Aerodynamics thread

[Engineer]

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

the canard is deflected down to minimize canard vortex interaction with the wing and unload the canard (reduce local AoA) while the wing is highly loaded at 30 degrees of AoA for example at max lift coefficient and near flow separation.
trailing edge flaps can do that trimming up to low AoA but at high AoA canards are deflected dowwards thus increasing lateral and directional stability by unloading the canard and wing before they reaches stall

---------- Post added at 11:20 PM ---------- Previous post was at 11:13 PM ----------



Su-27 has no TVC and does the Cobra and you just pretend this does not exist

The Cobra maneuver does not require the aircraft to be controllable. Thus, an aircraft capable of performing the maneuver does not make the aircraft controllable at high angle-of-attack. In fact, the maneuver has to be kept as short as possible on a Su-27 precisely because the aircraft is uncontrollable, while a Su-30 fitted with TVC doesn't have this time limitation.

For Su-27, the recovery is not achieved by active deflection of the tailplane, but via passive aerodynamics means. This is explained in

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:

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.

Note the use of the word "only" which excludes the use of the tailplane. Furthermore, the same paper states that conventional control (use of aerodynamic surfaces such as the tailplane) is loss at high AoA:

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 being lost means aerodynamic surfaces cannot be used in the control of the aircraft. Since tailplane is one of those surfaces, this also means tailplane cannot be used to control the aircraft. From

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, it is explained that an aircraft that is flyable at high AoA must be controllable, and this controllability can be achieved by thrust-vectoring:

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. C[sub]L[/sub] remains great enough in post-stall to overcome the aircraft’s weight.

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.

Hence, the use of tailplane on the F-22 does not prove your claim that tailplane is usable at high AoA. It only means that the problem is not an issue thanks to TVC.

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 statement does not support your claim that tailplane is effective at high AoA. In fact, the opposite is said in that

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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.

In another part of that same paper, the following is said:

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.

Thus, the fact remains that tailplane is ineffective at high AoA. Canard doesn't have this problem, as explained by

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:

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

The reason as explained above is that canard can remain un-stall, and deflect into negative AoA to provide pitch-down moment which also avoids stall. This is the same idea 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.

---------- Post added at 01:04 AM ---------- Previous post was at 12:53 AM ----------

when the negative deflection of the tail causes large lift losses.
hahaha it means no loss of effectiveness simple tailplanes bring up the nose by bring down the tail hahahahaha by deflecting down it reduces the AoA and lift at the tail hahahahahaha as such the triplane retains a canard to put up by the lift lost at the tail increasing pitching up and adding extra lift


Man you are comic

Laugh, because it is the only way you can ease your uncomfort in having your claims debunk by your own paper, once again.

The loss of effectiveness of the tailplane is also explained in

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, which specifically analyzed the Cobra maneuver. One of its statement is as follow:

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.

Another

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makes the following statement:

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, at high AoA the tailplane loses effectiveness, which is why

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considers the use of canards to provide supplemental trimming at high AoA.

 

[Quickie]

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

That is just an excuse, the FCS is written based upon aerodynamics, aerodynamic rules are not made on FCS programs but are independent natural laws of physics upon which FCS programs are written.

The problem is you've a problem with understanding physics. According to your altered world physics, it's okay to compare orange and apple. As long as they look round and they both can be eaten, then they must be similar in their properties, just as how you make inferences of a triplane experimental half model to the J-20.

 

[MiG-29]

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

The problem is you've a problem with understanding physics. According to your altered world physics, it's okay to compare orange and apple. As long as they look round and they both can be eaten, then they must be similar in their properties, just as how you make inferences of a triplane experimental half model to the J-20.

That is not what i have meant, the american study says canards or tailplane more or less are the same and the advantage from their point of view is the tailplane offers you simplicity.

The FCS is based on aerodynamics not on the arbitrary desires of the software developers, so youa re trying to imply because those studies are from the 1970s they do not count as if the laws of physics do not apply any more.

