Aerodynamics thread

[Air Force Brat]

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

Now Quickie, if you and I run mig off, who will we have to argue with, I like you both and both of you have demonstrated some fine thinking and made me think, and helped me understand, just because I'm a slow student, I would like to keep this post friendly and try to accept critical thinking from one another without critical comments, Not many of us are as interested in aerodynamics because it is pretty tuff to nail some of it down. Now if Dr. Song reads this forum, he will likely throw us all three off, so Dr. Song we anxiously await your arrival but have mercy on us all. We kind of got siege in a spot on the J-20 thread, he and player and several others like this stuff too. So both of you are fine men and thinkers, lets make this the best thread on Sino Defense, and we all love the aircraft, I am still waiting to hear some thought on the T-50? Not my dogs bigger than your dog, but how did they go about solving some of the challenges?

 

[MiG-29]

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

Now Quickie, if you and I run mig off, who will we have to argue with, I like you both and both of you have demonstrated some fine thinking and made me think, and helped me understand, just because I'm a slow student, I would like to keep this post friendly and try to accept critical thinking from one another without critical comments, Not many of us are as interested in aerodynamics because it is pretty tuff to nail some of it down. Now if Dr. Song reads this forum, he will likely throw us all three off, so Dr. Song we anxiously await your arrival but have mercy on us all. We kind of got siege in a spot on the J-20 thread, he and player and several others like this stuff too. So both of you are fine men and thinkers, lets make this the best thread on Sino Defense, and we all love the aircraft, I am still waiting to hear some thought on the T-50? Not my dogs bigger than your dog, but how did they go about solving some of the challenges?

i agree, Airforcebrat, we can do analysis like that, but remember, all forums have some sensibilities, which in general are difficult to overcome.


You know once i met a french fellow who told me, F-22 is not as good as it is claimed, he was in part right, before i posted some links to a paper that shows F-22 without TVC nozzles has not very good AoA in some areas.

Here in this forum there is the idea, that Song`s theories are revolutionary, new, unknown in the west, J-20 is uncompromised, and so on.

The reality is in Europe, the US and Russia there have been studied since the 1980s that explain all Song`s Aerodynamic theories, for example, there were studies for F-16s with twin fins

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, they were rejected, Rafale originally had studies too with twin vertical fins on wing span positions,

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TsAGI and NASA did similar studies, ruddervators are also old, F-117, XB-70, YF-23 and SR-71 had already all moving tails.

Chines are also not new, SR-71 had them, studies on forebody vortex control were done on F-5 and in fact if you studied about A-12 and SR-71, you will know the SR-71 deleted one ventral fin because it the SR-71 has longer chines that augmented lateral stability, while A-21 has an extra fin.
watch minute 6:20 to 6:50

[video=youtube;su8rDySH6DY]http://www.youtube.com/watch?v=su8rDySH6DY&feature=related[/video]

watch minute 6:40 to 7:20 and you will see fuselage blending and lateral stability are some of the functions of chines on SR-71, the chine in SR-71 is basicly a huge LERX

[video=youtube;h5hDjcF9lGo]http://www.youtube.com/watch?v=h5hDjcF9lGo&feature=related[/video]

In fact JAST was a stealth fighter with canards an american study of canards, delta wings, and chined fuselage

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.
DSI was developed in the USA, but here is a detail perhaps you might not now the basic principle was also studied on F-105 and in Russia in T-10E aerodynamic models.

Wing-Fuselage blending in fact is not new, there were studies since the 1920s

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, Burnelli designed the first aircraft with wing fuselage blending

.

Now fighters like S-54 (russian study)

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Su-37 and Rafale have LERX, canards, wing-fuselage blending, and another fact not commonly known, Su-27 has in LERXes a similar aerodynamic control to chines, that is why Su-27 and MiG-29 can do the cobra.

Forebody lift due to camber is as old as T-28, yes that trainer cousin of F-5 has fuselage camber and its fuselage generates lift due to camber

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.


