LCA news and discussion

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vina
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Re: LCA news and discussion

Postby vina » 22 May 2010 08:53

Vina From the plots shown Do you agree then that the elevator changes position at a rate greater than 2hz?


Is it just me , or is it the entire younger generation these days (there was a "graph" problem in the GSLV thread too) has totally lost the ability to read and analyze graphs and make any sense out of it.?

From the graphs you posted, all that I can conclude is that the FBW laws are very accurately close to real world and in fact,the guys who created those FBW laws should be totally complemented. The FBW law design calls for at most 2 to 3 deflections in a second and I dont see anything in the graph that contradicts it!.

As for the "serrated edges" of the lines in "real world" , how did you actually jump straight to the conclusion that it was the flight computer that actually made those commands, the system responded and got captured in the readings?. If anyone shows me the result of a experiment as a nice smooth line without fitting and approximation, it is either a fake or scaled out to such an extent that the experiment errors are smoothened out!. From the scale of the graph , it is apparent that these are well within experimental error /instrument error and random noise ranges!.

As an exercise, why dont you fit a nice smooth line through the serrations/variations in "real world" and then tell me how it holds up to your conclusion that it should be 20 hz!.

That was my first post on this forum that this rate is too small and has to be greater that is all.
I did bring up the 20Hz update rate based on the experience I had with FBW aircraft ( Just for people interested google bonanaza + fly-by wire)

Sorry, you are totally confused between the actual response rate of the control systems and the cycle speed of the control system. It doesn't stand to basic engineering reason in my opinon and fails basic sanity checks.

Like I said, for "google bonanaza + fly by wire" has a control surface that flaps at 20 hz, get me his name and show me a video of it flapping at that rate and I will build a shrine for him and elevate him from being a mere mortal to a saint/immortal in aerospace engg.

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Re: LCA news and discussion

Postby shiv » 22 May 2010 09:48

Like I said, for "google bonanaza + fly by wire" has a control surface that flaps at 20 hz, get me his name and show me a video of it flapping at that rate and I will build a shrine for him and elevate him from being a mere mortal to a saint/immortal in aerospace engg.


My response here
viewtopic.php?p=875803#p875803

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Re: LCA news and discussion

Postby geeth » 22 May 2010 10:37

May be there is some confusion about the rate/frequency at which the feedback is fed into the computer and the rate/frequency at which the command is given to the control surface. 20 Hz may be the feedback rate - i.e, if the flaps are 1 Deg down while cruising, then the flight control system checks 20 times every second whether it is maintaining this 1 Deg position. This way, the computer will know within 1/20th of a second, of any deviation from the set position (of 1 Deg), instead of (say) 1/2 a second and take corrective action that much earlier. In any case, the rate at which the flap moves cannot be 20 Hz. JMT

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Re: LCA news and discussion

Postby Indranil » 22 May 2010 10:50

I have a few clarifications to make and a few questions to ask.

Clarifications
1. What I wanted to say is that pilot input and control response is instantaneous. This is desired
2. Rajeev, I never meant to say that my friends words have more weight than yours. I work in high performance computing. So my knowledge in control systems is zilch. hence for my side of the argument I am trying to put whatever information I could gather.

Questions
1. I have been contradicting Rajeev all throughout and along the same lines as his other opposers have. Please read my posts again. Where is the question of satisfying me and him?
2. Rajeev all throughout said that he is speaking of really minuscule changes. Can somebody tell me, why that is not possible?
3. What is wrong with listening to Rajeev, who has field experience and has studied this subject. He has always substantiated his thoughts with reasons. Or does discussing mean not even giving a patient hearing

Lastly, Rajeev let us take this offline. We might be spamming this thread. You can email me.
Last edited by Indranil on 23 May 2010 04:19, edited 1 time in total.

akash_k
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Re: LCA news and discussion

Postby akash_k » 22 May 2010 14:58

hi,
if its ok with you, can u mail me ur email conversation on this topic. im interested in the discussion u've been carrying on.

thanks in advance.

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Re: LCA news and discussion

Postby Indranil » 23 May 2010 02:47

self deteted
Last edited by Indranil on 23 May 2010 10:27, edited 1 time in total.

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Re: LCA news and discussion

Postby rajeevcm » 23 May 2010 03:49

Post deleted
Last edited by rajeevcm on 23 May 2010 05:38, edited 1 time in total.

Indranil
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Re: LCA news and discussion

Postby Indranil » 23 May 2010 04:19

This message self destructed :)

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Re: LCA news and discussion

Postby akash_k » 23 May 2010 10:14

self delete
Last edited by akash_k on 23 May 2010 16:15, edited 1 time in total.