 

[MiG-29]

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

considers the use of canards to provide supplemental trimming at high AoA.

haha let us see why tailplanes are beneficial for supercruise and why the US and Russia has chosen tailplanes for their Mach 1.7 supercruising fighters


Lift, drag, and pitching moment of the basic wing-body, wing-canard,
and wing-tail are presented in Figure 83 at Mach numbars of 1.88 and 2.48.
In contrast to the data at subsonic and transonic speeds the canard has
less lift than the horizontal tail. The horizontal tail generates more
than double the incremental lift at M - 1.88 and no incremental lift is
evident for the canard at M - 2.48. Examination of the pitching moment
shown in Figure 83c indicates, however, that the canard is lifting duo to
the forward shift in neutrai point. It thus appears that the shock wave
interference between canard and wing causes a significant lift loss on the
main wing. Similarly, this loss in lift causes an increase in drag as reflected
in the lift-to-drag ratio data presented in Figure 83b. The horizontal
tail is clearly superior in performance at both Mach numbers.

and let us go to pitching moment


As shown, the canard configuration exhibits no nosedown
break, whereas the horizontal tail configuration breaks the stability at
lift coefficient of 0.73 and 0.93 for the 25- and 50-degree models.

Similar trends are noted for the 50-degree wing model, however, the
differences between measured and summed incret nts are smaller at low
angles of attack. The nosedown break is shifted to the higher angle of
attack for the measured values rather than for the summed values, indicating
changes of the characteristics of the horizontal tail due to the
canard.
At 12 to 16 degrees the model begins to pitchup and
the magnitude of this pitchup becomes more severe with increasing Mach
number. Similarly, after the pitching moment break (a 'ý.19 degrees) the
magnitude of the nosedown moment is increased with increasing Mach number.
The canard configurations show relatively constant incremental moment
variation with Mach number.
respectively.

 

[Quickie]

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

That is not what i have meant, the american study says canards or tailplane more or less are the same and the advantage from their point of view is the tailplane offers you simplicity.

The FCS is based on aerodynamics not on the arbitrary desires of the software developers, so youa re trying to imply because those studies are from the 1970s they do not count as if the laws of physics do not apply any more.

youa re trying to imply because those studies are from the 1970s they do not count as if the laws of physics do not apply any more

As usual, you're making up stories. - I never directly or indirectly implied that in anyway. What I was saying is that the study was on a very different design configuration.

For example, how can you possibly relate the following observation in the study (which you quoted above) to the very different J-20 configuration which obviously don't even have a horizontal tail?

The nosedown break is shifted to the higher angle of
attack for the measured values rather than for the summed values, indicating
changes of the characteristics of the horizontal tail due to the
canard.

 

[MiG-29]

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

As usual, you're making up stories. - I never directly or indirectly implied that in anyway. What I was saying is that the study was on a very different design configuration.

For example, how can you possibly relate the following observation in the study (which you quoted above) to the very different J-20 configuration which obviously don't even have a horizontal tail?

If you have payed some attetion to the graph you will see the figure shows data for three configurations, canard wing, tailplane wing and triplane.
So paper has validity, the problem for you is you think the American studies did not know what Song claims.

These papers were written in the 1970s a decade and a half before the YF-22 was hatched and helped in the F-22 design.
Now no configuration is perfect even see

"Commenting on the fighter's capacities, Gao said on the sideline of a National People's Congress meeting that the J-20 fighter has both advantages and disadvantages if comparing with the stealth jets of other countries, including F-22 of the United States"

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These means no fighter can do everything.
There are compromises to be paid in any configuration

 

[Engineer]

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

haha let us see why tailplanes are beneficial for supercruise and why the US and Russia has chosen tailplanes for their Mach 1.7 supercruising fighters


Lift, drag, and pitching moment of the basic wing-body, wing-canard, and wing-tail are presented in Figure 83 at Mach numbars of 1.88 and 2.48. In contrast to the data at subsonic and transonic speeds the canard has less lift than the horizontal tail. The horizontal tail generates more than double the incremental lift at M - 1.88 and no incremental lift is evident for the canard at M - 2.48. Examination of the pitching moment shown in Figure 83c indicates, however, that the canard is lifting duo to the forward shift in neutrai point. It thus appears that the shock wave interference between canard and wing causes a significant lift loss on the main wing. Similarly, this loss in lift causes an increase in drag as reflected in the lift-to-drag ratio data presented in Figure 83b. The horizontal ail is clearly superior in performance at both Mach numbers.

