LCA Tejas: News and Discussions

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Re: LCA Tejas: News and Discussions

Postby Raveen » 21 Apr 2015 07:07

vivek_ahuja wrote:So, the discrepancy with the Mirage-2000C numbers in the previous analysis also leads to other repercussions.

The issue of sustained-turn-rate (STR) was raised earlier on this page. Well, when you account for the aerodynamic characteristics as evaluated from the previous analysis I did, the numbers for the LCA versus the Mirage-2000C in a horizontal sustained turn at empty weight looks like this:

Image

Note: I put in the LCA Mk-2 as a basic analysis by replacing the engine with the newer F414 and left the aerodynamics as they have been reported by the ADA. So that's just a rough estimation of the LCA Mk-2 performance to show what a better engine can provide.

So yeah, unless someone finds me a way to refute the Mirage-2000C's outstanding performance numbers from the simulations, the picture looks "interesting" for the LCA, to say the least.

Anyway, this is an ongoing investigation from my side, but I thought you all needed to appreciate why I am worried about the earlier analysis on range performance for the two aircraft.

Bottom line: Range/Endurance and STR/ITR analysis are not decoupled. The aerodynamics binds both of them together for each aircraft. So an aircraft having very poor range on account of its aerodynamics is also going to have other effects visible in its maneuvering performance.

P.S.: I would like to see this spreadsheet analysis done years ago on BRF, if anyone has it. Perhaps it will yield some clues as it why my predictions are so much at odds with generally accepted wisdom for the LCA.

-Vivek


I am hoping/I know that the work they are doing to reduce the drag will help with the aero inefficiencies of the LCA design. There are obvious things they missed when it came to drag, and since they are so obvious, I am sure its inexperience with building TFTA fighters...the Mk2 will leverage the lessons learnt with Mk1 and I am sure will show significantly improved characteristics - the quantitative improvement remains to be seen.
Last edited by Raveen on 21 Apr 2015 07:50, edited 1 time in total.

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Re: LCA Tejas: News and Discussions

Postby srai » 21 Apr 2015 07:44

vivek_ahuja wrote:...

So yeah, unless someone finds me a way to refute the Mirage-2000C's outstanding performance numbers from the simulations, the picture looks "interesting" for the LCA, to say the least.

Anyway, this is an ongoing investigation from my side, but I thought you all needed to appreciate why I am worried about the earlier analysis on range performance for the two aircraft.

...

-Vivek


Let's check Mirage-2000 and LCA's performance against MiG-21, MiG-29 and F-16. That would probably show if the Mirage-2000 figures in your simulations are accurate.


ImageImage

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Re: LCA Tejas: News and Discussions

Postby Shankk » 21 Apr 2015 08:21

Saurav Jha ‏@SJha1618 1m1 minute ago New Delhi, Delhi
It is time for a major CAG report on the entire Tejas program. Let there be Doodh ka Doodh, Paani ka Paani.


Looks like ADA and HAL are pretty confident in how things will turn out.

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Re: LCA Tejas: News and Discussions

Postby pragnya » 21 Apr 2015 08:44

vivek_ahuja wrote:So, the discrepancy with the Mirage-2000C numbers in the previous analysis also leads to other repercussions.................


there is some info which might be useful for you wrt ITR of M2K. though i don't know the authenticity of the figures, this site has been existing for a long time.

http://www.mirage-jet.com/COMPAR_1/compar_1.htm

on a side note the ranges you showed of LCA wrt M2K was a tad surprising as LCA sports a more modern engine with better fuel fraction. so either the data is suspect or LCA must be too draggy but LCA TPs are on record it handles better than M2K which does give a hint that it may not be so draggy.

anyway you are better at these things and so i leave it to you.

but you great as always. :)

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Re: LCA Tejas: News and Discussions

Postby Singha » 21 Apr 2015 09:13

there was some talk HAL wanted to lease/buy a single Mig29 or Su30 from IAF to use as flying engine test bed.

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Re: LCA Tejas: News and Discussions

Postby vivek_ahuja » 21 Apr 2015 09:24

srai wrote:Let's check Mirage-2000 and LCA's performance against MiG-21, MiG-29 and F-16. That would probably show if the Mirage-2000 figures in your simulations are accurate.

Image


srai,

That's a wonderful data set! And its exactly what I needed to validate my results. Many thanks for you digging that out! :!:

So I went through that sheet and extracted the numbers for 15,000 ft AGL and the weight specified and plugged the same into my code. Since I was evaluating the load factors as a function of Mach number, I went into the plot above and extracted the values I needed for a given mach number and a load factor for the turn rate (load factors varied between 2.87 and 5.68 for a given Mach number). I then plotted the same versus my own FlightStream results to get the following:

Image

Unfortunately, the above plot makes me the bearer of bad news and confirms my suspicions: my Mirage-2000 numbers are correct.

