Aerodynamics thread

[Engineer]

Re: J-20 The New Generation Fighter Thread IV

Sorry Eng, I did not see your reply before I added my two cents, but you are indeed correct!
Mig actually the tail provides down force in normal cruise to keep the aircraft aerodynamically balanced, the canards do actually provide additional lift to the total lift produced by the aircraft, while there is no doubt the T-50 is state of the art as is J-20, there is nothing particularly radical or new in the T-50 design or construction,although the Lerx over the intakes are rather large, it is quite obviously a Sukhoi product, with lots of Flanker DNA.

That is true, as PAKFA simply reuses many of the ideas found on Su-27. The LEVCON is really just an oversized leading edge flap so happen to control vortex because the outboard end is exposed. The LEVCON cannot replace the functions of a canard, with pitch control being the prime example.

Chinese engineers want the J-20 to have low drag, high lift, does so without powerful engines and without compromise. The result is a low aspect ratio configuration which produces high lift and sounds contradictory when you first hear it. The approach is very complex due to all the interactions influencing one another, so the only compromise here is the choice of a very complex design over something less risky.

The American engineers also don't like to make compromise, but are on the opposite of the spectrum in my opinion. The strength of US lies in engine, so engineers can be more liberal when it comes to aerodynamics of the airframe. Things get solved by powerful engines at the end of the day. Take the F-35 for example. The aircraft is overweight, so there is a plan to produce an even more powerful engine than the F-135 to compensate.

Only the Russians have taken compromises. Jet engine technology in Russia was not as good as the West to begin with, and falls further behind of the West after the collapse of Soviet Union. That means Russia engineers can't do whatever they want with the fuselage and expect things to work out with very powerful engines. At the same time, Russia lacks the funding that China has to investigate alternative solutions. So, Russian engineers pieced together existing technologies and know-how resulting in something that resembles the Flanker.

 

[MiG-29]

Re: J-20 The New Generation Fighter Thread IV

There's one thing about canards and horizontal stabilizer that's been bugging me and I hope you guys can help answer me.

By using the horizontal stabilizer to control pitch and angle of attack, is the g-force on the pilot far less than it would have been the case with canards because the pivot is near the cockpit and not at the rear of the plane? If it is true, is it one the chief reasons the Americans don't use canards?

the reasons why americans do not use canards is simply the type of requirements their jets have.

Turn rate and roll rate are relate to the max lift the aircraft generates.
The use of tailplanes or canards is more an art than science since both have advantages and disadvantages.
J-20 was designed upon canards due to the solutions its creators wanted to achieve based on the combination of solutions and requirements they had.


Will the J-20 be superior to F-22? everything depends upon the speeds and altitudes it will operate and the tactics it uses.


A Canard is not better than a tailplane and viceversa, using a canard is not less practical than using tailplanes.

Lockheed, Chengdu, Sukhoi based their fighters upon a set of requierements which are different in some way to each other, and their fighters will use different tactics to be on top.


At the end of the day each design is more optimised for a speed and altitude range.


A MiG-29 is optimised for 600km/h and at 1km of altitude it will beat the F-15 in agility but the F-15 flying faster and higher and using BVR missiles is the top dog but if the F-15 gets slow and close the MiG-29 will have Eagle for dinner.


Same will be these fighters and for those reasons the americans skip canards because they plan to use other technologies in order to cover for whatever deficiency F-22 has with tailplanes or 2D TVC nozzles and its large cross section.


Eurofighter ate F-22 thanks to highly offbored missiles and HMS, F-35 will use similar technologies and PAKFA plans to use jamming, raw radar power and higher speed and agility to eat F-22.

J-20 looks like the chinese might use F-35 tactics

 

[airsuperiority]

Re: J-20 The New Generation Fighter Thread IV

the reasons why americans do not use canards is simply the type of requirements their jets have.

Turn rate and roll rate are relate to the max lift the aircraft generates.
J-20 was designed upon canards due to the solutions its creators wanted to achieve based on the combination of solutions and requirements they had.


Will the J-20 be superior to F-22? everything depends upon the speeds and altitudes it will operate and the tactics it uses.


A Canard is not better than a tailplane and viceversa, using a canard is not less practical than using tailplanes.

Lockheed, Chengdu, Sukhoi based their fighters upon a set of requierements which are different in some way to each other, and their fighters will use different tactics to be on top.


At the end of the day each design is more optimised for a speed and altitude range.

