LCA News and Discussions

shiv · Post by **shiv** » 02 Nov 2010 21:45

Kanson wrote:[
Canards are control surface like tail planes and its been used for a very long time and it has its own use. There are designs of double delta with canard. Eurofighter's early incarnation in one such design. So one cannot say as such double delta or cranked double delta wings does the job of canard. It doesn't. What i think is, given the specification and design parameters of LCA, for Tejas chosen wing form of cranked double delta, addition of canard becomes irrelevant or doesn't add any substantial benefits. Otherwise why NAVAL Tejas sports LEVCON which does some of the functions of Canard? So i think, double delta wing form does not mean, canard replacement.

Please correct me if I am wrong. Canards, like tailplanes are for pitch control - i.e control in the nose up-nose down axis. Pure delta wings (from whatever I understood of what I read) tend to suffer from loss of pitch control at high angles of attack because the airflow over the wing is affected in some way. That is described as vortex separation. Apparently if the vortex does not separate the airflow over the wing helps the wing to retain pitch control.

The way in which pitch control can be retained in delta wings at high angle of attack can be by using a completely separate wing such as a tailplane (as in the MiG 21) or a canard. A delta wing aircraft that has neither of these should suffer from high landing speed, very long take off distance and loss of pitch control at high AoA

But in those aircraft that are delta and do not have tailplanes or canards, the "vortex separation" is delayed by strakes (Mirage 2000) and by the "notch" of the double delta. I have absolutely no idea how this works and do not understand it at all. (In addition I suspect that the FBW enabled leading edge control surfaces of the LCA also help in some way.)

If strakes or a cranked double delta do the job of preventing vortex separation and helping to retain pitch control at high AoA - then they are doing exactly the same job as a canard or tailplane that are also merely surfaces that enable pitch control. That is what I mean by cranked double delta doing the job of canard. Please tell me if you think my understanding is wrong. Particularly, as far as I know, canards are not meant for anything other than pitch control (OK maybe roll in some cases). If canards have any other application, please tell me.

It's all about pitch control. It's not about maneuverability. Deltas are highly maneuverable at high altitude. Instability and FBW enhances maneuverability and lower altitudes. Maneuverability in the pitch axis may be aided by canards but elevons do the same job in pure deltas. It is only the loss of pitch control at high AoA that is the issue. That is where the Tejas's double delta serves the same purpose as a canard. And the Tejas' delta configuration is totally unique and nothing like any other aircraft on the net - bar none.

Mind you I may be totally wrong but would appreciate anyone being able to explain what is going on. Why should the Tejas NOT suffer from all the disadvantages of a pure delta even without canards or strakes.

Kartik · Post by **Kartik** » 02 Nov 2010 22:27

shiv wrote:Please correct me if I am wrong. Canards, like tailplanes are for pitch control - i.e control in the nose up-nose down axis. Pure delta wings (from whatever I understood of what I read) tend to suffer from loss of pitch control at high angles of attack because the airflow over the wing is affected in some way. That is described as vortex separation. Apparently if the vortex does not separate the airflow over the wing helps the wing to retain pitch control.

canards are for multiple things and the utility depends on where it is positioned and whether or not it is all-moving or fixed. Smaller fixed canards on aircraft like the Lavi and Cheetah were meant only to help in generating additional lift at high AoA and in generating turbulent wake vortices that would trail the canards and then re-attach to the low-pressure region on the wings behind the canards. That would delay the boundary layer separation that occurs at high alpha and leads to sudden drop in lift and consequently to stall. And that delay is in terms of alpha- the benefit being that you'd get a few more degrees of alpha before you'd stall.

Strakes do the same thing. They basically generate turbulent wake flow and that flow in turn helps in keeping the boundary layer of the air attached to the wing. Gripen originally didn’t use vortex strakes but it was an add-on after flight testing had progressed to high alpha tests (I remember reading a blurb in a very dated Flight International on this issue, more than a decade ago at a raddi-wala!). Obviously they discovered something during flight testing that revealed a need for such vortex generators even though there are all-moving canards as well. Mirage-2000s (as you pointed out) also use these vortex generating strakes over the intakes to generate wake vortices that assist in the same thing. The IJT Sitara also has new nose strakes and my guess is that they do the same thing since it has no LERXes. They must've discovered the need for these during high-alpha tests or in wind tunnel experiments.

Gripens also use the canards as large air brakes to reduce the landing roll. They have airbrakes on the fuselage as well but use the canards in tandem to increase the drag when landing. all-moving canards also help in maneuverability- by generating pitching moments that essentially due to their distance from the Center of lift and CG, act as surfaces that can generate a large moment and quickly pitch the aircraft up or down. Since they are right at the front of the aircraft, they are not "blanked" by the wing area in front of them, unlike other trailing edge surfaces.