And since the LCA numbers are based on ADA data, the above analysis is closer to correct than I would have ideally liked. But I am not in the business of fudging numbers to suit my viewpoint.

So where does that leave us?
1. ADA is not giving us correct numbers or the latest numbers: possible.
2. Is the LCA closer to the Mirage-2000 than it is to the Mig-21: quite possibly true.
3. Has perhaps that closeness (not better, but closeness) to the Mirage-2000 caused folks close to the program to slightly exaggerate for the media: possible.
...
4. Has Vivek totally lost it and spouting nonsense: very much possible. :mrgreen: 8)

-Vivek

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Re: LCA Tejas: News and Discussions

Postby shiv » 21 Apr 2015 09:38

On the general question of "underpowered" blah blah - please have a look at this
Image
---------------------------------
Image

The proof of the pudding can only come from the eating. The IAF must use it and decide, not pre-judge. No need to talk about bad or good news form paper specs - that is as bad as the IAF has done

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Re: LCA Tejas: News and Discussions

Postby vivek_ahuja » 21 Apr 2015 09:45

shiv wrote:The proof of the pudding can only come from the eating. The IAF must use it and decide, not pre-judge. No need to talk about bad or good news form paper specs - that is as bad as the IAF has done


That's fair enough. Its nice to know where the LCA stands relative to others in theory. But my analysis is not affiliated with anybody official. So it can be taken as entertainment value if required.

My contention, however, is that comparing the LCA as being "close to the Mirage-2000" is, quite frankly, a compliment for the little desi fighter. After all, it was meant to replace the Mig-21, not the Mirage-2000!

I think an analysis is due to compare the LCA with the Mig-21 to put that issue at rest.

Anyway, that's just my two cents.

-Vivek

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Re: LCA Tejas: News and Discussions

Postby shiv » 21 Apr 2015 10:03

vivek_ahuja wrote:
That's fair enough. Its nice to know where the LCA stands relative to others in theory. But my analysis is not affiliated with anybody official. So it can be taken as entertainment value if required.

My contention, however, is that comparing the LCA as being "close to the Mirage-2000" is, quite frankly, a compliment for the little desi fighter. After all, it was meant to replace the Mig-21, not the Mirage-2000!

I think an analysis is due to compare the LCA with the Mig-21 to put that issue at rest.

Anyway, that's just my two cents.

-Vivek


Vivek it's not about your analysis but how the analysis is interpreted and this is something that PR and advertising depts and sales depts anywhere understand.

Unless one produces a graph in which every parameter of the LCA exceeds every parameter of every other aircraft, 99% of people are going to say that it is a useless aircraft, fuelling the media and helping non techies in the IAF to do their hackthoo. It is OK for eggheads and academics to look at paper comparisons and do the fancy math, but the "in your face" conclusion that has been reached on this very page is that the LCA is not as good as the Mirage 2000 even though it is 20 years younger because 99% of BRFites cannot actually understand how you got the results, but they can understand the results. That is the "bad news'.

That is why I wanted to post a comparison of MiG 21 and HF 24. How come the HF 24 was retired and the MiG 21 is still around? The point is that graphs, no matter how accurate do not define real life situations when the flying LCA has a t/w ratio and altitude that falls on one point of the graph and an opposing aircraft happens to have a profile that falls on a point in the graph that puts its performance inferior to the LCA. Or both aircraft are on different graphs that need to be seen together to predict what will happen at one point in time. These are the real life situations that were described in the HF 24 scans that I posted.

In operational service aircraft are typically used where their performance can score over anything that goes over them in other situations. You know that some huge, heavy bombers at high altitude could outmanoeuvre the needle nosed supersonic fighters that were sent out to catch them. The graph tells the truth, but the shape of the graph can change if you change the context and parameters chosen - and those are the things that are the big variables in real life.

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Re: LCA Tejas: News and Discussions

Postby vivek_ahuja » 21 Apr 2015 10:12

pandyan wrote::shock: I dont know how you are pulling all this magic. and arriving at conclusion based on the data.


Honestly, saar, I am just doing my best to seed this forum with an appreciation for quantitative analysis. When it takes only a couple hours of my time to do something and put it up here, my argument is, why not?

I shudder to draw too many conclusions from my analysis simply because, as I said in my disclaimer, I am not officially representing anyone. I am simply reverse engineering public domain data to do some analysis.

My only credibility with any of this is that I wrote FlightStream and its underlying vorticity solver during my PhD. I now run, at least partly, a startup that markets the software commercially. It has been evaluated and used by several of the biggie aerospace firms in the States. It has had a dedicated session during the NASA OpenVSP seminar last year in California, and so on.

pandyan wrote:Did you also pitch your Flighstream software to ADA/HAL?