Agree on everything within that quoted box. Everything beyond that, no. And turn rates are also related to the amount of drag and speed of the aircraft.

And if tailplanes are artwork, are you saying every tailplane on every aircraft in history, from commercial 747 to sopwith camels to raptors, incorporate them for the sake of art just merely because it looks better? and the designers are stupid enough to waste money for an extra giant piece of metal so it fits their unknown Freudian fetish of giant metal pieces? do you remember there's something called the rudder as well?

i can't believe what i'm reading.

should i sign you up for aviation101, or kid's books on how planes work? you know, the basics, just in case you need some touch-ups on concepts

 

[MiG-29]

Re: J-20 The New Generation Fighter Thread IV

Agree on everything within that quoted box. Everything beyond that, no. And turn rates are also related to the amount of drag and speed of the aircraft.

And if tailplanes are artwork, are you saying every tailplane on every aircraft in history, from commercial 747 to sopwith camels to raptors, incorporate them for the sake of art just merely because it looks better? and the designers are stupid enough to waste money for an extra giant piece of metal so it fits their unknown Freudian fetish of giant metal pieces? do you remember there's something called the rudder as well?

i can't believe what i'm reading.

should i sign you up for aviation101, or kid's books on how planes work? you know, the basics, just in case you need some touch-ups on concepts

Look, the concept of art, is said do you know by who? one the Russian designer of Su-27, Oleg Samolovich why he said that?

watch minute 22 to 25

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Simply because when you chose a solution you chose advantages as well as disadvantages.

By picking a solution you are picking also some problems

Most Airliners like B-747 or Tu-204 more or less have the same requirements so they have the same solutions so they chose tailplane as a solution.

I know here we have plenty of J-20 fans so every one thinks Canards are better than tailplanes or the T-50 integral configuration is an old concept taken from Flanker and then you call it obsolete.

However as Oleg Samolovich says is both art and science.


All these design bureaux are betting the combination of solutions and with the right tactics they have the best design.


The concept of art is used because no solution is the perfect one.

Canards are draggy at level flight more than tailplanes, if you do believe it or not i do not care, but the same we can say about the podded configuration of T-50, it is more draggy than the side by side engine arrangement of F-22 or J-20.


So why they use those solutions?
Simply because each design trade offs something and tries to fix its shortcomings with other combination of solutions.

Yes T-50 is more draggy with podded nacelles but has a less volume than with S ducts and lift coming from the fuselage, plus the forebody nose of T-50 is much smaller than the huge J-20 or F-22 cross sections.

The designers J-20 and F-22 consider S ducts and boxy fuselages are worthed if stealth is obtained without radars blockers and it creates less problems for stealth.

And same can be applied to F-35 why create a jet with higher drag than F-16?
just for the sake of stealth? but if Europe has a radar capable of detecting F-35?

Then is not worthed as many in Europe are considering and up to a degree Lockheed and Sukhoi and even did relaxing stealth requieremts on F-35, T-50 and J-20 .


And you can see it in the canards of J-20 and its ventral fins and round nozzles


For such a reason air design is an art and a high bet, that only the right tactics can sometimes fix

 

[latenlazy]

Re: J-20 The New Generation Fighter Thread IV

Look, the concept of art, is said do you know by who? one the Russian designer of Su-27, Oleg Samolovich why he said that?

watch minute 22 to 25

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Simply because when you chose a solution you chose advantages as well as disadvantages.

By picking a solution you are picking also some problems

Most Airliners like B-747 or Tu-204 more or less have the same requirements so they have the same solutions so they chose tailplane as a solution.

I know here we have plenty of J-20 fans so every one thinks Canards are better than tailplanes or the T-50 integral configuration is an old concept taken from Flanker and then you call it obsolete.

However as Oleg Samolovich says is both art and science.


All these design bureaux are betting the combination of solutions and with the right tactics they have the best design.


The concept of art is used because no solution is the perfect one.

Canards are draggy at level flight more than tailplanes, if you do believe it or not i do not care, but the same we can say about the podded configuration of T-50, it is more draggy than the side by side engine arrangement of F-22 or J-20.


So why they use those solutions?
Simply because each design trade offs something and tries to fix its shortcomings with other combination of solutions.

Yes T-50 is more draggy with podded nacelles but has a less volume than with S ducts and lift coming from the fuselage, plus the forebody nose of T-50 is much smaller than the huge J-20 or F-22 cross sections.

The designers J-20 and F-22 consider S ducts and boxy fuselages are worthed if stealth is obtained without radars blockers and it creates less problems for stealth.

