LCA Tejas: News and Discussions

[JayS]

^^ brar_w

Thanks a lot for your efforts. Any info about LCA is welcome.

[uddu]

16 per year production rate is still very low. It need to be taken to a minimum of 25 per year and if we plan to export Tejas, then to 30 per year. What's this piddly 16. There's also a huge market out there for countries that will be replacing their Mig-21's and F5's

[putnanja]

16 per year production rate is still very low. It need to be taken to a minimum of 25 per year and if we plan to export Tejas, then to 30 per year. What's this piddly 16. There's also a huge market out there for countries that will be replacing their Mig-21's and F5's

You first need more orders to justify bigger production rate. For a total order of 40 planes, no one will build assembly line for 40/year. You need orders in hand before you can build bigger lines. Same is true for Airbus/Boeing too. For many planes, if you place order today, you won't get it for next 3-4 years at the earliest.

[Sanjay]

I really appreciate the incredible technical discussion. Not to say I follow it all but it shows BRF at its best.

For a complete layman (like me), what conclusions can we come to in respect of the LCA STR & ITR and its max AoA ?

One of the concerns I have about people like Prof Das is that they are obsessed with aerodynamic theory and dismisses ADA statements out of had without proof.

[srai]

I really appreciate the incredible technical discussion. Not to say I follow it all but it shows BRF at its best.

For a complete layman (like me), what conclusions can we come to in respect of the LCA STR & ITR and its max AoA ?
...

Here's a quote from Cmde Maolankar:

Attended my first Aero India [2013] this Saturday. I won’t describe the difficulties in getting into the show, but once I did, it was quite alright. The highlight for me was the conversations I had with Cmde Jaydeep Maolankar, Test Pilot of the Tejas program and Cmdr Sukesh Nagaraj (Deputy Project Director, NLCA). I was lucky to spot Mao sir alone and walked up to him, introduced myself and spoke of my association with BRF and then we had a conversation on the Tejas program for half an hour..he was incredibly frank, friendly, didn’t hold back any facts and only left when he got a call from someone..here are the salient points of our conversation, some of which we already know but am listing it anyway.

...
- When asked about the STR and ITR rates of the Tejas, he simply smiled and said “it’s enough, let me put it that way”. When I queried him further, asking about the ASR that the IAF had set based on the Mirage-2000 and MiG-29’s STR and ITR, his smile vanished and he got serious. He said that when people look at 10 different brochures and come up with requirements, without looking at whether meeting all those requirements is even possible for ANY one fighter, they set themselves and the program up for failure. He was very frank about this, stating that even those brochure specs were just that- brochure specs that even those famed fighters sometimes don’t meet. But they were taken as benchmarks anyway and then, without even bothering to look at the technological base in India, the ASR was prepared.
...

[Kartik]

Well, to put things in context, I was just chatting with a former MiG-21 Bis pilot over the weekend and I asked him what the max positive G that the Bis airframe was allowed to pull..the answer was 7Gs. That's it. So, the Tejas is an improvement in that respect. Obviously it means that STR will be better for the Tejas than the MiG-21.

There is a so-called 9G club of IAF pilots who pulled 9Gs in the Bis, but these were a select bunch of pilots. Pulling any higher Gs would overstress the airframe and it was beyond the published envelope for the Bis, so most pilots never even attempted to go beyond 7Gs..without a FBW, the pilot had to very aware of what he was doing, else he could push the jet into an unrecoverable situation.

And he also mentioned 2 very important things - first, the very high pilot workload coupled with lack of FBW, which meant that younger pilots (especially, but even experienced ones) found the MiG-21 a very challenging jet in missions..keeping a track of the target, surface or in the air, while keeping an eye on all instruments in the cockpit was difficult, to put it mildly..second, the very high landing speed..close to 250 kmph, coupled with terrible forward visibility meant that pilots were always nervy when coming in to land. If the weather wasn't good or there were cross-winds, the landing could become a scary experience for pilots.

The Tejas will alleviate both these issues, and for the guys who are doing the flying that is a key improvement. People lose track of the fact that avionics improvements actually can be a boon for the guy in the cockpit.

[deejay]

^^^ Yes, Kartik sir. The Mig 21 is a difficult machine to fly and with ever evolving modern warfare where the number of parameters one monitors always increases, it is a handful.

The landing speed very often was above 250 kmph as I believe the markings at lower speed ranges on the dial are splits of 30 /50 kmph with not much separation.

Another thing about G-loads. +7 G is very high G force. G LOC can occur very easily at +7G. It is very rarely do we have situations where a planned requirement of greater than +7G will be required.

Tejas will certainly reduce these loads. Not that Mig 21's are bad. But obsolescence is a reality for the Mig 21 now.

[JayS]

While I am going through tons of research papers enough for months of study on delta wings and canards, I have one more thought on the possible rreason for low sweep on the apex region:

One possibility is that the LCA would have had too much pitch-up moment and too much relaxed stability with normal delta of 62.5deg (in present config just extend the outboard LE to meet with fuselage just behind the roundel). With truncated apex the centre of life moves aft-wards reducing both, the static instability margin and pitch-up moment. This would result in increased trim drag. But considering that LCA has 5% static instability margin now, without that low sweep apex region it would be even more. More than 8% static instability is too much to handle even for FCS (actuator speed is bottleneck if I understand it correctly) (per what I read for Eurofighter which aimed at 16% but had to settle for 8% due to FCS limits and I have no reason to believe LCA has any more advanced FCS/actuators than EFT).

This is what I am thinking currently:

1. If I have to make a fighter with extremely small dimensions but with stellar ITR/STR numbers, I need max wing area that I can get for lowest possible wing loading.

2. If I use lower LE sweep to get more wing area, I will get into non-slender regime and will need canards/LERX to enhance lift at low to moderate AoA and better control at higher AoA.