But for all that, when I was a student several years ago, I had once talked to some NAL folks about FlightStream during an AIAA conference in the states. All of these gentlemen were CFD folks to the core, which meant that any other tool was, in their minds, to be smirked at derisively, if not openly mocked and laughed at. Anyway, that's exactly what happened. These gentlemen dismissed the tool as offering no real advantages to their existing CFD tools even though those advantages was exactly what my talk had just been about! And that was that. I never heard from them again. In the meantime, my start-up picked up some small business with the U.S. Aerospace firms and so that was that.

-Vivek

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Re: LCA Tejas: News and Discussions

Postby vivek_ahuja » 21 Apr 2015 10:18

shiv wrote:Vivek it's not about your analysis but how the analysis is interpreted and this is something that PR and advertising depts and sales depts anywhere understand.

Unless one produces a graph in which every parameter of the LCA exceeds every parameter of every other aircraft, 99% of people are going to say that it is a useless aircraft, fuelling the media and helping non techies in the IAF to do their hackthoo. It is OK for eggheads and academics to look at paper comparisons and do the fancy math, but the "in your face" conclusion that has been reached on this very page is that the LCA is not as good as the Mirage 2000 even though it is 20 years younger because 99% of BRFites cannot actually understand how you got the results, but they can understand the results. That is the "bad news'.


Right. Therein lies the problem that I wonder about as well. The problem with any quantitative analysis is that while the creator of the plots knows where the numbers are coming from, how do you convince the users of their veracity?

Its a very fair argument. And to which I have no easy answer, short of writing a peer-reviewed paper on the same. Even then, the peers would have to review the code and the output to be 100% sure of the analysis.

I don't know, but thinking out loud, does it make sense for other prominent BRF users to become proficient at using FlightStream so that one analysis can be vetted by others?


shiv wrote:In operational service aircraft are typically used where their performance can score over anything that goes over them in other situations. You know that some huge, heavy bombers at high altitude could outmanoeuvre the needle nosed supersonic fighters that were sent out to catch them. The graph tells the truth, but the shape of the graph can change if you change the context and parameters chosen - and those are the things that are the big variables in real life.


Agreed. Which is why I always emphasize that folks need to be careful of the context under which I try to do an apples to apples comparison. Generalizing the analysis without context is dangerous.

Not to mention, if the data used (like the ADA paper for the LCA data) is outdated and/or just not correct, then we are going on the wrong path and wouldn't know it.

Like I said: difficult questions for which there are no easy answers.


But the question is: under these circumstances, is it better it to have such analysis or not have it at all? If the answer is that we do not want the public perception shifting one way or another without real access to experimental data, then perhaps the correct recourse is for me to not put up such analysis?

Look, I am not adamant on this point. If the plots I put here are seen to be damaging, I will gladly snuggle back into the scenarios dhaga from which I have ventured out. Cerberus awaits, after all! :)

-Vivek

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Re: LCA Tejas: News and Discussions

Postby pragnya » 21 Apr 2015 10:34

shiv wrote:On the general question of "underpowered" blah blah - please have a look at this
Image
---------------------------------
Image

The proof of the pudding can only come from the eating. The IAF must use it and decide, not pre-judge. No need to talk about bad or good news form paper specs - that is as bad as the IAF has done


correct shiv. fwiw i made a quick calculation of T/W ratio of LCA in A2A mode and with 100% fuel and 4 R77s/2 R73s/LDP/100kg as pilot wt, i get about 0.89 t/w ratio which progressively increases to tad above 1 at 50% fuel.

empty wt taken - 6560kg
IF - 2500kg
engine thrust - 9163kg (tejas site)

when i had done this wrt Mig 21s many moons ago, LCA had better thrust/wt ratio. may be i need to check again.

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Re: LCA Tejas: News and Discussions

Postby Singha » 21 Apr 2015 10:51

> 4 R77s/2 R73s/LDP/100kg as pilot wt

thats not realistic imo.

for Mig21 you can put 1 centerline drop tank and 4 R77 under the wings ( it maxes out at 4 aam)

for Tejas you can out 1 centerline drop tank and 4 R77 + 2 R73 under the wings and no LDP

above would be typical air to air mission load.

for A2G mode,
LDP + two drop tanks on inner pylons, 1 bomb under centerline , 2 under the wings and 2 R73 on outermost.

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Re: LCA Tejas: News and Discussions

Postby pragnya » 21 Apr 2015 11:14

Singha wrote:> 4 R77s/2 R73s/LDP/100kg as pilot wt

thats not realistic imo.

for Mig21 you can put 1 centerline drop tank and 4 R77 under the wings ( it maxes out at 4 aam)

for Tejas you can out 1 centerline drop tank and 4 R77 + 2 R73 under the wings and no LDP

above would be typical air to air mission load.

for A2G mode,
LDP + two drop tanks on inner pylons, 1 bomb under centerline , 2 under the wings and 2 R73 on outermost.


thanks.

ok. i redid as per your post. removed LDP and included centreline drop tank (1200 litres).

again @ full internal fuel, t/w starts at 0.82 and after the drop tank has been ejected and 50% fuel is reached t/w comes 1.03.