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Re: LCA news and discussion

Postby Singha » 23 May 2010 10:16

to the ramparts boys! one tejas is up and doing barrel rolls at low level in the usual circuit...which passes right above my apt :)

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Re: LCA news and discussion

Postby Zameen » 23 May 2010 21:37

Hari Kota in passing mentioned circa may 2004: LCA time to double amplitude is 250ms.

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Re: LCA news and discussion

Postby putnanja » 23 May 2010 23:04

LCA PV2 from http://tarmak007.blogspot.com . Click on the images for bigger resolution ones.

What is the white stuff at the bottom of the wings? Appears to have some pattern to it.

Image

Image

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Re: LCA news and discussion

Postby Vikram W » 24 May 2010 05:24

They usually put a pressure sensitive paint coat on the plane for testing purposes.
but this one just looks a bad paint job

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Re: LCA news and discussion

Postby sum » 24 May 2010 08:59

Vikram W wrote:They usually put a pressure sensitive paint coat on the plane for testing purposes.
but this one just looks a bad paint job

I seriously doubt a "bad paint job"

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Re: LCA news and discussion

Postby shiv » 24 May 2010 09:20

Well when Pakis do a good paint job it's reason for mockery. When Indians do a bad paint job - again it's reason for mockery.

Maybe the bottom line is that we wish Indians could do a better paint job than Pakis? :shock: :lol:

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Re: LCA news and discussion

Postby Sid » 24 May 2010 09:56

sum wrote:
Vikram W wrote:They usually put a pressure sensitive paint coat on the plane for testing purposes.
but this one just looks a bad paint job

I seriously doubt a "bad paint job"


yup, both wings have similar marks.

This can be due to jigs/mounting it over some support structure while doing system integration/upgrades something like this http://2.bp.blogspot.com/_zUe7sq7m3h0/S ... 180149.JPG. But that's just my 2 paisa.

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Re: LCA news and discussion

Postby bodhi » 24 May 2010 15:29

Vikram W wrote:this one just looks a bad paint job


yeah right...a bad paint job to make sure LCH is the show stealer!!!

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Re: LCA news and discussion

Postby Pratik_S » 24 May 2010 16:05

Its not a bad paint job, even the best paint job wears off and comes off. Its not something new or something which is happening only to the LCA.

It might be some reading instruments attached to it, i am not sure. But its not a bad paint job, there is nothing like such.

@Mr Shiv
LOL

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Re: LCA news and discussion

Postby Vikram W » 24 May 2010 20:42

Was thinking about the paint and it occurred to me, the paints peeling in a loose pattern.
Isn't the paint peeling where the internal struts and supports of the wing would be???
due to vibration ?? re-riveting

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Re: LCA news and discussion

Postby karan_mc » 24 May 2010 20:51

Image

it has been earlier spotted with patches ,

Earlier Vina had to say this for the white patches

There is a tejas which has red tapes sticked all over its wings to study aerodynamic and stress data.

like this tape
http://upload.wikimedia.org/wikipedia/c ... d_pass.jpg

Patches might have been created when these tapes were removed peeling the paint off with them.
Last edited by Rahul M on 24 May 2010 21:46, edited 1 time in total.
Reason: do NOT post large images inline.

shiv
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Re: LCA news and discussion

Postby shiv » 24 May 2010 20:58

PLEASE DO NOT POST OUTSIZE IMAGES!!!! :x :x :x :x

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Re: LCA news and discussion

Postby PratikDas » 24 May 2010 21:26

Vikram W wrote:Was thinking about the paint and it occurred to me, the paints peeling in a loose pattern.
Isn't the paint peeling where the internal struts and supports of the wing would be???
due to vibration ?? re-riveting

I think you might be on the right track. Here's a picture from Livefist of the bottom surface of the wing:

Image

There seems to be a metal skeletal frame with inlaid panels. When compared to the photo we're talking about from tarmAK007, the paint seems to have peeled off just this metal frame.

Image

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Re: LCA news and discussion

Postby Sid » 24 May 2010 21:41

yup, Tape is the right answer. Take a look at this image http://4.bp.blogspot.com/_o_no4M2xEPY/S ... 746427.jpg.

but wassup with so much tape.

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Re: LCA news and discussion

Postby RamaY » 24 May 2010 21:42

^^^
Could they be the stress sensors attached to various points on the wing to study the stress/performance?

Another thought that comes to my mind is a new RAM paint...

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Re: LCA news and discussion

Postby putnanja » 24 May 2010 22:03

Thanks PratikDas, that photo of TD2 explains it. But I wonder what that tape is there for. Maybe vina/RamaY's answer about them being stress sensors might be right

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Re: LCA news and discussion

Postby shiv » 25 May 2010 05:59

Sid wrote:yup, Tape is the right answer. Take a look at this image http://4.bp.blogspot.com/_o_no4M2xEPY/S ... 746427.jpg.

but wassup with so much tape.