The way in which pitch control can be retained in delta wings at high angle of attack can be by using a completely separate wing such as a tailplane (as in the MiG 21) or a canard. A delta wing aircraft that has neither of these should suffer from high landing speed, very long take off distance and loss of pitch control at high AoA

But in those aircraft that are delta and do not have tailplanes or canards, the "vortex separation" is delayed by strakes (Mirage 2000) and by the "notch" of the double delta. I have absolutely no idea how this works and do not understand it at all. (In addition I suspect that the FBW enabled leading edge control surfaces of the LCA also help in some way.)

If strakes or a cranked double delta do the job of preventing vortex separation and helping to retain pitch control at high AoA - then they are doing exactly the same job as a canard or tailplane that are also merely surfaces that enable pitch control. That is what I mean by cranked double delta doing the job of canard. Please tell me if you think my understanding is wrong. Particularly, as far as I know, canards are not meant for anything other than pitch control (OK maybe roll in some cases). If canards have any other application, please tell me.

It's all about pitch control. It's not about maneuverability. Deltas are highly maneuverable at high altitude. Instability and FBW enhances maneuverability and lower altitudes. Maneuverability in the pitch axis may be aided by canards but elevons do the same job in pure deltas. It is only the loss of pitch control at high AoA that is the issue. That is where the Tejas's double delta serves the same purpose as a canard. And the Tejas' delta configuration is totally unique and nothing like any other aircraft on the net - bar none.

Mind you I may be totally wrong but would appreciate anyone being able to explain what is going on. Why should the Tejas NOT suffer from all the disadvantages of a pure delta even without canards or strakes.

You're correct here Shivji. The whole reason is to give adequate control over the aircraft at higher alphas-LEVCON, strake, canards all have this as the main purpose. The splitter-plate intake channel and notch does that too- basically takes the airflow that is right next to the intake, channels it and generates turbulent flow and deposits it right over the wing root. This is the best location to have the re-energised flow over and the lack of wing fences indicates that spanwise flow (and consequently the worst possible nightmare of wing-tip stall) is not an issue on the LCA wing- or at least not yet identified as an issue. The same solution is also used on the F/A-18. I earlier thought that this was a unique solution, but then someone (Indranil?) pointed out on BRF that the same thing was done on the F/A-18 C/D and E/F as well. Now I noticed something very similar to that on the LM/KAI T-50 Golden Eagle as well. Maybe all aircraft with intakes shielded by the wing need this solution as the air right next to the fuselage has to be dumped somewhere and the wing is the best location for it to be channeled over.

ramana · Post by **ramana** » 02 Nov 2010 22:32

Kanson<,
I recall that on the LCA the canards were discarded as they provide additional complexity to the FBW development and the current wing configuration was adequate.

Indranil · Post by **Indranil** » 03 Nov 2010 00:54

Shivji, you are right that the "notch" in the double delta will create a vortex very similar to the tip of a canard or the fuselage strake. Also please notice the turbulator at the wing join (in red) which runs between the notch and the bleed channel. I am pretty sure that the wing can handle high AoA pretty well. The F-16XL has the same wing shape ans is known for it's high AoA abilities.

Also notice the phenomenal twist in the wing at the wing join. It is not just a wash-out (it's too big for it). the leading edge is much higher than than the elevons. So, I am quite sure that this wing will have very good high AoA performance.

But the LCA would lose the maneuverability afforded by the canards. But as Ramanaji says, many of us will remember reading that ADA did away with the canard when they did not find that it provides any significant

Time for ADA to solve the intake issue.

Kartik thanks for pointing it out that T-50 Golden Eagle has a similar channel. I hadn't though about it but you are right, the boundary layer has to be dropped somewhere. In fact the Rafale, EF, drop it over the wing. J-10 (not with the recent DSI intakes) tries to do the same. F-16 doesn't even try

I also feel that the strakes on the IJT are from high AoA tests. The plane of the strakes is higher than the wing. Another reason is that I see a small strake near the top of rudder. I think it is for retaining some yaw control while at high AoA, when the rest of the rudder is in the wake of the wing. But I don't understand why they are that long, far away from the wing and so protruding. They could have been shorter and closer to the wing, right? What is the aerodynamics behind such a choice?

shiv · Post by **shiv** » 03 Nov 2010 06:57

indranilroy wrote: Also notice the phenomenal twist in the wing at the wing join.

The problem with calling the LCA as "tailless delta" is like calling Aishwarya Rai as "example of human being". The LCA is a "tailless cranked, twisted, double delta" Agreed that a lot of jokes can be made out of "cranked" and "twisted" but the fact is that if anyone is going to talk about the LCA and its development and future and FBW - being ignorant about the wing of the LCA means that he is likely to be talking crap. Wings are fundamental to flight and the configuration of the wings is is a basic consideration for any aircraft.

The wing choice of the LCA is totally unique. It only has some similarities with the F-16 XL. It is remarkable that the knowledge base about wings and aerodynamics available to the expert or layperson on the internet is vast but precious little has been written about the LCA's wing. A huge hoohaa is made of the F-16XL of which only 2 examples were ever built and it was alleged that it was killed by vested interests (the F/A 18 fanboys I think). But LCA with 400% more flying examples that have been doing the rounds for far longer still has very few people talking about it or even asking about the unique wing. Most people are cursing the LCA, led by Indians.

