Aerodynamics thread

[siegecrossbow]

I created this thread at Blitzo's request so we can stop cluttering threads about specific fighters with aerodynamic explanations, questions, and debates.

 

[Air Force Brat]

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

Hehe, I think you took my "what" for "why." I understood what you said but was asking you what control surfaces he's pulling in order to prevent the nose from dropping? We saw the photos that the canards were doing the opposit for the purpose that i.e. says. And I don't recall seeing other control surfaces doing much during a turn to lift the nose...

Dr. Song points out that the forward fuselage is a lifting body or airfoil shape, so it is always applying positive pitch, the canards do stabilize the aircraft and provide downforce, just as the tail does on a conventional configuration, as Dr. Song pointes out, some of this does appear counter-intuitive. Now you smart guys, don't laugh, but for you player, a turn is merely a climb around a circle, thats why you hold aft stick, and that explains why, in a 60 degree bank, you are pulling 2gs. In other words your 140 pound body, now weighs 280, and your 2300 lbs aircraft now weighs 4600 lbs. So you have to apply aft stick if you were trimmed for level flight at 2300 lbs. When you roll out and return to level flight the aircraft will again damp out and return to trimmed straight and level flight

 

[MiG-29]

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

Dr. Song points out that the forward fuselage is a lifting body or airfoil shape, so it is always applying positive pitch, the canards do stabilize the aircraft and provide downforce, just as the tail does on a conventional configuration, as Dr. Song pointes out, some of this does appear counter-intuitive. Now you smart guys, don't laugh, but for you player, a turn is merely a climb around a circle, thats why you hold aft stick, and that explains why, in a 60 degree bank, you are pulling 2gs. In other words your 140 pound body, now weighs 280, and your 2300 lbs aircraft now weighs 4600 lbs. So you have to apply aft stick if you were trimmed for level flight at 2300 lbs. When you roll out and return to level flight the aircraft will again damp out and return to trimmed straight and level flight

let us make a thread about Doctor`s song paper would not we? let us leave this topic for only news and pictures, i will create the thread

 

[siegecrossbow]

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

let us make a thread about Doctor`s song paper would not we? let us leave this topic for only news and pictures, i will create the thread

Sure. Sounds like a fine idea.

 

[Quickie]

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

View attachment 6259

This one. The canard were deflected downward which means the pilot was pushing the nose downward during a turning maneuver. Not logical at all.

It's difficult to draw conclusion from just one static picture. We can guess that:

1. the canards is still at some positive AOA although it may look negative in relation to the aircraft.


or, (in fact, I'm convinced now this is actually the case)

2. The J-20 is already pitching down with the canard in negative AOA, and is already in the process of returning to level and going on a straight path.

---------- Post added at 04:23 PM ---------- Previous post was at 03:50 PM ----------

The paper gives a perfect answer to the pictures of the J-20 deflecting its canard too much, and what surprised was the paper was written a year ago before these test flights

---------- Post added at 10:15 PM ---------- Previous post was at 10:11 PM ----------

The thing is some people here are puzzled with the seemingly lack of canard deflection or even its seemingly negative AOA in those maneuovres and NOT THAT there's too much of canard deflection. So in a way, those J-20 pictures have proven the article wrong if it's insinuating that the J-20 requires large canard deflections for flight controls.

Btw, in the video posted in the previous page, the Rafale deflected its canards at some extreme angle during landing, much more that of the J-20.

 

[tch1972]

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

[/COLOR]

It's difficult to draw conclusion from just one static picture. We can guess that:

1. the canards is still at some positive AOA although it may look negative in relation to the aircraft.


or, (in fact, I'm convinced now this is actually the case)

2. The J-20 is already pitching down with the canard in negative AOA, and is already in the process of returning to level and going on a straight path.

---------- Post added at 04:23 PM ---------- Previous post was at 03:50 PM ----------



The thing is some people here are puzzled with the seemingly lack of canard deflection or even its seemingly negative AOA in those maneuovres and NOT THAT there's too much of canard deflection. So in a way, those J-20 pictures have proven the article wrong if it's insinuating that the J-20 requires large canard deflections for flight controls.

Btw, in the video posted in the previous page, the Rafale deflected its canards at some extreme angle during landing, much more that of the J-20.

It could be due to the deployment of leading edge slat which act like a flap to alter the aerodynamics of the wing. Once flap/slat is deploy, the aircraft will be able to attain straight and level flight at lower airspeed and lower AOA. Hence it explain why the canard was deflected in such a way though I still think the angle it was deflected is absolutely crazy. And I expect the deflection to increase once that J20 get off the turn.

