LCA News and Discussions, 22-Oct-2013

[Philip]

NIce work Mitya,doesn't this underscore the need for a more powerful engine for the LCA to meet IAF performance parameters,which only the MK-2 hopefully will achieve?

[SaiK]

lal, what is "it" - drag?

[disha]

No one seems to be complaining of short legs on the naval front. Just the heavy tail hook as far as i have read in the neuj media.

+1 on the non-bolded part., for the bolded part - the heavy tail hook *and* the over-designed over-engineered heavy landing "legs". Because of designing it first time, everything on the landing gear got over-compensated which leads to a look that if LCA were to extend its legs out sideways and give a kick to say Thunder bandar standing by its side, the bandar will keel over.

Maitya'ji, nice post - did not think of flow re-attachment. Further, the delta wing is "cranked" - which IMVHO should delay the flow-detachment at a higher AoA only? Right?

[Victor]

3g)The SDRE LCA Wing Planform: So, they decided to have best of both the worlds ... have a wing which will have both non-slender and slender delta planform. And viola, you got the compound delta LCA wing design, with it's both a low-wing-sweep (50deg, so non-slender delta) and high-wing-sweep (~63deg aka in the "slender delta" territory) as you move from inboard (wing root) to outboard of a wing.

Thus for the relatively lower part of the high-AoA flight regime (say from around 18deg to 22deg etc), the outboard slender delta part of the wing would dutifully contribute to the vortex lift while keeping the drag as low as possible. And with further increase of AoA, as that part of the wing starts to stall due to vortex bursting etc, the inboard non-slender-delta part of the wing will come into play with it's flow-reattachment aspects and keep on further enhancing the lift co-efficient (while still keeping the drag down as low as possible).

So where is the need of any additional control surface like a canard (and thus without the weight and complexity penalty of an additional control surface etc), hain jee?

Thanks Maitya for this excellent description of what the LCA's compound delta does. Can you speculate or otherwise clue us in on what the Viggen, which had the exact same compound delta as the LCA, gained from also having canards? I read somewhere that it was to turn the nose up or down faster on its vertical axis besides helping in high AoA flight, facilitating better turns, shorter takeoffs and slower landing speeds.

Could you also comment on the following remarks of Air Marshal Matheswaran:

It would actually have been prudent to choose a canard-delta design considering the severe size and weight limitations. This was also the recommendation of the consultants in the early phase. It is strange that this was not followed. Instead we chose to rely on a pure tail-less delta design and thought that the combination of unstable platform and digital FBW flight control system would generate enough performance. This was not possible, as subsequent results have shown.

The Swedes seem to have done a lot of work with compound deltas since the 1950s. The predecessor to the Viggen, the Draken, also had a compound delta but it was reversed, with the high sweep before the low sweep.

[Gyan]

Super post Maitya. A new bie question is that why drop this/ LCA wing shape for AMCA? Rendering of AMCA in 1990s used to carry the same wing shape as LCA.

[Yagnasri]

My mango baniya mind failed to understand what Maithya guruji posted. But some things are clear from reading this thead. LCA is cheap. Designed and made in India. Capable of kicking a&& of most of the old and latest rubbish Lizard and his munna in the west of India can send against us. serious capability increase from Mig21,27, Jag etc, and I do not see any other argument against a major order for both mk1 and 2.

I am sold.

[member_28932]

Vipul Dave ji welcome to the wonderland. These guys are just ragging a new guy in the school. But they are right. Aspect ratio affects glide performance not the wing area (or wing loading). Better wing loading (increased area) is essentially to give better climb rate.

From your own wiki link for F-16XL:

The enlargements increased fuel capacity by 82%. The F-16XL could carry twice the ordnance of the F-16 and deliver it 40% farther.

Thus fuel had to be increased almost twice as much for half as much range increase. OTOH the MTOW (warload+extra fuel) bounced like a crazy ball.

Since we are discussing LCA (which seems like having a lower aspect ratio then even F-16XL) that would mean full efficiency in flying with MTOW at Leh and advanced landing grounds. If you recall almost all MMRCAs had difficulty in Leh (they never revealed why, but that only means they have something to hide otherwise you would have seen the marketing machines and the chamchas all over the net by now).

We will need the LCA over the highest of high Himalayas, besides other places. And this wing will be a killer app there. We simply cannot afford to place MKIs and MMRCA in the advanced strips considering how costly and difficult to replace they are. And just the way a much hated Marut gave a good account of itself where it mattered you can rest assured even LCA would perform the best where it matters.

Hope you stay around.

Thank you sir.

I am not convienced fully but I would like to argue only after some more reading on the subject.

Yes tejas shall be our leading aircraft for any combat in Himalayas.

Its engine did not work well in 2013.

Talking to reporters, the IAF chief said the indigenous aircraft will have to be modified further for operating in high-altitude areas as recently during trials in Leh, its engine "did not work".

http://articles.economictimes.indiatime ... -lca-tejas

In 2014. The scenario changed completly. Aircraft performed admirably well. It took off from Leh Airfield with design load with an ease. Scintist said that it took off so easily. Now they shall try some more load on it.

