Aerodynamics thread

[Air Force Brat]

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

The leading edge flaps only decrease lift.

The leading edge flaps increase camber, they increase lift without the need to pitch the nose up, they do however increase drag, and in order to maintain airspeed, you must pitch the nose down or increase thrust.

 

[siegecrossbow]

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

Calculator for computing Aircraft's center of mass and aerodynamic lift center.

Thnx to starriki.

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[MiG-29]

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

Calculator for computing Aircraft's center of mass and aerodynamic lift center.

Thnx to starriki.

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---------- Post added at 09:41 PM ---------- Previous post was at 09:41 PM ----------

Calculator for computing Aircraft's center of mass and aerodynamic lift center.

Thnx to starriki.

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perhaps you might like this

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[Quickie]

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

Su-33 is a true canarded aircraft, but if you mean is not a delta wing-canard aircraft it is true, Su-33 is not a delta wing canard aircraft.

If you look at this Rafale turning you can see it barely deflects the canards, in my opinion the difference is related to the light weight configuration the Rafale is flying (low wing loading) and the difference in static stability.

I think that difference in static stability, reflects a difference in role, as the paper originally claimed
[video=youtube;AcpT1ItVmno]http://www.youtube.com/watch?v=AcpT1ItVmno&feature=related[/video]


But the Chinese airplane appears to
have the center of gravity position somewhere
at MAC’s edge. It is fairly strange
for a maneuverable fighter, since balancing
of the aerodynamic forces and
the gravity will require relatively high deflection
of the control surfaces — canards
in the J-20’s case. Should this airplane try
to execute high-G maneuvers at subsonic
speeds, the deflection of the canards could
be a limitation.

This was predicted a year ago, in my opinion J-20 is indeed a striker interceptor


In our view the Chinese designers optimized
their new jet for M=1.3–1.6.constructed
Here comes the clue: the J-20 is a missile
launching platform able to evade enemy
interceptors by high cruise speed.
The J-20 may prove a good interceptor, —
very possibly. But its main task seems to
be anti-shipping: firing missiles at enemy
warships while denying their air defense
cover.

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[video=youtube;lKq1fZou_1Y]http://www.youtube.com/watch?v=lKq1fZou_1Y&feature=player_embedded[/video]
Compare with J-20 at 4:20 minute, you can see the J-20 is deflecting a lot its canards, reflecting the difference in static stability and role according to the paper

A few of us have argued against this view and we have seen how the J-20 is beginning to show its maneuverbility in one of the
latest test flights. I'm sure more will be coming.

Regarding the article, the analysis is wholely inadequate if it didn't even bother to consider the overall J-20 aerodynamics design. MAC of the wing is just one tiny aspect of the overall design, What about other critical aerodynamic aspects such as canards lift, body lift, the vortex generators and all the aerodynamics solutions as described in Dr. Song's paper? The aerodynamic centre of an aircraft is not determined by the position of the wing's MAC alone.

The videos don't prove a thing. Control surfaces tend to be deflected more at slower speed maneuovre. You can see the Rafale deflecting its canard at a high angle again in slow speed maneuovre at about 2:50.

The point is the Rafale has canards with short moment-of-arm and will use more of its front and hind wing slats for pitch control, maybe to the point of using the canards mostly for airflow and vortex control. And it's inappropriate, to the point of moronic, to discuss fighters of different designs on the basis of just canard deflections. Seeing how I'm falling to the trap of pointless discussion again, I think I'll just stop here.

 

[MiG-29]

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

A few of us have argued against this view and we have seen how the J-20 is beginning to show its maneuverbility in one of the
latest test flights. I'm sure more will be coming.

Regarding the article, the analysis is wholely inadequate if it didn't even bother to consider the overall J-20 aerodynamics design. MAC of the wing is just one tiny aspect of the overall design, What about other critical aerodynamic aspects such as canards lift, body lift, the vortex generators and all the aerodynamics solutions as described in Dr. Song's paper? The aerodynamic centre of an aircraft is not determined by the position of the wing's MAC alone.

The videos don't prove a thing. Control surfaces tend to be deflected more at slower speed maneuovre. You can see the Rafale deflecting its canard at a high angle again in slow speed maneuovre at about 2:50.

The point is the Rafale has canards with short moment-of-arm and will use more of its front and hind wing slats for pitch control, maybe to the point of using the canards mostly for airflow and vortex control. And it's inappropriate, to the point of moronic, to discuss fighters of different designs on the basis of just canard deflections. Seeing how I'm falling to the trap of pointless discussion again, I think I'll just stop here.

i think you are not understanding the article well, the article is talking about longitudinal static stability, this means, J-20 is rather not very unstable, the videos show a J-20 turning deflecting a lot it canards

compare with the Gripen, watch the gripen it turns tighter and deflects less its canards
[video=youtube;klf2hiix28w]http://www.youtube.com/watch?v=klf2hiix28w&feature=BFa&list=HL1331739815&lf=mh_lolz[/video]

[video=youtube;GcdFjgOMM2I]http://www.youtube.com/watch?v=GcdFjgOMM2I&feature=BFa&list=HL1331739815&lf=mh_lolz[/video]

From the point of view of the article the J-20 will be a very good interceptor, because it is fast, but what they say, is the role of the jet is interceptor striker, in few words something like the F-35 just larger.