I believe we are an ignorant nation. Sorry for the rant.

vic · Post by **vic** » 03 Nov 2010 09:29

The LCA is a "tailless cranked, twisted, double delta" ......................The wing choice of the LCA is totally unique.

On a side note, Lets assume that the wing of LCA is good but is it too complicated? Was it necessary? Could we have just copied the Mirage 2000 or F-16 wing? Does it bring substancial benefits?

Second aspect is whether is it easy to construct or manufacture? Does the construction of such a complicated wing add cost and weight?

Is the Wing like Kaveri engine, the design is too far advanced to be manufactered by us efficiently without weight and FBW complexity?

Now for jingo talk- If anybody noticed Boeing's offerings for 6th gen aircraft then one of the designs seems to be nearer to LCA wing concept with long leading edge and no horizontal tail or I got it wrong?

Indranil · Post by **Indranil** » 03 Nov 2010 09:37

^^^ Is there any particular reason why you think that building the wing would be more complex than others.

I see none, but would love to learn something new.

vina · Post by **vina** » 03 Nov 2010 09:42

Please correct me if I am wrong. Canards, like tailplanes are for pitch control - i.e control in the nose up-nose down axis.

This is the truth, the absolute truth, nothing but the truth. The rest is all spin/bullS**t put out by the fan boys of various vested interests.

Sorry, cant help but "punning", but as it was already said,

"Ishwar Satya hai, Satya hi Shiv hai, Shiv hi sundar hai". Satyam, Shivam, Sundaram!

images of Zeenat Aman in a skimpy see thru white sari flashing in the screen.. lrrrrrrlllllll , lrrrrrrrrrlll..

Contrary to what the Euro(trash) fan boys claim, the canard is not a super duper invention 'em Euros created. In fact, nothing can be further from the truth. The very first heavier than air plane that flew, the Wright Flyer, was a CANARD plane!. Just look up the pics of a Wright flyer and see if you point out the tail , elevator and other empennages!

Yes. As the wright brothers discovered, the canard is for pitch stability. Basic principles, nose pointing down, plane stable. Musharraf pointing down, tail unstable. Now, the elevator in the tail and the wing work together in a conventional plane to lift up the Musharraf if it goes down (either by itself or if the nose goes up for whatever reason).

Now the canard does the exact same thing. The canard usually is at a higher angle of attack than the main wings, so that when the nose goes up (same as musharraf going down), it stalls first and loses lift and nose goes down

!

You ask profound kweschuns such as is canard and cranked delta same-same? With a fixed canard (like in Viggen etc), yes, largely similar (notice the huge twist of the LCA at the wing root so that at high AOA/ musharraf down, it stalls first like canard?). With a movable canard like in the Euro(trash) canards, it is more complex , becuase it creates an extra control surface that can be manipulated. But then you can ask an even more profound kewschun and ask , is the LCA wing with a LEVCON same-same as a Euro(trash) canard?

. Ah what can I say..

Satyam, Shivam , Sundaram!.

Indranil · Post by **Indranil** » 03 Nov 2010 09:57

^^^ brings me back to a question. The wing root being at higher AoA than the tip is the washout which is used in almost all planes (unless ofcourse if there is a wash-in). But it is generally change in AoA from root to tip is a couple of degrees. for the LCA it seems like 10 or more degrees! Why such a big washout?

or is the back part near horizontal and the front part flat is near horizontal too. The part in the middle which joins the back to the front part is at much higher AoA. Could there be an explanation for this?

merlin · Post by **merlin** » 03 Nov 2010 11:26

Ok, finally found the printout of the post by an old poster with the handle Siva Mahalingam (post is from 6/1/98 in the old BR Forum). I have typed an extract below since my scanner is on the blink. Bear in mind the following disclaimer that the author has also written - "I have been following the development of the LCA since it's inception. The following is my assessment of the LCA in comparison with it's rivals. Most of the information is from articles and analysis in various aircraft publications and news releases. The comparison represents my opinions and is therefore not necessarily all correct, but I hope they will provoke discussion."

Extract:

"(LCA) Uses delta planform rather than close coupled canard arrangement of Gripen, Rafale, Eurofighter and Lavi/F10, or conventional aft tail arrangement of F16 and F22. Delta wing has the disadvantage of loss of control at high angle of attack due to airflow at wing root abruptly changing between straight back over wing to cutting upward and across fuselage. Mirage 2000 and Kfir/Cheetah Mirage III modifications have strakes /small canards in front of wing for this reason. Close coupled canard selected for Gripen, Rafael, Eurofighter, Lavi/F10 and aft tail selected for F22 also for same reason. These either provide alternative control surface unaffected by air flow changes or fixed canards to increase the angle of attach required to change airflow (Kfir) or strakes to induce a vortex which ensures the change will occur gradually and so not lead to loss of control (Mirage 2000). In the LCA the designers have solved the problem by using a reduced (compound) sweep at the wing root and using a wing which is high at the front (and low at the back (by tipping the fuselage forward) and with anhedral in order to avoid excessive roll stability). These features also have the beneficial effect of improving forward and sideways visibility. The effectiveness of the vertical fin is also increased by tipping the fuselage forward due to airflow being deflected onto the fin from the wing when the aircraft tries to go sideways (the F4 Phantom has downward tilted tailplane for same reason). This results in a smaller fin than the other aircraft, which saves weight and reduces lateral radar cross section.