2014:

The Tejas, which underwent crucial winter trials in February last year as well, will continue to stretch its legs over the forbidding north in an effort to achieve full weather compliance. Sources on Team Tejas confirm that the little jet performed admirably, and were confident of strapping on additional loads to the aircraft's pylons to push it even further.

http://www.sps-aviation.com/exclusive/? ... ter-trials

This shows our trength in R & D. In one year we changed the aircrft form an under performing platform to one which performed admirably well.

[vina]

This shows our trength in R & D. In one year we changed the aircrft form an under performing platform to one which performed admirably well.

Vipul Babu. Can you actually do something OTHER than posting old news article ? All of us can read the newspapers and the distilled garbage that DDM reports. What we actually want to see is some use of gray matter and some inferences. What you said unfortunately isn't one. That has to be based on science and not "feeling" , "seeing" and hearsay and someone said this, someone else said that etc.

I am not convienced fully but I would like to argue only after some more reading on the subject.

That is a splendid idea.

[member_28932]

Simply because when we have any product in your hand , it is evaluated based on 2 criterion. 1) against what it was designed to and 2) How does it perform against its counterparts. That will give us ideas about the improvement of any product. The argument that our adversary do not have it is meaningless. M2k is almost similar aircraft in terms of dimension and engine power. So compression is very much relevant. At least our new aircraft must match a decades old aircraft in performance.

Bad logic that is a recipe for a never-ending wild goose chase (IAF is cleverly using this logic to reject or delay India-made products). It is commonsensical and much better to benchmark a weapon system against what it will be realistically fielded against if a war breaks out. If it is better than that, deploy it -- don't just keep comparing it to weapon systems from much more advanced (but irrelevant for us) countries.

This means that we should be happy and be complecent because Tejas compares favorably to JF 17.

[PratikDas]

If we were being complacent, we wouldn't be designing the AMCA. But the AMCA will never be a success if we don't learn from manufacturing, deploying and servicing the LCA in hundreds. Those lessons have to be learned. The LCA is a sufficiently capable platform on its own.

[Philip]

As mentioned in an earlier post,laudable the achievements thus far may be,but are woefully 15 years late.Going through the latest Vayu,the 40th anniv. spl. there are excerpots from previous years.Dr.Kota H.who headed the programme officially said in the mid-'90s that 2 sqds would be ready by 1997! Therefore,while Mk-1 may have been rolled out quite some time ago,has undergone extensive testing,etc.,and could be an adequate replacement for vintage MIG-21s,the production capability still remains a Q mark and our dream of a 45 sqd. IAF will remain a dream,

The stream of info available thus far indicates that HAL has yet to get its series prod. act together so that numbers roll out steadily in large number.3 decades ago,the Nasik div. of HAL alone built 40+ MIGs annually,MIG-21s/23/27s! There are some other most interesting historical facts which I will collate and post later on.

[PratikDas]

^^^^ All logorrhoea considering the fact that late or not, we have to build our own aircraft in numbers to get into the aircraft manufacturing business or we'll forever be buying aircraft from other countries by paying a king's randsom. The ancillary benefits to every manner of Indian industry will be priceless.

[member_28932]

Well, not trying to prove anything since I am no aero guru but was not sure about AESAs being lighter than mechanical arrays. Thought ESA antennas are a lot heavier and require more cooling, which would probly add weight. Also not sure about 300kg ballast; this is used to mimic the weight of the mk2 (indicating the possibility that the latter will be heavier, not lighter) based on an article by B Karnad

I am not saying that AESA shall be lighter than MMR (In fact it will be much havier) but I simply said that AESA shall not have the stearing assembaly which shall save some weight (whiile pointing at some areas where the weight can be saved) . Yes, Mk1 has the dead weight for balancing.

[deejay]

My mango baniya mind failed to understand what Maithya guruji posted. But some things are clear from reading this thead. LCA is cheap. Designed and made in India. Capable of kicking a&& of most of the old and latest rubbish Lizard and his munna in the west of India can send against us. serious capability increase from Mig21,27, Jag etc, and I do not see any other argument against a major order for both mk1 and 2.

I am sold.

Well said Sir!

[Philip]

Pratik,there is no issue whatsoever regarding indigenization and developing/building our own weapon systems.The problem is that if schedules and parameters are not met within a reasonable timeframe,the systems become obsolete very quickly necessitating knee-jerk acquisitions yet again. The hard truth is that the LCA in final avatar req. by the IAF's ASR two decades ago ,will arrive only post 2020.The competition is not going to be static and would have long overtaken us. One interesting note in the Vayu spl. is that as far back as 1987,SAAB offered to collaborate with us on the LCA using its Gripen track record. has that happened we would've definitely cut down our dev. time by a decade at least.