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Re: LCA Tejas: News and Discussions

Postby JayS » 21 Apr 2015 11:25

vivek_ahuja wrote:So, the discrepancy with the Mirage-2000C numbers in the previous analysis also leads to other repercussions.

The issue of sustained-turn-rate (STR) was raised earlier on this page. Well, when you account for the aerodynamic characteristics as evaluated from the previous analysis I did, the numbers for the LCA versus the Mirage-2000C in a horizontal sustained turn at empty weight looks like this:


Note: I put in the LCA Mk-2 as a basic analysis by replacing the engine with the newer F414 and left the aerodynamics as they have been reported by the ADA. So that's just a rough estimation of the LCA Mk-2 performance to show what a better engine can provide.

So yeah, unless someone finds me a way to refute the Mirage-2000C's outstanding performance numbers from the simulations, the picture looks "interesting" for the LCA, to say the least.

Anyway, this is an ongoing investigation from my side, but I thought you all needed to appreciate why I am worried about the earlier analysis on range performance for the two aircraft.

Bottom line: Range/Endurance and STR/ITR analysis are not decoupled. The aerodynamics binds both of them together for each aircraft. So an aircraft having very poor range on account of its aerodynamics is also going to have other effects visible in its maneuvering performance.


-Vivek


Vivek,
Awesome analysis. I visited website for your software. Seems amazing. I had thought of using openVSP along with DATCOM to get some numbers. But I could never make my lazy a$$ move for that. :(

BTW do you think taking into consideration LE devices will change the results?? Not much in low AoA regime such as cruise but in manuevres LE devices should give atleast 5-10% (my guess) boost in L/D.

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Re: LCA Tejas: News and Discussions

Postby srin » 21 Apr 2015 11:29

vivek_ahuja wrote:But the question is: under these circumstances, is it better it to have such analysis or not have it at all? If the answer is that we do not want the public perception shifting one way or another without real access to experimental data, then perhaps the correct recourse is for me to not put up such analysis?

Look, I am not adamant on this point. If the plots I put here are seen to be damaging, I will gladly snuggle back into the scenarios dhaga from which I have ventured out. Cerberus awaits, after all! :)

-Vivek


Vivek - I think anything that increases the level of debate with actual data and scientific analysis is a welcome thing. I particularly mention yours and Nilesh's analysis. Otherwise, we'd just be talking about the HAL vs ADA vs IAF politics or Prodyut Das' opinions. Can't say for others, but I love your work.

One side note - the Mirage performance graphic said it was for 15000 ft altitude at *maximum power* (wet thrust). Are you using the same for LCA too ?

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Re: LCA Tejas: News and Discussions

Postby habal » 21 Apr 2015 11:45

nileshjr wrote:I feel stopping Kaveri is a grave strategic mistake. We could have built flight testing capabilities in near future which would have accelerated future programs a great deal.


they are working only on the core now. So they do not find it necessary to lug the entire engine as a single project. Is that true.

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Re: LCA Tejas: News and Discussions

Postby Cybaru » 21 Apr 2015 11:56

With the swedes trying hard to kill of LCA and the industry trying to take a piece of HAL's pie one way or another, maybe this isn't the best time to explore this until we are really sure we have numbers for all aircraft dead on.

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Re: LCA Tejas: News and Discussions

Postby shiv » 21 Apr 2015 14:07

vivek_ahuja wrote:Look, I am not adamant on this point. If the plots I put here are seen to be damaging, I will gladly snuggle back into the scenarios dhaga from which I have ventured out. Cerberus awaits, after all! :)

-Vivek

No the graphs are beautiful and I intend to use them to illustrate a point. (If I can)

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Re: LCA Tejas: News and Discussions

Postby JayS » 21 Apr 2015 17:19

indranilroy wrote:Don't know. There are quite a few papers by Anand Kumar which shows that their simulations had good fidelity. In one paper, he did match results with the LCA wind tunnel test results. For some tests it was a perfect match. IIRC, the vortex breakdown reaches the TE at 33 degrees and the apex at 52 or 55 degrees. Not just that they got good results even with matching sharp edges and round edges with various radii. Similar results were published people at Jadavpur university. We know that some development did go on there.


I do not know exact nature of the solvers this author is using, but without being too pedantic I can say that, Euler solvers and other linear theory based solvers are great at low speed low AoA regimes, give quite good results especially for conceptual or preliminary design. I would expect decent match at low-to-mod AoA but not so much at high AoA regimes. It would be interesting to see if this author has got accurate results at anything above 20-25degree AoA and how.
indranilroy wrote:So you are saying that because of the lesser sweep of the inboard section, the axis of vortex is more spanwise, taking it away from the fin. But when the primary vortex of the inboard section interacts with the primary vortex of the outboard section, the latter is energized and moves inboard.


