LCA News and Discussions

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Indaruta
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Re: LCA News and Discussions

Postby Indaruta » 10 Apr 2012 08:14

^^^
BS

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Re: LCA News and Discussions

Postby S_Prasad » 10 Apr 2012 09:01

Indaruta wrote:^^^
BS


Plus one ....

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Re: LCA News and Discussions

Postby merlin » 10 Apr 2012 14:40

Aditya_V wrote:Per discussion, AOA which I think right now is restricted 24 degrees, to increase it by a few degrees.


AoA is 22 deg. to be increased to 24 deg. as per plans for the LSP-6.

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Re: LCA News and Discussions

Postby suryag » 11 Apr 2012 10:52

Flight test update
LCA-Tejas has completed 1822 Test Flights successfully. (10-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-219,PV3-336,LSP1-71,LSP2-205,PV5-36,LSP3-47,LSP4-48,LSP5-78,LSP7-2)

LCA-Tejas has completed 1821 Test Flights successfully. (09-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-219,PV3-336,LSP1-71,LSP2-205,PV5-36,LSP3-47,LSP4-48,LSP5-77,LSP7-2)

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Re: LCA News and Discussions

Postby SidSom » 11 Apr 2012 14:11

AoA is 22 deg. to be increased to 24 deg. as per plans for the LSP-6.


This seems to be a very big issue with LCA. Question to Gurus.

What significant advantage does an additional 2 degrees of AoA provide

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Re: LCA News and Discussions

Postby SagarAg » 11 Apr 2012 14:24


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Re: LCA News and Discussions

Postby Jayram » 12 Apr 2012 00:19

Laymans interpretation.. Higher the AOA the better it is for Aircraft to do STOL's ie short takeoff's and landings. Good for those carrier based landings that the NLCA is supposed to do.. Also though not so evident higher AOA is better during recovery from steep dives causing the aircraft to handle high speed stall better and recover at a steeper angle than otherwise... so overall sharper handling..
Caveat All knowledge from Wiki so generic only...

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Re: LCA News and Discussions

Postby nachiket » 12 Apr 2012 00:49

A higher max AoA should also improve the sustained turn rate if I'm not mistaken. Since the aircraft is basically climbing in the direction of the turn, at a constant bank angle the only way to improve the rate of turn would be to increase the lift generated by the wings. This can be done by increasing airspeed (which is limited by the engine power available) and increasing the angle of attack (which is limited by the max angle of attack beyond which the aircraft will stall).
Aero gurus, bliss to forgive if I made mess of things in the above explanation.

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Re: LCA News and Discussions

Postby shiv » 12 Apr 2012 06:11

Well I have yet another theory. The aim is not just 2 degrees more of AoA. The 2 degrees is only to meet what the Air Force wanted IIRC. But even for that there will have to be plenty of testing with a stall recovery chute. Each degree of AoA will have to be tested at all speeds and attitudes before the flight control software can be modified to allow a pilot to get there freely (I'm guessing). But it won't stop at that they will go beyond those two degrees and take it to the limit, whatever that limit might be. Hopefully those 2 degrees more will not be the limit. It may be possible to achieve much higher AoA. I heard that the Gripen AoA testing continued for thousands of tests long after it went into service. I am guessing the same thing will happen here.

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Re: LCA News and Discussions

Postby merlin » 12 Apr 2012 11:33

Yes, 2 more degrees may be just to achieve design specs. They may use the testbeds for more later once FOC is done.

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Re: LCA News and Discussions

Postby suryag » 12 Apr 2012 13:09

Flight test update

LCA-Tejas has completed 1824 Test Flights successfully. (11-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-220,PV3-336,LSP1-71,LSP2-205,PV5-36,LSP3-47,LSP4-49,LSP5-78,LSP7-2)

from

LCA-Tejas has completed 1822 Test Flights successfully. (10-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-219,PV3-336,LSP1-71,LSP2-205,PV5-36,LSP3-47,LSP4-48,LSP5-78,LSP7-2)

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Re: LCA News and Discussions

Postby negi » 12 Apr 2012 22:38

In high AoA the aerodynamic characteristics are no longer linear for instance for a given aerofoil there comes a stage when lift seizes to increase with increase in AoA in fact drag starts to shoot up .The wing can stall and in extreme cases when it's wake disturbs the flow near the tail the AC may go into a spin.