[suryag]

Someone once told me, it is okie if people think you are stupid but do not open your mouth and confirm the same, applies very well to a lot of posters

[Shreeman]

Pratik,there is no issue whatsoever regarding indigenization and developing/building our own weapon systems.The problem is that if schedules and parameters are not met within a reasonable timeframe,the systems become obsolete very quickly necessitating knee-jerk acquisitions yet again. The hard truth is that the LCA in final avatar req. by the IAF's ASR two decades ago ,will arrive only post 2020.The competition is not going to be static and would have long overtaken us. One interesting note in the Vayu spl. is that as far back as 1987,SAAB offered to collaborate with us on the LCA using its Gripen track record. has that happened we would've definitely cut down our dev. time by a decade at least.

Phillip,

Haathi ke daant khaane ke aur..

LM and the engine, the mission computers confiscated, sanctions? What makes you think Saab would have ignored US bidding?

The timeline is a reflection of the realpolitik. People grow old, skills lapse, technology becomes obsolete. It is nothing short of a miracle that the LCA was realized at all. The engine is the normal story. If I were making decisions, I would resurrect a new canberra class aircraft (not the old aircraft itself, the class it belongs to) with two kaveris slapped on a lumbering long endurance air vehicle and burn some fuel until the substitue arrives. Thats where there are cobwebs.

[Yagnasri]

Philips sir, wa the money alloted for LCA properly? Timely? Sufficiently? We all what tomorrows weapons yesterday. How to get them without any money?

[Surya]

Phillip

For the nth time read Maolankars conversation with Kartik about ASRs etc.

As for Vayu - do we know if the owners or major contributors also double up as agents for Western manufacturers?

SAAB splashing ads is not disconnected

[Karan M]

Thank you sir.

I am not convienced fully but I would like to argue only after some more reading on the subject.

Yes tejas shall be our leading aircraft for any combat in Himalayas.

Its engine did not work well in 2013.

Talking to reporters, the IAF chief said the indigenous aircraft will have to be modified further for operating in high-altitude areas as recently during trials in Leh, its engine "did not work".

http://articles.economictimes.indiatime ... -lca-tejas

In 2014. The scenario changed completly. Aircraft performed admirably well. It took off from Leh Airfield with design load with an ease. Scintist said that it took off so easily. Now they shall try some more load on it.

2014:

The Tejas, which underwent crucial winter trials in February last year as well, will continue to stretch its legs over the forbidding north in an effort to achieve full weather compliance. Sources on Team Tejas confirm that the little jet performed admirably, and were confident of strapping on additional loads to the aircraft's pylons to push it even further.

http://www.sps-aviation.com/exclusive/? ... ter-trials

This shows our trength in R & D. In one year we changed the aircrft form an under performing platform to one which performed admirably well.

Vipul ji, please lurk more and understand the context better before making such posts. Its very hard to take anything you say seriously when you dont understand the topic you are trying to make points on.

For instance, the above. Do you know the IAF is referring not to the overall platform but the Jet Fuel Starter which has to be modified for Leh high alt ops? And that the same had to be done for the Su-30? In short, nothing like the quantum of claims you are making about "under performing platform to admirable one" etc etc. That such things are par for the course for all fighters and field modifications or component modifications have to be made?

Similarly, its very hard to explain the number of errata in your statements about weight, when you dont understand the issue or the context in which Tamilmani is making his estimates at this point.

[RKumar]

The hard truth is that the LCA in final avatar req. by the IAF's ASR two decades ago ,will arrive only post 2020.The competition is not going to be static and would have long overtaken us.

What is your expected delivery timeline for the 4+ gen multirole fighter for the FOC after issuing the ASR?
What time frame covers ASR 5, 10, 20, 40 years after FOC?

[brar_w]

Except maybe the Gripen there is really no model 4.5 generation project from a development, funding, and acquisition point of view (won't include the SH since it was based on an existing and proven aircraft) to compare the MK2 to. The Typhoon and the Rafale were extremely expensive development and acquisition programs. As a percentage of the National defense budget for example, both France and the UK spent a much much higher amount on developing and fielding the 100+ 4.5 generation birds than what the USAF spent on finding the 180 odd F-22's. From that angle the best thing bout the LCA is the cost aspect. Even if the MK2 comes online in the early 2020's, it is still great value for money.

[Indranil]

3g)The SDRE LCA Wing Planform: So, they decided to have best of both the worlds ... have a wing which will have both non-slender and slender delta planform. And viola, you got the compound delta LCA wing design, with it's both a low-wing-sweep (50deg, so non-slender delta) and high-wing-sweep (~63deg aka in the "slender delta" territory) as you move from inboard (wing root) to outboard of a wing.

Thus for the relatively lower part of the high-AoA flight regime (say from around 18deg to 22deg etc), the outboard slender delta part of the wing would dutifully contribute to the vortex lift while keeping the drag as low as possible. And with further increase of AoA, as that part of the wing starts to stall due to vortex bursting etc, the inboard non-slender-delta part of the wing will come into play with it's flow-reattachment aspects and keep on further enhancing the lift co-efficient (while still keeping the drag down as low as possible).