3. So ~60deg is my lower limit. But this slender wing is not giving me enough area.

4. So I extend the wing LE upstream increasing root chord. But then it results in too much static instability margin as my lift centre is move too much upstream. So I truncate the apex region, thereby reducing some lift upstream a bit to get to target 5% margin.

5. Now I have larger wing than what I could have with vanilla delta starting from same LE location. And also have instability margin within manageable limits.

A line diagram to explain above point: https://docs.google.com/drawings/d/1HSP ... sp=sharing

Just a wild thought.

[shiv]

Well, to put things in context, I was just chatting with a former MiG-21 Bis pilot over the weekend and I asked him what the max positive G that the Bis airframe was allowed to pull..the answer was 7Gs. That's it. So, the Tejas is an improvement in that respect. Obviously it means that STR will be better for the Tejas than the MiG-21.

There is a so-called 9G club of IAF pilots who pulled 9Gs in the Bis, but these were a select bunch of pilots. Pulling any higher Gs would overstress the airframe and it was beyond the published envelope for the Bis, so most pilots never even attempted to go beyond 7Gs..without a FBW, the pilot had to very aware of what he was doing, else he could push the jet into an unrecoverable situation.

And he also mentioned 2 very important things - first, the very high pilot workload coupled with lack of FBW, which meant that younger pilots (especially, but even experienced ones) found the MiG-21 a very challenging jet in missions..keeping a track of the target, surface or in the air, while keeping an eye on all instruments in the cockpit was difficult, to put it mildly..second, the very high landing speed..close to 250 kmph, coupled with terrible forward visibility meant that pilots were always nervy when coming in to land. If the weather wasn't good or there were cross-winds, the landing could become a scary experience for pilots.

The Tejas will alleviate both these issues, and for the guys who are doing the flying that is a key improvement. People lose track of the fact that avionics improvements actually can be a boon for the guy in the cockpit.

You've probably read this but this is what my late cousin Suresh wrote about the MiG 21
http://www.bharat-rakshak.com/MONITOR/I ... uresh.html

In the words of ACM Tipnis, “MiG-21 is a high demand aircraft”. It certainly is a quantum jump for an inexperienced pilot who has just finished his training on sub-sonic jet trainers like Kiran or Iskra. IAF is using the MiG-21 in the AJT role, which is neither optimal for training nor cost effective. (See appendix 1 about Flying Training)

MiG-21, although a high demand aircraft, is docile and has no aerodynamic vices. It has excellent handling characteristics and has served to provide very valuable flying experience to a large number of IAF pilots. Some like the previous and the present CAS swear by the aircraft. It is the docility of the aircraft that not only generates a good bit of confidence but also encourages forays into exceeding the limits of the stipulated flight envelope. In air combat maneuvers, many inexperienced pilots have got into trouble without realizing it. At high angles of attack, the induced drag increases sharply and unless the angle of attack is quickly reduced, the aircraft develops a high rate of descent, which cannot be arrested with the power available (even with reheat). Added to this, there is no protest from the aircraft like severe shudder, wing rocking. etc, prevalent in other types of aircraft. This gives a feeling of well-being and a number of pilots did not recognize the danger in time to take recovery action or eject.

[Kartik]

Tejas will certainly reduce these loads. Not that Mig 21's are bad. But obsolescence is a reality for the Mig 21 now.

I didn't get what you meant by Tejas will reduce these loads? The idea is you want an airframe that can withstand even greater loads and as a US Navy official recently stated, if a pilot can pull 7Gs, they can pull 9Gs too. At 8Gs max positive, the Tejas has an edge over the MiG-21 in terms of sustained turn rates, not to mention a definite edge over it in terms of instantaneous turn rates as well, something that is of great importance when you get into a dogfight.

[Kartik]

Well, to put things in context, I was just chatting with a former MiG-21 Bis pilot over the weekend and I asked him what the max positive G that the Bis airframe was allowed to pull..the answer was 7Gs. That's it. So, the Tejas is an improvement in that respect. Obviously it means that STR will be better for the Tejas than the MiG-21.

There is a so-called 9G club of IAF pilots who pulled 9Gs in the Bis, but these were a select bunch of pilots. Pulling any higher Gs would overstress the airframe and it was beyond the published envelope for the Bis, so most pilots never even attempted to go beyond 7Gs..without a FBW, the pilot had to very aware of what he was doing, else he could push the jet into an unrecoverable situation.

And he also mentioned 2 very important things - first, the very high pilot workload coupled with lack of FBW, which meant that younger pilots (especially, but even experienced ones) found the MiG-21 a very challenging jet in missions..keeping a track of the target, surface or in the air, while keeping an eye on all instruments in the cockpit was difficult, to put it mildly..second, the very high landing speed..close to 250 kmph, coupled with terrible forward visibility meant that pilots were always nervy when coming in to land. If the weather wasn't good or there were cross-winds, the landing could become a scary experience for pilots.

The Tejas will alleviate both these issues, and for the guys who are doing the flying that is a key improvement. People lose track of the fact that avionics improvements actually can be a boon for the guy in the cockpit.

