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PostPosted: 13 Apr 2012 04:36 
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^^^ 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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PostPosted: 13 Apr 2012 05:12 
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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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PostPosted: 13 Apr 2012 05:26 
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Location: Kamariya lollipop lagelu ...
AoA value of 35 deg is the maximum achievable figure as per design specifications.


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PostPosted: 13 Apr 2012 10:05 
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Gurneeshji,
Can you please post a link to that article.. Should make for an interesting read.

thanks.


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PostPosted: 13 Apr 2012 10:28 
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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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PostPosted: 13 Apr 2012 11:15 
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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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PostPosted: 13 Apr 2012 20:22 
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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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PostPosted: 13 Apr 2012 21:03 
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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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PostPosted: 13 Apr 2012 21:15 
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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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PostPosted: 13 Apr 2012 21:50 
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^^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:
Quote:
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:
Quote:
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
Quote:
(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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PostPosted: 13 Apr 2012 22:44 
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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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PostPosted: 14 Apr 2012 00:05 
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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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PostPosted: 14 Apr 2012 00:51 
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^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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PostPosted: 14 Apr 2012 08:51 
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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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PostPosted: 14 Apr 2012 09:06 
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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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PostPosted: 14 Apr 2012 09:20 
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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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PostPosted: 14 Apr 2012 18:09 
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indranilroy wrote:

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


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PostPosted: 15 Apr 2012 01:21 
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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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PostPosted: 15 Apr 2012 01:30 
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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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PostPosted: 15 Apr 2012 02:46 
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^^Thanks :)


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PostPosted: 15 Apr 2012 05:42 
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shiv wrote:
indranilroy 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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PostPosted: 15 Apr 2012 07:22 
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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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PostPosted: 15 Apr 2012 09:35 
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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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PostPosted: 16 Apr 2012 12:45 
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shiv wrote:
indranilroy 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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PostPosted: 16 Apr 2012 16:05 
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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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PostPosted: 16 Apr 2012 18:07 
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Merlin,
You have bijjli dak..


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PostPosted: 16 Apr 2012 18:39 
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Bala Vignesh wrote:
Merlin,
You have bijjli dak..


Mucho thanks. I hadn't seen that article before so much to digest in there.


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PostPosted: 16 Apr 2012 18:53 
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You are welcome ji.. Have sent another e-daak, on a different topic though..


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PostPosted: 17 Apr 2012 08:57 
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Flight test update

LCA-Tejas has completed 1827 Test Flights successfully. (13-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-220,PV3-336,LSP1-72,LSP2-205,PV5-36,LSP3-47,LSP4-49,LSP5-80,LSP7-2)

from

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)


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PostPosted: 18 Apr 2012 12:29 
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Flight test update

LCA-Tejas has completed 1828 Test Flights successfully. (16-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-220,PV3-337,LSP1-72,LSP2-205,PV5-36,LSP3-47,LSP4-49,LSP5-80,LSP7-2)

from

LCA-Tejas has completed 1827 Test Flights successfully. (13-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-220,PV3-336,LSP1-72,LSP2-205,PV5-36,LSP3-47,LSP4-49,LSP5-80,LSP7-2)


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PostPosted: 18 Apr 2012 12:57 
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:D
Soon expect a DMM writen article saying "Since LCA can not carry at least six Agni 5 (which itself is a outdated missle) under each of its wings it is a waste fighter. India should purcase F16 which will carry 12 Minutemen under each of its wing which can be used againt Maldeivs" :rotfl: :D


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PostPosted: 19 Apr 2012 12:31 
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Flight test update

LCA-Tejas has completed 1830 Test Flights successfully. (16-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-220,PV3-338,LSP1-73,LSP2-205,PV5-36,LSP3-47,LSP4-49,LSP5-80,LSP7-2)

from

LCA-Tejas has completed 1828 Test Flights successfully. (16-April-2012).
(TD1-233,TD2-305,PV1-242,PV2-220,PV3-337,LSP1-72,LSP2-205,PV5-36,LSP3-47,LSP4-49,LSP5-80,LSP7-2)


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PostPosted: 19 Apr 2012 12:40 
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Location: Desh ke baarei mei sochna shuru karo. Soch badlo, desh badlega!
4 flights in one day


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PostPosted: 21 Apr 2012 04:18 
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Any news on NLCA? Been quite some time since its anticipated first flight :((


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PostPosted: 21 Apr 2012 04:32 
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prabhug wrote:
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.

nope.. AMCA thread is appropriate. LCA has many enablers, but the program itself is not chartered to be compared with these two.


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PostPosted: 21 Apr 2012 09:02 
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Good news on NP1. FRRB clears first flight.

http://tarmak007.blogspot.com/2012/04/f ... t-one.html


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PostPosted: 21 Apr 2012 09:41 
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yay! eagerly waiting for the new AoAs.


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PostPosted: 21 Apr 2012 10:53 
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Sridhar wrote:
Good news on NP1. FRRB clears first flight.

http://tarmak007.blogspot.com/2012/04/f ... t-one.html



Quote:
While some crucial parts of NP-1 gave nightmares to both designers and engineers, including the bulky undercarriage, sources now confirm that the defects have been rectified.
The NP-1 will be put through another HSTT next week before the Aeronautical Development Agency (ADA) and HAL combine take a final call on the first flight. “Everything is in place and our engineers and technicians are leaving no stone unturned ahead of the first flight. We had some software snags which have been rectified at the right time,” HAL sources said.


Very good news if true


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PostPosted: 21 Apr 2012 11:53 
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Eagerly waiting for NP-1 to Touch the Sky with Glory :D


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PostPosted: 21 Apr 2012 21:14 
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clearance means, the undercarriage issue sorted out, what to watch would be the moveable levcon in action. AOA!


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