is dependent on that large initial pitch-rate. Hysteresis does not change physics and turn ineffective tailplane into an effective one.

---------- Post added at 12:13 PM ---------- Previous post was at 12:02 PM ----------

So here is where the hysteresis plays its part, by pitching very fast the jet goes to 110 degrees of AoA.

if the jet stalls then it will fall to earth simply like that, however lift is acting as drag why?
well lift at 90 degrees of AoA is horizontal while thrust is vertical and for moment is acting as lift however the Cobra can not go beyond 120 degrees why? simple because thrust can not overwhelm the aerodynamic components acting on the jet and so the jet runs the risk of vortex burst and flat spin.

Do you know what is going to happen if the vortices burst? simply yaw assymetries will spin the jet and the jet will fall into a flat spin.

Now you are thinking the MiG-29 has a horizontal or vertical trajectory, but it does not it is actually climbing on a diagonal which resembles more a curve, so it has a gamma angle with respect the horizon and it is the velocity vector of the flight path and a Alpha angle with respect the gamma angle because the aircraft is pitching down its tail.

That is what the author calls pitch angle

The author says lift becomes zero at 90 degrees but how come it has a pressure center?

that is contradictory, so what is what is tilting the Su-27? simple lift is horizontal at 90 degrees so it is acting as drag but as thrust goes to 110 degrees its ability to lift the jet decreases with the cosine of the angle of atack

Now during cobra the jet does not fly beyond 110 because that drag that is behind the center of gravity and the inertia of the jet will create a pitch down moment.

The tailplanes are contrary to your assertion that are stalled, are in reality are deflected with respect the angle of attack so they not create an over pitching and the limited pitching force they have will not disturb the pitch down force of the jet.

The fact that the aircraft is in a stall during Cobra is made clear by several papers. One of them is

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, saying:

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.

So, having already shot pass the AoA at which lift is the greatest, the aircraft is in a stall. In

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, a description for post-stall can be found:

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

Thus, a Cobra maneuver is referred to as post-stall maneuver precisely because the aircraft is already in a stall. Note that the definition for post-stall given above is synonymous with the definition for stall given by

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:

An aerodynamic stall is defined as a condition in which the wing attains an angle of attack greater than the angle of attack for maximum lift, resulting in a loss of lift and an increase in drag.

Thus, stalling doesn't require the aircraft to lose lift entirely. It only requires that the aircraft see a decreasing in lift for an increasing in angle-of-attack.

---------- Post added at 12:53 PM ---------- Previous post was at 12:13 PM ----------

Why i know the jet has tailplane pitching force?

first this


"Angle of Attack and tailplane deflection depend very strongly on the flight path angle in the post stall region, and practically do not depend in the below stall region "


all your theory that the tailplane is stalled makes no sense for a simple reason

why you have to deflect the tailplane depending in the angle of pitch if it is stalled?

if it has no force?

By the same flaw in your logic "tailplane deflection... practically do not depend in the below stall region" would mean tailplane is never used during regular flight. Quite clearly, that cannot be the case.

So why do you feel that the concept of stalling of the tailplane doesn't make sense? The reason is that you are desperately clinging to your belief that tailplane is not ineffective at high AoA, and are doing anything possible to distort statements to fit within that belief. However, you are unable to distort statements of fact that are concise and clear, and so these facts become non-sensible to you.

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requires the solving for trim condition as the first step in analyzing the Cobra maneuver, as explained in the following statement:

Analysis of maneuvers was preceded by solving the equation of longitudinal equilibrium. These equations can be obtained from dynamic equation of motion assuming that all accelerations and angular velocities are equal to zero.

Thus, the tailplane deflection gives no moment, resulting in zero angular velocities. This is completely opposite to your opinion that the paper is claiming tailplane is used in trimming. The explanation goes on and say:

Knowing that the supermanoeuvre aircraft has to be stable at the range of high angles of attack and unstable at the range of small angles of attack one can expect that at each, prescribed speed and for assumed canard setting the aircraft has two distinct, steady flight conditions (i.e. states of trim)

Thus, trim conditions refer to conditions that allow for steady-state flight. The paper never said that tailplane is used in trimming the plane.

the other source is even more clear


" 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); quoting "

The

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from which the above quote originates from also mentions lost of effectiveness of tail surface:

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.

Whether the tailplane is deflecting has no relevance as to whether the tailplane is effective in generating the pitch-down moment. An analogy is that flapping your arms wildly does not mean you are capable of flying.

and this does go well with


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

Actually, it doesn't go well in anything.

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which said "controls that will not be rendered ineffective by separated flow" is mentioning thrust-vectoring control. From the very paragraph which follows that bullet point:

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 thesis made it even more clear:

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.

In short, the use of "freedom from purely aerodynamic control surfaces" excludes the use of tailplane as a possibility. What you did here is

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. From

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:

The practice of quoting out of context, sometimes referred to as "contextomy" or "quote mining", is a logical fallacy and a type of false attribution in which a passage is removed from its surrounding matter in such a way as to distort its intended meaning.

