Re: J-20... The New Generation Fighter III
the tailplane is trimming and that allows hysteresis and inertial to pull down the nose, the article does not say the tailplane is pitching down the nose in a conventional way, the article says the nose goes down thanks to the lift going from a unstable position to one stable, from being before the center of gravity to behind the center of gravity, however the article says the tailplane is positioned to allow that shift to happen because it says
Hysteresis has nothing to do with use of tailplane for the recovery. The shift of aerodynamic center behind the center-of-gravity also has nothing to do with deflection of tailplane. In short, the article says absolutely nothing about the use of tailplane for generating pitch-down moment, therefore your claim that tailplane is used is unsubstantiated. It's that simple.
"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 "
This means simple that the pilot still needs to bring the tailplane to a -2 degrees of angle of deflection position after have been in -12 degrees of angle of deflection, this is done by pulling off the control stick
Wrong. That's your opinion of what it means, instead of what the statement actually means. Tailplane deflection depends on flight path angle means the latter affects the former. This is completely opposite to your assumption that the former is controlling the latter.
Whether the tailplane is moving at the recovery stage is irrelevant, just as flapping your arms wildly is irrelevant to your ability to fly. The fact is that the tailplane is ineffective at such high AoA, from the
:
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.
Your own source contradicts your position.
"Important conclusion from the analysis of the curves presented in FiG 7-15, is that is the post-stall region, the trim angle of attack is, depending in various design parameters, equal about 70 degrees, because above the post stall angle of attack the pitching coefficient (FiG 1,2) is negative and the pitching moment derivative with respect pitch rate (FiG5) is also negative it means that the positive pitch rate is decelerated, then will change sign and aircraft return back to its initial below-stall range of flight conditions"
the trim angle of attack has a specific position for the tailplane during cobra, and it is an angle of deflection of -2 degrees.
Wrong. That's another one of your opinion on what the statement is saying, versus what the statement actually is saying. The statement only says the followings:
- Angle-of-attack is at 70 degrees.
- Static pitch moment is negative (implying static stability).
- Pitch-rate moment is negative (implying dynamic stability).
No where in that paragraph ever mentions that tailplane is effective in the aircraft recovery. Your claim remains unsubstantiated.
Now the article does say this, the canard does not play any part in the cobra
canard deflection (delta_c) influences the angle of attack in the below-stall range, see Fig-10, but does not influence in the post stall range
The angle-of-attack being referred to here is the angle-of-attack of the tailplane. In other words, the statement addresses the influence of canard on the tailplane during Cobra maneuver. Regardless, the statement does not say anything about the use of tailplane for recovery. Your claim remains unsubstantiated.
Here is why you claim the tailplane is not affecting the angle of attack, and let us see why you claim what you claim.
My actual claim is that your claim of tailplane being effective at high AoA is incorrect and has no basis in reality. Tailplane being ineffective at high AoA is a simple fact.
We know tailplane cannot be used for recovery because at high AoA, the tailplane loses effectiveness, thus losing control on the aircraft. From Dr. Song's 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.
Then in your own
, it is also stated 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.
Further in the paper, the contributor to recovery during a Cobra maneuver is explained. The mechanism is due entirely to the 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 the center of pressure on main wing back and creating the strong nose-down aerodynamic pitching moment about the center of gravity
This makes sense, because when the tailplane becomes ineffective as a control device, it cannot be used to recovery the aircraft. This debunks your pseudo-aerodynamic theories on using tailplane for recovery.
You fall into two main contradictions from one side you claim the wing is stalled, this is in contradiction with the lift moving rearwards closer to the trailing edge where actually stalls first take place in a stalled wing.
The lift is actually behind the center of gravity during the cobra, how come?
Stall occurs when lift decreases as angle-of-attack increases. The definition that stall equates to disappearance of lift is nothing but another one of your pseudo-aerodynamic theories. From
:
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.
Another definition from the manual is the following, but with the exact same idea that stall does not equate to disappearance of lift:
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.
The lost of effectiveness of the tailplane is due to stall, which is explained in
where it mentions control difficulty:
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)
It so happen that the definition for a post-stall maneuver, such as the Cobra, is synonymous with the definition of stall. In this
, the definition for post-stall is given:
In the post stall regime, lift no longer increases but decreases with the angle of attack.
Thus, in a Cobra maneuver, the aircraft stalls thus control surfaces become ineffective. Increase the AoA of tailplane even more does not contribute to recovery.
Later your second contradicton is you claim that article says canards are used to control the cobra by quoting Song and not the article it self.
This is one of your favorite logical fallacies called
. The statement which you are arguing against is a statement of your own invention. In short, you are argue against yourself. From your past history, it is a sign of your own desperation is at work.
I am citing from Dr. Song's paper that canard is superior to tailplane at high AoA. Not once did I ever mention the use of canard in a Cobra maneuver.
