LCA Tejas: News and Discussions

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nachiket
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Re: LCA Tejas: News and Discussions

Postby nachiket » 02 Sep 2016 01:35

For a 1000 fighter fleet, only 100-odd should heavy fighters, 300 medium and 600 light.

Well that kind of went for a toss already with the 270 MKI fleet without being anywhere close to 1000 fighters.

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Re: LCA Tejas: News and Discussions

Postby malushahi » 02 Sep 2016 03:07

if it makes you feel any better, the mki fleet is around 100 anyways (accounting for availability). it is the lights and mediums that are the real concern.

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Re: LCA Tejas: News and Discussions

Postby Neshant » 04 Sep 2016 13:12

An explanation for the laymen out there, not so much all you experts..


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Re: LCA Tejas: News and Discussions

Postby Indranil » 06 Sep 2016 22:59

Image

This is very interesting. JayS, we thought this is the most unlikely option :D . Anyways, this is during takeoff, not landing.

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Re: LCA Tejas: News and Discussions

Postby JayS » 06 Sep 2016 23:37

^^ Even before reading your line below I instantly noticed that one particular thing. It is indeed interesting. Once a guy who was working on Delta wings in IITK, gave a an explanation how this particular config can help in LCA. I never really understood his explanation though.

Checked your comment on FB. After a second look, I notice the slats are deflected slightly upward or are at least upright rather than expected downward shift. There is hardly any flaperon deflection. Sure, its clean config TO so wings are not pushed to their limits to produce lot of lift and we will surely see more camber for MTOW take off. At least I think so.
Last edited by JayS on 07 Sep 2016 00:14, edited 1 time in total.

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Re: LCA Tejas: News and Discussions

Postby Indranil » 06 Sep 2016 23:54

Would you like to discuss it here. There are a few things:
1. That vortex (direction) at the LE of the LEVCON is very interesting.
2. No Slats either. This looks like close to 15 degree AoA. The vortex burst must have crept very close to the TE, if not already over it. I am not sure if they are using the pitch up moment due to that, added to the pitch up moment due to LEVCON.
3. But overall this config (in my mind) would decrease lift and increase drag? How is this useful for take off?

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Re: LCA Tejas: News and Discussions

Postby JayS » 07 Sep 2016 00:26

Check out this video from BIAS-2016.
https://www.youtube.com/watch?v=fN-jV2phTPA
From 0.47 onwards we can see slat movements at TO and some other manoeuvres, later. LCA deploys slats in conventional way while taking off or pulling turns. This particular config in the NLCA picture is very unusal and counter-intuitive. I am thinking could it be just a test config that they are trying out and not a usual TO config?? The first NLCA TO from INS Hansa ramp has no deflections of slats/LEVCON whatsoever. So at clean configuration NLCA can take off without the help of LE devices for sure.

To me also it looks like it will decrease the overall lift. Surely NLCA cannot use that one for MTOW. But I am still digesting the picture. That was very unepected.

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Re: LCA Tejas: News and Discussions

Postby Indranil » 07 Sep 2016 00:36

Yeah. This is what I expected.

Image

But thanks for the link to that video again. That was such an inspired and energetic display by LCA.

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Re: LCA Tejas: News and Discussions

Postby JayS » 07 Sep 2016 00:43

Remember the paper I shared with you recently from 1994?? Here is the conclusion from that paper that they drew for LEVCON deflection.

https://drive.google.com/file/d/0B9ijXlsoNPWza1l6eV9OMnpxOVk/view?usp=sharing

There isn't much change in C_L but substantial change in C_D with LEVCON deflection.


BTW what peculiarity you find with that tip vortex in that picture??

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Re: LCA Tejas: News and Discussions

Postby SaiK » 07 Sep 2016 00:56

Q: Is that the normal landing practice with slats/levcon up?

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Re: LCA Tejas: News and Discussions

Postby JayS » 07 Sep 2016 00:59

Image

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Re: LCA Tejas: News and Discussions

Postby SaiK » 07 Sep 2016 01:05

never mind.. saw your text later. thx

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Re: LCA Tejas: News and Discussions

Postby Indranil » 07 Sep 2016 01:21

JayS wrote:Remember the paper I shared with you recently from 1994?? Here is the conclusion from that paper that they drew for LEVCON deflection.

https://drive.google.com/file/d/0B9ijXlsoNPWza1l6eV9OMnpxOVk/view?usp=sharing

There isn't much change in C_L but substantial change in C_D with LEVCON deflection.

