LCA News and Discussions

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Re: LCA News and Discussions

Postby astal » 25 Jul 2013 11:28

Kartik wrote:
Perhaps wake penetration tests as well..


Thanks. Hope they go well too.

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Re: LCA News and Discussions

Postby Lalmohan » 25 Jul 2013 12:14

saik - air intake variable geometry is usually done to manage the onset of the shock wave during transonic flight regimes; think of the air intake like a tube you are blowing into, as alpha changes, the air flow into it will also change, eventually stalling. changing the air intake geometry to adjust for alpha is feasible (IIRC the F14 had something like this for low speed flight regimes - but this might be musharraf-talk) but normally the advantages are lost due to the additional weight and control system complexity. i also suspect that before you stall the airflow into the air intake, the wing will be well and truly stalled, making the whole thing moot

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Re: LCA News and Discussions

Postby merlin » 25 Jul 2013 12:25

Kartik wrote:
astal wrote:Kartik, Phillip,

If STR issue has been solved, the only know open issues are materials for radar nose cone and radar performance right?


Perhaps wake penetration tests as well..


And lightning protection tests, though I seem to recall reading its been moved to FOC.

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Re: LCA News and Discussions

Postby geeth » 25 Jul 2013 13:23

To cater for AoA, air intakes are raked - eg., f15, mig 23,27,29 etc. LCA does not have raked intake, so more susceptible to AoA problems. Variable Geo/adjustible air intakes are more for managing the shock waves at different Mach

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Re: LCA News and Discussions

Postby geeth » 25 Jul 2013 13:24

To cater for AoA, air intakes are raked - eg., f15, mig 23,27,29 etc. LCA does not have raked intake, so more susceptible to AoA problems. Variable Geo/adjustible air intakes are more for managing the shock waves at different Mach

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Re: LCA News and Discussions

Postby vina » 25 Jul 2013 13:59

geeth wrote:To cater for AoA, air intakes are raked - eg., f15, mig 23,27,29 etc. LCA does not have raked intake, so more susceptible to AoA problems. Variable Geo/adjustible air intakes are more for managing the shock waves at different Mach


Ayyo!! . You should pay careful attention to LalMullah, especially when he posts here and and not in the L&M thread about Lycreshwaris.

The YellCeeYea has a wing shielded inlet , the others have the inlet in the free stream. That is a big difference, and helps do away with variable geometry inlet and a simple fixed inlet will suffice. And any AoA and other stuff like surge ,buzz and separation are done away with as well , and any limits to that like AOA is more relevant to the wing (as it will happen first there) before the inlet

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Re: LCA News and Discussions

Postby vic » 25 Jul 2013 19:03

A Question to Gurus:-


Does the wing twist on LCA adds to drag?

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Re: LCA News and Discussions

Postby SaiK » 25 Jul 2013 19:15

exactly red mull.. i want to blame the 404 for that.(but fadec and controls and the parts may be indian/or may be not) .. and we can't say that for sure cause it is not our engine. may be we can handle this issue well with 414.

viv, which twist?

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Re: LCA News and Discussions

Postby Indranil » 25 Jul 2013 22:34

vic wrote:Does the wing twist on LCA adds to drag?


Answer: No. It reduces it. The twist is just a way to join the trailing edge of the wing to the leading edge of the tailplane. In this way, you take away the front section of the tailplane.

Explanation: I understand the dilemma you have there. From the front, it looks like it provides a larger cross-sectional area to oncoming air. This is true. But imagine level flight. You need to create lift equivalent to the weight of the aircraft. As long as you can produce laminar flow, the major form of drag at subsonic speed is induced drag where the only variable would be lift-to-drag ratio. The lift-to-drag ratio of LCA's wing is comparable to almost all other supersonic wings for fighters out there. You may ask how (Since a part of the wing is flying at a higher AoA, you can choose a much thinner aerofoil). And by removing the cross-sectional area of the trailing edge, the overall drag of the plane is actually reduced.

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Re: LCA News and Discussions

Postby vic » 26 Jul 2013 20:49

Thanx for the answer

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Re: LCA News and Discussions

Postby Raman » 27 Jul 2013 07:04

vic wrote:A Question to Gurus:-
Does the wing twist on LCA adds to drag?


As with all things aero, the answer is: it depends. :D

(I assume you are talking about span-wise wing twist (either geometric or aerodynamic) and not the reflex camber of the wing, which is something else altogether.)

The twist can potentially increase profile drag due to increased cross-sectional area, but it can reduce induced drag. The two main ideas for wing twist are:
- Different airfoil sections of the wing operate at different angles-of-attack, so the whole wing doesn't stall all at once - it is a more degraded effect
- Tailor the span-wise distribution of lift; the more elliptical the distribution, the lower the induced drag. The wing twist helps in reducing this.