The use of canards and thrust vectoring nozzles was studied in X-31 and in Europe in Eurofighter.

So what is J-20 and Song`s paper? well is an original chinese design, but the Chinese have based their fighter in knowledge first studied in the west and Russia that has led them to design J-20 as it is today

 

[MiG-29]

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

We tried to explain to you the how the J-20 generate lifts, especially body lifts, to shift the aircraft's AC but you choose to ignore it.


We have evidence of the J-20 using its canards to control aircraft pitch (through the effect of canards' moment of arm), but not so much for the other aircrafts that you mentioned, especially the Rafale and Gripen because these 2 aircrafts use the elevons for pitch control during those maneuovres.

You said the J-20 will pitch down if it were to deflect down its flap. I explained earlier why this is not necessary true for the J-20 but definitely true for Rafale and Gripen. In fact the elevons have to be deflected up for pitch up for these 2 aircrafts. (Their deflection, partly because of their large surface area, is not as noticeable as the canards or tail elevators).

If you're so convinced that these 2 aircrafts can in fact deflect the flaps down during landing (aircraft at a positive AOA) or climbing or better still, during a turn maneuovre. Show us the proof.

If you can't, then don't continue derailing this thread with your pseudo aerodynamic theory.

Rafale, Gripen, LCA and J-20 all have flaps not just elevons, the trailing edge flaps can work as elevons and flaps,
if you see the video you can see the Rafale applying small brief flap deflections at take off to increase lift and when the pitch up of take off happens the flaps will work as elevons and will deflect up.
watch from minute 2:00
[video=youtube;lR9Sf2lZDLA]http://www.youtube.com/watch?v=lR9Sf2lZDLA&feature=related[/video]


Rafale as well as J-20 can use flaps, LCA uses flaps too, otherwise they would only have elevons, but they do not only have elevons, they have flaps too.


Canards with negative deflection do increase lift at high AoA, they reduce the AoA of the canard by deflecting them down at high AoA, your theory that J-20 is killing lift does not explain why J-20 is not deflecting the flaps, flaps will give more lift and a pitch down force, so the tail will go up and the nose down, LCA and Mirage 2000 do that.

 

[Quickie]

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

Now Quickie, if you and I run mig off, who will we have to argue with, I like you both and both of you have demonstrated some fine thinking and made me think, and helped me understand, just because I'm a slow student, I would like to keep this post friendly and try to accept critical thinking from one another without critical comments, Not many of us are as interested in aerodynamics because it is pretty tuff to nail some of it down. Now if Dr. Song reads this forum, he will likely throw us all three off, so Dr. Song we anxiously await your arrival but have mercy on us all. We kind of got siege in a spot on the J-20 thread, he and player and several others like this stuff too. So both of you are fine men and thinkers, lets make this the best thread on Sino Defense, and we all love the aircraft, I am still waiting to hear some thought on the T-50? Not my dogs bigger than your dog, but how did they go about solving some of the challenges?

We have to keep the thread to a respectable level of standard.
For example, making suggestion that the J-20 should be able to deflect its flaps down during a turn to prove good design when all top-of-the-line jetfighters can't and won't do that for various reasons, and not to mention his newly invented theory of negative deflected canards can produce canard lift if the fuselage is at high enough AOA, is tantamount to making an argument just for the reason of frustrating the other readers.

---------- Post added at 06:51 PM ---------- Previous post was at 06:47 PM ----------

Rafale, Gripen, LCA and J-20 all have flaps not just elevons, the trailing edge flaps can work as elevons and flaps,
if you see the video you can see the Rafale applying small brief flap deflections at take off to increase lift and when the pitch up of take off happens the flaps will work as elevons and will deflect up.
watch from minute 2:00

The rafale was deflecting its elevons to control its pitch during the takeoff, not just deflecting down the flap to increase lift. Otherwise what will happen if the aircraft pitches up at a high AOA at the start of the takeoff?

your theory that J-20 is killing lift does not explain why J-20 is not deflecting the flaps, flaps will give more lift and a pitch down force, so the tail will go up and the nose down, LCA and Mirage 2000 do that.