That was for downward deflection. When the LEVCON was deflected upwards, I seem to have read somewhere the C_D went up.

JayS wrote:BTW what peculiarity you find with that tip vortex in that picture??

I did not expect the axis of the vortex to be as attached to the top surface as it is. I thought the flow would be more like that behind a spoiler. Also expected the axis to be more spanwise.

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Re: LCA Tejas: News and Discussions

Postby JayS » 07 Sep 2016 02:27

@agupta - What you are saying is correct but not the primary reason for LEVCON.

@IR
Change in C_L and C_D in both directions - i meant by the slop of the C_L or C_D vs Levcon angle curve . So downward deflection would increase C_L slightly but decrease C_D substantially. Upward deflection would decrease C_L slight but increase drag substantially. That is the effect on C_L is less prominent than the effect on C_D.

Actually for upward deflected LEVCON or a LE flap in general you get an attached LE vortex seating right on the flap/Levcon. I guess you were expecting somethink like what is seen with LERX as in F18 for example. Its similar to LE slats, only in slats the vortex is ahead of the top surface while for upward deflected flap, its behind the top surface.

Read following comment and see if you can make sense out of it. I understand it but not quite. Theres unsteady Aerodynamic stuff coming in here which I am not very sure is applicable for LCA as far as Landing/TO is concerned, but will be applicable for PAK-FA during manoeuvre.

LEVCON as such serves three major issues.
These being:
1. "Strong LE Vortex generation when it is deflected down"
2. "Attachment of Strong LE vortex when it is deflected up" and
3. "Creating a air-flow pattern in such a manner that required mass flow rate is maintained at engine inlet, when LEVCON is actually deflected upwards." This third application is not directly related to improve aerodynamic efficiency of wing but it rather helps engine to delay flame-out stage or we can say that it further delays the stall envelope of ENGINE only.

regarding 2nd point about attachment of LE vortex, if we consider example of flying creatures fluttering wings with high frequency (eg. bats. humming bird, dragon fly). They create additional lift by delaying separation of vortex which is generated at LE. Although for them the main purpose is to initiate hovering but when same concept is applied to fast moving air-vehicles, the application changes from hovering to additional lift generation. This concept is well established in case of flock of birds and even in formation flying by fighter jets. LEVCONs are mainly deployed when sudden change of AOA (particularly pitching up) is required (eg. dog fights, evasive maneuvers against SAMs).
Better understanding of difference in Pt. 1 and Pt. 2 can be done by actually comparing the change in aerodynamics which happens in both the cases.
But before going for comparison one major role of LEVCONs should be kept in mind and that how they actually work. Deployment of LEVCON is done to maintain smooth airflow over the wing.
LEVCON Deflected Down = Strong Vortex Generation at LE.
but this vortex is pushed back due to momentum force of air and gradually dies down as it rolls from LE to TE. The main application is during landings at short-strips which require high AOA. High AOA is necessary to produce enough drag to slow down the rolling distance once airplane touches down. But at the same time we do not want to undershoot the runway so we require just enough lift to actually touchdown at required point. This "just enough lift" is generated by downward deflection of LEVCON so the strong and smooth airflow is maintained over the wing hence increases the local airflow velocity on the wings without actually increasing the aircraft speed.

LEVCON Deflected Up = Strong Vortex Attachment at LE.
When LEVCON is deflected up a strong vortex is attached on LE. This is generally done when aircraft rapidly pitches up (eg. performing Pugachev's Cobra Maneuver). Now, here also momentum of flow should push down the vortex but going to the basics of force vectors, imagine wing at high AOA and this wing is succeeded the LEVCON so whatever momentum of air is there to push the vortex at LEVCON, it rolls back and hits the main wing. By the time it reaches the main wing, the momentum force (with force vector pointing towards TE and parallel to wing) gradually loses its strength resulting in attachment of vortex at LE for longer period.
Upward deflection also forces the packet of air deflecting down (downwash) and hence providing additional air mass flow rate at engine inlet when aircraft is at high AOA. If engine experiences more than required airflow, the computer sensors activates air-bleed-out-ports so as to maintain stoichiometric ratio in engine.

Closing comment is that it is important to calculate LEVCON geometry, size, shape and deflection range with utmost precision as if it over or under perform during maneuver, it can lead to crash landings (when deflected down), putting aircraft in spin (when deflected up) and/or engine flame out (when deflected up)


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Re: LCA Tejas: News and Discussions

Postby Indranil » 07 Sep 2016 02:59

Thank you.