They analysized the jet saying it looks well designed for supercruise but is more an interceptor.
It is okay with me, if you think it will be better but up to what i have seen up to now, J-20 displays not a great agility, specially since it deflects a lot the canards in relatively larger turn radius showing it has a lower lever arm than Eurofighter in order to reduce drag at supersonic speeds (eurofighter has its canard near the radome) since J-20 tries to keep the canards behind the supersonic shock wave, but this forced the jet to set the wings quit aft.

So my opinion is like many others who have declared J-20 is a interceptor striker, and with TVC nozzles it will become perhaps as good as F-22, but who knows perhaps later it will show better agility.

 

[Quickie]

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

i think you are not understanding the article well, the article is talking about longitudinal static stability, this means, J-20 is rather not very unstable, the videos show a J-20 turning deflecting a lot it canards

compare with the Gripen, watch the gripen it turns tighter and deflects less its canards
From the point of view of the article the J-20 will be a very good interceptor, because it is fast, but what they say, is the role of the jet is interceptor striker, in few words something like the F-35 just larger.

They analysized the jet saying it looks well designed for supercruise but is more an interceptor.
It is okay with me, if you think it will be better but up to what i have seen up to now, J-20 displays not a great agility, specially since it deflects a lot the canards in relatively larger turn radius showing it has a lower lever arm than Eurofighter in order to reduce drag at supersonic speeds (eurofighter has its canard near the radome) since J-20 tries to keep the canards behind the supersonic shock wave, but this forced the jet to set the wings quit aft.

So my opinion is like many others who have declared J-20 is a interceptor striker, and with TVC nozzles it will become perhaps as good as F-22, but who knows perhaps later it will show better agility.

As I said, the videos prove nothing. The gripen's canard position is quite similar to that of the rafale. The LCA Tejas does not even have canards, meaning it has zero canard deflection. Does that mean it's better than the gripen and rafale?

I know that the article is talking about longitudinal static stability. My point is it's directly related to the AC of the whole aircraft, i.e. the NP. That's why I said the article is wrong in determining the longitudinal static stability just by looking at the position of the wing's MAC (in relation to the CG) and not the aircrafts's overall AC.

 

[siegecrossbow]

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

There is a similar debate on F-16.net. Starting from page 13 of this thread:

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[Engineer]

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

i think you are not understanding the article well, the article is talking about longitudinal static stability, this means, J-20 is rather not very unstable, the videos show a J-20 turning deflecting a lot it canards

compare with the Gripen, watch the gripen it turns tighter and deflects less its canards

From the point of view of the article the J-20 will be a very good interceptor, because it is fast, but what they say, is the role of the jet is interceptor striker, in few words something like the F-35 just larger.

They analysized the jet saying it looks well designed for supercruise but is more an interceptor.
It is okay with me, if you think it will be better but up to what i have seen up to now, J-20 displays not a great agility, specially since it deflects a lot the canards in relatively larger turn radius showing it has a lower lever arm than Eurofighter in order to reduce drag at supersonic speeds (eurofighter has its canard near the radome) since J-20 tries to keep the canards behind the supersonic shock wave, but this forced the jet to set the wings quit aft.

So my opinion is like many others who have declared J-20 is a interceptor striker, and with TVC nozzles it will become perhaps as good as F-22, but who knows perhaps later it will show better agility.

There is a difference between J-20 being an interceptor and people portraying the J-20 as an interceptor. The authors of that article are of those people, and are pretty transparent about it by repeatedly saying "our view". Opinions do not equate to facts when not backed up by solid data. As far as the article is concerned, the bias is pretty clear with statements like this:

... it would probably be PLAAF sending their pilots to attack warships off the coast of a freedom-loving island not far from the mainland China.

The fact is, large deflection of canards does not indicate that the plane is stable. Rather, it is a clear sign that the aircraft is unstable. Here is an authoritative statement on the subject.

The requirement for high AOA pitch down control capability is closely related to the longitudinal static instability requirement. The greater the longitudinal static instability, the higher the demands for pitch down control capabilities.

The statement is from Dr. Song's paper. It basically says that the more unstable the aircraft is, the larger the demand is placed on the control surfaces for pitch.

Why do we see higher amount of canard deflection on J-20 than other fighter aircraft with canard configuration? The answer is provided here:

As described in chapter 3, the future fighter will hopefully increase its longitudinal static instability to around 10% its average aerodynamic chord length to enhance the trim's lift to drag and lift characteristics. As a result there should be a corresponding improvement in the pitch down control capability.

