LCA Tejas: News and Discussions

RKumar · Post by **RKumar** » 24 Mar 2015 00:26

HAL, where is SP-2 it is almost end of March?

Philip · Post by **Philip** » 24 Mar 2015 12:22

EADS? What naval fighter are they manufacturing? Why couldn't we have roped in Boeing.Lockheed,Dassault from the Western menu? At least these 3 manufacturers have/are producing naval fighters. SAAB too offered a Sea Gripen some time ago. That aircraft is closer in size and style to the LCA than any of the rest.Honywell is supposed to be the Jaguar upgrade collaborator. Are we handing out consultancy presents to every manufacturer under the sun? Germany operate no carriers,France uses naval Rafales ,Italy uses Harriers and Britain is buying F-35Bs. Then we have the Russians with their MIG-29K already being used by the IN and the SU-33 from Sukhoi.It would've been very easy to have roped either of them in given their long-standing relationship with the services,HAL,DRDO,etc.

Sometimes the decisions of our boffins and babus defies logic.

kancha · Post by **kancha** » 24 Mar 2015 19:02

Unrelated, but drove past the Salaria Enclave in Dwarka today. Heartening to see the Tejas displayed so proudly on the perimeter wall!

(Apologies for the poor quality of photo, taken from mobile from about 15m away)

rohitvats · Post by **rohitvats** » 24 Mar 2015 21:35

That poster also exists in front of main entrance to Subroto Park when going towards Vasant Kunj.

prat.patel · Post by **prat.patel** » 24 Mar 2015 23:41

With the LCA production now in crucial stage; MOD should think out of box to bring more visibility/clarity (and indirectly positive pressure on HAL to deliver + address personal perceptions issue) on production timelines progress.

Radical thought would be to go public with publishing updates on quarterly basis on the production status. No need to publish details that compromises IP/national security; but details like % completion per aircraft, on target with estimates or behind/ahead etc.

I know it is a double edged sword with respect to the DDM; but in a long run would be beneficial to the program because I am sure progress will be visible in numbers rather than one's perception vs other's.

I saw a question posted yesterday asking about status of SP-2. Voluntary disclosures on fixed periodic basis by HAL could avoid the anxiety and also unwanted speculations by DDM.

Am I being way off here with my expectations?

P.S. - This is my first post on this esteemed forum! Have been lurking for around couple of years. Finally got registered and happy to be here!

JayS · Post by **JayS** » 25 Mar 2015 02:21

I am looking through NAL archieves and there seems to be a trail of papers related to delta wing configuration studies right from early 70's or so. Pity the material is not accessible for mango people.

This one for example, seems to be connected to the study of effect of Canards with LCA wing. For the said configuration at least its seen that Canards are more detrimental than helpful.

Narayan, KY (1988) Effect of Canard on the Characteristics of a 65° Delta Wing-A Preliminary Analysis of Experimental Data. Project Report. National Aerospace Laboratories, Bangalore.

The experimental data available on a 65° swept-back, cropped delta wing with a canard has been analysed to study the effects of canard. Two sets of results are available : the first set is with a wing having sharp leading edges and the second set with a wing having rounded' leading edges. The tests were carried out at Mach numbers of 0.4 and 0.85 (Reynolds - number of 9.106 based on wing root chore) for the first set and at 0.5, 0.7, 0.85 and 1.2 (Reynolds number of 4.5.10^6 based on wing root chord) for the second set. The main effect of the canard is to delay leading edge separation in the forward part of the rounded leading edge wing. In the case of the sharp leading edge wing, although earlier measurements have shown that the canard is able to suppress leading edge separation, there is no direct evidence of this in the present measurements. However, the results do show a significant weakening of the wing vortex in the presence of the canard.

And finally I found something which talks about the lower-swept in-board part of Compound delta wing, though I can find only the abstract.

Sajeer, Ahmed and Sudhakar, S (2010) Experimental Study on Pitch up Problem Associated with Compound Delta Wings of Combat Aircraft Configurations. Project Report. National Aerospace Laboratories, Bangalore.