The advantage of using a delta are reduction in weight and complexity by doing away with the canards and their actuators, which is important in a very small aircraft. The disadvantage is that in order to achieve the same maneuverability as close coupled canard or aft tail configuration, a delta must be made more unstable and so place greater demands on the fly by wire system. The Gripen designers considered a delta arrangement but rejected it on the grounds that it was too risky. The weight savings and reduced drag from elimination of canards or tailplane should give LCA a good acceleration, rate of climb and rate of turn compared with F16, Rafael, Eurofighter. Lavi/F10 even though its small size means avionics, pilot and missiles will form a greater proportion of its weight."

Kersi D · Post by **Kersi D** » 03 Nov 2010 11:39

Surya wrote:where is Surut??

Sulur ? This is going to be the first base for Tejas

K

Kanson · Post by **Kanson** » 03 Nov 2010 12:28

shiv wrote:
Please correct me if I am wrong. Canards, like tailplanes are for pitch control - i.e control in the nose up-nose down axis. Pure delta wings (from whatever I understood of what I read) tend to suffer from loss of pitch control at high angles of attack because the airflow over the wing is affected in some way. That is described as vortex separation. Apparently if the vortex does not separate the airflow over the wing helps the wing to retain pitch control.

.....

But in those aircraft that are delta and do not have tailplanes or canards, the "vortex separation" is delayed by strakes (Mirage 2000) and by the "notch" of the double delta. I have absolutely no idea how this works and do not understand it at all. (In addition I suspect that the FBW enabled leading edge control surfaces of the LCA also help in some way.)

If strakes or a cranked double delta do the job of preventing vortex separation and helping to retain pitch control at high AoA - then they are doing exactly the same job as a canard or tailplane that are also merely surfaces that enable pitch control. That is what I mean by cranked double delta doing the job of canard. Please tell me if you think my understanding is wrong. Particularly, as far as I know, canards are not meant for anything other than pitch control (OK maybe roll in some cases). If canards have any other application, please tell me.

It's all about pitch control. It's not about maneuverability. Deltas are highly maneuverable at high altitude. Instability and FBW enhances maneuverability and lower altitudes. Maneuverability in the pitch axis may be aided by canards but elevons do the same job in pure deltas. It is only the loss of pitch control at high AoA that is the issue. That is where the Tejas's double delta serves the same purpose as a canard. And the Tejas' delta configuration is totally unique and nothing like any other aircraft on the net - bar none.

Mind you I may be totally wrong but would appreciate anyone being able to explain what is going on. Why should the Tejas NOT suffer from all the disadvantages of a pure delta even without canards or strakes.

Shiv ji, allow me to redefine the terms. Pitch control is not only provided by canards and tailplanes, wings too provide pitch-control. Second, lift is not provided by wings alone, canards and tailplanes (in some config) also provides lift. Same way for drag. Here the question is not which control surfaces provide pitch-control or better but whether the combination of control surfaces provides combined effective control that enhances the total effect at most of time under the "constraints", "conditions" and "expectations".

Canards provides lift in addition to wings. It provides better cruise comfort (pitch-trim) better than tailplanes (you can see civil & business jets having canards in addition to tailplanes;one could have wondered why so many control surface for civil planes contrary to military jets which was suppose to manoeuvre much more than civil jets). It increases manoeuverability by increasing the sustained turn rate (Su-30MKI in addtion to canard also has TVC which increase manoeuverability) and provides roll stability(in some config. it reduces roll stability). And i'm sure, google may show more benefits about canards. So the point i'm making from all these examples is the *combination* of control surfaces doing the job better under the conditions, constraints and from the expectations rather highlighting any one particular control surface.

Coming to Tejas, it wont be wrong if it is said, cranked double delta of Tejas does the job of canards, if we are speaking very generally like every other control surface. But if we take the performance parameter ( like AoA..climb rate etc) of Tejas under different weight configuration, over the entire spectrum of speed and altitude, can we able to say, cranked double delta does the job of canard over the entire performance chart ? With a fair amount of confidence, i can say it wont be. Just as every control surface that can do the job as other control surface in theory but differ in the effectiveness, Compound delta of Tejas can do part of the job of canards but it cannot replace the canards. It is a compromise as in any aircraft design. The study i quoted in the earlier post from NAL which deliberated the use of small T-tail for Tejas is meant to solve the "pitch-up" problem that Tejas currently facing. Another way of solving the same problem is through canards. So it is obvious that current compound delta wing form of Tejas doesn't replace the entire function of canards. It tries to imitate canards in the restricted fashion. This was my assertion.