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Re: LCA News and Discussions

Postby Indranil » 13 Apr 2012 00:57

^^^ While that is true. For LCA, the stall is supposed to set in near 35 degrees. So aerodynamically it is supposed to sail through the 22 to 24 degree. I can't comment about the structural and air intake issues.

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Re: LCA News and Discussions

Postby SaiK » 13 Apr 2012 02:56

what is "can't comment" meaning? do you work with team LCA?, and know about the issues? and a security risk to discuss them in open forum?

You can perhaps throw some light on the issues.

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Re: LCA News and Discussions

Postby Indranil » 13 Apr 2012 04:22

"I can't comment" means "I don't know enough to comment"

I don't know why ADA has limited the AoA to 24 degrees ... From open literature, I can tell you that it is not the aerodynamics of the wing ... that is all.

Whether we can discuss it on an open forum, I have said nothing which is not already known.

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Re: LCA News and Discussions

Postby Gurneesh » 13 Apr 2012 04:36

^^^ There is that High AoA pdf article that gives all the info one needs to understand this. All jingos need to read that article.

IIRC LCA can go to 35 deg AoA, but there are some limitations due to instabilities in yaw and roll that limit the designers to 24 deg. Going beyond it will mean having a perfect understanding of the aircraft characteristics and required FBW laws. The article mentions that 24 deg is a safe limit and further testing will increase it to the 'expected' (probably what IAF wants) limit of 26 deg.

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Re: LCA News and Discussions

Postby Indranil » 13 Apr 2012 05:12

and you are right, a lot of what I said in the last few comments is gleaned that article ... also B Harry had stated some of these details in his writings.

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Re: LCA News and Discussions

Postby negi » 13 Apr 2012 05:26

AoA value of 35 deg is the maximum achievable figure as per design specifications.

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Re: LCA News and Discussions

Postby Bala Vignesh » 13 Apr 2012 10:05

Gurneeshji,
Can you please post a link to that article.. Should make for an interesting read.

thanks.

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Re: LCA News and Discussions

Postby Singha » 13 Apr 2012 10:28

afaik the max AoA of F-16 and F-18 are claimed as 30' and 40' respectively with the F-15E around mid 20s. does it sound right?
rafale and EF would be up around 28-30 range?

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Re: LCA News and Discussions

Postby Indranil » 13 Apr 2012 11:15

Bala Vignesh wrote:Gurneeshji,
Can you please post a link to that article.. Should make for an interesting read.

thanks.


He is speaking of this
http://www.scribd.com/doc/78345390/Approach-to-High-Angle-of-Attack-Testing-of-Light-Combat-Aircraft-LCA-Tejas

Additional reading:
http://nal-ir.nal.res.in/9158/1/312.pdf

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Re: LCA News and Discussions

Postby SaiK » 13 Apr 2012 20:22

the raptor I read can do high alpha - about 60*. I have no idea how that transforms to a risk factor for landing at that angle. there must be extreme thrust to handle, high drag-no stall and plus fantastic sensors to collobroate with alphas to automatically reduce speed and angle, within safety limits.- the wheels must touch right?

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Re: LCA News and Discussions

Postby member_22872 » 13 Apr 2012 21:03

Indranilroy ji, Thanks for the paper. Do you know if design optimization in terms of code is also done in tandem with CFD codes for LCA or any other aircraft right now?

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Re: LCA News and Discussions

Postby shiv » 13 Apr 2012 21:15

SaiK wrote:the raptor I read can do high alpha - about 60*. I have no idea how that transforms to a risk factor for landing at that angle. there must be extreme thrust to handle, high drag-no stall and plus fantastic sensors to collobroate with alphas to automatically reduce speed and angle, within safety limits.- the wheels must touch right?


Thrust vectoring. IIRC the Su 30, MiG 35 and other TV variants can do something similar or better.