So where is the need of any additional control surface like a canard (and thus without the weight and complexity penalty of an additional control surface etc), hain jee?

Thanks Maitya for this excellent description of what the LCA's compound delta does. Can you speculate or otherwise clue us in on what the Viggen, which had the exact same compound delta as the LCA, gained from also having canards? I read somewhere that it was to turn the nose up or down faster on its vertical axis besides helping in high AoA flight, facilitating better turns, shorter takeoffs and slower landing speeds.

Could you also comment on the following remarks of Air Marshal Matheswaran:

It would actually have been prudent to choose a canard-delta design considering the severe size and weight limitations. This was also the recommendation of the consultants in the early phase. It is strange that this was not followed. Instead we chose to rely on a pure tail-less delta design and thought that the combination of unstable platform and digital FBW flight control system would generate enough performance. This was not possible, as subsequent results have shown.

The Swedes seem to have done a lot of work with compound deltas since the 1950s. The predecessor to the Viggen, the Draken, also had a compound delta but it was reversed, with the high sweep before the low sweep.

Looks like Maity ji is busy, so let me give it a try.

So what Maity ji has taught you till now is that lift is what gives you the ability to turn. The larger the lift you can generate, the faster you can turn. In the below picture Lift X sin(theta) = centripetal force. L X cos(theta) is what balances the weight of the aircraft.


As one increases the angle of attack of a wing, the lift and the drag increase almost monotonically (simplification) as shown by two parameters called coefficient of lift and coefficient of drag. But only to a limit (called the critical angle of a wing), at which the airflow separates (completely) from the top of the wing and wing stalls, i.e. lift falls drastically and drag increases exponentially. So there is a limit to how much lift one can generate and hence a limit to how fast a plane can turn.

Now when a fighter comes in to turn, it has a lot of initial speed, i.e. kinetic energy. So it can use its maximum lift capability to get into the tightest turn. But remember, drag also increases drastically. None of the fighters have enough thrust to overcome this level of thrust. So its energy bleeds off, i.e. its speeds falls down. This period of the turn is called the instantaneous turn and the turn rate is called instantaneous turn rate. But this can't continue forever (generally lasts a few seconds). If the speed of the aircraft continues to fall, then at some point it will go below its stall speed, i.e. it will fall to the ground like a stone. This can be overcome by losing potential energy of the plane, but in doing so you lose height i.e. become the cannon-fodder of your opponent. So to maintain a horizontal turn, the pilot has to lower the drag, i.e. decrease the lift aka lower his AoA. By how much? Till the point that the drag is balanced by the thrust of the engine. At this point, the rate of turn is decreased to the sustained rate of turn. So, the instantaneous turn rate is determined by the maximum lift generating ability of the aircraft and the propensity to reach this state as soon as possible. On the other hand, the sustained turn-rate is determined by the drag and the thrust.

The delta wing is excellent instantaneous turn-rates, because it generates large amounts of lift and naturally wants to reach higher AoA. This is because the leading edge of delta wings readily creates large vortices which add to the lift (called vortex lift). But obviously, this fast rate of turn also bleeds off the energy very fast. Beyond this point, the drag of the delta wing (at low altitudes) and slow hard turns is more than the classical wings. Therefore for maintaining the same rate of turn, a delta wing plane at low altitudes needs to have a better thrust to weight ratio.

So, we have learnt that various wings have various advantages and disadvantages. But aircraft designers have to take care of the whole flight envelop. So what should they do? They chose a design point, and make the plane excellent at that envelop around that design-point. Next they try to add things to mitigate the disadvantages at the off-design points. For example, most planes with conventional wings use LERXes with sharp edges and high sweep which generate vortices like the leading edge of a delta wing. The F-16 uses the slats and flaps as part of wings to increase its area (decrease wing-loading) etc. For delta wings, there are two primary methods:1) use a close coupled-canard and 2) use variable extended slats. A close-couple canard works by shedding a vortex which combines with the vortex of the leading edge of the delta-wing and energizes it (the exact aerodynamics is really long and winded to explain in a forum post like this). The variably-extended slats like in (Mirage 2000 and LCA) also work in the similar way. Going from the wing-root to the wing-tip, the vortices from the inner slat (at lower AoA) energizes the vortices from the outer slat (at higher AoA). I will not go into the details here because it depends on a lot of parameters like the sweep of the wing, the AoA, the sharpness of the edge etc.

In case of LCA, the wing and lift is not at all the problem. The co-efficient of lift increases monotonically till about 35 degrees of AoA. The same goes for Co-efficient of drag. The L/D ratio is one of best too by virtue of its very low wing loading. This gives it excellent ITR and roll rates. You now know that LCA would most probably be limited to 26 degree AoA, because at this AoA it generates enough lift to give it extremely good turn-rates. There is unconfirmed reports by Sjha, that it might even be taken to 28 degrees. The designers (as Maity sahab pointed out) went for a compound delta wing, where the outer part of the wing (with larger sweep) provides the capability for excellent ITR, whereas the inside of the wing helps with STR (kind of like 2-design points). The kink in the delta (can be imagined as the innermost slat with no extension) generates a vortex which energizes the vortex from the innermost actual slat, very similar to the what a fixed canard would have done. The question is how can we make the STR of LCA better. One way is to increase the thrust (brute-force), and the second way is to make it more efficient, i.e. increase the Lift-to-drag ratio. Designers of LCA Mk2 are going for both. The late Commodore says, the thrust could be increased on Mk1 (because intakes don't let the Mk1 obtained maximum thrust) and that in itself is enough.