Experiments were carried out on two compound delta wing configuration with first sweep angle of 50°& 55° and a second sweep of 60° in the 0.3m Trisonic wind tunnel for a Mach number range of 0.5 to 0.85 in the angle of incidence range 0° to 20°. Data was also generated for a baseline delta wing configuration with sweep angle of 60°. The results were analyzed to understand the effect of variation in first sweep and Mach number for the existence of pitch up. Oil flow visualization has been carried out for the limited case to infer the flow field associated with the pitch up. Analysis of the aerodynamic data showed the presence of pitch up in all the three configuration tested. Decrease in first sweep has shown an increase in the magnitudes of the pitching moment and occurrence of pitch up shifting to lower incidence angles. Increase in Mach number has shown similar variation and no pitch up was observed at Mach number of 0.85 for the configuration having compound sweep of 50°/60°. Surface flow patterns supplements the force data and indicates the flow pattern over the wing is affected by first sweep and is predominantly dominated by a vortex from the first sweep and considerable difference in flow pattern is observed over the area covered by the first sweep compared to single 60° delta configuration.

Indranil · Post by **Indranil** » 25 Mar 2015 07:05

^^^ Nice work.

Kartik · Post by **Kartik** » 25 Mar 2015 09:12

rohitvats wrote:That poster also exists in front of main entrance to Subroto Park when going towards Vasant Kunj.

Also seen in Bangalore, near Hebbal junction.

Kashi · Post by **Kashi** » 25 Mar 2015 11:57

Kartik wrote:Also seen in Bangalore, near Hebbal junction.

Mekhri circle you mean..

Kartik · Post by **Kartik** » 25 Mar 2015 13:28

Just past Mekhri circle, towards Hebbal junction

jamwal · Post by **jamwal** » 25 Mar 2015 13:35

Same LCA poster in front of Air Force Cantt near Chanakyapuri too.Saw it a couple of weeks back

Raveen · Post by **Raveen** » 25 Mar 2015 19:50

nileshjr wrote:
Sajeer, Ahmed and Sudhakar, S (2010) Experimental Study on Pitch up Problem Associated with Compound Delta Wings of Combat Aircraft Configurations. Project Report. National Aerospace Laboratories, Bangalore.

Experiments were carried out on two compound delta wing configuration with first sweep angle of 50°& 55° and a second sweep of 60° in the 0.3m Trisonic wind tunnel for a Mach number range of 0.5 to 0.85 in the angle of incidence range 0° to 20°. Data was also generated for a baseline delta wing configuration with sweep angle of 60°. The results were analyzed to understand the effect of variation in first sweep and Mach number for the existence of pitch up. Oil flow visualization has been carried out for the limited case to infer the flow field associated with the pitch up. Analysis of the aerodynamic data showed the presence of pitch up in all the three configuration tested. Decrease in first sweep has shown an increase in the magnitudes of the pitching moment and occurrence of pitch up shifting to lower incidence angles. Increase in Mach number has shown similar variation and no pitch up was observed at Mach number of 0.85 for the configuration having compound sweep of 50°/60°. Surface flow patterns supplements the force data and indicates the flow pattern over the wing is affected by first sweep and is predominantly dominated by a vortex from the first sweep and considerable difference in flow pattern is observed over the area covered by the first sweep compared to single 60° delta configuration.

Great work! Now someone please explain what this means.

Yagnasri · Post by **Yagnasri** » 25 Mar 2015 22:17

In respect of LCA. Need is to create a SPV in the form of a Company with HAL and others selected to bring in capital and exparties (like GE or Land T) higher level of production of high tech equipment with LCA production facilites transfered to it. A significant portion of the shares can be publicly held. A order of 600 ACs with most of them getting exported to friendly nations will be a good project. A higher thurst Kaveri or other Eng powered LCA can be a good option for many nations like V'nam etc. Makes a good business sense to do.

JayS · Post by **JayS** » 26 Mar 2015 10:31

Raveen wrote: Great work! Now someone please explain what this means.

I am trying to put the pieces of puzzle together with meagre amount of hard evidence, I cannot prove what I am gonna say, but so far from a number of papers I have gone through, it makes sense. So take it FWIW!!