You've probably read this but this is what my late cousin Suresh wrote about the MiG 21
http://www.bharat-rakshak.com/MONITOR/I ... uresh.html

In the words of ACM Tipnis, “MiG-21 is a high demand aircraft”. It certainly is a quantum jump for an inexperienced pilot who has just finished his training on sub-sonic jet trainers like Kiran or Iskra. IAF is using the MiG-21 in the AJT role, which is neither optimal for training nor cost effective. (See appendix 1 about Flying Training)

MiG-21, although a high demand aircraft, is docile and has no aerodynamic vices. It has excellent handling characteristics and has served to provide very valuable flying experience to a large number of IAF pilots. Some like the previous and the present CAS swear by the aircraft. It is the docility of the aircraft that not only generates a good bit of confidence but also encourages forays into exceeding the limits of the stipulated flight envelope. In air combat maneuvers, many inexperienced pilots have got into trouble without realizing it. At high angles of attack, the induced drag increases sharply and unless the angle of attack is quickly reduced, the aircraft develops a high rate of descent, which cannot be arrested with the power available (even with reheat). Added to this, there is no protest from the aircraft like severe shudder, wing rocking. etc, prevalent in other types of aircraft. This gives a feeling of well-being and a number of pilots did not recognize the danger in time to take recovery action or eject.

yes Shiv saar, I had read that article a long time ago..but always good to refresh one's memory.

So it was a docile aircraft up until you pushed it beyond what were its published limits. And good flying characteristics generally include a very noticeable warning sign before the aircraft actually departs controlled flight. Lack of severe shudder, wing rock, etc. would be a dangerous phenomenon on a high performance fighter that lacks FBW..no wonder most pilots would have avoided pushing it past the G limit during air combat maneuvering due to a fear that once absorbed in the contest, they could spill over into a stall condition.

[Prasad]

I think he meant workload not physical loads.

[Singha]

At high angles of attack, the induced drag increases sharply and unless the angle of attack is quickly reduced, the aircraft develops a high rate of descent, which cannot be arrested with the power available (even with reheat)

^^ whole description and lack of warning and graceful degration sounds like very trailing edge soviet era disposable philosophy to me. I think it has a very high landing speed also.

[Singha]

IAF should conduct some DACT exercises of the Tejas mk1 with all its other a/c incl Su30, Mig29, M2k and Jaguars to understand the matter fully and figure out any weak points and workarounds needed.

this should infact have been done earlier using 2-3 Tejas as no weapons need to be fired...atleast positioning and energy contests for BVR and all out WVR can surely be tried out now itself.

its time 2 tejas were given to tacde instructors to use and develop the fighting manual.

[DexterM]

Isn't it a sign that no one from TACDE has been near this aircraft yet?

Not one person from any OCUs - folks who would create the curriculum. ALL of this is planned for when FOC is done, and the keys for a spanking new hangar is handed over to an AM or two.
Extremely discouraging signs. ADA too has quietly sat back and is focusing on NLCA changes - of course they would prioritize whichever program has most responsive teams handling them.

Are HAL or ADA looking for program management professionals? Serious question.

[rohitvats]

Isn't it a sign that no one from TACDE has been near this aircraft yet?

Not one person from any OCUs - folks who would create the curriculum. ALL of this is planned for when FOC is done, and the keys for a spanking new hangar is handed over to an AM or two. Extremely discouraging signs. <SNIP>

Did you think through your statement above? You want instructors from TACDE or OCU to fly an aircraft which had till recently not even been released for flying by regular fighters? And even here, the first lot will go ASTE (Aircraft Systems and Test Establishment) and then will handover happen to No.45 Squadron. Unless I'm way off the mark here, no one except Test Pilots have flown the aircraft. And the documentation about every aspect of the a/c from flying to maintenance is in the process of hand-over to IAF.

[DexterM]

Yes Rohit, think about this - if you need two years for building the curriculum that takes a year to implement, wouldn't you want your senior most instructors to have had a look by now (can't go back into the past, can we)?

ASTE will get the first two SP1 and SP2. They will need these for roughly a year before handing over to 45. When are we going to be in a position to have TACDE get involved? Probably 5 years from now?
IOC is done - it is safe enough for the TACDE to run through the simulators and trainer version. Did you read only my statement or did you miss the context of Singha's statement on DACT? If yes, read it again please.

Why don't we approach this with a rough schedule instead:
Certification by ASTE (Dependencies - HAL handover of SP2)
Curriculum development starts at 45 (Step 1)
Deployment of Seniors as Trainers (Step 2 + HAL Tejas Trainer Versions)
Certification for trainers for OCUs (?)
Next steps? --> TACDE and back to Curriculum
This is only the pilots - what about maintenance crews and workshop preparedness teams?

So, if you had to crunch the timelines, would you not have your key war preparedness teams involved in the planning by now?
If not, why not?

[Singha]

there are ways to speed up the curriculum development and training of instructor pilots in atleast flying the plane to its limits. no great FCS or structural change has taken place since IOC-1 so it could have been started even then. now they have put in more system and tested the A2G stuff also , further scope for curriculum work.

if they are serious about speeding up its induction into a frontline sqdn at the earliest they need to step up the pace of absorption and learning.

if they are happy putting it on backburners and tinkering with it forever in Sulur, while pining for the Rafale current mode is fine.

[DexterM]

Thinking through a little more:
Who will be the instructors for Sq 45?
How do they get certified for this type?
Is there a curriculum in place or does it evolve as the unit is established? (2 aircraft every quarter)
Do we start with 20 pilots, some of whom will seed or rotate through other units as instructors for this type?
Or do we start with a smaller batch of a flight or two and work our ways to a larger number?
When should an OCU be considered? Two years down the line or now? (Some sqns are already flying half their numbers, so does the other half undergo training first?)

Would appreciate input from folks who've been through this process. A workflow with timelines would be even better.
(Even better if we could build it for the type).

[deejay]

Tejas will certainly reduce these loads. Not that Mig 21's are bad. But obsolescence is a reality for the Mig 21 now.

I didn't get what you meant by Tejas will reduce these loads? The idea is you want an airframe that can withstand even greater loads and as a US Navy official recently stated, if a pilot can pull 7Gs, they can pull 9Gs too. At 8Gs max positive, the Tejas has an edge over the MiG-21 in terms of sustained turn rates, not to mention a definite edge over it in terms of instantaneous turn rates as well, something that is of great importance when you get into a dogfight.