I was saying only the first part. But now that you bring the other point, I am thinking about it. There is a possibility that the inboard LE vortex gets under the separated fluid layer from outboard LE and make it attach farther inboard (moving primary attachment line towards centre). This would enlarge the area of effect of the LE vortex. Can't say for sure. I need to see the available CFD results with me more carefully.

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Re: LCA Tejas: News and Discussions

Postby srai » 21 Apr 2015 18:55

vivek_ahuja wrote:...
P.S.: I would like to see this spreadsheet analysis that Singha et. al. are talking about, if anyone has it. Perhaps it will yield some clues as it why my predictions are so much at odds with generally accepted wisdom for the LCA.

-Vivek


The two people who would have that Excel spreadsheet. Here are the posts of what was discussed back then (23 Feb 2010):
...

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Re: LCA Tejas: News and Discussions

Postby Indranil » 21 Apr 2015 19:15

nileshjr wrote:I do not know exact nature of the solvers this author is using, but without being too pedantic I can say that, Euler solvers and other linear theory based solvers are great at low speed low AoA regimes, give quite good results especially for conceptual or preliminary design. I would expect decent match at low-to-mod AoA but not so much at high AoA regimes. It would be interesting to see if this author has got accurate results at anything above 20-25degree AoA and how.

AFAIR, they are not mere Eulerian solvers. In fact, the papers are not about the wing design, but the design of new solvers which can be used to study vortices from a highly swept delta wing, especially at medium to high AoA and around the wing apex.

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Re: LCA Tejas: News and Discussions

Postby Shalav » 21 Apr 2015 21:35

@Cybaru

I don't use my VSNL ID now. Write to jaihind outlook. xom

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Re: LCA Tejas: News and Discussions

Postby vina » 21 Apr 2015 22:22

vivek_ahuja wrote:I then ran similar numbers for the LCA and the Mirage-2000C at 20,000 ft ASL and got the following (note: aerodynamic coefficients corrected for the LCA reference areas and lengths):
Image Image


The Mirage numbers are wrong. No way a fighter which needs to go supersonic (thin wings with low aspect ratios) and needs to maneuver hard is going to have L/D ratios approaching commercial passenger long haul jet liners. You can google up the typical numbers yourself (wiki entry for Lift to drag ratio gives the B747's in cruise as 17, which is not far off from the numbers you put for M2K) . For concorde the cruise L/D , the same link says is around 7. Fighters typically have very low glide ratios. No way a M2K goes 16 unit for 1 unit drop in altitude.

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Re: LCA Tejas: News and Discussions

Postby JayS » 21 Apr 2015 22:33

Was just going through old mil archives and there is a thread when LCA had its first flight. From that I got this. Posted by a poster with handle "Arun_S".

Take it FWIW:

http://forums.bharat-rakshak.com/viewtopic.php?f=10&t=268&start=80#p27883
From BR Forum by Arun_s:

Just Chipped in to say that the LCA can carry maximum External Store(Wepons, etc) of 4,700Kg and this data is quite reliable. That means MTOW of 13.7 ton. That would allow following maximum range LCA configuration:
7.5 Ton Fuel: 3T (Internal) + 0.5T (internal reserve) and 4T (5 external tanks). 1.5 Ton Air Defense Payload:………..i) Two long/medium range missiles of upto 750 Kg on outer hardpoints. OR………..ii) two 1500 lb bombs (Cluster or singular) Total cruise fuel: 6.5Ton (Assumeshe balance 1Ton fuel for combat and takeoff) With previous post assumptions that gives flight time of 1.9 Hr(115 Min), range of 1721 Km and combat radius of ~860 Km. Compare that with Mig21.
Typical LCA confign is more likely with only 3 fuel tanks and 4 weapons: A. 5.9 Ton Fuel: 3T (Internal) + 0.5T (internal reserve) and 2.4T (3 external tanks) B. 2.3 Ton (5060 lb) Air Defense Payload: That would allow:……. 4 air-defence missiles (long & short range) for defensive role OR ……. 2 air defence missiles & 2 bombs of 2000 lb each that gives flight time of 1.4 Hr(86 Min), range of 1300 Km and combat radius of ~650 Km.
LCA confign with only 2 fuel tanks and 5 weapons: A. 5.1 Ton Fuel: 3T (Internal) + 0.5T (internal reserve) and 1.6T (2 external tanks) B. 3.1 Ton (6820 lb) Air Defense Payload: That would allow:……. 5 air-defence missiles (long & short range) for defensive role OR……. 2 air defence missiles & 3 bombs of 2000 lb each that gives flight time of 1.2 Hr(72 Min), range of 1085 Km and combat radius of ~540 Km.


And he quoted Dr. Kota Harinarayana for LCA ferry range of 3000km in other post.

Looks like numbers from ADA to me. 540 km combat radius looks familiar to me. But this was in 2001 and these numbers may not be applicable now as they are.