I have been looking for this for long time. The results here show that the lower-swept inboard section increases not only the magnitude of pitch-up but also it pushes the onset to lower AoA. Which means that the low sweep on inboard section makes the wing produce more lift at low AoA (as compared to pure delta config), thus shifting the centre of lift further upstream, giving more pitch-up moment. Now there are many interesting implications of this. Sure, increased pitch-up moment bad, but perhaps its managable and in return you get better lift at lower AoA.

Pure deltas are good for high AoA regime but not so much at low AoA. What typically has been done is to have wing designed with lower sweeps (~50deg) which are decent in low AoA regime and then introduce a highly swept inboard section to enhance lift in high AoA regime with the LEV. ADA/NAL seem to have gone the other way. They made the wing with larger sweep (62.5deg) which is decent at high AoA regime but not so much at lower AoA. So they made the inboard section with 50deg sweep which gives enhanced performance at low AoA overall. The inboard section falls in non-slender delta regime and works more like normal wing for low-moderate AoA and like typical delta only at high AoA. The outboard part is in slender delta regime and works like typical delta wing. So with this config we have a wing which works well enough at low and high AoA. To alleviate the increased pitch up ADA seems to have done some work e.g. the TE of wing is not straight but is at 4deg (This is what F-16XL people also did). They have passive fuel flow control to control the CG movement and there are plans to incorporate active fuel flow control in future. I am sure they must have used few tricks in FCS as well.

Regarding the Canard, if we go by what the above mentioned papers say, Canards weaken the LEV of the wing. So a canard on LCA wing perhaps would weaken the inboard LEV, which incidentally dominates the flow structure on the wing. If this indeed the case then clearly canards are significantly detrimental to high AoA lift for LCA. Also they say that the main effect is to delay separation on LE of rounded wing. We have those 6 LE slats doing this work currently (they also give a slight enhancement in lift and manoeuvrability at transonic speeds.). Also canards would be increasing the total pitch-up moment. So basically they are not seeing any appreciable increase in aerodynamics rather there are some adverse effects. Some other factors are also there like for a statically unstable a/c for trimming you will need negative lift generating canard (canard no more giving additional lift but adding to drag and affecting main wing airflow by giving up-wash. On contrary horizontal stabilizer would give + lift while providing pitch-down moment). Perhaps due to all these and maybe some more profound reasons ADA/NAL in their better judgement did away with canards.

One more thing, I had mentioned it before here. I think the lower sweep inboard section has one more advantage. It keeps flow nice and smooth over the centerline of the a/c and over the vertical tail by shifting the LEV towards outboard section. (Higher the sweep closer the vortices to the center-line). By keeping those vortices away from tail keeps it effective over all the AoA range and saves it from adverse effects such as buffeting due to vortex bursting which is highly unpredictable phenomenon. This issue is there in F/A-18, F-35 and perhaps for F-22 too. Those a/c need strengthening of tails, but since they all have twin tail its more critical than it would be in LCA with single VT. Whether its considered by ADA and was a factor in deciding for low-sweep inboard section or is a by-product, or I am totally wrong I do not know. But I have seen LCA's CFD pictures published here and there which makes me think on this line.

Hope I am not too wrong.

Singha · Post by **Singha** » 26 Mar 2015 10:46

the rafale and ef do have pretty high and meaty tails.

maitya · Post by **maitya** » 26 Mar 2015 12:14

nileshjr wrote:
Raveen wrote: Great work! Now someone please explain what this means.
... Pure deltas are good for high AoA regime but not so much at low AoA. What typically has been done is to have wing designed with lower sweeps (~50deg) which are decent in low AoA regime and then introduce a highly swept inboard section to enhance lift in high AoA regime with the LEV. ADA/NAL seem to have gone the other way. They made the wing with larger sweep (62.5deg) which is decent at high AoA regime but not so much at lower AoA. So they made the inboard section with 50deg sweep which gives enhanced performance at low AoA overall. The inboard section falls in non-slender delta regime and works more like normal wing for low-moderate AoA and like typical delta only at high AoA. The outboard part is in slender delta regime and works like typical delta wing. So with this config we have a wing which works well enough at low and high AoA. ...