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Re: LCA News and Discussions

Postby rgsrini » 13 Apr 2012 21:50

^^Thanks indranilroy.
Superb primer by Wg. Cmdr. Vikram Singh, in plain English. I am glad that the LCA team is openly publishing the characteristic, challenges and testring strategies etc. I am not sure if this is unique to LCA or if other countries publish so openly as well.

It appears that the testing philosophy is "Departure prevention" rather than actual "spin recovery", while being prepared for an actual spin recovery in the event of a departure.

I am quoting some pieces here because it is extremely interesting for me personally and I am assuming it will be for some of you as well.

On some of the challenges:
The correction factors are initially estimated from CFD studies andwind tunnel measurements and therefore can have significant errors especially attransonic Mach Nos. Thus in any new combat aircraft programme a significant part ofthe flight test programme consists of experiments which are directed towards aero datavalidation and air data calibration. Based on the flight test results and the closeness ofmatch with the corresponding wind tunnel data the envelope is systematically expandedin stages to ultimately cover the boundaries including the nonlinear high angle of attack regimes



On testing Philosophy:
However, a full investigation of HAoA characteristics of a highperformance ac including spinning is a very high risk, high cost and time consumingproposition. Considering the large number of external stores configurations and theneed to clear a two seater version, the test campaign could well take a few years ofwork up, flight test, analysis, re design and certification.

it was decided that the ac would not be intentionally spun.Departure prevention, rather than spin recovery, will form the basis of test philosophywith full preparation for an OOCF event and its recovery.


On recovery techniques
(a) Recovery With Control Surfaces

    (i) Deflect full OUT-SPIN rudder simultaneously with IN-SPIN aileronsfollowed by down elevator after 2 sec delay. Recovers within 2 turns.
    (ii) Some other configurations (stores, zero slats etc.) showed moredifficult recovery.
    (iii) Some configurations required 18.5 deg In-Spin Aileron(e.g. Zero Slat, A/B etc.)
    (iv) Some configurations required 25 deg In-Spin Aileron(e.g. Ext. Store configs.)
    (v) Recovery from Inverted Spins easier (Neutral Aileron sufficient)
(b) Recovery With Spin Parachute
    Restore rudder and aileron to NETURAL.After a delay of about 2 secs, deploy parachute and restore elevator to neutral.Recovery within 2 turns.

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Re: LCA News and Discussions

Postby SaiK » 13 Apr 2012 22:44

How do they measure corrections from metrics alone or the design itself has certain tolerance and limiting factors that is included?

for example, let us say inlets.. when you start your design, assume you don't use CFD.. and then you run over CFD, and it points out certain corrections.

Now, you limitations again is with design factors as well. Did they begain designing from CFD given inputs, or they started off with some general baseline design, and started applying the correction factors?

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Re: LCA News and Discussions

Postby nachiket » 14 Apr 2012 00:05

indranilroy wrote:"I can't comment" means "I don't know enough to comment"

I don't know why ADA has limited the AoA to 24 degrees ... From open literature, I can tell you that it is not the aerodynamics of the wing ... that is all.

Whether we can discuss it on an open forum, I have said nothing which is not already known.

What about the air intakes? They have to worry about compressor stall as well at high AoA.

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Re: LCA News and Discussions

Postby SaiK » 14 Apr 2012 00:51

^should be well covered by stator vanes angles (digital controls) right? doesn't the GE404 one have it? and ours is fully FADEC-ed. Or is that still outside of the game plan here?

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Re: LCA News and Discussions

Postby Indranil » 14 Apr 2012 08:51

nachiket wrote:
indranilroy wrote:"I can't comment" means "I don't know enough to comment"

I don't know why ADA has limited the AoA to 24 degrees ... From open literature, I can tell you that it is not the aerodynamics of the wing ... that is all.

Whether we can discuss it on an open forum, I have said nothing which is not already known.

What about the air intakes? They have to worry about compressor stall as well at high AoA.

I meant exactly as I said ... I just do not know ... I do not know anybody who is privy to such information.

I was just answering from the aerodynamics point of view. What we know openly, I have not seen a graph where there is any deviation from linearity of CL max till 30 degrees. However the same cannot be said about roll and yaw. According to the paper, they see a fall in the moments at about 25 degree. The author says that the rudder can be used to artificially provide stability upto 30 degrees. However, to be on the safer side they are going to restrict AoA to 26 degrees.