So does the Rafale and Gripen. Why do you have to leave them out.
The J-20 does deflect its canard negatively for pitch down. The J-20 will not deflect its flaps down for most of the maneuovres for the same reasons that all jetfighters do, including the rafale and gripen. Why should this be a problem only for J-20.

Canards with negative deflection do increase lift at high AoA, they reduce the AoA of the canard by deflecting them down at
high AoA

I'm putting this on record that you are still claiming this for a number of times already that:

A negatively deflected canard will actually increase the canard lift if the aircraft fuselage is at a high AOA.

If you still claim that this is true, how can the discussion be meaningfully continued?

 

[MiG-29]

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

We have to keep the thread to a respectable level of standard.
For example, making suggestion that the J-20 should be able to deflect its flaps down during a turn to prove good design when all top-of-the-line jetfighters can't and won't do that for various reasons, and not to mention his newly invented theory of negative deflected canards can produce canard lift if the fuselage is at high enough AOA, is tantamount to making an argument just for the reason of frustrating the other readers.

---------- Post added at 06:51 PM ---------- Previous post was at 06:47 PM ----------



The rafale was deflecting its elevons to control its pitch during the takeoff, not just deflecting down the flap to increase lift. Otherwise what will happen if the aircraft pitches up at a high AOA at the start of the takeoff?




So does the Rafale and Gripen. Why do you have to leave them out.
The J-20 does deflect its canard negatively for pitch down. The J-20 will not deflect its flaps down for most of the maneuovres for the same reasons that all jetfighters do, including the rafale and gripen. Why should this be a problem only for J-20.




I'm putting this on record that you are still claiming this for a number of times already that:

A negatively deflected canard will actually increase the canard lift if the aircraft fuselage is at a high AOA.

If you still claim that this is true, how can the discussion be meaningfully continued?

Rafale or any canard delta deflect the canards negatively, see at minute 4:14

[video=youtube;NbyAa7_MzxE]http://www.youtube.com/watch?v=NbyAa7_MzxE&feature=related[/video]

the difference is Rafale does not deflect as much as J-20
see this picture

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Rafale has Lerxes, canards and wing-fuselage blending compare Rafale A and Rafale C see how the C variant has blending


First rafale C

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Rafale A less wing fuselage fileting

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[Quickie]

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

Rafale or any canard delta deflect the canards negatively, see at minute 4:14

the difference is Rafale does not deflect as much as J-20
see this picture

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Rafale has Lerxes, canards and wing-fuselage blending compare Rafale A and Rafale C see how the C variant has blending


First rafale C

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Rafale A less wing fuselage fileting

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I've already explained to you many times. The rafale uses its close coupled canards for airflow and boundary layer separation control. I have seen the Su-33 deflecting its canards at an even more negative angle than the rafale. Problem is you still failed to understand the pitch up moment is not due to the result of the canards' moment force but due to the action of the elevons. It would be impossible for the rafale to use its canards for pitch control because of its canards' short moment of arm and the resulting drag and loss of lift, as explained in one of the studies you yourself posted earlier.

Even if the rafale were to fix its canards at zero deflection, it still should be able to do its maneouvres using its elevons at the cost of much loss in lift and increase in drag. It would be something like the LCA then.

On the canard deflections, in the recent videos that we've seen, the J-20 only deflects its canards slightly during a few tight turn maneuovres. You failed to understand that the J-20 uses it long coupled canards as pitch control surfaces just like how the F-22 uses its tail horizontal stabilizer for the same function. By this count, we should see the same amount of elevators action in the F-22 as we should see for the J-20's canards during the maneuovres. Would you then say the F-22 is deflecting its elevators too much ?

I still think that it's difficult to continue the discussion if you continue to invent new pseudo theories like that of "A negatively deflected canard will actually increase the canard lift if the aircraft fuselage is at a high AOA."

So, this is probably going to be my last reply to this thread.