Nileshjr, you may want to go thru this post (of mine) which deals with this very same aspects of the LCA Wing planform design (aka non-slender inboard and then slender outboard) and it's implications wrt managing the vortex-flow and squeezing out more lift without too much compromise on the drag side.

http://forums.bharat-rakshak.com/viewto ... 0#p1774291
...
they also found out that vortex breakdown is not a limiting phenomenon as far as the lift force is concerned for non-slender wings - on the contrary, flow reattachment is the key lift-enhancing contributor.
...
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).

The flow-reattachment phenomenon over the non-slender part wing is a key differentiator.

Also, you may want to refer to Indranilji's post here and refer to how the notch formed due to non-slender/slender "joining" on the wing leading edge creates a vortex flow that further enhances the lift regime on the slender-part of the wing. Plus the vortex from the non-slender part of the wing energizes the flow over the "immediate-neighbor" slender part of the wing, enhancing lift without sacrificing too much on drag.

http://forums.bharat-rakshak.com/viewto ... 0#p1775430
...
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.
...

DexterM · Post by **DexterM** » 26 Mar 2015 12:39

Indranil, Maityaji, a request: These nuggets are lost in the thread. This is what makes BRF so much better as a learning resource!
Could we please consolidate these into post or find a home for this on the main site?

maitya · Post by **maitya** » 26 Mar 2015 12:49

DexterM wrote:Indranil, Maityaji, a request: These nuggets are lost in the thread. This is what makes BRF so much better as a learning resource!
Could we please consolidate these into post or find a home for this on the main site?

^^^ Not sure, but I think Indranilji have agreed to do/attempt something similar (he's an aeroguru, so he will pick and choose which ever posts he thinks should be there) but only after first-week-of-April (?).

Singha · Post by **Singha** » 26 Mar 2015 13:51

The benefits of the wing are seemingly nullified by the short barrel fuselage.
No other recent plane barring jf17.
Even much older planes have better fuselage shapes.

Iaf siktat to make it fit small old shelters has now cost us 8 yrs and counting to rectify in mk2.

JayS · Post by **JayS** » 26 Mar 2015 15:22

maitya wrote: Nileshjr, you may want to go thru this post (of mine) which deals with this very same aspects of the LCA Wing planform design (aka non-slender inboard and then slender outboard) and it's implications wrt managing the vortex-flow and squeezing out more lift without too much compromise on the drag side.
http://forums.bharat-rakshak.com/viewto ... 0#p1774291
...
they also found out that vortex breakdown is not a limiting phenomenon as far as the lift force is concerned for non-slender wings - on the contrary, flow reattachment is the key lift-enhancing contributor.
...
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).
The flow-reattachment phenomenon over the non-slender part wing is a key differentiator.

Also, you may want to refer to Indranilji's post here and refer to how the notch formed due to non-slender/slender "joining" on the wing leading edge creates a vortex flow that further enhances the lift regime on the slender-part of the wing. Plus the vortex from the non-slender part of the wing energizes the flow over the "immediate-neighbor" slender part of the wing, enhancing lift without sacrificing too much on drag.
http://forums.bharat-rakshak.com/viewto ... 0#p1775430
...
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.
...

Maitya Sir,

I have read those posts in past. I am going through as much literature as I can now after being lazy for long time. This is just my hypothesis at this stage, kinda thinking aloud.

About what Indranil says about the 'kink' vortex and it re-energizing the outboard part like a canard induced vortex or a dog-tooth on LE would do. Is he refering to the LE vortex from whole inboard section or a tiny vortex that would be forming due to the discountinuity at LE (this kinda tiny vortices will form at all junctions between slats as there is discountinuity).

The vortices produced by canards or LERX, those ones are small but concentrated vortices whereas the one coming from the LE of inboard section of LCA is a huge thing. I have been baffled by this before but now this above posted abstract clears my doubt and it makes sense. That LE vortex dominates the whole flow on the wing suction side.

There are some differences in the way a canard vortex, for example, would stabilize flow over the wing. The vortex from Canards or LERX that we see on other planes are, apart from being smaller and concentrated, are nearer to centerline and are with much more sweep angle that the main wing LE vortex. So these vortices actually pull the main wing LEVs inboard, in turn enabling them to affect more portion of wing to get better lift enhancement. Or in another scenario where the LERX vortex is quite close to main wing vortex, the main wing vortex goes on to wrap around the LERX vortex (they two kinda entagle like two snakes with the stronger and smaller LERX vortex forming the core). Here the LERX vortex makes the wing vortex stronger i.e. re-energizes.