Sorry I meant work load for pilots.

[Kersi D]

Well, to put things in context, I was just chatting with a former MiG-21 Bis pilot over the weekend and I asked him what the max positive G that the Bis airframe was allowed to pull..the answer was 7Gs. That's it. So, the Tejas is an improvement in that respect. Obviously it means that STR will be better for the Tejas than the MiG-21.

There is a so-called 9G club of IAF pilots who pulled 9Gs in the Bis, but these were a select bunch of pilots. Pulling any higher Gs would overstress the airframe and it was beyond the published envelope for the Bis, so most pilots never even attempted to go beyond 7Gs..without a FBW, the pilot had to very aware of what he was doing, else he could push the jet into an unrecoverable situation.

And he also mentioned 2 very important things - first, the very high pilot workload coupled with lack of FBW, which meant that younger pilots (especially, but even experienced ones) found the MiG-21 a very challenging jet in missions..keeping a track of the target, surface or in the air, while keeping an eye on all instruments in the cockpit was difficult, to put it mildly..second, the very high landing speed..close to 250 kmph, coupled with terrible forward visibility meant that pilots were always nervy when coming in to land. If the weather wasn't good or there were cross-winds, the landing could become a scary experience for pilots.

The Tejas will alleviate both these issues, and for the guys who are doing the flying that is a key improvement. People lose track of the fact that avionics improvements actually can be a boon for the guy in the cockpit.

You've probably read this but this is what my late cousin Suresh wrote about the MiG 21
http://www.bharat-rakshak.com/MONITOR/I ... uresh.html

In the words of ACM Tipnis, “MiG-21 is a high demand aircraft”. It certainly is a quantum jump for an inexperienced pilot who has just finished his training on sub-sonic jet trainers like Kiran or Iskra. IAF is using the MiG-21 in the AJT role, which is neither optimal for training nor cost effective. (See appendix 1 about Flying Training)

MiG-21, although a high demand aircraft, is docile and has no aerodynamic vices. It has excellent handling characteristics and has served to provide very valuable flying experience to a large number of IAF pilots. Some like the previous and the present CAS swear by the aircraft. It is the docility of the aircraft that not only generates a good bit of confidence but also encourages forays into exceeding the limits of the stipulated flight envelope. In air combat maneuvers, many inexperienced pilots have got into trouble without realizing it. At high angles of attack, the induced drag increases sharply and unless the angle of attack is quickly reduced, the aircraft develops a high rate of descent, which cannot be arrested with the power available (even with reheat). Added to this, there is no protest from the aircraft like severe shudder, wing rocking. etc, prevalent in other types of aircraft. This gives a feeling of well-being and a number of pilots did not recognize the danger in time to take recovery action or eject.

I believe that this is in the report Grp Cap (Late) K Suresh said in his presentation to PM / President / Lok Sabha / Parliament / .....

This full article was printed in VAYU. Dr Shiv can u e-mail this article ro give a link to VAYU ?

K

[Indranil]

While I am going through tons of research papers enough for months of study on delta wings and canards, I have one more thought on the possible rreason for low sweep on the apex region:

One possibility is that the LCA would have had too much pitch-up moment and too much relaxed stability with normal delta of 62.5deg (in present config just extend the outboard LE to meet with fuselage just behind the roundel). With truncated apex the centre of life moves aft-wards reducing both, the static instability margin and pitch-up moment. This would result in increased trim drag. But considering that LCA has 5% static instability margin now, without that low sweep apex region it would be even more. More than 8% static instability is too much to handle even for FCS (actuator speed is bottleneck if I understand it correctly) (per what I read for Eurofighter which aimed at 16% but had to settle for 8% due to FCS limits and I have no reason to believe LCA has any more advanced FCS/actuators than EFT).

This is what I am thinking currently:

1. If I have to make a fighter with extremely small dimensions but with stellar ITR/STR numbers, I need max wing area that I can get for lowest possible wing loading.

2. If I use lower LE sweep to get more wing area, I will get into non-slender regime and will need canards/LERX to enhance lift at low to moderate AoA and better control at higher AoA.

3. So ~60deg is my lower limit. But this slender wing is not giving me enough area.

4. So I extend the wing LE upstream increasing root chord. But then it results in too much static instability margin as my lift centre is move too much upstream. So I truncate the apex region, thereby reducing some lift upstream a bit to get to target 5% margin.

5. Now I have larger wing than what I could have with vanilla delta starting from same LE location. And also have instability margin within manageable limits.

A line diagram to explain above point: https://docs.google.com/drawings/d/1HSP ... sp=sharing

Just a wild thought.

Getting more wing area from the same root chord, yes.
But, I don't get the relaxed stability part. They could have always moved the wing around to achieve it, they don't need to clip the wing for it.

[JayS]

Getting more wing area from the same root chord, yes.
But, I don't get the relaxed stability part. They could have always moved the wing around to achieve it, they don't need to clip the wing for it.

They could move the wing, but if indeed static instability margin was an issue with plain delta, then to reduce it you would shift the wing aftwards but that would increase overall length as well as total weight of the a/c. (I am assuming that shifting CG would be a tougher job for a small jet like LCA than shifting Centre of Pressure). And also to have same wing area (as is there with current config) with plain delta would also need longer length.

Lots of assumptions and speculations. But while I am looking for some hard proof I am thinking 'Laterally'. There are many more reasons/factors which could result in a particular wing shape other than pure aerodynamic.