I vaguely recall someone talking about conducting tape for static discharge or some such thing.

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Re: LCA news and discussion

Postby Vikram W » 25 May 2010 07:25

The mystery of the peeling paint is solved !! full points to pratik :)

so looks like the paint does not adhere to struts (probably titanium/alloys) well. Also, the composites have a primer on them before the final coat. Is this the RAM coating ?

Also, another question comes up here is , wasn't the RAM coating for metal parts , while composites by virtue of their properties are anyways radar neutral.

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Re: LCA news and discussion

Postby Vikram W » 28 May 2010 05:58

damn, i killed the thread :(

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Re: LCA news and discussion

Postby Gaur » 28 May 2010 10:18

I have an embarrassingly newbie question. I am designing a 3d model of Tejas. The airframe model is complete and now I have to add weapons. Now my knowledge of weapons and their loadouts is non existent. So I came across the following pic:
Image
Now, please help me with the loadout. Please consider that I want to use the heaviest "looking" loadout. I plan to use R-73 for hardpoints 1,7,8 and R-77 for 2,6. I plan to fit a droptank at 4. For 3,5 I plan to use Kh-59. Now, could anyone offer a different loadout which would "look" more heavy.
For eg: I seem to remember seeing a pic of gripen carrying 3 drop tanks (at 3,4,5). Is it possible for LCA to carry 3 drop tanks? The hardpoints seem to be strong enough but is there anything preventing tejas from doing that. Because if it can then it will be a much more favorable loadout for me as it will negate the need to model Kh-59.
Any suggestions?

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Re: LCA news and discussion

Postby Neshant » 28 May 2010 11:09

Something like 20 hz or 50 hz as elevator flapping rates is ridiculous. There is no way anyone can engineer a large structure for that.


I didn't wade too much into the past messages so forgive me if I'm talking out my hat here.

But 20 hz or 50 hz elevator adjustments might not necessarily mean full scale deflection. What kind of mechanical device/motor controls these flaps and what is its resolution? A hz is a cycle per second but cycle of what? It could be that a cycle in this case is a slight adjustments of point-something of a degree per step of the flap. A series of 20 small step adjustments in 1 second I imagine is possible.

Also a full 20 * step resolution per second would be the theoratical maximum occuring only in a sharp roll. Most of the time the pilot would be in level flight and it might only be making mechanical adjustments of 2 or 3 steps and not wearing the flaps or motors down. The software should certainly accommodate a short term burst of 20 steps as if the pilot needs to conduct an emergency roll manouver during combat and the aircraft speed, environment sensors and flight control laws permit it, the move should be executed. It might strain the system but as long as its below the absolute maximum the system can take, the emergency manouver should be carried out even if it wears down the lifespan of whatever components.

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Re: LCA news and discussion

Postby Srivastav » 28 May 2010 13:27

Gaur wrote:I have an embarrassingly newbie question. I am designing a 3d model of Tejas. The airframe model is complete and now I have to add weapons. Now my knowledge of weapons and their loadouts is non existent. So I came across the following pic:......SNIP

A long time back we had this discussion on BR regarding hardpoints 2,6 having dual launchers for R-77....Itll be great if you can do a model with that in mind. Ofcourse, i do understand all this is time incentive and i apoligize if iam asking for too much.

P.S- if SHAR can do dual luancher, so can LCA (in my most humblest mango aadmi opinion)

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Re: LCA news and discussion

Postby Kartik » 28 May 2010 13:40

Gaur wrote:I have an embarrassingly newbie question. I am designing a 3d model of Tejas. The airframe model is complete and now I have to add weapons. Now my knowledge of weapons and their loadouts is non existent. So I came across the following pic:
Image
Now, please help me with the loadout. Please consider that I want to use the heaviest "looking" loadout. I plan to use R-73 for hardpoints 1,7,8 and R-77 for 2,6. I plan to fit a droptank at 4. For 3,5 I plan to use Kh-59. Now, could anyone offer a different loadout which would "look" more heavy.
For eg: I seem to remember seeing a pic of gripen carrying 3 drop tanks (at 3,4,5). Is it possible for LCA to carry 3 drop tanks? The hardpoints seem to be strong enough but is there anything preventing tejas from doing that. Because if it can then it will be a much more favorable loadout for me as it will negate the need to model Kh-59.
Any suggestions?


it doesn't carry R-73s on the hardpoint no.8. That is reserved for the LDP pod.

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Re: LCA news and discussion

Postby Gaur » 28 May 2010 14:37

^^
Thanks for the info. And can Tejas carry 3 drop tanks? AFAIK, 3 & 5 do not have any fuel lines to carry the fuel but I will be happy to be corrected as it will save me a little work.