In short, J-20 is more unstable than existing fighter aircraft. The higher un-stability increases the demand on canards. With this increase in demand, of course we should see a corresponding increase in the amount of deflection. Recent photos and videos of J-20 under high-G maneuver verify this design objective.

Later in the paragraph:

Control surfaces placed behind the center of mass, including the vertical stabilizers and trailing edge flaps, generate pitch down control torque by increasing lift. They are considered positive load control surfaces. Control surfaces placed in front of the center of mass, like the canards, are negative load control surfaces. 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.

So, completely opposite to what the article claims, the limitation in control surfaces deflection exist for aircraft with traditional configuration and not one with canard-delta configuration. In other words, part of the article contradicts with facts. Attempts to force aerodynamic principles to fit a certain view, as that article has done and a certain member on this board likes to do, are bound to run in to contradictions like the above.

 

[no_name]

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

My own view is that turning is like generating lift for the aircraft sideways. (abit with some downward lift to counter gravity.)

In J-20's case the nose area has excessive lift compared to the rest of the aircraft, therefore the canard has to work to 'press the nose down' in line with the rest of the plane, so that the aircraft does not pitch too much and stall.

So it's a balance between how quickly you can change the heading of the plane's nose (which will determine the direction that the enging is pushing the plane forward, as the nose/tail is aligned down the centre of the plane) versus having enough speed in the direction that the nose is pointing to continue to generate the required lift for countering gravity. A nose that moves too fast risk decreasing the velocity of the plane and make it stall.

I think that this problem exists in J-20 and needed to be corrects actually shows that the plane is pretty maneuverable to the extent that it has to be reined in. It is not being corrected because it is a flaw, other plane don't need to correct for this because they didn't have enough nose lift in the first place.

 

[MiG-29]

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

There is a similar debate on F-16.net. Starting from page 13 of this thread:

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thanks, it is a nice debate, do not take me wrong, the J-20 might be an interceptor (i think it is) however TVC nozzles can transform it in many was see

Flight tests of thrust-vectoring designs began in the early 1990s with airplanes like NASA’s modified F/A-18 and F-15, the Rockwell/MBB X-31, and a modified Air Force F-16. In 1994, the X-31 demonstrator was fitted with what German program managers called a “poor man’s thrust vectoring nozzle”—three paddle-like vanes that pushed into the exhaust stream—and the results were spectacular. Without thrust vectoring, the X-31 lost twice as often as it won against the F/A-18 in mock combat; with it, the X-31 didn’t lose once in 129 matches.

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the advantage is while we look at the videos of Gripen and Rafale turning without deflecting too much the canards, there is the J-20 advantage of no carrying weapons externally, at heavy weights, Rafale loses agility and some supercruise ability.


So if you add TVC nozzles and no external weapons perhaps it can be an air superiority, people sometimes think F-22 is excellent without TVC nozzles but it is not, is not that much better than F-15 or F-16, so who knows with TVC nozzles it might become a more deadly weapon

TVC nozzles might improve the J-20 to the level of perhaps achieve F-22 agility, because i know F-22 expands a lot its AoA with TVC nozzles
see figure 9-15. Role rate performance, showing the effect of thrust vectoring. (Courtesy of LMAS)

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and see Figure 5: Maximum pitch up, pitch down of the YF-22 aircraft compared with F-16 [6].

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---------- Post added at 04:52 PM ---------- Previous post was at 04:36 PM ----------

As I said, the videos prove nothing. The gripen's canard position is quite similar to that of the rafale. The LCA Tejas does not even have canards, meaning it has zero canard deflection. Does that mean it's better than the gripen and rafale?

I know that the article is talking about longitudinal static stability. My point is it's directly related to the AC of the whole aircraft, i.e. the NP. That's why I said the article is wrong in determining the longitudinal static stability just by looking at the position of the wing's MAC (in relation to the CG) and not the aircrafts's overall AC.

Do you think the J-20 will deflect the canards further to turn tighter?
In my opinion J-20 will improve not becuase as you think its aerodynamics are uncompromised, but because once it adds TVC nozzles it will increase high AoA agility

see the advantages

3D Thrust Vectoring Enabling Enhanced Aircraft Flight Performance with Lower Operational Cost
Safety:
Additional control device.
Reduced aircraft loss rate due to low speed departure.
A/C Superior Performance and Handling Qualities:
extended flight envelope.
increased angle of attack (including post stall).
increased rolling rate.
Mission Performance:
Reduced take off & landing distance.
Increased thrust and reduced fuel consumption by means of afterbody drag reduction at supercruise conditions and nozzle exit area optimisation for the whole flight envelope.
Life Cycle Cost Reduction:
Engine life increase.
A/C life increase.
No aircraft or engine structural modifications required, currently studied for the EF2000 aircraft, could not require either airframe or engine structural reinforcement.

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So in my opinion what will transform J-20 will be TVC nozzles, now the jet, seems similar to the predictions done by the paper, but TVC can transform it, if China adds a right engine in the region of 15-17 tonnes of thrust and TVC nozzles