FYI, for SAAB Viggen, the reason for lower sweep inboard section is not vortex aerodynamics but rather stability requirements and performance trade off. They would have happily chopped off the whole apex region as it was not creating any significant lift but increasing length of a/c and weight and the chopped-off delta was giving better subsonic characteristics. But it was also creating longitudinal stability issues (bad dCm/dCl) and not so good area ruling and suboptimal supersonic performance due to increased effective thickness of root section. Of coarse the apex region in Viggen is in wake of a huge canard and thus it has reduced lift. Also chopped off delta means smaller root chord which means lesser structural strength resulting in heavier wing construction. So the low sweep solution is in-fact a trade-off between full apex to having no apex at all. (Viggen wing has in fact 3 LE sweeps - 45 - 59.x - 63).

BTW, I got one interesting snippet from another forum where the poster is supposedly quoting from an paper presented by ADA scientist (Dr. S R Mohan) in SAROD-2007. I cannot find the paper anywhere ( ). But here is the line:

http://forum.keypublishing.com/showthre ... Asia/page9

A three panelled wing with outboard anhedral, single pitch control surface and no leading edge device evolved into a two panelled wing with split elevons, no anhedral and a three piece leading edge slats on each wing

It reminded me of the often shown old LCA pic with three piece wing.


If above quote is accurate then this is the first authentic ADA reference I have seen that explicitly says there is no Anhedral on LCA.

I have one more reason to believe that LCA has no Anhedral as I told you over email some time ago.

[Indranil]

I believe in the "no anhedral" part. Actually, I never had that in the equation, although I must admit that your investigations have brought more clarity. Also, anybody serious about planes knows that the final configuration is often a compromise, result of one or more balancing acts. But I am not on board with you on the reasons to clip the apex. I understand that you are trying to come up with a theory, and I really like your rigour. But there are conventional techniques to overcome what you are suggesting. For example, you know that Mk1 is flying with a balast in its nose for CG management. I don't think they would go down this unconventional route for this.

My theory is different and I have to spend more time into developing it completely. They had decided quite early that the plane will be as small as possible. The designers have never hid their admiration for the Gnat. Also, I believe that they had decided on a delta wing quite early. Now, they had to take care of the off-design points. That's why the 3 slats (to arrest pitch-up) and the conical camber (for better efficiency at subsonic manoeuvring) were added. Also, they had to find a way in which apex of the wing "shielded" the inlets. I don't understand inlet design enough to tell you whether the LE of the inboard wing generates an oblique shock wave for supersonic flight. It is certainly close enough, and that will explain a lot! But let's set that aside, and return to subsonic flight. It can be just another case of handling another off design point. A complete delta with a huge sweep sucks at slow speed. So part of the wing has lesser sweep for low speed handling. Then selecting the sweep-angles which generate vortices that interact favourably, was the only thing left. That number comes out to be 50/52.5 degrees.

For others (not as aero-inclined as Nilesh):
1. Tejas's wings are not the bottleneck for supersonic flight. Its fuselage is. We have to live with it still Mk2. Also, I (personally) don't like the finish on LCAs (even SP-1). That makes a huge difference in supersonic flight. But, the HAL chief has said that the finish will be much better on serially produced specimens. Let's see. The finish on the Hawks and Su-30s are much better, so HAL certainly has the capability.
2. Tejas's wings give it great instantaneous turning rates. It has every thing going for it.
3. The problem is instantaneous turning rate and sustained turn rates have some contradictory demands. For example, while the classical planar delta wing like what you see on a Mig-21 is excellent in the former, it is not good for the latter. And that is what the LCA designers have tried to provide with various modifications to the classical delta wing. Nilesh and I are trying to understand each of these modifications in detail. Unfortunately, we are throwing darts in the dark, with whatever little information we have in the open.
4. Exact figures on acceleration, turn-rates, top speeds, cruise speeds etc. cannot be calculated like this. We can only guess by looking at other similar platforms. These numbers have to come from ADA, TPs, publications etc.

Anyways, the wing seems to be working to ADA's satisfaction. They had every chance of changing it on Mk2, but they did not. Not one bit, except enlarging it slightly for the new Navy Mk2 version.

[Singha]

Tejas's wings are not the bottleneck for supersonic flight. Its fuselage is

^^ you hit the juggler vein there. The fat barrel fuselage is 1960s chic.

[Cain Marko]

For others (not as aero-inclined as Nilesh):<br abp="740">1. Tejas's wings are not the bottleneck for supersonic flight. Its fuselage is. We have to live with it still Mk2. Also, I (personally) don't like the finish on LCAs (even SP-1). That makes a huge difference in supersonic flight. But, the HAL chief has said that the finish will be much better on serially produced specimens. Let's see. The finish on the Hawks and Su-30s are much better, so HAL certainly has the capability. <br abp="741">2. Tejas's wings give it great instantaneous turning rates. It has every thing going for it. <br abp="742">3. The problem is instantaneous turning rate and sustained turn rates have some contradictory demands. For example, while the classical planar delta wing like what you see on a Mig-21 is excellent in the former, it is not good for the latter. And that is what the LCA designers have tried to provide with various modifications to the classical delta wing. Nilesh and I are trying to understand each of these modifications in detail. Unfortunately, we are throwing darts in the dark, with whatever little information we have in the open. <br abp="743">4. Exact figures on acceleration, turn-rates, top speeds, cruise speeds etc. cannot be calculated like this. We can only guess by looking at other similar platforms. These numbers have to come from ADA, TPs, publications etc.<br abp="744"><br abp="745">Anyways, the wing seems to be working to ADA's satisfaction. They had every chance of changing it on Mk2, but they did not. Not one bit, except enlarging it slightly for the new Navy Mk2 version.

Thank you Indranil for providing that English translation. Much of what you say and makes sense even for non-aeroengineer and arm chair jernails like me. Appreciate this. At the same time, it is amazing how much one can be close to what the gurus are saying based on simply having an interest in the matter and doing some amateurish research - basically oogling at fighter a/c every now and again and reading up on what forumites might say.