---------- Post added at 01:10 PM ---------- Previous post was at 12:53 PM ----------

later you are claiming the jet is stalled? really?

To start the Su-27 will stall at 70 degrees of static pitch up AoA, at 40deg of AoA already it starts to have wing rock instabilities, at 70 degrees of AoA it stalls and flat spins, that is real stall of a Su-27.

However the jet does not stall otherwise it will depart

The russian source is clear why it does not stall

due to turbulent flow, the aircraft experiences lateral instability and the risk of stall and depart into flat spins
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 .



and they go and say the Su-27 does not stall during the Cobra

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

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


рулями=tailplanes


this goes perfectly with

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


So you can say to me the same theory Engineer says, but you are wrong because the Su-27 does not stall, you are free as he is to believe what ever you want, but i do not agree and i understand well the papers, i know perfectly all these papers say what they say

The Cobra maneuver is called a post-stall maneuver. One definition for post-stall is given in

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:

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

This is the same definition given by

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for stall:

An aerodynamic stall is defined as a condition in which the wing attains an angle of attack greater than the angle of attack for maximum lift, resulting in a loss of lift and an increase in drag.

Thus, the idea of post-stall is synonymous with that of stall, characterize by large angle-of-attack, decreasing in lift and increasing in drag. Another definition for post-stall can be found within

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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.

The above statement unequivocally points out that stall occurs in a post-stall maneuver. In short, an aircraft within a Cobra maneuver has already stalled. Whether C[sub]L[/sub] remains great enough is entirely irrelevant, as the only requirement for stall is that lift has passed the point of maximum and is on a decline, as explained in the

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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.

CL being large but having passed the point of maximum still means the aircraft is in a stall. This isn't a religion and is not matter of belief. The papers have very clearly contradicted you and debunked your pseudo-aerodynamic theories.

 

[MiG-29]

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

Analysis of maneuvers was preceded by solving the equation of longitudinal equilibrium. These equations can be obtained from dynamic equation of motion assuming that all accelerations and angular velocities are equal to zero.



:

Longitudinal equilibrium does mean the aircraft is in balanced and will continue in the same trimmed condition, in fact it means the forces are at equilibrium or in few words tailplane pitch moment force exists

" An aeroplane in longitudinal equilibrium is trimmed by using trim tabs on the elevator or by adjusting the tailplane" or it is called free stick stability

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The basic word trimmed means the tailplane is balancing and has a pitch force, so the text a no moment says tailplane does not have a pitch force, but rather the analysis method is static and not dynamic in few words it is a snapshot in time of a given condition of analysis, since the Cobra means a drop in speed and a continous pitch of 110 degrees back and forth and the whole proccess if highly dynamic

 

[Engineer]

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

Longitudinal equilibrium does mean the aircraft is in balanced and will continue in the same trimmed condition, in fact it means the forces are at equilibrium or in few words tailplane pitch moment force exists

" An aeroplane in longitudinal equilibrium is trimmed by using trim tabs on the elevator or by adjusting the tailplane" or it is called free stick stability

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The basic word trimmed means the tailplane is balancing and has a pitch force, so the text a no moment says tailplane does not have a pitch force, but rather the analysis method is static and not dynamic in few words it is a snapshot in time of a given condition of analysis, since the Cobra means a drop in speed and a continous pitch of 110 degrees back and forth and the whole proccess if highly dynamic

Wrong. For equilibrium to exists, all forces and moments must balance out to zero, meaning linear and angular acceleration are both zero. This in turn means tailplane is not slowing down or speeding up the pitch rate in anyway -- tailplane is not used. The

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is pretty clear on the requirements for equilibrium to occur:

Analysis of maneuvers was preceded by solving the equation of longitudinal equilibrium. These equations can be obtained from dynamic equation of motion assuming that all accelerations and angular velocities are equal to zero.

The

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is also pretty clear on what the word "trim" means. Specifically, in the context of the paper trim refers to the condition that keeps all forces and moments balanced -- the so call steady-state flight condition. The paper did say anything about active use of tailplane:

Knowing that the supermanoeuvre aircraft has to be stable at the range of high angles of attack and unstable at the range of small angles of attack one can expect that at each, prescribed speed and for assumed canard setting the aircraft has two distinct, steady flight conditions (i.e. states of trim).

Throughout the analysis the tailplane is kept at a condition to provide no angular acceleration, meaning tailplane is not used in recovery in anyway, debunking your claim. Put it in another way, the deflection of tailplane is simply an artifact from finding steady-state flight conditions, and does not cause any change in the aircraft's dynamic, meaning it has nothing to do in recovering the aircraft. From the same paper, it is explained that recovery can only provided by shifting of aerodynamic center behind the center-of-gravity:

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.

Why is that the case? That's because the tailplane is ineffective at high AoA:

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.

You are also wrong in claiming the analysis is static. While your analogy of a snapshot is correct, these are snapshots taken of the state variables, and these state variables contain dynamic terms. Thus, analysis of steady-state flight conditions does not prevent dynamic flight from being analyzed; hence the use of "steady-state condition" instead of "static condition".