---------- Post added at 05:04 PM ---------- Previous post was at 04:48 PM ----------

To my memory, all the photos of J-20 doing a turn show the same pattern, for which i.e. has an explanation, and Mig-29 seems to have one, too. To my layman's eye, I just don't see any control surfaces doing apparently enough to lift the nose in order for the turn to happen.

i.e. says it's the lift that makes the plane turn. Fine, but that lift has to be more on the nose end and can't be equal on the whole bottom of the plane, or it would only push the plane higher and higher, instead of making it run in circles, wouldn't it?

Or, are some of the control surfaces pushing down the tail during a turn? Otherwise, and again to my layman's reasoning, the plane would have gone off at a tangent instead of turning circles.

No. lift is always on the wing. I suppose you mean the CG (Center of Gravity).

the J20 concerns had it leading edge slat deploy which means the plane can attain straight and level flight with lower AOA. Hence canard have to be trim downward and I can imagine J20 doing straight and level flight at low speed with it nose pointing down .

Any photo of J20 doing a turn without leading edge slat? I am sure the canard won't be deflected in such a way.

 

[MiG-29]

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

@mig, it's not a discrimination against you or anything, but let's be frank, past threads which you've contributed to (especially this one) have been diverted with pages and pages of aerodynamic posts by you and others. There was that (again I say, interesting) aerodynamics thread a few months back where there were dozens and dozens of pages of posts. Preferably they should be in a different thread rather than the main J-20 thread where members and visitors will likely be attracted to. Most will want to see pics and news and information tidbits about J-20 rather than long winded, multiple post spanning analysis and debates on aerodynamics.

Just sayin, imho.

I do not believe you at all, if you would have point out others for going out off topic i could believe you are interested in keeping the thread`s main topic, but you have singled out my with the only purpose of blame me and not leting me post my opinions, funny an the funniest thing of all, J-20 is an airplane and flies thanks to aerodynamics, it will be impossible from time to time people wonder off topic simply because many reports mention the aerodynamics of the jet.

Or like it happened to siege, he wonder aerodynamic aspects by looking at a video, So i do not believe at all in your reasons of single out me.

If we all are really interested in keeping the thread on topic, this thread should only post pictures, videos news and brief comments, something not every one is doing, but you have single out me as the only offender when there are much more.

in fact from few pages ago the thread is full of aerodynamic questions and replies, but you got offended because i posted an article that does not go well with your views, and you have singled me out as a single offender, when in fact from 3-5 pages others have engaged in aerodynamics but you did not mind that

---------- Post added at 07:47 AM ---------- Previous post was at 07:43 AM ----------

inteesting report

---------- Post added at 07:52 AM ---------- Previous post was at 07:47 AM ----------

It's difficult to draw conclusion from just one static picture. We can guess that:

1. the canards is still at some positive AOA although it may look negative in relation to the aircraft.


or, (in fact, I'm convinced now this is actually the case)

2. The J-20 is already pitching down with the canard in negative AOA, and is already in the process of returning to level and going on a straight path.

---------- Post added at 04:23 PM ---------- Previous post was at 03:50 PM ----------



The thing is some people here are puzzled with the seemingly lack of canard deflection or even its seemingly negative AOA in those maneuovres and NOT THAT there's too much of canard deflection. So in a way, those J-20 pictures have proven the article wrong if it's insinuating that the J-20 requires large canard deflections for flight controls.

Btw, in the video posted in the previous page, the Rafale deflected its canards at some extreme angle during landing, much more that of the J-20.

i have seen videos of of other jets turning and they do not deflect the canards as much as J-20 while turning, but if you want to continue let us move to the aerodynamics thread or leave it and keep personal our own opinions

 

[delft]

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

the leading edge flaps of the wing only increase lift, the F-15 uses its elevators only for roll and vertical tail for yaw control.

The leading edge flaps only decrease lift.

 

[Quickie]

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

i have seen videos of of other jets turning and they do not deflect the canards as much as J-20 while turning, but if you want to continue let us move to the aerodynamics thread or leave it and keep personal our own opinions

I've seen the Su-33 deflecting its canards at some extreme angle although admittedly it's not a true canard aircraft. We have also seen how the Rafale deflects its canards at a much higher degree than the J-20 during landing. Another thing is the J-20 is capable of going into a higher alpha than other jetfighters and this would mean a wide difference in AOA between the canards and the aircraft fuselage but that doesn't mean the canard itself is at a high AOA.

 

[MiG-29]

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

I've seen the Su-33 deflecting its canards at some extreme angle although admittedly it's not a true canard aircraft. We have also seen how the Rafale deflects its canards at a much higher degree than the J-20 during landing. Another thing is the J-20 is capable of going into a higher alpha than other jetfighters and this would mean a wide difference in AOA between the canards and the aircraft fuselage but that doesn't mean the canard itself is at a high AOA.

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