Kanson · Post by **Kanson** » 03 Nov 2010 12:49

ramana wrote:Kanson<,
I recall that on the LCA the canards were discarded as they provide additional complexity to the FBW development and the current wing configuration was adequate.

Yes ramana, you must be right on the complexity of FBW. But from the available information, the wing design was frozen(if i'm not wrong) in late 80s much before the development of FBW started. It is not without any reason ADA guys referred canards/levcon in Tejas as "moustaches" ( Dassault influence). But if you could share the snippets about cancellation of canards in Tejas due to fbw complexity, we are ready to sip it.

sathyaC · Post by **sathyaC** » 03 Nov 2010 13:06

Surya wrote:where is Surut??

it is not "Surut" it is called Sulur near Coimbatore TN,
it is 27 km from Coimbatore city

Kanson · Post by **Kanson** » 03 Nov 2010 14:05

shiv wrote:
indranilroy wrote: Also notice the phenomenal twist in the wing at the wing join.
The problem with calling the LCA as "tailless delta" is like calling Aishwarya Rai as "example of human being". The LCA is a "tailless cranked, twisted, double delta" Agreed that a lot of jokes can be made out of "cranked" and "twisted" but the fact is that if anyone is going to talk about the LCA and its development and future and FBW - being ignorant about the wing of the LCA means that he is likely to be talking crap. Wings are fundamental to flight and the configuration of the wings is is a basic consideration for any aircraft.

The wing choice of the LCA is totally unique. It only has some similarities with the F-16 XL. It is remarkable that the knowledge base about wings and aerodynamics available to the expert or layperson on the internet is vast but precious little has been written about the LCA's wing. A huge hoohaa is made of the F-16XL of which only 2 examples were ever built and it was alleged that it was killed by vested interests (the F/A 18 fanboys I think). But LCA with 400% more flying examples that have been doing the rounds for far longer still has very few people talking about it or even asking about the unique wing. Most people are cursing the LCA, led by Indians.

I believe we are an ignorant nation. Sorry for the rant.

I think, your assertion is atleast partially true. There are not many great articles expounding on the Tejas & its wing. But why to single out Tejas alone. There is no such thing for any other indigenous products. It partially reflect the defense journalism and also lack of knowledgeable defense analysts or the state of defense affair. Leaving that, the knowledge about Tejas was not promoted and its restricted within the orgs dealing with Tejas. If there is anything available it is mostly restricted to selected libraries and if even something is available over net that was couched in mumbo jumbo tech. journals that too comes with restricted access. Not freely available to everyone. So what to do. Or whatever appeared during the 80s and 90s in print section must have disappeared over time. Carrying on your thoughts i like to ask, why Tejas is called "cranked compound delta", the official term? Why it is called cranked? Of course we know the literal meaning of crank. But the same Saab Draken which is a double delta is not called a cranked double delta or cranked compound delta. Is this called as cranked, becoz of the twist near the wing root or becoz of the change in angle of delta from one delta to another? or due to some other reason? Or why F-16xl is called as cranked arrow instead of calling simply as double delta?

shiv · Post by **shiv** » 03 Nov 2010 15:03

Aaaaaah

Some really interesting posts:

First let me "dispose of" two posts for later discussion. Both interest me but the subject is different from pitch control etc.

vic said:

On a side note, Lets assume that the wing of LCA is good but is it too complicated? Was it necessary? Could we have just copied the Mirage 2000 or F-16 wing? Does it bring substancial benefits?

Merlin had typed:

"The disadvantage is that in order to achieve the same maneuverability as close coupled canard or aft tail configuration, a delta must be made more unstable and so place greater demands on the fly by wire system."

Let us leave this discussion for a later time. These two posts sum up one of the arguments made by Prodyut Das. In any case vic's query is at least partially answered in Merlin's post. Merlin thanks for typing that up.

Some thoughts:

When I used to make balsa wood models I was taught to "balance" the plane by adding weights front or aft to bring the CG of the model to a spot just under the middle of the mainwing. That would lead to stable flight. Technically a "balanced" plane like this would not need a tailplane at all. It the ailerons doubled up as elevators (elevons) the actions of pitching the nose up or down could eb performed by the elevons. The problem here as I see it is twofold.

For "pitching up" the elevons have to point upwards. That pushes the back of the wings down and since this force was behind the CG (center of wings) the musharraf went down and nose up. Al iz vel. But when the nose goes up, it carries the front (leading edge) of the wings also up and that made the back of wing (trailing edge) where the elevons were there fall into a "wind shadow" where there was less airflow, making those elevons ineffective. Also the nose up plane will keep tipping back till it stalls. And falls.