But in LCA the situation is different. The effect is much more profound and the inboard LE vortices are actually the dominent feature. Maybe I am not quite good in articulating what I am thinking. See the below two images. Do you see the difference?? Even for Viggen the canard vortices pass between the main wing vortices and thus stabilize the flow. The concept is explained in one US patent by SAAB which can be found through google.

Could you please tell me source for the re-attachment part you have mentioned. Want to see it in more details. There are other aspects with non-slender deltas such as vortex shedding, dual vortex formation etc. Would be interesting to see how all this fit into LCA mystery.

Would have been great if ADA/NAL made public some of there studies like NASA does.

Edit:

There is much better CFD picture for LCA (quite recent and with RANS code) from this publication "Computational Fluid Dynamics in Aerospace Industry in India" from Defence Science Journal, Vol. 60, No. 6, November 2010, pp. 639-652. I don't know how to attach snapshot here. But you can see it in the paper itself (fig. 7).

http://www.google.se/url?sa=t&rct=j&q=& ... 7033,d.bGQ

Notice the vortical structure here at M=0.7 and AoA = 18 deg. The paper says

It is seen that the leading edge vortices are strengthened as the flow develops progressively away from the leading-edge of the wing.

I don't know what that exactly means. The tendency of development of additional vorticity away from LE is typical feature of non-slender delta wing (due to this it shows features like double vortex structure or formation of vortical structure downstream of LE even when it does not have vortex attached to LE). Not sure if it connected to that or the author wants to convey something else.

But its fascinating to see how clean the flow in the centre of the wing looks even at 18 deg AoA. Had LCA not have the lower sweep inboard or if it had canard the flow there would be all messy. (its not clear from it but looks like the BL in that area is separated and forms a vortex which moves along LE underneath the inviscid layer which goes over the wing nicely. It perhaps reattaches behind the vortex as you said, but its difficult to conclude based on this figure alone. I am saying this from my experience of studying 3D flow structure of quite complicated flow few years ago).

Also it seems that without the inboard section, the LE vortices would have been much more inboard.

Gyan · Post by **Gyan** » 26 Mar 2015 19:47

Gurus, a small question. Does the wing of LCA provide any special benefits for low level flights like Jaguar or it will continue to be somewhat bumby like Mirage 2000?

Karan M · Post by **Karan M** » 26 Mar 2015 19:54

Actually, it was the Mirage which had no bump flights thanks to FBW

Gyan · Post by **Gyan** » 26 Mar 2015 21:59

After 100m Mirage 2000 starts getting bumpy and below 60 meters really bumpy. Anyway I don't care for Mirage, what about our LCA?

Karan M · Post by **Karan M** » 26 Mar 2015 22:50

is that sure? many vids on net of low flying mirages.
also bhavnani said the opposite

Indranil · Post by **Indranil** » 27 Mar 2015 01:10

To everybody.

1. No ji, sir etc. for me. I really don't like it.
2. I am not an aero guru. I education and work is in high performance computing. I read a lot about aerodynamics as a passion and an unfulfilled childhood dream.
3. Once, I get over this "busy" period, I would like to make a LCA wiki page. If anybody else wants to kick-start it, please go ahead. I will be thankful and help you in anyway possible.

Nilesh,
I have only been able to go through through your posts cursorily. As I have said before, it is brilliant work. I wish others (me included) kept up the quality of their posts rather than the quantity. Please keep digging, and please post the abstracts/summaries here. It will help all of us who are trying to piece together the "whys" from scant public information. Mine are theories as well. Together, we may come up with a better theory. I will post the summary of my theory: You don't have to go though the whole wordy posts earlier.

As data on the LCA wing was not so forthcoming, I was reading up on the studies of the cranked arrow and reverse engineering them onto LCA wing. Interestingly, the cranked arrow also has a higher pitch-up than the pure delta. The theory is that the outboard wing stalls faster pushing the center of lift more inboard and forward. In LCA, I expected the opposite to happen, but it does not! We cannot see the wing as just a study of its planform. We have to look at it in unison with its large washout and its active triple slats. I will take a relook into this whole thing again, whenever I can. By the way, if Ajai Shukla is to be believed, Tejas already has active fuel proportioner.