I don't know anything about the intakes. I have not seen any information in open literature.

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Re: LCA News and Discussions

Postby Indranil » 14 Apr 2012 09:06

venug wrote:Indranilroy ji, Thanks for the paper. Do you know if design optimization in terms of code is also done in tandem with CFD codes for LCA or any other aircraft right now?

No 'ji' please :-).

I am sorry I did not get what you are asking. Are you asking of optimizations in CFD codes? Or design optimizations found using CFD analysis incorporated into the prototypes?

For the first question, I don't know, but I would guess so ... I know NAL does some work related to this ... Otherwise, I work in HPC and will be available for hiring in 2-3 years ;-)

If you are speaking about the second question, the answer is definitely an yes. You can see some of the optimizations in LSP 7.

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Re: LCA News and Discussions

Postby Indranil » 14 Apr 2012 09:20

SaiK wrote:the raptor I read can do high alpha - about 60*. I have no idea how that transforms to a risk factor for landing at that angle. there must be extreme thrust to handle, high drag-no stall and plus fantastic sensors to collobroate with alphas to automatically reduce speed and angle, within safety limits.- the wheels must touch right?


That is because of TV. http://www.sfte-ec.se/data/Abstract/A2000-II-02.pdf

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Re: LCA News and Discussions

Postby shiv » 14 Apr 2012 18:09


:shock:
Oh my. What a fabulous article. An arcane and detailed subject written with great clarity. +10

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Re: LCA News and Discussions

Postby Vashishtha » 15 Apr 2012 01:21

Ive always wondered if HAL have built in house CFD programs for LCA or they used a software from third parties.....

Hoping for the former, i bet we are not short of programmers cum aerospace engineers in this country...

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Re: LCA News and Discussions

Postby Sagar G » 15 Apr 2012 01:30

Vashishtha wrote:Ive always wondered if HAL have built in house CFD programs for LCA or they used a software from third parties.....

Hoping for the former, i bet we are not short of programmers cum aerospace engineers in this country...


HAL is the production agency and ADA is doing all the R&D related with LCA. AFAIK ADA uses commercially available CFD packages and they also have the capability of CFD programming so no worries here.

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Re: LCA News and Discussions

Postby Vashishtha » 15 Apr 2012 02:46

^^Thanks :)

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Re: LCA News and Discussions

Postby Anujan » 15 Apr 2012 05:42

shiv wrote:

:shock:
Oh my. What a fabulous article. An arcane and detailed subject written with great clarity. +10

Here is a video of scale model of F104 tested in a wind tunnel with spin recovery chutes


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Re: LCA News and Discussions

Postby member_22872 » 15 Apr 2012 07:22

Indranilroy :), thanks, I meant the second one, it would be great to know how they carried out the optimizations. HPC! wow, nice to know. I work in CFD looking into CUDA now.

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Re: LCA News and Discussions

Postby SaiK » 15 Apr 2012 09:35

now, raptor is successful with pitch-axis vectoring alone.. that increases the stealth characteristics as well when compared to pak-faish rears that does 360* tv. perhaps roll and yaw need not required high vectoring and it fits well to augment thrust on pitch alone.

now, if the thermal signature does only reduce by 30%, then I would choose 360% tv, and use a retractable probe based infra jammer and dispense flares when approached from rear. why waste money, when this is more elegant and efficient way to destroy the chaser say at 50ft away from rear., and focus on the kill mission.

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Re: LCA News and Discussions

Postby merlin » 16 Apr 2012 12:45

shiv wrote:

:shock:
Oh my. What a fabulous article. An arcane and detailed subject written with great clarity. +10


How can I see that article? Every one of my browsers is horribly mangling that page (Firefox, Chrome, IE)?

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Re: LCA News and Discussions

Postby prabhug » 16 Apr 2012 16:05

There is an article here

http://defensetech.org/2010/12/31/j-20-vs-f-35-one-analysts-perspective/#comment-267669

Can we analyze how relevant is LCA is with these points.


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