Okay now, we come to your question. Why did Viggen have a canard in spite of having a compound a delta like Tejas. I have already answered part of that question, because it did not have independent slats like the Mirage 2000 and Tejas (though it tries to do something similar with a dogtooth). The other part of the answer lies in the plane. Remember, what I told you about the design-point. The design-point of that plane was for STOL performance. For that the plane needs to be able to turn its nose up at low speeds. But then the Viggen's elevons were attached to the end of its wings (aka with a short lever arm). So it needed secondary help (aka the canards which had flaps to provide positive lift). Another part of the answer was the Viggen's airframe itself. The Viggen was a pioneer being one of the first fighter planes to use a turbofan engine. However, given the technology of the engines then, the airframe had become very fat and bulky. If they had gone for a traditional wing, the plane would have become really fat, i.e. too much increased in wave-drag (which affects cruise-speed, range and top-speed). So, Viggen's designers (kind of) broke the wing into two wings. The smaller of the two doubles up as a canard. This kind of canard which shares the burden of generating lift along with the main wing is called a high-loaded canard. Of-course it produces other advantages (and also disadvantages).

Anyway, there are many ways of building a plane to do the same thing. Even within canards there are various ways. The canards that you see EF is a lightly-loaded canard aka a control canard, i.e. it does not produce any lift. The canard on Gripen and Rafale are mostly control canards, but can transition to a loaded canard when required (this is only possible with a FBW). For example, one can see Rafale's canards change roles while taking off from an aircraft carrier. It transitions from a control canard to a highly loaded canard soon after the plane leaves the flight deck. Also there is no silver bullet to building a plane which works exceptionally well across the entire (extremely wide) flight envelop of a modern fighter. Otherwise, all planes would have been the same. For example, three of the best designs from an aerodynamic perspective IMHO are the F-16, Mig-29 and the Rafale. These three have the cleanest airframes which use almost all the possible advantages that can be extracted out of airflows around an airplane. The Rafale is probably the best of the lot because it learned a lot from the other two. It uses the boundary layer over the wing (which the other two don't) and a complex interplay between the canard and the wing-body blend. It places its wing at the exact height where the leading edge can be extended with an extremely sharp LERX by the side of the air intake (not present in the initial prototypes). Anyways, none of these 3 look alike. Therefore, ex. AVM Matheswaran's comments can only be put down as bias. Tejas Mk1's short-comings are not a want of canard. Anybody who knows aerodynamics will tell you that easily, as has been evidenced by numerous studies. Believe it or not!

[Indranil]

By the way, Victorji,

Did you know that for the F-16 the horizontal stabilizers come in the wake of the wing at greater than 25 degrees AoA, i.e become ineffective (like in the IJT). This is called a deep-stall (or super-stall) and is mostly unrecoverable. Therefore the F-16 is limited by its FBW to 25 degrees AoA. But if you pushed the FBW against many limiters, you might accidentally overshoot this boundary. In that case, there is large switch to override the FBW and try to regain control (if possible), otherwise eject. Also, did you know that it flew with too small a stabilizer (a life threatening shortcoming) for 2 years after entering production. Nobody, except Langley (I believe) caught this in the wind-tunnel testing and flight-testing. Because, you have taken ADA/HAL to the butchers fro LCA/IJT.

[Akshay Kapoor]

Another illuminating post Indranil. I also asked some questions to Maitya. Would you be kind enough to take a stab at them if you can ? I am reposting. Another question, how is the Mig 21's wing compared to the LCA.

Maitya,

thank you for taking the effort to post this. This is what BR should incubate...knowledge building and thoughtful analysis. But I digress. Couple of quick questions.

1, 2 (especially 2)- Delta wing vs metal wing LF and WL. What is the difference in quantum of turn achieved (degrees of ITR and STR) because of composite vs metal in LCA's case. I know that's a hard question as there are several variables but an educated guess would be very welcome.

3 b - Correct, the limiting factor is the thrust weight not wing design. So with LCA MK1 engine what STR do you think we can reach realistically. What would be doable say with total weight of 9.5/10 tonnes (half fuel plus missiles) ?

3 g - Silly question I'm sure - the regime shift from slender to non slender is seamless in terms of AoA increase. So as the pilots maneuver and increase AoAs from 18 to 26 is there a section of AoA flow detaches at X say 20 for slender but the regime shift from slender to non slender has already happened at Y say 18 so flow has come back and there is no problem ? Obviously its all been tested till 26 AoA so it is fine but I just wanted to understand this in the regime shift terms.