This is new to me. Somehow the upward deflection of the LEVCONs works very differently from what I had thought in my mind (opposite of LEVCON deflected down). This absolutely fascinating. A little caught up till tomorrow night. First thing to dig into day-after-tomorrow.

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Re: LCA Tejas: News and Discussions

Postby vina » 07 Sep 2016 08:33

indranilroy wrote:This is very interesting. JayS, we thought this is the most unlikely option :D . Anyways, this is during takeoff, not landing.


I think that what is happening here, is that it is generating vortex lift (which happens at high angle of attack in delta wings), by deflecting the LEVCON (which is in reality a chine that can moved), sort of like the pictures in this Vortex Lift link, with a couple of pics from ONERA (the French aero R&D agency, they are really good) and in particular a chine with a diamond wing.

My guess is , they by putting up the levcon/chine up in the airflow , they are creating the vortex and in mimicking what would normally happen at a much higher angle of attack , where the Delta transitions into vortex lift. That probably explains why the slats and flap positions remain as in normal level flight as the effective camber does not need to be increased to generate more lift during take off.

Yawn, the Dhoti wallahs have fiddled around and played around and found a way to produce higher lift in Deltas than usual in the lower angles of attack.

Dayuum. Pah, do you know how that this is the country with the largest number of people without toilets? Why do you guys want to go around waving things this way and that in the air . Close down, all this experiementation, use that money to build toilets and of course go and buy the Gripen or F16 or Mig 29K or Rafale (by paying a lot more money) which you can only adore/worship and not fool around with by putting your filthy paws on it.

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Re: LCA Tejas: News and Discussions

Postby Indranil » 07 Sep 2016 22:33

vina wrote:
indranilroy wrote:This is very interesting. JayS, we thought this is the most unlikely option :D . Anyways, this is during takeoff, not landing.


I think that what is happening here, is that it is generating vortex lift (which happens at high angle of attack in delta wings), by deflecting the LEVCON (which is in reality a chine that can moved), sort of like the pictures in this Vortex Lift link, with a couple of pics from ONERA (the French aero R&D agency, they are really good) and in particular a chine with a diamond wing.

My guess is , they by putting up the levcon/chine up in the airflow , they are creating the vortex and in mimicking what would normally happen at a much higher angle of attack , where the Delta transitions into vortex lift. That probably explains why the slats and flap positions remain as in normal level flight as the effective camber does not need to be increased to generate more lift during take off.

I am pretty sure that they are using vortex lift. The LEVON is about 40 degrees AoA there (10 degrees for take off and 30 degrees wrt to the wing) But it is not just vortex lift. The vortex is affecting the airflow over the wing, probably the way that JayS is suggesting, but I have to learn and think more about it. In a way, it should be similar to the interaction of the vortex generated by a close couple canard and the airflow over the wing. Rafale M uses its canards the same way when coming in to land.

Image

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Re: LCA Tejas: News and Discussions

Postby JayS » 08 Sep 2016 01:02

Great. Thanks for that Rafale pic. I found one vid which shows what Canard is doing during the arrested recovery for Rafale. In video below from 3.52 onwards. Check out:
https://www.youtube.com/watch?v=4mehij8v5HI

Also Naval Rafale keeps the canards horizontal while taking off while the AF Rafale deflects its canards pitch up first and then pitch down.

LEVCON and closed coupled canards do not work quite the same way.

A video clearly showing control surface deflections during TO and landing for Rafale:
https://www.youtube.com/watch?v=-qOlr9WaBBQ

BTW Indranil, check the FB page. The admin changed the description text of the pic now.

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Re: LCA Tejas: News and Discussions

Postby Indranil » 09 Sep 2016 00:15

Looks like they are flying with LEVCON in that fixed position for now. It is detrimental to TO, but favorable for approach. Question is how? And Rahulm is smiling somewhere :D

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Re: LCA Tejas: News and Discussions

Postby JayS » 09 Sep 2016 20:32

@IR

There have been statements appearing in a number of places which says "LEVCON on NLCA is for reducing the landing speed of NLCA". If you want to reduce landing speed while keeping lift the same then you necessarily have to increase C_L somehow. Due to this I have always considered that LEVCON deflecting downwards would be helping the Landing of NLCA. Upward deflection was never comprehensible for me.

