Aerodynamics thread

[Air Force Brat]

You have read this argument of mine before, but I will write this again for the benefit of others. US experimented with thrust-vectoring on F-15, F-16 and F-18, but never decide to equip those aircraft in service with such technology. So, the Russian's emphasis with thrust-vectoring should be seen as nothing more than a marketing gimmick, especially when the Russians have a significant interest in making their older planes more sell-able.

Now, I am not saying thrust-vectoring has no purpose whatsoever. Thrust-vectoring can turn un-flyable situations into flyable ones. However, we should appreciate why those situations are un-flyable to begin with, and realize how it isn't a good idea to put the aircraft into those situations as a result. Indeed, exercises have shown that use of thrust-vectoring can led to a more superior aircraft being defeated.

So when someone tells me how much better an aircraft is with thrust-vectoring alone, that is no different than telling me that the same aircraft is aerodynamically complete garbage.

So moving forward to the J-20, do you have any "observations", gut feelings etc how or why 2011 would compare with 2001-2002, regarding the specific modifications to the new prototype? I realize it is a process of "refinement", but the smaller inlets/mods to LEVCONS? I guess I would ask, is what strikes you as you look at 2011 in relation to the early birds??

 

[F-15]

The issue of contention isn't whether the center-of-lift shifts. The issue is whether LEVCON can be equivalent to canard in providing pitch authority, on top of providing vortex lift. As you have correctly pointed out, LEVCON is mainly for lift enhancement, not for pitch control. It is also plain clear from a simple law of physics that LEVCON with much shorter moment arm cannot compete with canard. Therefore, LEVCON does less than a canard, and cannot be said to be better. For someone to argue otherwise is like saying flap is better than canard, and I'm sure you will agree such argument is absurd.

Without experimental data is easy to opine, the data says that the deflections of LEVCON, slats, and elevon change the pitching moment

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Any increment in pitching moment means Levcons change pitch thus they are pitch control devices
guess what the aircraft is doing

 

[F-15]

Thanks again Eng, and I wish I were able to remain as kool as you brother when explaining this, you do have one convert here, as I loved the conventional lay-out, and failed to recognize the many benefits of the canard, and why they were so important to the J-20 until you layed it all out for me, I do appreciate your patience, and you are quite an outstanding teacher, I wish you could go to Oshkosh and observe all the amateur experimental aircraft, as I would love to hear your perspective on many of these aircraft.

A cessna never will tell you what is a LEVCON only this F-106 will tell you the answer if you grasp the basic principle
[video=youtube;tLYe6qAxaM4]https://www.youtube.com/watch?v=tLYe6qAxaM4[/video]
read and use your imagination and intelligence

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[F-15]

You have read this argument of mine before, but I will write this again for the benefit of others. US experimented with thrust-vectoring on F-15, F-16 and F-18, but never decide to equip those aircraft in service with such technology. So, the Russian's emphasis with thrust-vectoring should be seen as nothing more than a marketing gimmick, especially when the Russians have a significant interest in making their older planes more sell-able.

Now, I am not saying thrust-vectoring has no purpose whatsoever. Thrust-vectoring can turn un-flyable situations into flyable ones. However, we should appreciate why those situations are un-flyable to begin with, and realize how it isn't a good idea to put the aircraft into those situations as a result. Indeed, exercises have shown that use of thrust-vectoring can led to a more superior aircraft being defeated.

So when someone tells me how much better an aircraft is with thrust-vectoring alone, that is no different than telling me that the same aircraft is aerodynamically complete garbage.

Levcons Increase STR Sustained turn rates and reduces landing speeds thus the pitch moment increment change translates into higher lift thus they are working like Canards do

See evidence in the following link

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Too much Blah blah blah, the only people that says Thrust vectoring is not good is the people that do not have it in their aircraft, if you have it you use it, thus F-22 has it.

 

[jobjed]

Without experimental data is easy to opine, the data says that the deflections of LEVCON, slats, and elevon change the pitching moment

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Any increment in pitching moment means Levcons change pitch thus they are pitch control devices

Educate yourself on the difference between qualitative and quantitative data. 'Engineer' knows very well that LEVCONs incurs changes in 'pitching moment'. The contention arises as to the the quantity of that moment.

The issue is whether LEVCONs can be equivalent to canards in providing pitch authority

Your source merely confirms qualitatively a fact on which we already have a consensus - that LEVCONs induce an "incremental change in aerodynamic coefficients" - and doesn't assist in settling the dispute as to the quantity; it's an irrelevant addition to this discussion.

Levcons Increase STR Sustained turn rates and reduces landing speeds thus the pitch moment increment change translates into higher lift thus they are working like Canards do

See evidence in the following link

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Too much Blah blah blah, the only people that says Thrust vectoring is not good is the people that do not have it in their aircraft, if you have it you use it, thus F-22 has it.