Finally what STR and ITR do you think we have on MK1 ? What will it be on MK 2 after nose plug etc ?

[Karan M]

The only darn thing that held the LCA back was the decision to stick to MiG-21 dimensions, including length. Now they have relaxed that, the fuselage will be shaped better to minimize drag - the nose plug etc. On a plus side, we have really advanced in subsystems and packaging. We had to make everything w/same function as on larger aircraft- Su's, MiGs etc, but sized for a MiG-21. Ergo it will help us when we move to the AMCA, every ounce of compact packaging counts.

[Indranil]

1, 2 (especially 2)- Delta wing vs metal wing LF and WL. What is the difference in quantum of turn achieved (degrees of ITR and STR) because of composite vs metal in LCA's case. I know that's a hard question as there are several variables but an educated guess would be very welcome.

Maity sir, made a mistake there. He said the wing loading is the weight of the wing divided by the area. It is actually weight of the aircraft borne by the wing divided by its area. So what the composites allow is lowering the weight of the aircraft borne by the wing. It might also give better structural qualities like rigidity. Let us look at it this question in steps.

Step 1) Suppose Mig-21 wings were replaced by composite wings of the technology used in Mk1. What would be the advantage? The primary advantage is that the overall weight of the aircraft goes down. This lowers the wing loading, induced drag, and allows higher bank angle. Effectively, everything becomes better ITR, STR, range, speed at particular thrust etc.
Step 2) How about the composite wing technology being used for Mk2? Well, basically the entire under side and the structural elements will be a single piece. This will make the wing even more lighter and stiffer. So, all the above advantages will be accentuated, along with a providing better stability at higher Gs.
Step 3) How about the wing shaping and variable slats. The aerodynamics associated with these features were not known at the time when Mig-21s were designed. The Mig-21s are supersonic darts (that is their design point). It was not initially designed for turning duels. But the plane is such a beauty, that for its era it could take down anything its path. Anyway, I digress. The LCA-type wings would give Mig 21s the capability to also handle slow-hard turns at lower-altitude that was its Achilles' heel.

3 b - Correct, the limiting factor is the thrust weight not wing design. So with LCA MK1 engine what STR do you think we can reach realistically. What would be doable say with total weight of 9.5/10 tonnes (half fuel plus missiles) ?

I really do not know the answer for this. This is too non-linear a flight-domain to speculate for me. Too many things that I don't know. What is the thrust that the engines are generating? What is the drag? I don't think it can be answered by using pen and paper. It has to be flown. My gutt feeling is that if it was 8.5 tonnes (as designed), it would have managed 18 degrees. I think right now it is about 16 degrees. But higher gurus like Raman sir, Vina, Ulanbatori, Lal mullah can comment.

3 g - Silly question I'm sure - the regime shift from slender to non slender is seamless in terms of AoA increase. So as the pilots maneuver and increase AoAs from 18 to 26 is there a section of AoA flow detaches at X say 20 for slender but the regime shift from slender to non slender has already happened at Y say 18 so flow has come back and there is no problem ? Obviously its all been tested till 26 AoA so it is fine but I just wanted to understand this in the regime shift terms.

No, the outside of the wing does not completely stall. It just becomes less effective, the load borne by different parts of the wing shifts, and the transition is continuous. So, there is no marked feeling of the shift.

Finally what STR and ITR do you think we have on MK1 ? What will it be on MK 2 after nose plug etc ?

Mk1s ITR must be better than the Mirage 2000 (owing to better wing-loading). Mirage's ITR @ 15,000 ft. (4,572m) with two IR Missiles and 50% Int. Fuel is 22, 17.5, 13, and 10.5 degrees at Mach 0.7, Mach 0.9, Mach 1.2 and Mach 1.5 respectively. The Mk2's ITR will be less than the Mk1, because of higher weight, but will still be better than the Mirage.

In STR, I think Mk1s STR is currently around 16 degrees. I expect it to be around 19-20 degrees for Mk2.

[Akshay Kapoor]

Thank you Indranil for such a detailed response especially the ITR at different thrusts compared to M2K. Much appreciated.

16 Degrees STR sounds fine when compared to about 13 for Mig 21 (I read it somewhere on the weekend) and ITR is better. Please correct me if I am wrong. Am no expert on flight and aerodynamics but from what you say it seems that LCA is better than Mig 21 in all flight regimes. Even in intercept ? So is there anything the supersonic dart can do that this joy to fly cannot ? Purely in areodynamics terms not avionics ?

[Indranil]

I don't think anybody really questions the fact that the LCA is better in every aspect to the Mig-21 except top-speed.

[Indranil]

Head to the 2015 calendar of Tejas home page of Facebook. Some wonderful discussions there.

The following picture explains a lot of the vortex interations that I was talking about:


Also, the following picture shows the All-up weight. If those tanks are full, it marks more than 3.5 Tons of payload.