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Re: LCA News and Discussions

Postby Indranil » 27 Jul 2013 08:14

Raman sahab,


Just checking with you. I completely agree with you on the washout. My description of the effect of reflex camber on induced drag is not wrong, is it?

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Re: LCA News and Discussions

Postby SaiK » 27 Jul 2013 22:02

in the sense how to make the airfoil as dynamic it can be? wouldn't more multiple flaps helps rather a single large one (provided it can be controlled - well studied wing dynamics)?

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Re: LCA News and Discussions

Postby Indranil » 28 Jul 2013 09:55

SaiK wrote:in the sense how to make the airfoil as dynamic it can be?

For what?

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Re: LCA News and Discussions

Postby Raman » 29 Jul 2013 08:13

indranilroy wrote:Raman sahab,


Just checking with you. I completely agree with you on the washout. My description of the effect of reflex camber on induced drag is not wrong, is it?


Surely you know that I don't deserve 'sahab'! :-)

As for your explanation, honestly, I didn't quite follow your post. The reflex camber is provided so that tail-less airplanes get some "assistance" from the airfoil for trimming the airplane to level flight. As such, you can think that it reduces trim drag vs solely relying on flaperons for trim. However, since their function is to provide a moment to trim the airplane by providing a "lifting force" (in the downward direction) at the trailing edge, I'd imagine that there will be a penalty to be paid in terms of induced drag.

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Re: LCA News and Discussions

Postby Lalmohan » 29 Jul 2013 11:50

SaiK wrote:in the sense how to make the airfoil as dynamic it can be? wouldn't more multiple flaps helps rather a single large one (provided it can be controlled - well studied wing dynamics)?


it depends! :twisted:

trade-off between ability to achieve a more tailored wing section to your needs versus mechanical complexity of creating said shape (and weight penalties)

large aircraft often have multi-stage flaps, small aircraft not so often

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Re: LCA News and Discussions

Postby RKumar » 29 Jul 2013 18:52

Did anyone notice that LCA flight data updates are purged? Cutoff date is 30-Mar-2011. Wonder why??

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Re: LCA News and Discussions

Postby SaiK » 29 Jul 2013 18:56

someone is manupulating records?

red mull, i agree.. wonder what is the weight gain for each additional control system slat/moveable surface wise - assume for both electric and hydraulic.

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Re: LCA News and Discussions

Postby Lalmohan » 29 Jul 2013 19:58

there is also the strength of the control surface itself - and its ability to fold into the wing and maintain the right shape

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Re: LCA News and Discussions

Postby SaiK » 29 Jul 2013 20:17

assume a single torque beam/geared and controlled separately to be interfaced with the control surface.. devicing that should not be a problem.. the only multiplicity are the embedded systems that cater to each slat that has to respond differently. i'm not considering strengthening a big issue(weight wise).

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Re: LCA News and Discussions

Postby Lalmohan » 29 Jul 2013 20:24

no, multi-stage flaps follow a specific pattern - they do not go at random in different directions. they are used to make 'a flat wing curvier' so that its lift/drag curve is altered (from high speed low drag to low speed and as low a drag as possible) - if you look inside a wing (next time you are flying on a commercial liner) you'll see them follow a track and arrange in a particular order - it is quite predictable. you'll also see some airbrakes further ahead that can be put up after landing. you might see slats (at the leading edge) that come forward. i am not aware of any aircraft having multi-stage slats (but am willing to be corrected). in fact on the newer aircraft, once it has touched down and is slowing and the wing is 'all opened up' - you'll be astonished at how slender the wing really is and how much of it has been moved to make the flaps and slats and brakes work. the structure of the wing is something truly marvellous - making wing design (both aero and structural) one of the hardest things to do in engineering

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Re: LCA News and Discussions

Postby SaiK » 29 Jul 2013 20:42

just throwing up the idea.. i may not be wrong on the possibilities, but may be on the efficient design. but, i have no idea which performs better.

the challenges are always tougher, as we get tough.. LCA as a platform should be experimented with all kinds of new designs. /jmt

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Re: LCA News and Discussions

Postby Lalmohan » 29 Jul 2013 21:34

well - to be clear, you don't want multi-stage flaps all going in different directions - they must form a smooth curved shape - so sending them along a guide rail (adjustable) is the most efficient way

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Re: LCA News and Discussions

Postby SaiK » 29 Jul 2013 21:40

would not that applies to say even controls on couple of flaps.. the directions should be controllable, else what is the point? yes on the other points.. i think such designs can go where no eagle has gone before.