And same can be applied to F-35 why create a jet with higher drag than F-16?
just for the sake of stealth? but if Europe has a radar capable of detecting F-35?

Then is not worthed as many in Europe are considering and up to a degree Lockheed and Sukhoi and even did relaxing stealth requieremts on F-35, T-50 and J-20 .


And you can see it in the canards of J-20 and its ventral fins and round nozzles


For such a reason air design is an art and a high bet, that only the right tactics can sometimes fix

I think you're operating under a premise of false equivalency. Just because there are trade-offs does not mean one solution cannot be better than the other on the net whole. You keep redirecting towards this idea of nothing's perfect, but I don't think anyone really cares about whether a solution is perfect or not. What people are fixated on is the end comparison. There is such a thing as better and worse, even in "art".

 

[latenlazy]

Re: J-20 The New Generation Fighter Thread IV

Hehe, this is a rarity: Regarding the "artwork" concept, even before reading his further explanation, I seem to understand or appreciate what Mig-29 (or that Russian) means better than you guys here, . And therefore I had no problem with it.

It's more an art than science only in that not only whatever choices you may make will mean compromises one way or the other, but also sometimes the different compromises due to different choices made will give an overall equal set of costs and benefits.

I agree with the sentiment, but it just isn't relevant at all. It's a sidetrack to the primary point, which is, all things considered, what exactly are we looking at. Is the J-20 a platform that has comparatively more lift or not? Does it have trade offs or not? If it does what are those trade offs? If it doesn't, why not?

Mig-29 constantly references the entire "all planes have trade offs", but there's hardly a discussion of what those trade offs are. He asserts something very general and when someone makes an argument for why that's wrong, instead of addressing those points he simply resorts to the "all planes have trade offs" argument as if everyone else doesn't know that. The issue here is that people dispute him on the specifics, and instead of engaging on the critique of the specific, he merely tries to wall off with general statements.

 

[MiG-29]

Re: J-20 The New Generation Fighter Thread IV

Classic Avoidance, its called you got me, but I can't admit the truth, 1. Eurofighters did not eat the Raptor, the Germans suggested that, the Raptor boys called "foul", Col. Moga is to classy to nail em. 2. T-50 is never gonna be a fifth gen, it will be agile, it may even be fast, it will "maybe" supercruise, It "ain't" stealthy, it too will have "excuses", but then I guess thats fitting! With the cancelation of F-22 production, the big rush for fifth gens is now a marathon, not a 100 meter dash!

Sorry again you are wrong, in fact since i know you do not believe me the canard does indeed create more drag than the tailplane at level flight and how it is configuration related i let you read these two articles


read page 33

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read figure 6 and 7 explanations

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if you still can not understand it well i won`t try you to convince you physics are like that you like them or not

But the last article if you understand it will explain you why F-22 used tailplanes specially if you read the explanation for figure 9.


About F-22 being beat by Eurofighter

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If you believe it or not it won`t change what happened

About Pakfa

read

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Saddly airforcebrat, you need to read more, aircraft are optimised and the tactics will always try to cover for some shortcomings

If you do not believe it watch these videos

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or read this

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Any good assesment of J-20 needs these basics to understand the J-20 potential capabilities.


As the MiG-23 article and F-35 article explains

Regards enjoy a good reading

 

[MiG-29]

Re: J-20 The New Generation Fighter Thread IV

I think you're operating under a premise of false equivalency. Just because there are trade-offs does not mean one solution cannot be better than the other on the net whole. You keep redirecting towards this idea of nothing's perfect, but I don't think anyone really cares about whether a solution is perfect or not. What people are fixated on is the end comparison. There is such a thing as better and worse, even in "art".

I am not operating upon false premises, you simply do not understand that jets do not have a single configuration.

We do not know how many configurations were studied for J-20, but at least the americans have given us a good assesment of the F-35

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If you read this articel specially page 33 you will see all configurations do have advantages and dis-advantages, all have compromises, tactics are developed to ensure a fighter can use its strengths in a way it will avoid its weaknesses and use all its strengths and these are a direct result of what elements were taken and what advantages and disadvantages the design it has

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watch this because this still aplies to modern aircraft like F-22 and J-20

 

[latenlazy]

Re: J-20 The New Generation Fighter Thread IV

Well, I hate to be a pessimist, but we have BHO, the Russians have Vlad, I'm just prayin that you guys end up with someone like these two in order to maintain parity? I love and trust you guys, really I do, but big GUV doesn't like the kind of freedom we all enjoy, and I know you guys are enjoying your freedom, because I sure love mine! Back on Topic, whats the name of the airfield where the two J-20s are now undergoing T an E? I'm sure I'm getting it wrong, any way I'm thinking its likely that Chengdu will roll out 2003 after the Chinese New Year, I'm hoping we see the WS-15, but thats prolly a long shot?