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Re: LCA Tejas: News and Discussions

Postby JayS » 21 Apr 2015 22:50

indranilroy wrote:
nileshjr wrote:I do not know exact nature of the solvers this author is using, but without being too pedantic I can say that, Euler solvers and other linear theory based solvers are great at low speed low AoA regimes, give quite good results especially for conceptual or preliminary design. I would expect decent match at low-to-mod AoA but not so much at high AoA regimes. It would be interesting to see if this author has got accurate results at anything above 20-25degree AoA and how.

AFAIR, they are not mere Eulerian solvers. In fact, the papers are not about the wing design, but the design of new solvers which can be used to study vortices from a highly swept delta wing, especially at medium to high AoA and around the wing apex.

Hmm. May be. The paper from where we got the figure said its from Euler simulation. ADA/NAL between them have a bunch of codes.

There an older paper by same author, 1993, i guess, which show results from both Euler and RANS solvers. Its available from google, but I can't find link now. There you could see the how Euler code could not predict vortex breakdown point accurately. RANS was better in that respect.

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Re: LCA Tejas: News and Discussions

Postby JayS » 21 Apr 2015 23:39

The data posted by srai and link by pragnya are same data as far as I can see (and supposedly from Dassualt itself and with lots of masala perhaps). But one of the data points from the data is:

Air Superiority Mission - Radius of Action
Two IR Missiles + Four BVR Missiles + Maximum Tanks
Combat - 5 Min. @ Max Power - 30,000ft. (9144m) - Mach 0.8
Tanks dropped prior to combat - Self defence Missiles retained.

Mirage 2000 >> 2 Magic +4 MICA +3 tanks >> 780 nm

5min combat >> ~ 250*5 kg fuel spent in combat manoeuvre itself (from that data tables). And rest used at 0.8 cruise. 780 nm ~ 1444 km. It says action of radius of 1444 km. Which matches with Vivek's data point of 2886 km range that too with 5 min of combat. Unbelievable!! Are these figures real??

@ Vivek:

Found this performance model for M2K for some simulator/game I guess. The author also uses the same dataset for calibration at some places. Look at the L/D curves he got. You are in a better position to judge, so leaving it to you.

http://www.checksix-fr.com/downloads/falcon4/Topolo/Beta/Falcon4M2K.pdf

L/D Graph
Last edited by JayS on 22 Apr 2015 11:32, edited 2 times in total.

Indranil
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Re: LCA Tejas: News and Discussions

Postby Indranil » 22 Apr 2015 00:05

I guess it is time for creating a "learned" questionnaire for the TPs and ADA designers. We can pass it to reporter(s) of our choice and she/he can add his/her questions and find answers. There are some good reporters we can chose from. LCA's strengths needs to be brought out in the open, especially at this juncture. A lot of reporters get their stuff from BRF. Its time to cut through bronchitis, and get the actual stuff out there.

Tejas needs to be saved, and whatever we can do towards this will be time well-spent. Nilesh, do you want to compile the questionnaire? Call out names, and the poster can contact you through email.

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Re: LCA Tejas: News and Discussions

Postby ramana » 22 Apr 2015 00:10

Saurav Jha I would suggest.
Develop the questions in GDF.

Thanks, ramana

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Re: LCA Tejas: News and Discussions

Postby sankum » 22 Apr 2015 00:13

LCA mk1 with full external payload of 3500kg with max external fuel tanks+2*250kg PGM and 200kg LDP weight estimate is as follows.

LCA mk1 clean weight 9800kg with full internal fuel of 2458Kg, pylons, pilot, cannon ammo etc. and 2 SR R73 AAM.

Clean weight 9800 Kg+ 2*1075 kg( 2*1200lt external underwing tanks)+ 650Kg(725lt centerline tank)+200kg LDP+ 2*250Kg laser guided bombs=13300Kg(MTOW)

From Vivek's plots 6.5t empty weight+5 t fuel weight we get ranges for 1800Kg payload.

sea level 1100Km range i.e, 550Km radius range.

20000ft 1300Km range i.e, 650Km radius range

30000ft 1200Km range i.e, 600Km radius range

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Re: LCA Tejas: News and Discussions

Postby vivek_ahuja » 22 Apr 2015 01:33

vina wrote:The Mirage numbers are wrong. No way a fighter which needs to go supersonic (thin wings with low aspect ratios) and needs to maneuver hard is going to have L/D ratios approaching commercial passenger long haul jet liners. You can google up the typical numbers yourself (wiki entry for Lift to drag ratio gives the B747's in cruise as 17, which is not far off from the numbers you put for M2K) . For concorde the cruise L/D , the same link says is around 7. Fighters typically have very low glide ratios. No way a M2K goes 16 unit for 1 unit drop in altitude.


That's exactly why I brought that up. The only way the Dassault flight data works is for these numbers that have been generated for L/D versus CL. There is just no other way to get that level of range from the Mirage-2000C with the low L/D numbers we typically associate with delta wings.

So either the Dassault data is plain wrong and/or lies, or they have a wonderful fighter in the Mirage that is beyond belief.

nileshjr wrote:Unbelievable!! Are these figures real??