1. 2400 ltrs or 1945 kg of fuel + weight of tanks
2. 1000 kgs of LGBs
3. 210 kgs of A2A missiles
4. 200 kgs of LGB pod

[Victor]

Therefore, ex. AVM Matheswaran's comments can only be put down as bias. Tejas Mk1's short-comings are not a want of canard. Anybody who knows aerodynamics will tell you that easily, as has been evidenced by numerous studies. Believe it or not!

AVM Matheswaran was simply stating that the consultants ADA hired had recommended the canard-delta layout early in the design stage because of the imposed size limitations but ADA/HAL ignored the advice. Where's the bias here? It sounds like simple self-preservation and concern for comrades, coming from a top notch combat pilot, experimental test pilot and instructor at TACDE. I think we need to either accept what he is saying as the truth or call him out as a traitor. Might as well throw in past Air Chiefs and most senior IAF officers because they all say the same thing. Simple as that. If OTOH it is being made out that ADA/HAL knew more than the consultants they hired with taxpayer money to advise them, we have a major problem.

[srai]

^^^

Anyone wants to calculate the range of the max load out configuration above with those external tanks carrying 2400 ltrs of fuel?

[srai]

Therefore, ex. AVM Matheswaran's comments can only be put down as bias. Tejas Mk1's short-comings are not a want of canard. Anybody who knows aerodynamics will tell you that easily, as has been evidenced by numerous studies. Believe it or not!

AVM Matheswaran was simply stating that the consultants ADA hired had recommended the canard-delta layout early in the design stage because of the imposed size limitations but ADA/HAL ignored the advice. Where's the bias here? It sounds like simple self-preservation and concern for comrades, coming from a top notch combat pilot, experimental test pilot and instructor at TACDE. I think we need to either accept what he is saying as the truth or call him out as a traitor. Might as well throw in past Air Chiefs and most senior IAF officers because they all say the same thing. Simple as that. If OTOH it is being made out that ADA/HAL knew more than the consultants they hired with taxpayer money to advise them, we have a major problem.

Please stop making such vast generalisations (and falsely attributing your viewpoint to people who have served) unless you can provide direct quotes from all of them! Besides, it's not a black-or-white scenario. A lot of variations were studied and one of them was chosen. Every design has its pluses and minuses.

[Victor]

^ What do you mean by false attribution? ACM Naik was speaking for the entire IAF when he slammed HAL/ADA in public. Is there still any doubt about what the IAF thinks? Serving officers will never make statements in public. IMO, the fact that MoD did not butt in says a lot for its own view of ADA/HAL. But that still doesn't answer the point Matheswaran made: when ADA hired a consultant, why did it ignore their advice? Obviously, the reason was not shared with the IAF.

Let's not lose sight of the fact that we are arguing here because ADA has just said LCA will need to drag its butt for another YEAR to get FOC. Why is anyone defending this rubbish? Or is it acceptable?

[srai]

By the way, Victorji,

Did you know that for the F-16 the horizontal stabilizers come in the wake of the wing at greater than 25 degrees AoA, i.e become ineffective (like in the IJT). This is called a deep-stall (or super-stall) and is mostly unrecoverable. Therefore the F-16 is limited by its FBW to 25 degrees AoA. But if you pushed the FBW against many limiters, you might accidentally overshoot this boundary. In that case, there is large switch to override the FBW and try to regain control (if possible), otherwise eject. Also, did you know that it flew with too small a stabilizer (a life threatening shortcoming) for 2 years after entering production. Nobody, except Langley (I believe) caught this in the wind-tunnel testing and flight-testing. Because, you have taken ADA/HAL to the butchers fro LCA/IJT.

LCA Mk.1 -> 26 AoA.

...

3 b - Correct, the limiting factor is the thrust weight not wing design. So with LCA MK1 engine what STR do you think we can reach realistically. What would be doable say with total weight of 9.5/10 tonnes (half fuel plus missiles) ?

I really do not know the answer for this. This is too non-linear a flight-domain to speculate for me. Too many things that I don't know. What is the thrust that the engines are generating? What is the drag? I don't think it can be answered by using pen and paper. It has to be flown. My gutt feeling is that if it was 8.5 tonnes (as designed), it would have managed 18 degrees. I think right now it is about 16 degrees. But higher gurus like Raman sir, Vina, Ulanbatori, Lal mullah can comment.
...

Finally what STR and ITR do you think we have on MK1 ? What will it be on MK 2 after nose plug etc ?

Mk1s ITR must be better than the Mirage 2000 (owing to better wing-loading). Mirage's ITR @ 15,000 ft. (4,572m) with two IR Missiles and 50% Int. Fuel is 22, 17.5, 13, and 10.5 degrees at Mach 0.7, Mach 0.9, Mach 1.2 and Mach 1.5 respectively. The Mk2's ITR will be less than the Mk1, because of higher weight, but will still be better than the Mirage.

In STR, I think Mk1s STR is currently around 16 degrees. I expect it to be around 19-20 degrees for Mk2.