Performance of lift has nothing to do with use of tailplane in recovery from a high AoA, thus this doesn't support your claim and is nothing more than a fallacy called

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. Let see what

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has to say with regards to tail at high AoA:

TRISURFACE CONFIGURATION
...
A sketch of this configuration is shown in Figure 20. The rationale behind the configuration is to use the horizontal tail for trim at low-to-moderate angles of attack and to supplement the tail trim power with the canard at higher angles of attack when the negative deflection of the tail causes large lift losses.

Thus, the paper studies a tri-plane configuration where canard is used to provide pitch authority at high AoA. Why? Because of loss in effectiveness of the tailplane.

---------- Post added at 11:04 AM ---------- Previous post was at 10:53 AM ----------

and let us go to pitching moment


As shown, the canard configuration exhibits no nosedown break, whereas the horizontal tail configuration breaks the stability at lift coefficient of 0.73 and 0.93 for the 25- and 50-degree models. Similar trends are noted for the 50-degree wing model, however, the differences between measured and summed incret nts are smaller at low angles of attack. The nosedown break is shifted to the higher angle of attack for the measured values rather than for the summed values, indicating changes of the characteristics of the horizontal tail due to the canard. At 12 to 16 degrees the model begins to pitchup and the magnitude of this pitchup becomes more severe with increasing Mach number. Similarly, after the pitching moment break (a 'ý.19 degrees) the magnitude of the nosedown moment is increased with increasing Mach number. The canard configurations show relatively constant incremental moment variation with Mach number. respectively.

This paragraph isn't comparing the effectiveness of active deflection canard and tailplane for providing nose-down moment. Rather, it is talking about the change in stability vs. change in angle-of-attack and how these relate to change in moment. Deflection for canard and tailplane is constant. Nose-up pitch moment as seen in canard is expected, since the canard maintains positive AoA throughout. Nose-down pitch moment seen in the tailplane is due to the shift in stability, and is the same phenomenon as observed in

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, which 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.

Thus, the paragraph you have quoted above does not support your pseudo-aerodynamic theories that active deflection of tailplane is used to provide nose-down pitch moment at high AoA.

 

[MiG-29]

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

This paragraph isn't comparing the effectiveness of active deflection canard and tailplane for providing nose-down moment.

As shown, the canard configuration exhibits no nosedown
break, whereas the horizontal tail configuration breaks the stability at
lift coefficient of 0.73 and 0.93 for the 25- and 50-degree models

did you see the figure 37? the tailplane has negative pitch moment values already at 16 and 22 degrees of AoA of course you did not see because you can not believe what your eyes are seeing

hahahahahahaha

 

[Quickie]

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

If you have payed some attetion to the graph you will see the figure shows data for three configurations, canard wing, tailplane wing and triplane.
So paper has validity, the problem for you is you think the American studies did not know what Song claims.

These papers were written in the 1970s a decade and a half before the YF-22 was hatched and helped in the F-22 design.
Now no configuration is perfect even see

"Commenting on the fighter's capacities, Gao said on the sideline of a National People's Congress meeting that the J-20 fighter has both advantages and disadvantages if comparing with the stealth jets of other countries, including F-22 of the United States"

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These means no fighter can do everything.
There are compromises to be paid in any configuration

As usual, you're missing the point, and you just can't expect people here to forever point out your error for you.

Do you think the tailess canard-wing model, as shown in Fig. 1 in the study, is even flyable? It's meant to collect experimental data, basically to be used in conjunction with the rest of the experitmental data to determine how the canards, wings and horizontal tails interact with each other. The model configuration in Fig. 1 is nowhere near the configuration of any flyable aircraft in existence in this world, but you even has the audacity to compare it with the J-20.