Instead of having this kind of lafda affecting your plane, it is better to put a tailplane far faar away from the mainwing. Not only is that tailplane unaffected by the airflow above the mainwing, it is also far away from the CG that allows a smaller force to cause a greater deflection. If the nose goes up too high the mainwing stalls and loses lift. But as this happens the lift in the tailplane tends to act via he CG to "tip" the plane in the opposite direction - i.e musharaf back up and nose level. That restores airflow over the mainwing and the plane continues to fly.

If you have a tailplane why add a canard? Weird stuff. Only MKI does that and it has thrust vectoring to boot. I suspect that the canards add some degree of pitch control to the TV engines. The TV in the MKI is, after all in the pitch axis and the TV nozzles are far behind the CG while the canards are far forward of the CG and can effectively balance each other out and can be used for deadly high AoA maneuvers like Cobra. But this is OT here.

So if you don't want a tailplane, you can have a canard instead. A canard is a tailplane in front. Fixed canard also provides some lift. If nose goes up the canard stalls first and loses lift making the nose drop down. A moving canard, like a moving tailplane can cause pitch up and pitch down movements. If the leading edge of the canard is pointed up (to increase canard AoA) the canard generates more lift and rotates plane on its CG - nose up - musharraf down. This is exactly the movement required to do either a backward somersault (Kulbit maneuver) or a Cobra. But as we all know Cobra can be done without canard - like MiG 29. And there is more to Cobra than just high AoA.

But the other interesting thing that either canard or tailplane do is when you make the plane unstable. I used to make my models stable. But if you move the CG to a point that is nearer the back of the mainwing (tail-heavy), then the plane tends to pitch nose-up. How to remedy this? You can use a tailplane that generates enough lift to bring the musharraf up. Or you can used a canard that generates a nose down force to do the same thing. Such a plane that is being artificially balanced can do some weird and wonderful maneuvering if it does not crash. That is where FBW steps in.

What LCA does is to be unstable and yet manage to fly stably with FBW but without tailplane or canard. Only High AoA tests - to be done with LSP 6 will show whether the LCA can recover after attempting a Cobra like nose-up. I would love to make a 1/100 model of LCA and see how it behaves after a stall.

ShivaS · Post by **ShivaS** » 03 Nov 2010 15:12

When I used to make balsa wood models I was taught to "balance" the plane by adding weights front or aft to bring the CG of the model to a spot just under the middle of the mainwing. That would lead to stable flight. Technically a "balanced" plane like this would not need a tailplane at all. It the ailerons doubled up as elevators (elevons) the actions of pitching the nose up or down could eb performed by the elevons. The problem here as I see it is twofold.

and thats a flying wing no?

vina · Post by **vina** » 03 Nov 2010 15:29

If you have a tailplane why add a canard? Weird stuff. Only MKI does that and it has thrust vectoring to boot. I suspect that the canards add some degree of pitch control to the TV engines. The TV in the MKI is, after all in the pitch axis and the TV nozzles are far behind the CG while the canards are far forward of the CG and can effectively balance each other out and can be used for deadly high AoA maneuvers like Cobra. But this is OT here.

My guess. I think the MKI would have put on weight all around, more so in the nose /front part(to make it twin seat, extra avionics etc and the PESA radar). So , what you can do is add more ballast in the mushrraf or you "lift" the front, by putting in canards. Also, notice, that aircraft CG tends to shift backwards during flight and the plane gets more stable (nose down further) during high speed flight, so a canard can prevent that sort of and keep the maneuverable by preventing it from becoming "too" stable.

vina · Post by **vina** » 03 Nov 2010 15:32

ShivaS wrote:and thats a flying wing no?

Satyam, Shivam and Sundaram. Ja, das ist ein flying wing.

But then remember, only with FBW the B-2 Spirit flying wing was a success. The earlier Northrop flying wings back in those early days suffered from serious stability problems (especially in cross winds) and had to be given up.

In fact, when Jack Northrop who was confined to a wheelchair for some like 25 years or so was shown the top secret B2 Spirit flying, he was said to have remarked "Now I know why God kept me alive all these years". The flying wing is of course most efficient . Funnily enough , the B2 has exactly the same span as Northrop's original flying wing. Coincidence eh wot?

Indrajit · Post by **Indrajit** » 03 Nov 2010 18:33

Flying wing concept is the future of military & civvy aviation,the Germans were successful in operationalising Horten -229 AKA Gotha-229 which outran and out turned Me-262 in air combat,unfortunately it was too late to change the outcome of the war for Germany.Having said this imagine Jack Northrop also thought the same,only the Germans were having an advanced design with Jet propulsion,the time is very near when we will see most of the UCAVs with a tailless delta or a flying wing design.

Gurus can always rubbish my thoughts.

Raman · Post by **Raman** » 03 Nov 2010 19:22

When I used to make balsa wood models I was taught to "balance" the plane by adding weights front or aft to bring the CG of the model to a spot just under the middle of the mainwing. That would lead to stable flight. Technically a "balanced" plane like this would not need a tailplane at all.