According to Saurav Jha,

...
The Mk-II design will specifically address the sustained turn rate (STR), climb rate and transonic acceleration shortfalls of the Mk-I. The ASR requires a STR of 18 degrees (same as the F-16's) and Mk-II will close in on that. The climb rate will also be more or less satisfactorily reached. Transonic acceleration is expected to be realized fully. Moreover the Mk-II airframe will certainly be able to reach and fly through Mach 1.8 in a dive.
...

Here are some more ITR figures for Mirage-2000:

...
At 30,000 –35000 ft and 5G the ITR is 10- 12°/second.

At 36,000 ft and Mach 2 the Mirage can maintain a 3G turn.

At an altitude of 40,000 ft and Mach 1.05 pulling the stick nearly full-aft produces 4.5G and an angle of attack(AoA) of 25°.

At 22,000 ft and Mach 0.9 the application of 8G produces an ITR of 20°/second. The AoA is then 27°.
The application of 9G increases the ITR to 24°/second and 28° AoA.

From the same site, some selective comparison flight data supplied by Dassault vs F-16 and F-18.

Code: Select all

Manoeuvrability
Instantaneous turn rate @ 15,000 ft. (4,572m) - Two IR Missiles - 50% Int. Fuel
 
				Mach 0.7	Mach 0.9	Mach 1.2	Mach 1.5
				°/sec		°/sec		°/sec		°/sec

Mirage 2000		22			17,5		13			10.5

F16 C				18			17.5		13			10.5

F18 C				18.5		14.5		11			8.5

[Raman]

AVM Matheswaran was simply stating that the consultants ADA hired had recommended the canard-delta layout early in the design stage because of the imposed size limitations but ADA/HAL ignored the advice.

Configuration changes are not made on the basis of gut feeling - they require a large number of trade studies backed by reams of CFD and wind-tunnel data.

Rather than ADA/HAL "ignoring" the advice, it is almost certain that they considered the configuration, but discovered that it was suboptimal.
The model on the left is a wind-tunnel model of an LCA configuration with canards.

[srai]

^ What do you mean by false attribution? ACM Naik was speaking for the entire IAF when he slammed HAL/ADA in public. Is there still any doubt about what the IAF thinks? Serving officers will never make statements in public. IMO, the fact that MoD did not butt in says a lot for its own view of ADA/HAL. But that still doesn't answer the point Matheswaran made: when ADA hired a consultant, why did it ignore their advice? Obviously, the reason was not shared with the IAF.

Let's not lose sight of the fact that we are arguing here because ADA has just said LCA will need to drag its butt for another YEAR to get FOC. Why is anyone defending this rubbish? Or is it acceptable?

Please provide direct quotes as well as all of the design recommendations made by the consultants and the trade-offs they highlighted.

[Ramu]

^ What do you mean by false attribution? ACM Naik was speaking for the entire IAF when he slammed HAL/ADA in public. Is there still any doubt about what the IAF thinks? Serving officers will never make statements in public. IMO, the fact that MoD did not butt in says a lot for its own view of ADA/HAL. But that still doesn't answer the point Matheswaran made: when ADA hired a consultant, why did it ignore their advice? Obviously, the reason was not shared with the IAF.

Let's not lose sight of the fact that we are arguing here because ADA has just said LCA will need to drag its butt for another YEAR to get FOC. Why is anyone defending this rubbish? Or is it acceptable?

A noob question. How does the canard affect aircraft stealth? None of the 5th gen planes seem to have it.

[Raman]

Let's not lose sight of the fact that we are arguing here because ADA has just said LCA will need to drag its butt for another YEAR to get FOC. Why is anyone defending this rubbish? Or is it acceptable?

Neither ADA/HAL nor IAF appears to have a clue on running a de novo fighter program.
There is enough blame to go around. The only solution is bash on until the job is done.

[brar_w]

^ What do you mean by false attribution? ACM Naik was speaking for the entire IAF when he slammed HAL/ADA in public. Is there still any doubt about what the IAF thinks? Serving officers will never make statements in public. IMO, the fact that MoD did not butt in says a lot for its own view of ADA/HAL. But that still doesn't answer the point Matheswaran made: when ADA hired a consultant, why did it ignore their advice? Obviously, the reason was not shared with the IAF.

Let's not lose sight of the fact that we are arguing here because ADA has just said LCA will need to drag its butt for another YEAR to get FOC. Why is anyone defending this rubbish? Or is it acceptable?

A noob question. How does the canard affect aircraft stealth? None of the 5th gen planes seem to have it.

There is a myth floating around that canards hamper it yet there are folks on record who have claimed that it is not a case when you specifically factor in canards into designs of stealth aircraft. The father of the JSF propulsion system spoke of this when he said that the GD folks talked their designers (skunk works) away from canards because they were dead against it. Boeing uses Canards in one of their 6 generation designs submitted against the USAF RFI back in 2010 and later refined for the USN RFI issued a few years later. Northrop Grumman also proposed a canard design for the NATF based on their YF-23 submission.