Exactly my thought. Something doesn't add up somewhere. I will review my simulations again, but it would be good to trace the veracity of that Mirage data. I think maybe Dassault might have messed up ranges with radii of action? That happens a lot, unsurprisingly, even in industry.

-Vivek

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Re: LCA Tejas: News and Discussions

Postby JayS » 22 Apr 2015 01:44

nileshjr wrote:
srin wrote:Basic aero pooch out of curiosity: for area rule, do they calculate cross-sectional area with the external stores and without ? Because, pylons and drop tanks seem to noticeably increase the cross-sectional quite a bit ...


I dont know what they do as a matter of fact but if I am designer I would choose one typical config depending upon intent of the aircraft and use that to design at one particular design point. For ex: for interceptor, aircraft with 2 WVR missles at wingtip and other pylons absent or with fairings put on them. But I would keep it simple, perhaps just a clean config as far as area rule is concerned. I wouldn't want to have an aircraft config with truckload of bombs/missiles right at the design stage.


Srin, you had asked this question some time ago. I found one fact regarding M2K. According to this link: http://www.fighter-planes.com/info/mir2000.htm

M2K is area ruled carrying four air-to-air missiles (which four, is not mentioned, perhaps 2BVR + 2 WVR)

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Re: LCA Tejas: News and Discussions

Postby sankum » 22 Apr 2015 02:12

LCA mk1 weight estimates for air to air missions.

R 77 is 190kg missile with 60 Kg launcher for a total weight of 250Kg.

2*R 77 + 2*R 73 with max external fuel

Clean weight 9800 Kg+ 2*1075 kg( 2*1200lt external underwing tanks)+ 650Kg(725lt centerline tank)+ 2*250Kg(2* R77) =13100Kg

200kg optronic pod can be carried for recce mission in above configuration and weight reaches MTOW of 13300kg.

4*R 77 + 2*R 73 with centerline fuel tank of 725litres.

Clean weight 9800 Kg+ 650Kg(725lt centerline tank)+ 4*250Kg(4* R77) =11450 Kg

600Kg ARM missile can be carried in place of centerline fuel tank of 725litres.

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Re: LCA Tejas: News and Discussions

Postby JayS » 22 Apr 2015 02:23

vivek_ahuja wrote:
nileshjr wrote:Unbelievable!! Are these figures real??


Exactly my thought. Something doesn't add up somewhere. I will review my simulations again, but it would be good to trace the veracity of that Mirage data. I think maybe Dassault might have messed up ranges with radii of action? That happens a lot, unsurprisingly, even in industry.

-Vivek



Looks like there is only one dataset, that too given by Dassault and everyone uses those values only.

Disclaimer: I am doing this Range calculation for the first time for any jet. Doing some very crude back-of-the envelop calculations. So take it FWIW. They might be totally off.

According to the dataset @max power, M0.8 and 15000ft fuel consumption is 275 kg/min (assuming that is with A/B.for combat manoeuvre).
Max fuel capacity is 8000lit. Assuming 1000lit for reserve/taxiing/TO/Landing etc. Usable fuel in air is 7000lit. With 5 min combat as mentioned earlier about 275*5~1400kg ~ 1800lit fuel is spent. This leaves 5200 lit fuel. Now if the jet has 1444 km of combat radius, even with economical cruise of ~M0.8 at high altitude it would take around ~2885/850 ~ 3.4hrs to and fro. That gives fuel consumption rate of ~5200/205 ~ 25lit/min ~ 20kg/min. That's ridiculously less as compared to 275kg/min at max thrust. It should be of the order of 100+kg/min and then the combat radius would be <1450/2.5 ~ 580 km. Now that looks more realistic.

There is easy way of sanity check. The M2K data is given along with F-16 and F-18. It should be relatively easy to get numbers for those two birds and then we can match up it with this dataset. Can someone please throw in some realistic numbers for F-16??

EDIT: Checked sfc values of M53 from wikipedia. And that gives us:
64 kN (14,300 lbf) military thrust
95 kN (21,384 lbf) with afterburner
Overall pressure ratio: 9.8:1
Bypass ratio: 0.36:1
Specific fuel consumption:
0.90(kg/daN.h) Dry engine thrust >>> 96kg/min (my guess of 100kg/min is sensible then)
2.10(kg/daN.h) military thrust >>> 332kg/min

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Re: LCA Tejas: News and Discussions

Postby srai » 22 Apr 2015 04:13

^^^

It's obvious that 1,450km is the range (one-way) of Mirage-2000 and not the combat radius.