The above is not correct. The "aerodynamic center" of the wing is about 25% of chord from the leading edge and you are correct that you must balance the CG against this point for stability. However, in addition, all conventional airfoils generate a pitching moment that (usually) forces the nose down when generating lift. This is the reason why airplanes also need tail planes that must be continuously trimmed during flight. Flying wings use reflexed camber airfoils where the trailing edge is pointed slightly upwards to counteract the pitching moment.

shiv · Post by **shiv** » 03 Nov 2010 19:27

Kanson wrote: Why it is called cranked? Of course we know the literal meaning of crank. But the same Saab Draken which is a double delta is not called a cranked double delta or cranked compound delta. Is this called as cranked, becoz of the twist near the wing root or becoz of the change in angle of delta from one delta to another? or due to some other reason? Or why F-16xl is called as cranked arrow instead of calling simply as double delta?

Well this is some information I got from google chacha
http://www.centennialofflight.gov/essay ... Tech10.htm

The Space Shuttle's wing, known as a "cranked delta" because the leading edge of the wing has a slight bend near its midpoint,

Unable to see a "twist"

tsarkar · Post by **tsarkar** » 03 Nov 2010 20:26

Cranked refers to the difference or change in longitudinal dihedral starting from wing root to wing tip. Longitudinal dihedral is the angle of wing with respect to the fuselage. Best way to notice a crank is side view.

Tejas wing root section is at a higher dihedral vis-à-vis rest of the wing. Side views make it apparent.

http://frontierindia.net/album/main.php ... alNumber=4

Note the longitudinal angle of the wing root with respect to the fuselage.
Then note the longitudinal angle of the wing tip with respect to the fuselage.
You will notice a change in this longitudinal angle from wing root to wing tip. The change in this longitudinal angle is called “crank”.

Added later -
Since the leading edge at root is at a higher dihedral than the rest of the wing, pitches the nose down before a stall at high AoA. The crank negates the need for a canard. The crank also, in some ways, makes the aircraft unstable and enables maneurability. Because the max AoA will differ from root to tip, validating the FBW software is critical before testing the aircraft.

shiv · Post by **shiv** » 03 Nov 2010 20:31

tsarkar wrote:Cranked refers to the difference or change in longitudinal dihedral starting from wing root to wing tip. Longitudinal dihedral is the angle of wing with respect to the fuselage. Best way to notice a crank is side view.

Thanks for the explanation.
Would the Stuka be a cranked wing then?

ramana · Post by **ramana** » 03 Nov 2010 20:32

Kanson, Hormuz Mama had an article in Interavia in late 80s about the LCA and gave a lot of design details. I used to have the copy till the LCA flew when I threw it away thinking it was a done deal. Sadly was msitaken.

tsarkar · Post by **tsarkar** » 03 Nov 2010 20:38

No, the Stuka is specifically not a cranked wing. The dihedral is constant across the entire wing. The entire wing is at a fixed longitudinal angle with respect to the fuselage.

This Tejas picture compared to the Stuka picture makes it clearer.

http://4.bp.blogspot.com/_zUe7sq7m3h0/T ... 022630.JPG

You can make out the longitudinal angle of Tejas wing to Tejas body changes from root to tip. Whereas the longitudinal angle of the Stuka wing to Stuka body is constant.

The Stuka is gull wing. A bend in wing to accomodate a larger propellor or shorter undercarriage (that is more robust and offers better rough field or aircraft carrier recovery load capabilities than a longer undercarriage). Gull wings were found only in Stuka or WW2 Corsair for enabling shorter & sturdier undercarriage and larger propellors.

chackojoseph · Post by **chackojoseph** » 03 Nov 2010 20:48

DRDO hands over Indian Integrated Life support technology for Tejas fighter aircraft Project

Link corrected..

chackojoseph · Post by **chackojoseph** » 03 Nov 2010 21:01

Have a look at the LRU's of ILSS. Click it to enlarge.

ILSS Pic

Indranil · Post by **Indranil** » 03 Nov 2010 21:16

Merlin, Thank you so much for that post.

It answered my last question as well. I had figured out the the wings high AoA at the root could not be just washout and I was right that the front part of the wing is higher than the back part, and a middle part with higher AoA joins both of these. Your post explains the reason for this. I had not noticed the anhedral. But it makes perfect sense. I have to say the LCA's wing do look pretty well thought out. I am quite sure that it will provide very very good performance to the LCA. Prof. Das should be happy with it, by going extreme FBW, the LCA team has foregone the need for a bigger tail and canard. That is weight savings.

Go on LCA team, just give us a better intake and take this birdie to some extremes where the FBW is tested.

I hope other Indians understand that LCA Tejas Mark II will be a phenomenal plane. It is light but it will be truly in a class of its own with it's multirole capability, AESA radar, modern avionics, good TWR and low wing loading. It has enormous potential !!!