But in last few days I have been thinking something else. It started with that paper from 1994 that has a study on LEVCON, that I shared with you sometime ago. I got another latest reference making me feel confident enough in this reasoning now. The paper is in this location:

http://www.ijraset.com/fileserve.php?FID=2860

Its rather poorly written but you will love it for its contents.

So here is the thing with upward deflected LEVCONs:

LEVCON when deflected upwards increases drag drastically and reduce lift as well, resulting in a significant reduction in L/D. How does this help in landing, it helps you decelerate faster. The loss of lift I think can be compensated somewhat using TE devices and increasing the AoA to slightly higher value. You can come in fast for landing but by the time you hit the deck the speed would be much reduced. There are three aerodynamic parameters we are talking about here - Lift, Drag and Pitching moment:

1. This is indisputable that there is significant increase in drag due to +30deg LEVCON deflection. The 1994 paper (a snippet from it in figure below)
https://drive.google.com/file/d/0B9ijXlsoNPWza1l6eV9OMnpxOVk/view?usp=sharing shows it clearly. It also tells us why the downward deflection is limited to 20deg (not much increase in L/D from 20 to 30deg). The figure showing variation for aerodynamic parameters with LEVCON deflection is slightly confusing in this paper. The figure is this (right graph in the pic):
https://drive.google.com/file/d/0B9ijXlsoNPWzSmE2RmxWY01fZkk/view?usp=sharing
By matching the description to the figure, IMO they have considered downward deflection as +ve and upward as -ve.

2. Next thing is Lift - this is little fuzzy. According to this paper above, life should be increasing by a small amount. But if you see this latest 2015 paper from the link I gave, its amply clear that there is a good deal of reduction in the life when LEVCON is in +30deg position. My thinking it, ADA guys must have compensated this loss of life by increasing the elevon downward deflection for landing. I think the 1994 paper got it wrong because its based on an Euler code (and perhaps due to low quality mesh as well) which is not the best thing when it comes to vortex dominated flow. The latest simulation results are from viscous NS solver and is much more accurate. Notice how the LEVCON lifts the LE vortex above the wing surface detaching it from the wing as you go downstream. It drives the flow from apex into the main LE vortex, (exactly opposite to what down deflected LEVCON does to alleviate the pitch up issue) energizing it, and I think also delaying bursting. But since its not fully attached to wing surface life is reduced. You will find good agreement in the vortex on LEVCON that you were intrigued by (in that TO pic of NLCA from FB) and this CFD results.

3. Next thing is the change in Pitch moment Cm. Both papers agree that there will be significant +ve change in pitch moment i.e. more pitch up moment as compared to undeflected LEVCON which itself gives increased pitch up moment than the no LECVON configuration. If you are increasing deflection on elevon that will reduce the pitch up but not so much as to compensate for change in LEVCON fully. So we have a net increase in Cm. Now, in my opinion this higher Cm value allows trimming of NLCA at higher AoA for landing. So net lift can be increased again.

In summay, +30deg LEVCON should increase C_d significantly, reduce C_L significantly (but not as much change as the drag sees), and increase Cm significantly. The reduced lift can be compensated for by increasing downward deflection of Elevons and increasing thr AoA. Also the LEVCON now has effectively energized the primary LE vortex and also detached it from the wing surface near the TE of the wing (which reduces the lift), delaying burst. With this NLCA can come in for landing at at slightly higher than desirable speed but the it will decelerate much faster and the speed at which it hits the deck could be at the desirable limits.

This is the best explanation so far I could come up with based on available information.

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Re: LCA Tejas: News and Discussions

Postby JayS » 09 Sep 2016 22:14

Qusetion for Rahulm:

The pitch up and air break flutter issue you were talking about and the solution - take a look at this and tell me is that what it was or something different.

https://drive.google.com/file/d/0B9ijXlsoNPWzZTJFQjZmMGxNa1U/view?usp=sharing

As usual, answer as per your discretion.

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Re: LCA Tejas: News and Discussions

Postby Indranil » 09 Sep 2016 23:11

Jay, thank you. currently my thinking is pretty much the along the same line as yours.

However, another thing that I am also thinking about is the distribution of life on the wing. If we want to decrease the pitch-up moment, we would want the LE to not generate much lift. Now, the LEVCON has a sharp edge. When deflected 30 degree up relative to the wing which itself is flying at around 15 degree AoA, it is flying at 45 degrees of AoA. At that point, it is pretty much not generating any lift at all. You may recollect that delta wings with rounded LE typically see the cliff on the Cl/AoA curve at around 22 degrees. Wings with sharper AoA notice it faster. Therefore, the lift from the LEVCON is almost nullified.