Srivastav,
Thanks for the suggestion. I will consider dual launchers.

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Re: LCA news and discussion

Postby marimuthu » 28 May 2010 14:51

Deleted. Gaur edit your post also
Last edited by marimuthu on 28 May 2010 15:01, edited 1 time in total.

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Re: LCA news and discussion

Postby shiv » 28 May 2010 14:53

Neshant wrote:
Something like 20 hz or 50 hz as elevator flapping rates is ridiculous. There is no way anyone can engineer a large structure for that.


I didn't wade too much into the past messages so forgive me if I'm talking out my hat here.

But 20 hz or 50 hz elevator adjustments might not necessarily mean full scale deflection.



I am not an expert either, but let me put a figure on the time it takes to achieve full deflection. Let me assume for the sake of discussion that a full deflection of an aileron from neutral position can be achieved in a quarter of a second. That is fast. For an aircraft to do that the aileron has to move "BANG!!" Anyone lying on the wing using the aileron as a pillow would have his head knocked off.

How many commands should come from the computer to cause this fastest, fullest deflection?

50 commands? 20 commands? 1 command?

Assume that 50 commands need to be sent (50 Hz). If 50 commands are needed for one fast, full deflection of the aileron, what will one command of that series achieve? Assume that one command achieves 1/50th of the full deflection (as you suggest).

But the computer has already calculated that it wants full deflection as fast as possible. Sending 50 separate commands is pointless. After each 1/50the command the computer has to wait for the sensors to indicate that the required movement has been achieved, and then send the second of fifty commands, wait for the movement and verification, then send the third etc. The verification is being done at 80 times a second (12.5 msec). So computer sends one command. The aileron moves 2%, then the computer waits 12.5 msec for the update and then sends the next command. So a full movement of the aileron is done in 50 separate steps with 12.5 msec verification gaps between steps. Note that full deflection of the aileron will require (12.5 * 50)=0.625 seconds for verification alone in addition to 250 msec for full movement of the aileron. That means that by sending 50 separate commands the computer is getting a full deflection only after 0.875 seconds - almost one full second when the fastest achievable speed is only one quarter second (0.250 sec) This is absurd.

Please don't say that the computer does not need to wait for verification between commands. If the computer does not need verification then there is no need for FBW. The pilot will be as good as the computer in sending commands without knowing the exact deflection. In any case the rate of verification (updates of sensors) is 80 times a second (for LCA)

All that the computer needs to do is calculate and say "I want X degrees of movement" and send one command for that. If the computer wants full deflection it ends one command. After it sends that command the aileron will take 250 milliseconds anyway to move to that position. If the computer did not want full deflection it will ask only for maybe half deflection. half deflection may occur in 150 msec and the computer will know 12.5 msec after that about the position. All done in less than 1/5th of a second. But with 50 commands a second the computer again takes ages to execute the command - 25 separate steps to reach half deflection with 24 * 12.5 msec pauses for sensor update.

Believe me, 2 Hz or 3 Hz is a perfectly good rate of control. Even the references that I dug up say that adding a FBW actually reduces the rate and number of commands the surfaces get compared with the approximate analog control that the pilot executes using his eyes and seat of his pants for sensors. Control is better and wear and tear is less. By sensing faster the computer can exert just as much control as needed without over correcting and retracting (or under-correcting and further correcting) as human pilots do. The computer does it in one step. Period. No need for 20, or 50 steps a second.

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Re: LCA news and discussion

Postby Gaur » 28 May 2010 14:59

marimuthu wrote:Gaur Mail me. Will discuss offline. Replace x with a.

Mail sent.

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Re: LCA news and discussion

Postby Gaur » 28 May 2010 19:45

Does anybody know the dimensions of drop tanks carried by Tejas (both 1200lt and 800lt).
Also, which capacity tank is this one carried by tejas?
Image

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Re: LCA news and discussion

Postby Hiten » 28 May 2010 20:00

An article from Feb-March issue of Technology review. Don't think it was posted


Supersonic Tejas

Achieving speed of Mach 1.6, equivalent of 1,699 kilometers per hour, Light Combat Aircraft (LCA) Tejas is India’s first indigenous supersonic, light weight fighter aircraft. There has been no looking back ever since the LCA took its maiden test flight on January 4, 2001.


Their pics not widely posted elsewhere I think.

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Re: LCA news and discussion

Postby krishnan » 28 May 2010 20:07

Some realy nice pics. Especially the last one .

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Re: LCA news and discussion

Postby Craig Alpert » 28 May 2010 20:17

That cockpit looks swell, more inline with a True 4+ generation Fighter Jet... Just hope that the Naval aircraft would have a Higher back seat FOV a la Su-30MKI, but all in good times.. Amazing HD pics btw, and notice the metion of AURA on the last page..


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