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Re: LCA News and Discussions

Postby Lalmohan » 29 Jul 2013 21:42

the directions are indeed controllable, but they move in concert - together - all in the same direction to form a new smooth shape - otherwise you create an excellent air brake and lift dumper and fall out of the sky faster than you can shout "musharraff!!"

and flaps and slats only ever move downwards (and retract back into their place) - they don't go against the camber of the wing

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Re: LCA News and Discussions

Postby SaiK » 29 Jul 2013 21:49

but then, the very aspect of differential air movement and drag adjustment is what we want to have that finer controls right? why should all be in the same direction. we need to have a wind tunnel study for this.

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Re: LCA News and Discussions

Postby Indranil » 30 Jul 2013 03:08

Raman wrote:As for your explanation, honestly, I didn't quite follow your post. The reflex camber is provided so that tail-less airplanes get some "assistance" from the airfoil for trimming the airplane to level flight. As such, you can think that it reduces trim drag vs solely relying on flaperons for trim. However, since their function is to provide a moment to trim the airplane by providing a "lifting force" (in the downward direction) at the trailing edge, I'd imagine that there will be a penalty to be paid in terms of induced drag.

I read my explanation myself. I made mistakes which I should and would correct in this post.

I agree that LCA would have to pay the trim drag penalties of a tailless config. But, it does not look like LCA's reflex camber is used for the typical usage of low moment. It is too huge for that alone. Other than the F-16XL, I haven't seen any plane with such a huge reflex camber.

The guys at ADA seemed to have fixed 2 things:
1. Air intakes by the side of the fuselage. Once this decision is made, it was desirable to have the the leading edge of wings above the and in front of the intakes to assist airflow into the air intakes at higher AoA.
2. They later on decided on having a tailless configuration to keep the plane light and simple. (ADA did study a configuration with a close coupled canard and a compound delta wing besides a conventional layout)

Part of the reason for the second choice was by having a large tailless delta, the wing loading went down. By increasing the wet area, the skin friction drag is increased, but the wave interference and trim components of drag are lower. For the F-16XL, the “clean airplane” drag is slightly lower during level flight, and forty percent lower when bombs and missiles are added (though a lot of this is related to the semi-conformal mounting of the hardpoints and making them being staggered from inboard to outboard, lowering the interference drag). Apparently, F-16 XL's wing gives it 25% greater lift to drag in supersonic flight and 11% greater lift to drag in subsonic flight (I don't know how much of this can be attributed to the active suction glove).

I made a mistake in the previous explanation. I said, this arrangement removes the cross sectional area of the horizontal stabilizer, which helps in reducing induced drag wave drag.

I have learnt to learn. I will only be happy to be corrected.

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Re: LCA News and Discussions

Postby Indranil » 30 Jul 2013 04:29

SaiK wrote:but then, the very aspect of differential air movement and drag adjustment is what we want to have that finer controls right? why should all be in the same direction. we need to have a wind tunnel study for this.


Saik sahab,

I could not follow all that you wrote.

It is fairly simple. The inboard surfaces on LCA's trailing edge are mainly for pitch control, while the out board surfaces take care of roll control. However, due to the FBW control system, when performance requires it, all four surfaces can act in either pitch or roll. Each of these control surfaces can be moved at different angles but in fixed step intervals. The intervals are chosen carefully and provide the required granularity required.

I see no use of having many control surfaces. In fact you might end up with ineffective ones if you cut them too narrow in span or length.

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Re: LCA News and Discussions

Postby Manish_Sharma » 30 Jul 2013 04:46

Is IOC-2 going to make LCA equal to all things that Bison does?

Like switching on its radar and fire a bvr missile?

Or

We have to wait for LCA's FOC that it starts doing all the things done by bison?

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Re: LCA News and Discussions

Postby srai » 30 Jul 2013 09:57

^^^
Here it is in short:

LCA Mk.1 IOC 1/2 -> +8g, AoA 26 degrees, M1.6, spin recovery, wake penetration, LGB, dumb bombs, WVR-AAM, drop tanks, ECCM

LCA Mk.1 FOC -> full flight envelope, BVR AAM w/ MMR, Guns, Rockets, plus @squadron level - support infrastructure w/ parts inventory, qualified pilots, technicians, syllabus

LCA Mk.2 -> primarily focused on flight performance improvements through higher TW ratio and slight airframe design refinements; AAR

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Re: LCA News and Discussions

Postby vishvak » 30 Jul 2013 10:08

Thank you, sraiji.

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Re: LCA News and Discussions

Postby Lalmohan » 30 Jul 2013 12:44

SaiK wrote:but then, the very aspect of differential air movement and drag adjustment is what we want to have that finer controls right? why should all be in the same direction. we need to have a wind tunnel study for this.


wind tunnell studies have been going on for the last 75 years - on exactly this

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Re: LCA News and Discussions

Postby Manish_Sharma » 30 Jul 2013 13:30

Many thanks Srai ji ! :-)

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Re: LCA News and Discussions

Postby JayS » 30 Jul 2013 16:59

New ADA site (I liked it, much better than last one) flashes this in Latest News:

1. Tejas detachment operated successfully during the month of July 2013.

What does this refer to exactly??