Additionally, the strong and large votex generated by the LEVCON is probably pushing the point of reattachment on the main wing further back. Overall, the lift near the the front of the wing is being decreased and vortex bursting is being delayed increasing the lift at the back. This minimizes the pitch up moment at approach AoA. This is allowing them to have better control as they are coming down, probably even letting them flying 1-2 degrees higher AoA: i.e. more drag and more lift. The need for the airbrakes is getting nullified thanks to this increased drag. The increased lift is allowing them to have more margins or even fly 5-10 knots slower in approach.

Will reply in more detail tomorrow.

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Re: LCA Tejas: News and Discussions

Postby SaiK » 10 Sep 2016 17:10

I am getting slowly sick with this (approach and news media)
http://www.freepressjournal.in/india/in ... eal/924008

Gripen deal looks attracting since its makers, Swedish firm Saab, have proposed to set up capabilities in India to make the aircraft in India and further extend technological cooperation in developing a Mark II version of the Tejas light combat aircraft.

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Re: LCA Tejas: News and Discussions

Postby Indranil » 13 Sep 2016 00:11

JayS wrote:In summay, +30deg LEVCON should increase C_d significantly, reduce C_L significantly (but not as much change as the drag sees), and increase Cm significantly. The reduced lift can be compensated for by increasing downward deflection of Elevons and increasing thr AoA. Also the LEVCON now has effectively energized the primary LE vortex and also detached it from the wing surface near the TE of the wing (which reduces the lift), delaying burst. With this NLCA can come in for landing at at slightly higher than desirable speed but the it will decelerate much faster and the speed at which it hits the deck could be at the desirable limits.

This is the best explanation so far I could come up with based on available information.

I have to agree. This is the best explanation we have as of now. By the way, that Tubercle Levcon paper was nice. I wished they explained the results a bit more though.

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Re: LCA Tejas: News and Discussions

Postby JayS » 13 Sep 2016 01:15

^^ I am having some second thoughts with this explanation. It will essentially remain the same with some modifications. For example, despite the new reference paper we got, which shows reduction in Lift for 30deg up LEVCON, it seems that upward LEVCON is suppose to have higher lift. All other references point to that - seems 1994 ADA paper got it right after all. Increase in drag and pitch up moment remains unchanged. In one other paper I even saw a sentence saying "This increase in drag can be used in reducing speed in Landing" So I am quite confident now on this one. I need to sort out the lift thing slightly. I will keep refining the hypothesis. But right now my laptop HD has turned read-only somehow and I cant seem to be able to do much.

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Re: LCA Tejas: News and Discussions

Postby Indranil » 13 Sep 2016 01:36

I have yet to find a paper to say that the upward deflection increases overall lift at any AoA. I find the results of this latest paper most plausible. The upward deflection is lowering the overall lift, but the reduction is most at the apex/LE hence less pitch up.

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Re: LCA Tejas: News and Discussions

Postby JayS » 13 Sep 2016 02:01

Removed: Duplicate.
Last edited by JayS on 13 Sep 2016 02:12, edited 1 time in total.

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Re: LCA Tejas: News and Discussions

Postby JayS » 13 Sep 2016 02:05

One is the ADA paper from 1994 itself. For another one, look for work by D. Rao of Vigyan Inc. done for NASA - this one is experimental data - lot of it. This work gives sufficiently complete picture to understand essential behaviour of LEVCON. One patent from same person is a good summary:

https://patents.google.com/patent/US5094411A/en?inventor=Dhanvada+M.+Rao

From this patent:
The drag increase at negative deflections on the other hand can be utilized to reduce the landing speed.


The simultaneous increments of lift and drag obtained by up-deflected vortex flaps have potential for reducing the landing speed, provided a trim condition can be attained at moderately low angles of attack. Taking advantage of a longitudinally unstable configuration, trailing edge flaps can be used to balance the nose-up moment increment of negatively deflected vortex flaps to yield a high value of the trimmed lift coefficient.


Note that negative deflection here means upward deflection.
I saw this after I wrote that post last time. This gives me a good confirmation for my thinking. So I am even more confident about it now.

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Re: LCA Tejas: News and Discussions

Postby JayS » 13 Sep 2016 02:20

From FB page:

KH-2013 taking off for a regular test sortie with the new quartz radome..