Vivek K · Post by **Vivek K** » 03 Nov 2010 23:31

indranil, thank you for your analysis and for walking us through this. The LCA team had this design 15 yrs ago. Mind boggling to think what could have been without sanctions, ......!

Indranil · Post by **Indranil** » 04 Nov 2010 01:19

Thank you Vivek ji. Frankly, I did not know much about the wing when I started asking the questions. It has been a treasure hunt for me. And I must say that it has been very gratifying to learn from pundits here.

Question. Kanson ji has been speaking about an ongoing NAL discussion to add a small elevator on the tail. Kansonji any more details about the same. Others what could the efficacy of such a structure. I can totally understand it on the NLCA. But people have to convince me why that structure would be an advantage on the IAF LCA.

Cons (Sorry to start negatively)
1. More complex FBW
2. Increase RCS
3. Increased weight
4. Will it actually help in high AOA? A T elevator is not very good at high AoA as it comes in the wake of the wing. With a big delta wing, all the more so.

Pros
1. Shorten take off and landing distance (very important for the NLCA), and I can totally see why they want it on the NLCA.
2. (Claim)Will increase the manoeuvrability of the aircraft if the weight gain is not significant. (Where I am having a problem)I have to say that in most manoeuvres, one is not trying very hard to pitch the nose down (nobody heres about minimum angle of attack

). With a tail heavy delta, the first thing that the plane would want to do is pitch up (LCA supposedly also has this tendency)! It is simple. Imagine a triangle of metal flying through the air, you pitch it up ever so slightly, what would it want to do further? Keep pitching further up. You will actually have to work to hold it from going all the way to 180 degrees. Once you have held (balanced it with control surfaces) it at whatever angle you want (say 28

), it wants to slow down, because it's a air brake now, You would need a good TWR and low drag to push it through at this position. By adding surfaces, we are adding weight(lowering TWR) and increasing drag.
3. May help in sustained turn rate (albeit in a very bumpy way)
4. (Claim) It can be used as role inducing. Kanson ji is learned enough not to ask that question. For others imagine arm length for the moment from the elevator and that from the elevons. I can assure you that for a light aircraft like the LCA and the size of the elevons, that plane can be made to spin much faster than what the FBW, pilot would ever want.
5. The airbrakes, seem to have a pitch up effect, this can be nullified with the elevators especially when the are in that T-shape. What's more, it will augment the airbrakes in their functionality.

Alternatives
1. Pitch control canard like the EF (I would rather not have it, but it will be more effective in pitch control at higher AoA)
2. Go for 2D TVC, much smoother ride, much more effective (is not affected by the orientation of the plane), if the EF200 guys are to be believed the weight gain is not much, also increases efficiency and directed power,

Your says please?

Indranil · Post by **Indranil** » 04 Nov 2010 01:38

OT ALERT

My aeromodel building has taken a back seat for some time. But I will try to finish a project of mine which has been awaiting my attention for a while.

I would love to build a ducted fan aeromodel for the LCA. I hope to learn more about it's control surfaces by then (especially the leading edge flaps). Looking forward to building it.

Shivji, I am waiting for the pundits on your "build your own plane" thread to finalize on their plane. If it comes out well, I will try to build that too.

Gaur · Post by **Gaur** » 04 Nov 2010 01:50

indranilroy wrote: 2. Go for 2D TVC, much smoother ride, much more effective (is not affected by the orientation of the plane), if the EF200 guys are to be believed the weight gain is not much, also increases efficiency and directed power,

IMHO, not the best idea. Weight increase of 600-700 kg will not do LCA any good.
Plus, would it not require heavy modifications in FBW? Also, TVC is said to be most helpful in post stall maneuvers. So, the airframe and the intake should first be able to handle those extreme AOA.

Indranil · Post by **Indranil** » 04 Nov 2010 02:16

^^^ Gaurji, you are right. The TVC can definitely be used for post stall manoeuvres and that's where they say that it scores over non TVC and not by making the plane suddenly turn faster.

But TVC can be used just as elevators, infact if you see the Su-30 demos (link), check when the plane takes off, the TVC works in unison with the elevators. And just think about it. you are creating a force which has a component which is not going through the CG. It will obviously create a torque. so it will act as an elevator. What people tend to assume is that it has a capability to turn the plane faster, which is not true.

If Euroject is to be believed, then their TVC would be around 40 kgs. That would at least be the weight of the actuators plus weight of the elevator, plus strengthening the tail to be able to undertake more shear and strain. Movement of things around to balance the CG again ( I don't think they would just add a balast and increase the weight in the front). None of this has to be done if you use a simple TV to just work as an elevator, give a more oval outlet than circular. No more mumbo jumbo. also this TVC by ITP doesn't need major changes to the engine. If we can get past the bureaucracy, may be we can get it on our engines.

Eurojet pushes for TV for typhoon (this has been posted here before).

Eurojet partner ITP of Spain is responsible for the design of the EJ200's TVN, and has attempted to optimise the device for simplicity of operation while adding as little weight as possible (about 40kg/88lb per engine).