 

[Engineer]

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

If you have payed some attetion to the graph you will see the figure shows data for three configurations, canard wing, tailplane wing and triplane.
So paper has validity, the problem for you is you think the American studies did not know what Song claims.

These papers were written in the 1970s a decade and a half before the YF-22 was hatched and helped in the F-22 design.

Whether the study has validity has no correlation as to whether the study is relevant to J-20. A paper being valid also does not automatically make your pseudo-aerodynamic theories about tailplane being used at high AoA true.

The problem here is that you are conducting

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, a logical fallacy where you are searching for single statements and then distorting them in a desperate attempt to support your incorrect beliefs. However, careful study of those papers, such as

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, reveal they have little to do with the J-20:

TRISURFACE CONFIGURATION
The canard, if in proper position for favorable interference, is not as efficient a trimming device for a stable configuration.

In the above statement alone, there are three hints that the paper is not relevant to J-20. The first is the tri-surface configuration, which is obviously not the configuration of J-20. The second is the study of closed-couple canard, which is not the type of canard used by J-20. The third is that the paper study the contribution of canard to a stable configuration, whereas J-20 is an unstable aircraft.

In Dr. Song's paper, it is stated that the canard for J-20 has long moment arm, and that LERX is used to enhance the vortices of the canards to retain the benefits of closed-couple canards:

Canards on close coupled canard configuration aircraft have relative short lever arms. Employing the LERX canard configuration can increase the canards’ lever arms while retaining the benefits of positive canard coupling. Considering the overall lift enhancement effect and pitch down control capabilities, we can set the canards’ maximum relative area to around 15% and the maximum canard deflection to 90 degrees.

In short, Dr. Song solved the conflict of lift vs. trim in canard placement. Since J-20 canards have long moment arm, the trimming difficulty of a closed-couple canard as described

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simply isn't relevant.

Now no configuration is perfect even see

"Commenting on the fighter's capacities, Gao said on the sideline of a National People's Congress meeting that the J-20 fighter has both advantages and disadvantages if comparing with the stealth jets of other countries, including F-22 of the United States"

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These means no fighter can do everything.
There are compromises to be paid in any configuration

No configuration can do everything, and what a traditional configuration cannot do is the use of tailplane in high AoA situation. This is the result of having to deflect the tailplane to an even higher AoA in order to generate pitch-down moment, which in turn leads to the stall of the tailplane. This is why canard is superior to tailplane, as explained by 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.

---------- Post added at 11:41 AM ---------- Previous post was at 11:34 AM ----------

As shown, the canard configuration exhibits no nosedown break, whereas the horizontal tail configuration breaks the stability at lift coefficient of 0.73 and 0.93 for the 25- and 50-degree models

did you see the figure 37? the tailplane has negative pitch moment values already at 16 and 22 degrees of AoA of course you did not see because you can not believe what your eyes are seeing

hahahahahahaha

At 16 and 22 degrees AoA means the paragraph talks about low angle-of-attack. In other words, the paragraph doesn't support your claim that active deflection of the tailplane is used in recovery in the Cobra maneuver. What is high angle-of-attack? It would be 80[sup]o[/sup] - 120[sup]o[/sup] as explained in

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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.

By "conventional control is usually lost", the paper refers to the lost of effectiveness of aerodynamic control surfaces such as the tailplane. In another part of the same paper, the ineffective tailplane is stated even more explicitly:

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.

But of course, you do not see because you cannot believe what your eyes are seeing.

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also says the samething:

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.

Of course, you do not see that either because you cannot believe your own sources are debunking your pseudo-aerodynamic theories.

So, as you can see, your empty accusation of others being in denial is a result of

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of your own emotion onto others.

In your desperate attempt to prove something that has already been debunked many times, you now try to pass nose-down pitch moment at low angle-of-attack as a proof of tailplane's effectiveness at high angle-of-attack. It's too bad for you that your B.S. can be spotted from kilometers away. ROFL!