Jai Hind.
#TejasOfficialArchive #Tejas_LCA #NFTC #IADN
Please share the Post only with the Tags and Write Up. Kindly do not Edit or Copy this Photo. Copyright: #ADA

Image

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Re: LCA Tejas: News and Discussions

Postby Indranil » 13 Sep 2016 03:08


It is a good find, but we should be a little careful because:
1. LCA's leading edges are not sharply beveled.
2. LCA's wings are not a true delta.
3. Fig. 7 and 8. are related to when all the LE flaps are deflected symmetrically.

However we can use the principles. I think the following lines capture the essence
This is consistent with the vortex suppression effect of positive leading edge camber. Conversely, vortex augmentation caused by the up-deflected flaps results in a lift increase at the lower angles of attack but accelerates the onset of stall due to an earlier vortex breakdown.

Actually, this is not too far away from what the Tubercle LEvcon paper was also saying. The -ve deflection increases the lift at the lower the AoA, by combining its vortex with the primary vortex of the rest of the wing. But this leads to earlier vortex breakdown.

So, basically at the lower AoA of landing and takeoff, Cl and Cd are both higher with -ve deflection. This is great for landing. But don't know about take off, I think they will go for best Cl/Cd. Most likely, they will just keep the LEVCON neutral. For higher AoA high speed maneuvers, they will use the LEVCONs/LE slats in positive deflections for best Cl/Cd at those AoA.

Other things race through the mind though. All the physical components are there. But the FBW is yet to use them to there full potential:
1. May be the LEVCON used to increase both ITR (-ve deflection) and STR (+ve deflection) of LCA.
2. Clearly the LE slats can also be use to augment control at higher AoA, thus the AoA-limit of the FBW can be increased even higher.

This is why we need to have our own programs, and not spend 8B on 36 airplanes, which by the way will at best start coming in from 2019 :shock:

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Re: LCA Tejas: News and Discussions

Postby JayS » 13 Sep 2016 04:13

indranilroy wrote:It is a good find, but we should be a little careful because:
1. LCA's leading edges are not sharply beveled.
2. LCA's wings are not a true delta.
3. Fig. 7 and 8. are related to when all the LE flaps are deflected symmetrically.


1. LEVCON have sharp LE. I always wondered why LEVCONs in NLCA have sharp edges (that is rather odd), perhaps for this reason.
2. Doesn't matter. The physics doesn't change drastically in this regime of angles.
3. Of coarse LEVCONs will always be deflected symmetrically in NLCA. But this patent tries to use it for roll etc. So he has that distinction. Check his other work, you will find more NLCA LEVCON type configs to.

The rest of the wing LE does not matter a great deal here. Whether you have a rounded edge or sharp one, only will change the AoA at which vortex sheet will separate and the location of separation line. We can neglect these things for this particular study, IMO.

I do not see any reason why these results should not be valid for NLCA without much tempering. I have thought about various things including wing sweeps, Mach numbers, Re numbers, AoA ranges etc. And we have enough cross validation from multiple sources to see that all of these results are coherent.

indranilroy wrote:However we can use the principles. I think the following lines capture the essence
This is consistent with the vortex suppression effect of positive leading edge camber. Conversely, vortex augmentation caused by the up-deflected flaps results in a lift increase at the lower angles of attack but accelerates the onset of stall due to an earlier vortex breakdown.


That means it shifts the Cl vs AoA curve either towards left or towards right depending on +ve or -ve deflection i.e. change effective AoA of the wing.

indranilroy wrote:Actually, this is not too far away from what the Tubercle LEvcon paper was also saying. The -ve deflection increases the lift at the lower the AoA, by combining its vortex with the primary vortex of the rest of the wing. But this leads to earlier vortex breakdown.


Sadly the paper has no data on C_l values for Levcon deflection, only Cm values. Because the whole point of Tubercle LEVCON is to reduce the pitch up effect of LEVCON and delay the stall slightly or make it smooth. From the Cp plots it gives an impression that there is a good deal of reduction in lift if you compare 0deg vs 30deg LEVCON deflection. So I was confused. It looks like the post processing is not consistent (color scale) or something is amiss there.
indranilroy wrote:So, basically at the lower AoA of landing and takeoff, Cl and Cd are both higher with -ve deflection. This is great for landing. But don't know about take off, I think they will go for best Cl/Cd. Most likely, they will just keep the LEVCON neutral. For higher AoA high speed maneuvers, they will use the LEVCONs/LE slats in positive deflections for best Cl/Cd at those AoA.