Song`s papers says the canard is better to control poststall once the wing is stalled
To begin, Song`s claims are denied by the article why? because it says
You are wrong on both accounts. First of all, Dr. Song's paper says the canard is superior to tailplane at high AoA, and his condition does not require the wing to be stalled first. His exact statement is as follow:
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.
From the above, we can see the reason he gave is that the trailing edge control surfaces have to increase their AoA in order to generate pitch-down moment. He pointed out a fact (not a claim) that increase in AoA of these control surfaces will cause their stall. Your
agrees with Dr. Song's statement, saying:
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 other words, contradiction to Dr. Song's statement(s) is nothing but your dream and has no basis with reality. This is not surprising, since we know r. Song is a world-class aircraft designer who designed the J-10 and J-20, back up by a team of engineers who perform computer analysis and wind-tunnel testings. His statements in the subject of aerodynamics are equivalent to facts.
canard deflection (delta_c) influences the angle of attack in the below-stall range, see Fig-10, but does not influence in the post stall range
This quote doesn't support your position that tailplane is effective at high AoA. What this statement addresses is the influence of canard on the tailplane during Cobra maneuver. We know from Dr. Song's paper that trailing edge control surfaces are ineffective at high AoA, while canard is more superior because it can provide the pitch-down moment needed without stall:
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.
Now i am an open person, why because one of the articles i posted says while canard stalling after the wing will worsen the pitch up, why? simple the wing is pitching down and the canard up, this will create a very high pitch up force on the airplane worsening the stall.
"What would happen if the wing stalled but the canard didn't? In that case, the canard would raise the nose while the wing let the tail drop. There would be a sudden increase in the airplane's angle of attack. This is not good!"
However the article says
"It is not true, however, that you can never let the back wing stall on a canard. Even on a stalled airplane, there are forces at work (lift, drag and gravity) - and each of these forces has a lever arm back to the center of gravity. It's OK to have both the canard and the wing stalled, as long as the pitching moments trying to lower the nose are greater than those trying to raise the nose"
While that
is informative, your use of it constitutes a fallacy known as
and is a logical fallacy. Why? Because you are using the quotes only to sound technical, but the information you have quoted has absolutely nothing to do with the J-20.
That article refers to fixed canards, specifically those on the Beechcraft Starship that are 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:
The canards on J-20 can be fully articulated. When the aircraft is in a high AoA condition, the canards are deflected downward, aligning with the oncoming airflow thereby having zero AoA. As explained in this
:
the aircraft operates at an attackangle .alpha. much greater than the angle of attack for maximum lift so that the fixed wing 15 is either completely or partially stalled while the canard surfaces 19 are deflected in a negative sense through the deflection angle-.delta..sub.c. The absolute deflection magnitude of the canard surfaces 19 is approximately the same as the attack angle .alpha. for the entire aircraft so that such canard surfaces 19 are nearly aligned with the local air flow and are, therefore, unstalled.
Thus, the canards do not stall. To bring the nose down, the canards are deflected further downward into negative AoA, but the canards still do not stall. This is why canards are superior to tailplane in generating pitch-down moment, as explained by Dr. Song:
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.
So i believe it is possible the canard aircraft could bring the jet out of a high pitch up position.
But i do not think it is easy, and in fact i do not think it will be different to the SU-27, hysteresis has to happen, however i never seen a video of a jet doing the cobra with canard delta wing and no TVC nozzles.
Irrelevant. Hysteresis does not mean active deflection of tailplane is used for recovery. There is one mechanism for recovery, which is explained in this
:
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" unequivocally excludes other means of recovery, meaning the active deflection of the tailplane does not recovery the aircraft.
Now the assertion of song that you can bring a jet out of post stall stall, when engines fail is not like you are imaging
This accident proves how hard is to do it,
Wrong again. Dr. Song's paper addresses the use of pure aerodynamic for control on the J-20. His assumption is that TVN can fail, and cannot be relied upon to guarantee safe recovery. His exact statement is as follow:
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.
No where did he talk about aircraft recovery during engine failures while the aircraft is in a post-stall situation. You've got caught lying red-handed.
this Su-30MKI crashed because the TVC nozzles fail
Wrong. This Su-30MKI crashed due to pilot error, as explained by this
:
A joint probe by India and Russia into the crash of IAF's Sukhoi aircraft over Jaisalmer in April has given a clearance to the quality of the fighter plane, indicating that the mishap took place due to human error.
Another one of your b.s. debunked.
and same was this accident, here we see the F-22 crashing due to mistakes that made pulling the taiplane and TVC nozzles to different directions
Wrong. That accident happened because of design fault in the flight control system which resulted in
pilot-induced-oscillation. The tailplane and TVC nozzles are fully in sync.
One more of your b.s. debunked.