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Re: LCA News and Discussions

Postby rajanb » 30 Jul 2013 17:38

nileshjr wrote:New ADA site (I liked it, much better than last one) flashes this in Latest News:

1. Tejas detachment operated successfully during the month of July 2013.

What does this refer to exactly??


I think this has reference to point 3. in the same list:

3. Emergency jettison of all stores tested during detachment at Jamnagar.

Regards

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Re: LCA News and Discussions

Postby merlin » 30 Jul 2013 17:46

srai wrote:^^^
Here it is in short:

LCA Mk.1 IOC 1/2 -> +8g, AoA 26 degrees, M1.6, spin recovery, wake penetration, LGB, dumb bombs, WVR-AAM, drop tanks, ECCM

LCA Mk.1 FOC -> full flight envelope, BVR AAM w/ MMR, Guns, Rockets, plus @squadron level - support infrastructure w/ parts inventory, qualified pilots, technicians, syllabus

LCA Mk.2 -> primarily focused on flight performance improvements through higher TW ratio and slight airframe design refinements; AAR


LCA Mk.1 IOC-2 will not have AoA 26 degrees. Neither will it have spin recovery. ECCM looks doubtful too (judging by lack of reports on PV-3 testing).

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Re: LCA News and Discussions

Postby JayS » 30 Jul 2013 17:51

indranilroy wrote:I read my explanation myself. I made mistakes which I should and would correct in this post.

I agree that LCA would have to pay the trim drag penalties of a tailless config. But, it does not look like LCA's reflex camber is used for the typical usage of low moment. It is too huge for that alone. Other than the F-16XL, I haven't seen any plane with such a huge reflex camber.

The guys at ADA seemed to have fixed 2 things:
1. Air intakes by the side of the fuselage. Once this decision is made, it was desirable to have the the leading edge of wings above the and in front of the intakes to assist airflow into the air intakes at higher AoA.
2. They later on decided on having a tailless configuration to keep the plane light and simple. (ADA did study a configuration with a close coupled canard and a compound delta wing besides a conventional layout)

Part of the reason for the second choice was by having a large tailless delta, the wing loading went down. By increasing the wet area, the skin friction drag is increased, but the wave interference and trim components of drag are lower. For the F-16XL, the “clean airplane” drag is slightly lower during level flight, and forty percent lower when bombs and missiles are added (though a lot of this is related to the semi-conformal mounting of the hardpoints and making them being staggered from inboard to outboard, lowering the interference drag). Apparently, F-16 XL's wing gives it 25% greater lift to drag in supersonic flight and 11% greater lift to drag in subsonic flight (I don't know how much of this can be attributed to the active suction glove).

I made a mistake in the previous explanation. I said, this arrangement removes the cross sectional area of the horizontal stabilizer, which helps in reducing induced drag wave drag.

I have learnt to learn. I will only be happy to be corrected.


I never noticed that LCA and F16XL has reflexed camber. Are you sure??

The figure you mentioned are w.r.t. original F-16 config. The major difference came simply due to complete new wing design. Regarding the effect of suction glove, @M=2 it would not be that significant as compared to F16XL without suction glove, would it?? Skin drag is as it is a small component of total drag at that speed.

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Re: LCA News and Discussions

Postby Indranil » 30 Jul 2013 20:14

nileshjr wrote:
I never noticed that LCA and F16XL has reflexed camber. Are you sure??

The figure you mentioned are w.r.t. original F-16 config. The major difference came simply due to complete new wing design. Regarding the effect of suction glove, @M=2 it would not be that significant as compared to F16XL without suction glove, would it?? Skin drag is as it is a small component of total drag at that speed.


F-16XL had a reflex camber the back of the wing sloped up at 3 degrees.
Image

Of course the changes were due to a new wing design. The question is what in the wing design changed so drastically?
1. The low wing loading along with the suction glove allowed for better laminar flow reducing drag. So having a wing which morphs into the tail plane gives you a large wet area giving you a good L-D ratio. Both LCA and F-16XL also had a large washout for optimized induced drag.
2. The way the payload was carried, semi confirmal pylons in staggered fashion both reduced form drag and interference drag.

Image

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Re: LCA News and Discussions

Postby Philip » 30 Jul 2013 22:15

Don't these two configurations go back to the Draaken and Viggen experience?

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Re: LCA News and Discussions

Postby Indranil » 30 Jul 2013 22:33

In what way?


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