Agreed, For TO, neutral position makes most sense.
indranilroy wrote:Other things race through the mind though. All the physical components are there. But the FBW is yet to use them to there full potential:
1. May be the LEVCON used to increase both ITR (-ve deflection) and STR (+ve deflection) of LCA.
2. Clearly the LE slats can also be use to augment control at higher AoA, thus the AoA-limit of the FBW can be increased even higher.

This is why we need to have our own programs, and not spend 8B on 36 airplanes, which by the way will at best start coming in from 2019 :shock:


1. Possible. Need to fly and see how much gain is there. Also there will be unsteady aerodynamics coming into picture, as the LEVCON turned up at turn initiation and rapidly turned down to maintain a steady turn.
2. Main problem they have is yaw control at higher AoA, I dont know how much slats will be useful. As such slats too small in size, are only used for small gain in thrust (reverse drag - this reduces wing lift slightly) and to direct flow over the wing LE more smoothly. I don't think they can provide enough control forces. But no harm in trying,

Can't agree more on having multiple parallel programs for RnD to pave way for future. One reason why Unkil is so much more ahead of all is precisely this reason. I am looking through some engine programs from 1970s and 80s and the sheer magnitude of work done on science projects is mind blowing. Our people are smart and frugal. Just give them few billion $$ and some time. At times I just wish for another nuclear test which will put lots of sanctions on us. Clearly we can't refrain ourselves from importing.

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Re: LCA Tejas: News and Discussions

Postby shiv » 13 Sep 2016 06:23

JayS wrote:
Can't agree more on having multiple parallel programs for RnD to pave way for future. One reason why Unkil is so much more ahead of all is precisely this reason.


On a completely different note - and I don't mean to digress. I was upset on Twitter by an Indian Express news item that counted the cost in Rupees per Olympic medal. As I see it - when it comes to fundamental cutting edge research in military tech, spending twice the money cannot guarantee 2x value. If bean counters are going to count beans after every failure, India is never going to generate the national commitment to invest and invest till it hurts on research.

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Re: LCA Tejas: News and Discussions

Postby saumitra_j » 13 Sep 2016 07:25

indranilroy wrote:This is why we need to have our own programs, and not spend 8B on 36 airplanes, which by the way will at best start coming in from 2019 :shock:

Indranil sir,
I have someone very close in the family who is deeply embedded in India's R&D ecosystem. Based on my discussions with him, I think we have a serious issue with trained, skilled manpower as well as private sector taking risks in R& D; Money is no more the problem. However, no amount of money can build the trained manpower that we need in the timelines that are looking at. There are many reasons for lack of trained manpower - and desi attitude is one of the biggest one! I will give you a short anecdote: Somebody I know used to do a lot of work on CFD analysis with Fluent and has now started his own company providing consultancy using OpenFOAM. He offered FREE CFD analysis for all the models of vehicles of a famous auto manufacturer but was refused! There just does not seem to be an appetite for doing new things around manufacturing or taking risks! You will not believe it but until very recently, there was only ONE private manufacturer of specific types of heat pipes and ISRO had to import them at about INR 2lakhs per piece from Russia! Now ISRO is trying to develop this manufacturer as a vendor so that they can space qualify the heat pipes and save valuable money as this one costs less than half the price of the one manufactured in Russia. Now, there are private vendors in the space but all are MNCs and generally sanctioned from dealing with ISRO! The point I am trying to make is that this 8Billion for 36 planes is dictated by the fact that we are not there as yet, and still have a long way to go before GOI will have the confidence to pump that money back in India. The private sector in high tech is still developing with a lot of small and medium sized companies taking up the work..but it is still work in progress!

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Re: LCA Tejas: News and Discussions

Postby saumitra_j » 13 Sep 2016 07:37

shiv wrote:
JayS wrote:
Can't agree more on having multiple parallel programs for RnD to pave way for future. One reason why Unkil is so much more ahead of all is precisely this reason.


On a completely different note - and I don't mean to digress. I was upset on Twitter by an Indian Express news item that counted the cost in Rupees per Olympic medal. As I see it - when it comes to fundamental cutting edge research in military tech, spending twice the money cannot guarantee 2x value. If bean counters are going to count beans after every failure, India is never going to generate the national commitment to invest and invest till it hurts on research.