 

[MiG-29]

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

I've already explained to you many times. The rafale uses its close coupled canards for airflow and boundary layer separation control. I have seen the Su-33 deflecting its canards at an even more negative angle than the rafale. Problem is you still failed to understand the pitch up moment is not due to the result of the canards' moment force but due to the action of the elevons. It would be impossible for the rafale to use its canards for pitch control because of its canards' short moment of arm and the resulting drag and loss of lift, as explained in one of the studies you yourself posted earlier.

Even if the rafale were to fix its canards at zero deflection, it still should be able to do its maneouvres using its elevons at the cost of much loss in lift and increase in drag. It would be something like the LCA then.

On the canard deflections, in the recent videos that we've seen, the J-20 only deflects its canards slightly during a few tight turn maneuovres. You failed to understand that the J-20 uses it long coupled canards as pitch control surfaces just like how the F-22 uses its tail horizontal stabilizer for the same function. By this count, we should see the same amount of elevators action in the F-22 as we should see for the J-20's canards during the maneuovres. Would you then say the F-22 is deflecting its elevators too much ?

I still think that it's difficult to continue the discussion if you continue to invent new pseudo theories like that of "A negatively deflected canard will actually increase the canard lift if the aircraft fuselage is at a high AOA."

So, this is probably going to be my last reply to this thread.

that is okay but here is not my mistake as you claim

Kersh's work indicated that the lift coefficient increased as the fixed-canard
deflection angle was varied from 0 to -7 degrees, at this angle of attack
TABLE 4: ALPHA = 34,

Canard Deflection -7 Degrees
This deflection produced a canard angle of attack of 27 degrees

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As it was mentioned in Volume 2 that small negative deflections had a
beneficial effect on performance at low angles of attack and only minor un-
favorable effects at high angles of attack.
In general, the incremental change in
lift due to either positive or negative deflection is relatively constant
with Mach number at each angle of attack for all configurations

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The absolute deflection magnitude of the canard surfaces is approximately the same as the attack angle .alpha. for the entire aircraft so that such canard surfaces are nearly aligned with the local air flow and are, therefore, unstalled. Thus , the canard surfaces remain effective as lift surfaces in providing the required forces and moments for controlling the entire aircraft.

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Aircraft with canards do that, so is not seudo aerodynamics it is simply you can not prove otherwise


tell me why this Rafale is turning and deflecting negative its canards?

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But you know let us leave it here if you want, as long as you do not that canards are deflected negatively and they can generate lift at high AoA the is no point to discuss specially if you do not understand this

The other drawback with the aft-set wing is that it is difficult to use flaps. Flaps almost double the lift produced by the wing, but on a lifting canard this would produce such a strong nose-down pitching moment that only a very large foreplane could overcome it. Consequently, flap size and effectiveness become factors in the thorny issue of canard sizing.[

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[Quickie]

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

that is okay but here is not my mistake as you claim

Kersh's work indicated that the lift coefficient increased as the fixed-canard
deflection angle was varied from 0 to -7 degrees, at this angle of attack
TABLE 4: ALPHA = 34,

Canard Deflection -7 Degrees
This deflection produced a canard angle of attack of 27 degrees

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As it was mentioned in Volume 2 that small negative deflections had a
beneficial effect on performance at low angles of attack and only minor un-
favorable effects at high angles of attack.
In general, the incremental change in
lift due to either positive or negative deflection is relatively constant
with Mach number at each angle of attack for all configurations

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The absolute deflection magnitude of the canard surfaces is approximately the same as the attack angle .alpha. for the entire aircraft so that such canard surfaces are nearly aligned with the local air flow and are, therefore, unstalled. Thus , the canard surfaces remain effective as lift surfaces in providing the required forces and moments for controlling the entire aircraft.

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Aircraft with canards do that, so is not seudo aerodynamics it is simply you can not prove otherwise


tell me why this Rafale is turning and deflecting negative its canards?