One question I had about the LCA wing structure is why LEVCONs were not chosen for the mk2 when they are already working on them on the NLCA. Is their function purely for slow speed control as in during carrier landings? But then, the Pakfa has them too. What do gurujan say?

[Abhay_S]

^^^ Nice info regarding LCA Design( i like the 'not as aero-inclined' part )

One question i have is what advantage/disadvantage does this design provide in combat?

[Indranil]

Thank you Indranil for providing that English translation. Much of what you say and makes sense even for non-aeroengineer and arm chair jernails like me. Appreciate this. At the same time, it is amazing how much one can be close to what the gurus are saying based on simply having an interest in the matter and doing some amateurish research - basically oogling at fighter a/c every now and again and reading up on what forumites might say.

You get it because I am also a non-aeroengineer. All my knowledge is also interest-based.

One question I had about the LCA wing structure is why LEVCONs were not chosen for the mk2 when they are already working on them on the NLCA. Is their function purely for slow speed control as in during carrier landings? But then, the Pakfa has them too. What do gurujan say?

All I can tell you is that they considered it for Tejas Mk2. They looked at it because they found that the LEVCONs provided better lift-to-drag ratio at higher AoA (better efficiency). This would mean better STR. But they dropped it. The benefits must not have been great enough, or the new engines would be providing enough oomph to acquire the specified STR. Why carry around extra weight during other times?

^^^ Nice info regarding LCA Design( i like the 'not as aero-inclined' part )

One question i have is what advantage/disadvantage does this design provide in combat?

That is a very broad question, my friend. You have to take any one parameter and study (there is enough on the net) what aspects of aircraft design affect that parameter. Then, if you want to understand what was done in case of LCA, you should definitely ask. This way you will learn more, and gurus will be much more inclined to answer.

[putnanja]

Can someone please point out the Levcons in the IN LCA version? I can't figure it out myself

[vardhank]

@indranilroy Noob-ish question: would an 'active' solution have worked/been possible? I'm thinking of an extendable-retractable LREX type thing (a miniature swing wing, if you will) that can provide the wing shape needed at the apex to suit different needs?

[srin]

I believe in the "no anhedral" part. Actually, I never had that in the equation, although I must admit that your investigations have brought more clarity. Also, anybody serious about planes knows that the final configuration is often a compromise, result of one or more balancing acts. But I am not on board with you on the reasons to clip the apex. I understand that you are trying to come up with a theory, and I really like your rigour. But there are conventional techniques to overcome what you are suggesting. For example, you know that Mk1 is flying with a balast in its nose for CG management. I don't think they would go down this unconventional route for this.

My theory is different and I have to spend more time into developing it completely. They had decided quite early that the plane will be as small as possible. The designers have never hid their admiration for the Gnat. Also, I believe that they had decided on a delta wing quite early. Now, they had to take care of the off-design points. That's why the 3 slats (to arrest pitch-up) and the conical camber (for better efficiency at subsonic manoeuvring) were added. Also, they had to find a way in which apex of the wing "shielded" the inlets. I don't understand inlet design enough to tell you whether the LE of the inboard wing generates an oblique shock wave for supersonic flight. It is certainly close enough, and that will explain a lot! But let's set that aside, and return to subsonic flight. It can be just another case of handling another off design point. A complete delta with a huge sweep sucks at slow speed. So part of the wing has lesser sweep for low speed handling. Then selecting the sweep-angles which generate vortices that interact favourably, was the only thing left. That number comes out to be 50/52.5 degrees.

For others (not as aero-inclined as Nilesh):
1. Tejas's wings are not the bottleneck for supersonic flight. Its fuselage is. We have to live with it still Mk2. Also, I (personally) don't like the finish on LCAs (even SP-1). That makes a huge difference in supersonic flight. But, the HAL chief has said that the finish will be much better on serially produced specimens. Let's see. The finish on the Hawks and Su-30s are much better, so HAL certainly has the capability.
2. Tejas's wings give it great instantaneous turning rates. It has every thing going for it.
3. The problem is instantaneous turning rate and sustained turn rates have some contradictory demands. For example, while the classical planar delta wing like what you see on a Mig-21 is excellent in the former, it is not good for the latter. And that is what the LCA designers have tried to provide with various modifications to the classical delta wing. Nilesh and I are trying to understand each of these modifications in detail. Unfortunately, we are throwing darts in the dark, with whatever little information we have in the open.
4. Exact figures on acceleration, turn-rates, top speeds, cruise speeds etc. cannot be calculated like this. We can only guess by looking at other similar platforms. These numbers have to come from ADA, TPs, publications etc.

Anyways, the wing seems to be working to ADA's satisfaction. They had every chance of changing it on Mk2, but they did not. Not one bit, except enlarging it slightly for the new Navy Mk2 version.

Thank you very much, Indranil and Nilesh. I can now claim to understand the reason behind the compound delta - all because of this discussion between you guys.

And now, one request - can you similarly analyze the AMCA planform too ? There are two big differences that I can see - diamond shape wings and tail.

[Indranil]

@indranilroy Noob-ish question: would an 'active' solution have worked/been possible? I'm thinking of an extendable-retractable LREX type thing (a miniature swing wing, if you will) that can provide the wing shape needed at the apex to suit different needs?

Though not for the LERX, retractable strakes (HARV) and canards (Mirage Milan/ Tu-144) have been tried before. But there are 3 principal problems that one can see.

1. Speed. Imagine a fighter in a dogfight, twitching and turning. How quickly could one retract and expand? Would it not be better to go for a canard instead, which only turns about its CG without displacing mass?
2. Space. Where will it retract into? We are speaking of a large piece here.
3. Weight. Would the trade-off be worth it, like in the case of swing-wings? Generally, such solutions are stop-gaps to an elegant solution. I find the LCA solution elegant enough, and I say this without bias.