Yanliang is the city. CFTE (China Flight Test Establishment) is the facility.

I am not operating upon false premises, you simply do not understand that jets do not have a single configuration.

We do not know how many configurations were studied for J-20, but at least the americans have given us a good assesment of the F-35

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If you read this articel specially page 33 you will see all configurations do have advantages and dis-advantages, all have compromises, tactics are developed to ensure a fighter can use its strengths in a way it will avoid its weaknesses and use all its strengths and these are a direct result of what elements were taken and what advantages and disadvantages the design it has

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watch this because this still aplies to modern aircraft like F-22 and J-20

Perhaps it is not I who doesn't understand that jets have different configurations, but you who do not understand that different configuration do not always mean net parity of results (I need to emphasize the word net here). The point I'm trying to make isn't that trade offs don't exist in flight design, but that despite those trade offs sometimes one design will still come out the aerodynamic superior on the net whole.

 

[Engineer]

Re: J-20 The New Generation Fighter Thread IV

Sorry again you are wrong, in fact since i know you do not believe me the canard does indeed create more drag than the tailplane at level flight and how it is configuration related i let you read these two articles


read page 33

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read figure 6 and 7 explanations

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if you still can not understand it well i won`t try you to convince you physics are like that you like them or not

But the last article if you understand it will explain you why F-22 used tailplanes specially if you read the explanation for figure 9.

Again, it is you who are wrong. Page 33 within that

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showed nothing of the sort in your claims. In fact, canard and tailplane configurations have the identical scores for all but one category of drag. For supersonic trim drag, the two configurations also have the same scores with unstability.

Tags: canard vs. tailplane; drag comparison; sinodefenceforum; imgageshack; imgur;

As for Figures 6 and 7 in

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, the trim configuration used in that simulation is non-optimal for a canard configuration. Specifically, canard configuration is naturally unstable, while the simulation had a constrain most likely in stable or with positive static margin. This is explained in the text and corrected with another comparison.

The asymmetry between canard and aft-tail designs disappears when the trim constraint is relaxed. Results from the multiple surface optimization program without a trim constraint are plotted in figure 8. (Note that imposing no trim constraint is equivalent to setting the static margin to an optimum value.) The symmetry of figure 8 is expected from consideration of Munk's stagger theorem. Since the induced drag of a system of lifting surfaces is independent of their streamwise position (as of course are wing and tail structural weight and parasite drag) it follows that, for minimum drag, the load carried by a canard surface will be equal to that carried by an aft-tail of equal size. One parameter that is not independent of the streamwise position of wing and tail is the neutral point. Thus, this symmetry only applies when the static margin is not constrained.

The text go on and showed that using optimal static margin, there is no difference in drag of both configurations.

Figure 9 shows the static margin at which the airplane trims with optimal load distributions. In order to achieve the drag values shown in figure 8, most canard designs must be statically unstable while most aft-tail designs require small positive static margins.

Tags: Design and Analysis of Optimally-Loaded Lifting Systems; Imgur; canard vs. tailplane; drag comparison; optimal static margin;
You are intentionally trying to mislead via

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.

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not quoted in your post has the same conclusion on drag, saying:

For unstable aircraft, canard designs may have a C[sub]L[sub]max[/sub][/sub] and/or drag advantage.

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citing the advantages of canard over tailplane in the context of lift-induced drag:

Because the canard generates upward lift, unlike with a tail plane which produces downward or negative lift, there is a reduction in the lift required from the main wing. This reduction in the required lift generation by the wing to over come the weight of the aircraft a reduction in lift-induced drag by the wing. As well as removal of the negative lift generated by the tailplane and the associated lift-induced drag. Overall drag and lift requirements of the aircraft is reduced.

Engineers at Chengdu chose canard configuration for a very obvious reason, and that is the configuration allows for the least amount of compromises. The only compromise is the dramatically increased complexity as well as risks associated with aerodynamics and control. Let's face it, you have an axe to grind with the canard configuration because you have an axe to grind with the J-20. If PAKFA were to use canard configuration, you would praise the configuration to no end.