P.S. You might enjoy reading the following two docs:
1. Mason thesis
2. NASA study

Eric Leiderman · Post by **Eric Leiderman** » 27 Mar 2015 06:25

http://swarajyamag.com/economy/indias-c ... from-past/

India’s indigenous combat aircraft programmes have another chance to fulfill their potential. However, that is only possible once lessons from the past are heeded to.

srin · Post by **srin** » 27 Mar 2015 10:15

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

JayS · Post by **JayS** » 27 Mar 2015 11:11

indranilroy wrote:To everybody.

1. No ji, sir etc. for me. I really don't like it.
2. I am not an aero guru. I education and work is in high performance computing. I read a lot about aerodynamics as a passion and an unfulfilled childhood dream.
3. Once, I get over this "busy" period, I would like to make a LCA wiki page. If anybody else wants to kick-start it, please go ahead. I will be thankful and help you in anyway possible.

Nilesh,
I have only been able to go through through your posts cursorily. As I have said before, it is brilliant work. I wish others (me included) kept up the quality of their posts rather than the quantity. Please keep digging, and please post the abstracts/summaries here. It will help all of us who are trying to piece together the "whys" from scant public information. Mine are theories as well. Together, we may come up with a better theory. I will post the summary of my theory: You don't have to go though the whole wordy posts earlier.

As data on the LCA wing was not so forthcoming, I was reading up on the studies of the cranked arrow and reverse engineering them onto LCA wing. Interestingly, the cranked arrow also has a higher pitch-up than the pure delta. The theory is that the outboard wing stalls faster pushing the center of lift more inboard and forward. In LCA, I expected the opposite to happen, but it does not! We cannot see the wing as just a study of its planform. We have to look at it in unison with its large washout and its active triple slats. I will take a relook into this whole thing again, whenever I can. By the way, if Ajai Shukla is to be believed, Tejas already has active fuel proportioner.

P.S. You might enjoy reading the following two docs:
1. Mason thesis
2. NASA study

I have those docs, and a whole bunch of other docs already. Have read the thesis report already and only a cursory glance at the other a long time ago. Most of the times, you can get a good idea of overall thinking and phylosophy of a research/design group by looking at their work history, because they always tend to build on there own experiences.I am trying to get the docs connected to LCA precisely for the reason that its not that easy to "reverse engineer" stuff from other configurations. However, by looking at data for various aerodynamic features we can contruct fairly clear picture, because of the way most of the wings are designed, starting with a clean config designed for design point and adding aerodynamic features to it to alleviate problems it has on other operating points. So we can in some way recontruct the design logic to some extent, but it needs some academic regor and not just consory readings or simple extrapolation of facts. Thats what we can try to do.

Anyways, regarding the pitch up, the thesis you had linked says that, there are two main reasons for pitch-up in various delta configurations, which are either separately or together act based on config and flow regimes. Of coarse both of them more or less push the centre of lift forward (and hence the pitch-up). One is what you mentioned, stall on outboard section (for ex on F-16XL, so they tried fences to reduce side-slip of airstream). The other reason is the vortex burst. As the AoA increases the onset of burst move forward, killing lift on TE parts and effectively reducing life and moving centre of lift forward. So one needs to tackle both of them to reduce pitch-up. F-16XL also has a notch on the LERX at the point where it starts near the cockpit. This one reduces the intensity of LE vortex and perhaps pushes onset of burst towards higher AoA. Infact it seems that pure delta itself inherently has pitch-up tendency and to reduce this one can have TE at an angle such that it increases area of wing towards the TE.

The LE slats has a number of advanteges. One, they control sepatation on blunt LE. Second, they give what is called as Zero incidence for all the LE, which means less drag (According to some theories if a wing is maintained with zero-incidence angle along all its spans it gives minimum drag for given life). Three, they produce slight positive lift and are helpful in little improvement in manuvarability at transonic speeds. Of-coarse wash out is there for obvious reasons but I don't think LCA has a typical linear washout on it. I am trying to figure out this one currently. The inboard section looks really funcky (apart from sweep angle) and is difficult to describe it. Its not annhedral, its not setting angle, its not simple washout. But I found one new aerodynamic feature, which looks promising, for one, its used on a lot of delta fighter in past, and other, ADA/NAL has papers published on this topic in 60's and 70's. I am trying to dig in more stuff.