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Re: LCA Tejas: News and Discussions

Postby Vayutuvan » 22 Apr 2015 04:26

vivek_ahuja wrote: ... FlightStream during an AIAA conference in the states.

vivek: What was the "h" for the LCA/Mirage/other airframes you simulated? How many nodes in the mesh? Are the elements shells (with 5 DOF - sans drilling DOF)? By the way most are layered laminates with at least three layers and stiffened with beams. A flat (as opposed to hierarchical one) model of complete air frame with small enough h would have to close to 1 billion DOF. Elements have to formulated specifically with three or more layers with orthotropic properties (or sometimes even anisotropic properties) in a coordinate system that is local to each element and coupled with 3D beams (6 dof at each node with two nodes on a beam plus an orientation node). For example BAE in the past (about 5-10 years ago) considered a one gigadof fluids/structures coupled problem to be the holy grail of Aerospace. Today it is possible to do the structures part on a reasonably equipped (2 TB RAM and 16-32 cores) desktop. Modal, fluids, and fluid structure interaction will be the real difficult task.

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Re: LCA Tejas: News and Discussions

Postby ramana » 22 Apr 2015 04:35

vivek, If you uses similar L/D for Mirage as the LCA (for LCA is designed with M-2000 in mind some old Interavia article in the late 980s) what would you get? Or it that too trivial?

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Re: LCA Tejas: News and Discussions

Postby Cain Marko » 22 Apr 2015 04:52

srai wrote:
vivek_ahuja wrote:...
P.S.: I would like to see this spreadsheet analysis that Singha et. al. are talking about, if anyone has it. Perhaps it will yield some clues as it why my predictions are so much at odds with generally accepted wisdom for the LCA.

-Vivek


The two people who would have that Excel spreadsheet. Here are the posts of what was discussed back then (23 Feb 2010):
...


Whoa! How did you manage to dig that up Srai? In any case, I am afraid I have lost the said file, which Shalav was kind enough to create and give. Too many computer and hard-drive changes mean that I have lost plenty of useful stuff.

In any case, from what I can tell (just off the cuff numbers and such) for advertised ranges on internal fuel (this is not combat radius unless stated otherwise):

Mirage 2000: 1800km (my guess is ABs are not used on such a trip otherwise numbers would be a lot worse since the M2k is notorious for poor SFC with AB)

MiG-29A: 1600km
MiG-29M/35: 2000km
MiG-29K: 1800km+

F-16A: 2000km

Gripen C: 800km (Combat radius), so range ~ 2000km?

Where did I pick up these figures? Like I said - approximations from memory - derived from umpteen hours of trawling over the web years ago. Based on this, my guess for the Tejas would be around the ~ 1800 one way trip on internal fuel. But Vivek Sir's analysis suggests sadder possibilities? Even so, it would be a LOT better than the Mig-21 and possibly the vanilla 29 as well.

All in all, perhaps the IAF has some real reasons to push for the mk2 afterall?

For those of you who might be interested in SFC numbers, a site that is sort of useful:
http://www.jet-engine.net/

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Re: LCA Tejas: News and Discussions

Postby shiv » 22 Apr 2015 05:24

vivek_ahuja wrote:
vina wrote:The Mirage numbers are wrong. No way a fighter which needs to go supersonic (thin wings with low aspect ratios) and needs to maneuver hard is going to have L/D ratios approaching commercial passenger long haul jet liners. You can google up the typical numbers yourself (wiki entry for Lift to drag ratio gives the B747's in cruise as 17, which is not far off from the numbers you put for M2K) . For concorde the cruise L/D , the same link says is around 7. Fighters typically have very low glide ratios. No way a M2K goes 16 unit for 1 unit drop in altitude.


That's exactly why I brought that up. The only way the Dassault flight data works is for these numbers that have been generated for L/D versus CL. There is just no other way to get that level of range from the Mirage-2000C with the low L/D numbers we typically associate with delta wings.

So either the Dassault data is plain wrong and/or lies, or they have a wonderful fighter in the Mirage that is beyond belief.

Let me add one more possibility.

No aircraft manufacturer who is looking to survive and thrive by exporting his ware is ever going to publish exact data that might in any way remotely make his aircraft appear inferior to anything else within a radius of 20,000 km. If he does that he is committing hara kiri. I have never seen public data from Russians that make their aircraft look inferior to others. I have never seen public data from Americans that make their aircraft look inferior to others. I have never seen public data from the French that make their aircraft look inferior to others. I have seen plenty of data from all these sources that make other aircraft look worse than theirs. You do not make brochures that say that someone else is better.

Only ADA who are not even required to export half a toothpick can afford to publish data that is anywhere near accurate. That is also because if they bluff, aero labs around the world will dismiss their data outright because they are seen as competitors
Last edited by shiv on 22 Apr 2015 05:37, edited 1 time in total.

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Re: LCA Tejas: News and Discussions

Postby brar_w » 22 Apr 2015 05:30

In cases where you are seeking the absolute performance data you go out and use the data given in the flight manual itself. In case of the F-16C, it is public information.

https://publicintelligence.net/hellenic ... t-manuals/
Last edited by brar_w on 22 Apr 2015 05:49, edited 1 time in total.


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