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But you know let us leave it here if you want, as long as you do not that canards are deflected negatively and they can generate lift at high AoA the is no point to discuss specially if you do not understand this

The other drawback with the aft-set wing is that it is difficult to use flaps. Flaps almost double the lift produced by the wing, but on a lifting canard this would produce such a strong nose-down pitching moment that only a very large foreplane could overcome it. Consequently, flap size and effectiveness become factors in the thorny issue of canard sizing.[

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The other drawback with the aft-set wing is that it is difficult to use flaps. Flaps almost double the lift produced by the wing, but on a lifting canard this would produce such a strong nose-down pitching moment that only a very large foreplane could overcome it. Consequently, flap size and effectiveness become factors in the thorny issue of canard sizing.

Already explained this is not an issue with J-20 because of its forebody lifts as have been discussed so often here but you choose to ignore it. Again, the Glacier is a very different aicraft with very high aspect wing, no comparison here. As for the rest, I've already explained why you're mistakened till I turned blue but it seems like you are still unable to understand.

The problem is you have the tendency to post studies that you don't really understand and make wrong presumptions based on the wrong understanding of the studies.

You may be a good jetfighter salesman to an average layperson or the politicians with little knowledge on this sort of thing and who's going to have a say on the buying decision.

Still, to the people who are only slightly knowleageble in this sort technical knowledge, they will be able to see the holes in your argument. For example, you said that the lack of deflection in the close coupled canards of the Rafale is something to be trumpetted about. But do you know that it's also a indication of how high the max AOA the aircraft is able to achieve?

In the videos that I've seen, the Su-33 was seen to deflect its canard at a high negative angle when going high alpha indicating that it probably has a higher max AOA than the Rafale. But of course you're convinced that small canard deflection is good thing by all counts.

 

[MiG-29]

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

Already explained this is not an issue with J-20 because of its forebody lifts as have been discussed so often here but you choose to ignore it. Again, the Glacier is a very different aicraft with very high aspect wing, no comparison here. As for the rest, I've already explained why you're mistakened till I turned blue but it seems like you are still unable to understand.

The problem is you have the tendency to post studies that you don't really understand and make wrong presumptions based on the wrong understanding of the studies.

You may be a good jetfighter salesman to an average layperson or the politicians with little knowledge on this sort of thing and who's going to have a say on the buying decision.

Still, to the people who are only slightly knowleageble in this sort technical knowledge, they will be able to see the holes in your argument. For example, you said that the lack of deflection in the close coupled canards of the Rafale is something to be trumpetted about. But do you know that it's also a indication of how high the max AOA the aircraft is able to achieve?

In the videos that I've seen, the Su-33 was seen to deflect its canard at a high negative angle when going high alpha indicating that it probably has a higher max AOA than the Rafale. But of course you're convinced that small canard deflection is good thing by all counts.

Well since you say you are knoledgeable i have a few questions

how does J-20 generate bodylift and here i do not want your opinion or your theories but verifyable third party sources such as TsAGI, NASA or other aerodynamic studies


Song`s paper says wing-fuselage blending but so is T-50` patent.


other question is simply why fighters use relaxed stability and how this influences canard deflection?
And third and last does stealth and aerodynamics have contradictions and compromises?

 

[Quickie]

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

Well since you say you are knoledgeable i have a few questions

how does J-20 generate bodylift and here i do not want your opinion or your theories but verifyable third party sources such as TsAGI, NASA or other aerodynamic studies


Song`s paper says wing-fuselage blending but so is T-50` patent.


other question is simply why fighters use relaxed stability and how this influences canard deflection?
And third and last does stealth and aerodynamics have contradictions and compromises?

Why do you have to look for those studies? Basic aerodynamic theory is good enough for the things we're discussing and repeating them countless times here will be indeed very tedious.

We know why jetfighters use relaxed stability. As to its influence on (degree of) canard deflection, you're the one who said it'll reduce the requirement for pitch control, specifically, by reducing the canards size and its moment arm. We've already argued against this wrong notion and pointed out that increasing the instability will actually increase the requirement for pitch control surface effectiveness.

As for the third, already answered.