Completely agree Shiv sir, bean counters, audit teams and the fear of all the three letter agencies prevents anyone from taking any big risks. That also means that private sector who do not have to deal with such bean counters can take up at least some areas of work and risks...but that attitude is still developing. We only have a handful of private players who are willing to risk it.

I also think that any comparison with Unkil is an exercise in futility as Unkil is overloaded with resources - be it top class institutions or money. Running parallel R&D program requires tons of resources ...both money and human skills. No country apart from the US has those kind of resources IMHO. Also, Unkil has one more thing which no other country in my humble opinion has: An institutional ability to learn from failures in matters of R&D and high tech. This makes sure that no effort is wasted and the next generation is able to pick up where the old one stopped. In Indian context, failure is taken very badly in most places and very few institutions in India have the ability to actually learn from it, ISRO being a prime example!

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Re: LCA Tejas: News and Discussions

Postby shiv » 13 Sep 2016 07:46

saumitra_j wrote:Also, Unkil has one more thing which no other country in my humble opinion has: An institutional ability to learn from failures in matters of R&D and high tech. This makes sure that no effort is wasted and the next generation is able to pick up where the old one stopped. In Indian context, failure is taken very badly in most places and very few institutions in India have the ability to actually learn from it, ISRO being a prime example!

I have said this before and I will say it again. The US picks up smart, hardworking young people from India and employs them with enough money for them to live happily. When the US needs taxi drivers they look to Somalia.

In India the bean counters and self haters kick in from day 1. We start with "We can't do it", and the minute there is a setback we say ' "There - I told you so. Waste of money. This failure has cost us X thousand crores."

Even the jingos do this. This is a national characteristic.

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Re: LCA Tejas: News and Discussions

Postby Zynda » 13 Sep 2016 11:27

saumitra_j wrote:Based on my discussions with him, I think we have a serious issue with trained, skilled manpower as well as private sector taking risks in R& D; Money is no more the problem. However, no amount of money can build the trained manpower that we need in the timelines that are looking at. There are many reasons for lack of trained manpower - and desi attitude is one of the biggest one!


^^+1. I've been saying the same thing based on chirps from a lot of birds. I'm yet to see a working system put in place to attract & retrain skilled manpower resources both in Govt and Pvt institutions.

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Re: LCA Tejas: News and Discussions

Postby JTull » 13 Sep 2016 14:12

shiv wrote:
saumitra_j wrote:Also, Unkil has one more thing which no other country in my humble opinion has: An institutional ability to learn from failures in matters of R&D and high tech. This makes sure that no effort is wasted and the next generation is able to pick up where the old one stopped. In Indian context, failure is taken very badly in most places and very few institutions in India have the ability to actually learn from it, ISRO being a prime example!

I have said this before and I will say it again. The US picks up smart, hardworking young people from India and employs them with enough money for them to live happily. When the US needs taxi drivers they look to Somalia.

In India the bean counters and self haters kick in from day 1. We start with "We can't do it", and the minute there is a setback we say ' "There - I told you so. Waste of money. This failure has cost us X thousand crores."

Even the jingos do this. This is a national characteristic.


As Narayana Murthy very aptly noted that Indians have highest ego per unit of achievement.

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Re: LCA Tejas: News and Discussions

Postby Rahul M » 13 Sep 2016 14:25

isn't that the opposite of the point being made ? that we downplay our strengths and multiply negativity ?

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Re: LCA Tejas: News and Discussions

Postby JTull » 13 Sep 2016 17:59

Rahul M wrote:isn't that the opposite of the point being made ? that we downplay our strengths and multiply negativity ?


I'm talking of the 'I told you so' attitude. Talk is cheap and we, as Indians, do that a lot. Just look at the success of this forum... :D

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Re: LCA Tejas: News and Discussions

Postby Bhaskar_T » 13 Sep 2016 20:12

Why SP-3 isn't flying? By own estimates of HAL (when SP-2 took to skies), SP-3 and SP-4 was to fly on 1st July. Then, upon realization, SP-3, SP-4 was dropped from LCA induction ceremony and since then 2.5 months are gone. One of my jingo friend (fan of videshi imports) pinched me "Runway geela hai, isiliye nahin ud raha SP-3". Felt like to punch him :-/

I recall some ChaiWala mentioned (few weeks ago) that SP-3 could fly anytime. Mathrubhumi and NolanPinto who did few good programs on LCA production assembly this year had my hopes high, I remember those pics of so many LCA's on jigs. I still think if HAL can deliver SP-3 and SP-4 this year, it would be a commendable achievement.


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