JayS · Post by **JayS** » 27 Mar 2015 11:38

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

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

Stores indeed affect the overall performance big time. These things comes later in detailed design and flight-testing, but at preliminary design stage, i think one chooses basic config.

As a designer you would keep certain things in mind about store effects on the performance from previous experiences but while putting numbers on paper you would probably not include them. Someone in the know can correct me if I am wrong.

Funfact -1 : Sometimes well designed confirmal external storage tanks actually give better aerodynamic characteristics than the original design.

Funfact -2 : Area rule can be applied locally as well, not looking at the whole aircraft but looking at small area around attached external tank only for example. I vaguely remember how area rule was applied by Whitecomb to nacelle-wing integration issue by streamlining the channel around the interface (never checked this thing but perhaps this principle led eventually to achievement of placement of nacelles quite close to the wing without affecting the aerodynamics of wing drastically, advent of CFD also helped a lot). Area rule is a philosophy in essence.

Indranil · Post by **Indranil** » 28 Mar 2015 06:12

nileshjr wrote: I have those docs, and a whole bunch of other docs already. Have read the thesis report already and only a cursory glance at the other a long time ago. Most of the times, you can get a good idea of overall thinking and phylosophy of a research/design group by looking at their work history, because they always tend to build on there own experiences.I am trying to get the docs connected to LCA precisely for the reason that its not that easy to "reverse engineer" stuff from other configurations. However, by looking at data for various aerodynamic features we can contruct fairly clear picture, because of the way most of the wings are designed, starting with a clean config designed for design point and adding aerodynamic features to it to alleviate problems it has on other operating points. So we can in some way recontruct the design logic to some extent, but it needs some academic regor and not just consory readings or simple extrapolation of facts. Thats what we can try to do.

Anyways, regarding the pitch up, the thesis you had linked says that, there are two main reasons for pitch-up in various delta configurations, which are either separately or together act based on config and flow regimes. Of coarse both of them more or less push the centre of lift forward (and hence the pitch-up). One is what you mentioned, stall on outboard section (for ex on F-16XL, so they tried fences to reduce side-slip of airstream). The other reason is the vortex burst. As the AoA increases the onset of burst move forward, killing lift on TE parts and effectively reducing life and moving centre of lift forward. So one needs to tackle both of them to reduce pitch-up. F-16XL also has a notch on the LERX at the point where it starts near the cockpit. This one reduces the intensity of LE vortex and perhaps pushes onset of burst towards higher AoA. Infact it seems that pure delta itself inherently has pitch-up tendency and to reduce this one can have TE at an angle such that it increases area of wing towards the TE.

The LE slats has a number of advanteges. One, they control sepatation on blunt LE. Second, they give what is called as Zero incidence for all the LE, which means less drag (According to some theories if a wing is maintained with zero-incidence angle along all its spans it gives minimum drag for given life). Three, they produce slight positive lift and are helpful in little improvement in manuvarability at transonic speeds. Of-coarse wash out is there for obvious reasons but I don't think LCA has a typical linear washout on it. I am trying to figure out this one currently. The inboard section looks really funcky (apart from sweep angle) and is difficult to describe it. Its not annhedral, its not setting angle, its not simple washout. But I found one new aerodynamic feature, which looks promising, for one, its used on a lot of delta fighter in past, and other, ADA/NAL has papers published on this topic in 60's and 70's. I am trying to dig in more stuff.

I am aware of the advantages of using variable slats to obtain optimized manoeuvring polar, especially for a highly swept wing.

By the older planes, are you referring to the F-106? I actually find it most similar to the F-16XL. My current theory on the "washout" is based on Lamar's famous paper of 1981 (Development of a Vortex-Lift Design Procedure and Application to a Slender Maneuver-Wing Configuration).