To quote your vaulted source,

The Levcon is initially planned... for the low landing speed capability and other cruise performance.

Does "cruise performance" sound like 'aerial acrobatics' to you? Just the alliteration of the latter would tell you otherwise, never mind going into the physics. Again, as other members have reiterated countless times, no one is denying that LEVCONs influences total lift. 'Engineer' had already clarified that "LEVCON is mainly for lift enhancement, not for pitch control" whereas the Chengdu birds' canards are very much for "pitch control". You can be pedantic if you want and argue that "lift enhancements" are technically undramatic forms of "pitch control", but then I'll just stop replying to you.

Neither of us have access to fair, valid and controlled test results that compare pitch authority of LEVCONs vs canards on an unbiased fuselage nor are we professionals with qualifications in fighter aircraft design - so I'll just analogise with a concept with which we're both familiar. If we represent pitch as torque on an aircraft's centre-of-lift, then the further away the force is applied on the CoL, the higher the torque and 'pitching moment'. Canards are generally further away from the CoL as they are separated from the wing while LEVCONs are, by definition, attached to the wing's leading edge. Hence, assuming ceteris paribus, canards provide more torque/pitching moment than LEVCONs, making for a more responsive and manoeuvrable airframe. I invite you to find evidence that show the contrary.

 

[F-15]

, but then I'll just stop replying to you.

.

Please do it, because increments in LIFT translate into increased STR in few words not only it rolls better but also turns better, that is what the paper says and by the way, on LCA, (that paper talks about it) the LEVCON was used for only the naval version that is too small to be fitted with canards thus they used the LEVCONs for such purpose and the need is for STOL.

It is easy to see in this image the LCA has LEVCONs due to its small size, thus LEVCONs are much more practical, and that is what the paper talks but better think i am pedantic and stop replying me because that paper is from DRDO, the Indian equivalent of NASA

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[latenlazy]

Please do it, because increments in LIFT translate into increased STR in few words not only it rolls better but also turns better, that is what the paper says and by the way, on LCA, (that paper talks about it) the LEVCON was used for only the naval version that is too small to be fitted with a canard thus they used the LEVCON for such purpose and the need is for STOL.

It is easy to see in this image the LCA has a LEVCON due to its small size, thus a LEVCON is much more practical, and that is what the paper talks but better think i am pedantic and stop replying me because that paper is from DRDO, the Indian equivalent of NASA

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Better compared to what?

By your logic, even slats are pitching devices. I don't think that is wrong btw, but if that's all you're saying about LEVCONs, then it's hardly a significant point. If your interest is in arguing that LEVCONs are BETTER pitching devices than something else though, unless you can come up with hard data, simply insisting it doesn't make it so.

 

[F-15]

Better compared to what?

By your logic, even slats are pitching devices. I don't think that is wrong btw, but if that's all you're saying about LEVCONs, then it's hardly a significant point. If your interest is in arguing that LEVCONs are BETTER pitching devices than something else though, unless you can come up with hard data, simply insisting it doesn't make it so.

Read what is pitch moment first, then watch the Pakfa video of page 35 of this thread then we talk

 

[Engineer]

Without experimental data is easy to opine, the data says that the deflections of LEVCON, slats, and elevon change the pitching moment

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Any increment in pitching moment means Levcons change pitch thus they are pitch control devices
guess what the aircraft is doing

The question is, does LEVCON provide superior performance in comparison to canard? You do not have experimental data to give an affirmative answer, it is that simple.

On the other hand, we already have experimental data such as

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and

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confirming canard can provide superior performance in pitch authority in addition to increasing lift compared to a traditional configuration. Again, better means doing more, where as all you can do is to show LEVCON does portion of what canard does.

 

[Engineer]

Levcons Increase STR Sustained turn rates and reduces landing speeds thus the pitch moment increment change translates into higher lift thus they are working like Canards do

See evidence in the following link

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The paper says that LEVCON increases sustained turn rate, which the paper explicitly links to lift enhancement. The rest of your statement about how LEVCON can cause change in pitch moment like canard can is entirely your own creation.

Too much Blah blah blah, the only people that says Thrust vectoring is not good is the people that do not have it in their aircraft, if you have it you use it, thus F-22 has it.

Really?

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. Moreover, the US tested thrust-vectoring on F-15, F-16 and F-18 and none of them gets retrofitted with thrust-vectoring.

Also, if thrust-vectoring is so good as you think, why bother with moving aerodynamic surfaces such as LEVCON? And if LEVCON is so good, then why need thurst-vectoring on top of the additional tailplane? So you see, your own arguments destroy your own arguments. It makes more sense that neither is doing a good enough job, which is why they are used together.