As an aside, a related history lesson. Rewind back to the 60s. After the advent of the jet age and upto the Vietnam war, people had gone for speed with the highly swept deltas at the price of subsonic manueverability. They thought that aircrafts were merely delivery system for missiles (sounds familiar?). Come the war, that was not true anymore. Aircrafts found out ways to evade missiles, and soon fighters came face to face. And, in this situation, the more manueverable and vastly cheaper Mig-17s were engaging the Phantoms! The world started leaning back towards manueverability. Initially, they started with swing wings. Then they realized it is very innefficent to carry all that weight around, and went for the fixed wings that you see today. The fixed wing solutions come at a price because most modern fighters are optimized for subsonic manueverability. Therefore, they have to take care of supersonic flight by using very powerful modern engines. Again, there is a bandwagon of people who believe fighters are merely carriers of weapons ...

[brar_w]

As propulsion and other design features, and technology evolved they also began to ask for some pretty serious maneuverability even at the higher speeds. With reduced RCS cranking became a legitimate tactic and in case of the ATF it became almost a differentiator (amongst competitors) if some are to be believed . The requirements were at the time 6G sustained @ Mach 1.7 after a ripple Missile launch, later reduced to 5.5G @ Mach 1.6 and 5G @ Mach 1.7. The Typhoon also had some sort of defined sustained G requirement at supersonic speed as well.

[JayS]

As propulsion and other design features, and technology evolved they also began to ask for some pretty serious maneuverability even at the higher speeds. With reduced RCS cranking became a legitimate tactic and in case of the ATF it became almost a differentiator (amongst competitors) if some are to be believed . The requirements were at the time 6G sustained @ Mach 1.7 after a ripple Missile launch, later reduced to 5.5G @ Mach 1.6 and 5G @ Mach 1.7. The Typhoon also had some sort of defined sustained G requirement at supersonic speed as well.

Supersonic maneuverability requirement comes from BVR philosophy I believe.

BTW Rafale did 6G turn at M=1.6 within its first 10 flights IIRC. Just the other day I was reading old magazin article which said that Rafale did M=1.8 (max design), 8G (max at that time) and 6G @ M=1.6 within first 10-11 flights of its very first prototype. That's some impressive stuff. Interestingly that prototype was also using GE F404.

Thank you very much, Indranil and Nilesh. I can now claim to understand the reason behind the compound delta - all because of this discussion between you guys.

And now, one request - can you similarly analyze the AMCA planform too ? There are two big differences that I can see - diamond shape wings and tail.

I still don't understand the LCA wing fully. Worse is there is not authentic source to confirm all this.

For me, let me first understand LCA wing fully then I would go for AMCA. But its more conventional as in its more in line with other similar 5th fighters. The 'two big differences' make them world's apart.

[brar_w]

Supersonic maneuverability requirement comes from BVR philosophy I believe.

BTW Rafale did 6G turn at M=1.6 within its first 10 flights IIRC. Just the other day I was reading old magazin article which said that Rafale did M=1.8 (max design), 8G (max at that time) and 6G @ M=1.6 within first 10-11 flights of its very first prototype. That's some impressive stuff. Interestingly that prototype was also using GE F404.

Cranking is a fairly legitimate maneuver in a BVR engagement. The objective is to launch a missile (ideally be the first to do so) and pull high sustained G's to get out of the area to avoid incoming salvos, and then re-engage while using yourself and your wingman for missile updates. The Typhoon I have read somewhere has demonstrated a sustained 5 G performance at Mach 1.5 (or 1.6) at around 40,000 feet. The ATF initial requirement was Mach 1.7 and 6G's @ 35-40,000 feet with 6 missiles and 50% fuel (not entirely sure whether fuel requirement was 50% or 60%) but it was later relaxed to 5g's @ mach 1.7 and 5.5g's @ mach 1.5 (AB) The point being that you need to get out of the area in a sniper like scenario because the opening of your bays and missile launch (MAWS) is lighting up sensors. You can pull a lot of distance between yourself and a potential threat at those speeds especially if you can sustain mach 1.72 supercruise at 40K with 50% fuel and full internal weapons (a2a). If reports at the time were to be believed the cranking requirement literally killed the Northrop and MD team.

Haven't come across any numbers on sustained supersonic G's for mach numbers on the Rafale. Could you share your material? Was the prototype fighter pulling sustained G's at Mach 1.6? If so with what weapons and how much aprox fuel?

[JayS]

I believe in the "no anhedral" part. Actually, I never had that in the equation, although I must admit that your investigations have brought more clarity. Also, anybody serious about planes knows that the final configuration is often a compromise, result of one or more balancing acts. But I am not on board with you on the reasons to clip the apex. I understand that you are trying to come up with a theory, and I really like your rigour. But there are conventional techniques to overcome what you are suggesting. For example, you know that Mk1 is flying with a balast in its nose for CG management. I don't think they would go down this unconventional route for this.

I have never studied Delta wings seriously before. But now I am doing it. Rigor is needed as the physics itself it quite complicated.

I know of the ballast. I do not believe ADA would put ballast to adjust CG location right from Preliminary design stage. They must have been forced to use it after the config was frozen. The reason simply could be over-estimation of RADAR weight/cockpit weight. Once you freeze design in Aerospace, you don't change it unless its very critical. After fixing CG location, they could have found out that they were not able to get that CG location anyhow during detailed design phase. Nobody will do any changes in configuration at that stage in Aerospace. But wing location fixing I am talking about happens in very early stage (Conceptual design). At that time changing its location is not that big deal. Hundreds of configurations of all sorts are evaluated in conceptual design stage.