The question is how to develop a wing for a fighter for supersonic cruise while maintaining subsonic manoeuvrability. Obviously the base condition is the planar supersonic wing on the Mig-21/Viggen with fixed camber. However, they struggle at off-design points, i.e. generating subsonic or transonic manoeuvre lift. The next in line is the Mirage 2000, which has a fixed camber, but employs variable LE slats to handle the off-design points. Next comes the LCA, which also employs a variable camber along the span, subject to structural constraints. None the less the large camber (near the root) is for manoeuvrability and the small camber (near the tip) is for supersonic cruise. It has been shown that such nonplanar cambered wings with variable highly cambered LE (or variable slats) gives significantly better polars than a planar wing. Is my theory really off?

Indranil · Post by **Indranil** » 28 Mar 2015 09:08

K Mehta ji,

Please check your message box.

K Mehta · Post by **K Mehta** » 28 Mar 2015 09:46

Sorry indranil I realized what I was reading was the proposed thrust vectoring ej200 on LCA article. Will send you some pics of rc model of LCA

And we should not ji each other.

Indranil · Post by **Indranil** » 28 Mar 2015 10:08

Wow! I have tried to make a RC model of the LCA before. I wanted to make the wing as is and failed miserably.

JE Menon · Post by **JE Menon** » 28 Mar 2015 12:09

Non technical question:

There was s pic floating around of the LCA in flight nose towards camera and wings bent almost flexibly like a bird... Does anyone have it or a link to it?

JayS · Post by **JayS** » 28 Mar 2015 13:10

indranilroy wrote:I am aware of the advantages of using variable slats to obtain optimized manoeuvring polar, especially for a highly swept wing.

By the older planes, are you referring to the F-106? I actually find it most similar to the F-16XL. My current theory on the "washout" is based on Lamar's famous paper of 1981 (Development of a Vortex-Lift Design Procedure and Application to a Slender Maneuver-Wing Configuration).

The question is how to develop a wing for a fighter for supersonic cruise while maintaining subsonic manoeuvrability. Obviously the base condition is the planar supersonic wing on the Mig-21/Viggen with fixed camber. However, they struggle at off-design points, i.e. generating subsonic or transonic manoeuvre lift. The next in line is the Mirage 2000, which has a fixed camber, but employs variable LE slats to handle the off-design points. Next comes the LCA, which also employs a variable camber along the span, subject to structural constraints. None the less the large camber (near the root) is for manoeuvrability and the small camber (near the tip) is for supersonic cruise. It has been shown that such non-planar cambered wings with variable highly cambered LE (or variable slats) gives significantly better polars than a planar wing. Is my theory really off?

I was referring to B-58, F-106, Mirage, Viggen etc.
I am thinking we are deceived by the LCA wing shape. But I want to be sure that what I am thinking is correct and need to read more. There is a lot of reading material and I am trying hard to get the papers from ADA/NAL people published in AIAA conferences or Journal of Aircraft. But its almost impossible to get papers from AIAA conferences.

LCA does seem to have variable camber. The question is how do you get that camber starting from plain delta wing.

K Mehta · Post by **K Mehta** » 28 Mar 2015 17:00

indranil
apologies for the screwup, rc model is not mine but its still nice. Kolkatta class pic is from open day at wind tunnel.

Indranil · Post by **Indranil** » 29 Mar 2015 03:45

Nilesh,
Ah, so you are looking at similar planes as I was. Do read about the Mirage 2000, but I don't think the other planes will help you that much. Anyways, I hope that we can learn the wing better at the end of the exercise. By, the way you have mail and your last post is edited for obvious reasons.

K Mehta,
Arre, no apologies required.

Thank you for the pictures.

Austin · Post by **Austin** » 29 Mar 2015 22:31

Air International writeup on AeroIndia

Made in India - Piotr Butowski

http://s000.tinyupload.com/index.php?fi ... 4683356465

shiv · Post by **shiv** » 30 Mar 2015 19:29

JE Menon wrote:Non technical question:

There was s pic floating around of the LCA in flight nose towards camera and wings bent almost flexibly like a bird... Does anyone have it or a link to it?

You mean this one?
http://www.photoyogi.com/Aviation-Photo ... knqw7XM/X3

member_28657 · Post by **member_28657** » 30 Mar 2015 22:21

Any word on delivery of the IFR probe and quartz radome from Cobham? It was supposed to be November first and then got pushed to March, I believe.