My theory is different and I have to spend more time into developing it completely. They had decided quite early that the plane will be as small as possible. The designers have never hid their admiration for the Gnat. Also, I believe that they had decided on a delta wing quite early. Now, they had to take care of the off-design points. That's why the 3 slats (to arrest pitch-up) and the conical camber (for better efficiency at subsonic manoeuvring) were added. Also, they had to find a way in which apex of the wing "shielded" the inlets. I don't understand inlet design enough to tell you whether the LE of the inboard wing generates an oblique shock wave for supersonic flight. It is certainly close enough, and that will explain a lot! But let's set that aside, and return to subsonic flight. It can be just another case of handling another off design point. A complete delta with a huge sweep sucks at slow speed. So part of the wing has lesser sweep for low speed handling. Then selecting the sweep-angles which generate vortices that interact favourably, was the only thing left. That number comes out to be 50/52.5 degrees.

I understand only supersonic inlet design for high mach numbers well enough. Transonic regime is totally different ball game.

Anyways, the wing seems to be working to ADA's satisfaction. They had every chance of changing it on Mk2, but they did not. Not one bit, except enlarging it slightly for the new Navy Mk2 version.

Unless there are severe disadvantages with the wing performance, they would never change wing configuration. Such change at this change means MK-2 development time goes up really high as the whole FCS calibration will have to be re-done. Smaller issues will only be dealt with fine-tuning of existing config or introduction of smaller features (such as wing fences/LE dogtooth etc)

Perhaps the LCA has unsatisfactory characteristics for Navy's requirements, hence changes in NLCA. As such its a different plane, different project.

[JayS]

Supersonic maneuverability requirement comes from BVR philosophy I believe.

BTW Rafale did 6G turn at M=1.6 within its first 10 flights IIRC. Just the other day I was reading old magazin article which said that Rafale did M=1.8 (max design), 8G (max at that time) and 6G @ M=1.6 within first 10-11 flights of its very first prototype. That's some impressive stuff. Interestingly that prototype was also using GE F404.

Cranking is a fairly legitimate maneuver in a BVR engagement. The objective is to launch a missile (ideally be the first to do so) and pull high sustained G's to get out of the area to avoid incoming salvos, and then re-engage while using yourself and your wingman for missile updates. The Typhoon I have read somewhere has demonstrated a sustained 5 G performance at Mach 1.5 (or 1.6) at around 40,000 feet. The ATF initial requirement was Mach 1.7 and 6G's @ 35-40,000 feet with 6 missiles and 50% fuel (not entirely sure whether fuel requirement was 50% or 60%) but it was later relaxed to 5g's @ mach 1.7 and 5.5g's @ mach 1.5 (AB) The point being that you need to get out of the area in a sniper like scenario because the opening of your bays and missile launch (MAWS) is lighting up sensors. You can pull a lot of distance between yourself and a potential threat at those speeds especially if you can sustain mach 1.72 supercruise at 40K with 50% fuel and full internal weapons (a2a). If reports at the time were to be believed the cranking requirement literally killed the Northrop and MD team.

Haven't come across any numbers on sustained supersonic G's for mach numbers on the Rafale. Could you share your material? Was the prototype fighter pulling sustained G's at Mach 1.6? If so with what weapons and how much aprox fuel?

http://aviationweek.com/site-files/avia ... ale%20.pdf

This one does not say what mach number 6G was pulled, but IIRC the page from which I got this link from say it was M1.6. I can't remember where exactly I read that one (been reading too much stuff these past few days). Will have to dig out that one. So take the M1.6 number FWIW. 6G at supersonic speed is confirmed from above doc. It does not mention weapon load.

Also one more correction, I had said M1.8 is max design point but its M2.0 as per this article.

But I was impressed by the confidence French had in the prototype.

[brar_w]

NileshJi, The link said that the prototype pulled 6G's at supersonic speed. I was talking about a sustained G performance at supersonic for the purpose of cranking. The F-16 can pull its design G's at supersonic speeds along with other fighters. Here's a direct quote from a pilot who has 2000 hours on the Viper (along with 500 on the Mig29, and 900 on the F-15)

F-16, once the centerline tank is empty (or jettisoned) can go to nine Gs regardless of airspeed or Mach number.

This is obviously not the same as sustaining 9 G's at any mach number

I have come across numbers on the ATF requirement ( from the most definitive book on the matter authored by the Program Manager himself) and the F-22A performance figures (M 1.7, sustained 5G's) from Janes (July 7, 2005). I have the Typhoon data in my notes but don't have the exact source of the 40,000 feet, Mach 1.6 Sustained 5G performance. I also do not have the fuel state (Internal, 50%? or some external) or weapon load for the Phoon with that performance, but I'll look around.

[Singha]

it seems in red flag the rafales also engaged in bvr sniping hiding behind the larger rcs of the su30s. they were in and out per reports, but no details on speed and height.

[brar_w]

it seems in red flag the rafales also engaged in bvr sniping hiding behind the larger rcs of the su30s. they were in and out per reports, but no details on speed and height.

Sniping for whatever purpose is a tactic employed by various aircraft under various scenarios..I was referring to the fact that as combat aircraft have advanced we have gone back and forth with design features as Indranilji has rightly pointed out. But when it comes to what is going on now, they have placed emphasis on this aspect of maneuverability as well. Not only did they require high speed without augmentation but also the ability to do some serious maneuvers at that speed in support of a tactical maneuver that is routinely employed post missile launch but that gets a new meaning of sorts when the aircraft doing it has the ability to sneak up and increase kinematic range due to speed, altitude and stealth. F-22A, PAKFA, Typhoon will employ this fully at high speeds and altitudes..Expect other 5th generation fighters (including AMCA) to employ them to a lesser degree as well. Close in combat will obviously be Subsonic and this why none of the fighters are looking to relax agility or maneuverability in that criteria or let go of other development areas (HMS/HMD, HOBS missiles, IR sensors and training etc).