LCA Tejas: News and Discussions

abhik · Post by **abhik** » 23 Jan 2016 20:04

SriKumar wrote:
abhik wrote: Can't comment on calculating AoA using the angle of the smoke, but even if it was valid you would have to know what angle the picture was taken vis a vis the direction of the aircraft. If the aircraft was moving perpendicular to the viewer's line of sight then you would get the true angle, if it was moving along the line of sight the angle would always appear to be 90degrees.
Will the true angle will be more than than angle calculated from the picture? Or will it be less?

The true angle will be less, I think. Imagine holding a right triangle(where the base represents the direction of motion, the hypotenuse is the direction the aircraft is pointing, and the angle between then representing the AoA) level and its surface perpendicular to to your line of sight. At this orientation the apparent angle will be the true angle. Now if you rotate the triangle along the height the apparent angle will keep increasing until it reaches 90degrees at which point you see only a line(as the hypotenuse and the height merge). Of course this holds true only if direction of motion is level with the ground, or at least not at a significant angle (then the apparent angle will be less).

NRao · Post by **NRao** » 23 Jan 2016 20:13

shiv wrote:Someone please tell me why it would be erroneous to calculate AoA from this image? So what is the AoA of the Tejas in this low speed high AoA pass (Screen grab of display in Bahrain)

I do not see why you cannot. It is a matter of geometry and trigonometry. And for that you will need lines that show the proper directions (your picture does not). once you get that straightened out, then it is angles and known distances (proportions). That is what architects are taught in a class called Perspective - this is a science, no voodooism to it.

abhik · Post by **abhik** » 23 Jan 2016 20:20

Not very straightforward to calculate direction etc, for example in the below rocket launch video (@4min30s), the rocket appears, to a causal viewer, to be heading towards earth rather than away from it.
https://youtu.be/oxMuxZWtiOU?t=4m31s

member_28108 · Post by **member_28108** » 23 Jan 2016 20:24

^ take a piece of cardboard and hold it at an angle and use a torch to project the shadow onto a wall. Now vary the torch postion and you can see you can change the shape from a line to a plane through varying quadrilaterals so the angle can be made to vary from zero to 90 depending on how you project it.
This is formalized in engineering drawing as projections.
Have a look at say
http://www.slideshare.net/avutu_kunduru ... -of-solids

where you can see how the angle can change

member_28108 · Post by **member_28108** » 23 Jan 2016 20:25

N Rao precisely - it can be calculated if you can project it to all 3 planes. When you have only one plane you cannot extrapolate the others due to parallax.

NRao · Post by **NRao** » 23 Jan 2016 20:33

abhik,

There will always be a problem when we humans get out of bound - get into abnormal situations. So, when a human enters a chamber where they are conducting sound tests the human is allowed ONLY for a few minutes (or less) - the mind cannot take that kind of "dead" silence. Humans get disoriented - because of that silence.

Similarly with space and this direction. My youngest is a scuba diver and used to be a head life guard at a local "pool" that was an abandoned quarry - the water is clean until you stir it and then it gets murky as milk. He is not claustrophobic, until he has to don that suite and jump under piers to look for a missing 2/3 year old. Why? Because there is no sense of up or down in that milky water. But provide him with a means to determine that (the posts in a pier) and he gets far better. Number those pole and it gets even better - situational awareness.

So, actually, direction and distance are very, very easy to compute, provided you know some fundamental things - else it is not even possible. If you are unable to find which way is earth it is because your normal senses have gone off-line and not because it cannot be computed.

NRao · Post by **NRao** » 23 Jan 2016 20:34

prasannasimha wrote:N Rao precisely - it can be calculated if you can project it to all 3 planes. When you have only one plane you cannot extrapolate the others due to parallax.

I was taught that in the 1969!!!! In India that too.

In fact, that picture (by Shiv) is bland - just a shadow. IF there were some distinct light/shadow then it would be even more easier to figure it out. THAT science is called Physiography.

BTW, one could also use a brute force method and develop a very simple algo and have a computer tell us what that angle is.

nirav · Post by **nirav** » 23 Jan 2016 20:58

NRao wrote:
prasannasimha wrote:N Rao precisely - it can be calculated if you can project it to all 3 planes. When you have only one plane you cannot extrapolate the others due to parallax.
I was taught that in the 1969!!!! In India that too.

In fact, that picture (by Shiv) is bland - just a shadow. IF there were some distinct light/shadow then it would be even more easier to figure it out. THAT science is called Physiography.

BTW, one could also use a brute force method and develop a very simple algo and have a computer tell us what that angle is.

Or go by the official statement by Team Tejas on FB that LCA is going to pull 22 degress AoA.

Shiv Saar, you've put a lot of guys' dimags at work with the poocch of yours ..

member_28108 · Post by **member_28108** » 23 Jan 2016 21:01

All we can say with this projection is that the angle of attack could"not be more than" the observed value as the maximal angle of projection would be the true angle which would be the enface angle projection..

NRao · Post by **NRao** » 23 Jan 2016 21:09

Or go by the official statement by Team Tejas on FB that LCA is going to pull 22 degress AoA.

You do need a means for independent verification.

Shiv Saar, you've put a lot of guys' dimags at work with the poocch of yours ..

Woken a part of the brain that has been dormant for a few decades. But, fun to share.

JayS · Post by **JayS** » 23 Jan 2016 21:23

shiv wrote:It is possible that no one on here knows what angle of attack actually means - and I include myself in that. But I think I do, so I want to know why the angle between the long axis of the smoke generator and the approximate axis of the trailing smoke does not reflect the angle of attack in level flight. The plane is flying level at slow speed.

This may be a good opportunity to find out what we all like to howl about and ask a lot of intelligent sounding questions about

It is correct to say that the smoke trail would show the general path the aircraft traces. But it would not trace the path that a/c CG would be following. There would be some offset. Though this should not affect the kind of angle calculation you want to do. But this approximation would be valid only for the trace farther enough downstream from the wing. Reason being, the smoke gets entrained in those two giant vortices coming from the delta wing which have general direction of backwards and slightly upwards even in level flight. Which means the smoke will go upwards immediately behind the wing. If you use this part of the smoke trail to get a/c velocity vector, you are bound to get higher AoA. See the pic below:

http://gallery.tejas.gov.in/Gallery/Aer ... -DPTRSgD/A

You can see the smoke trail is slightly offset from the path that the CG of the a/g has passed through and the offset is because the smoke moves slightly upwards (relative to the wing surface) immediately behind the wing.

One more unknown is relative direction of the wind wrt to the flight path which we will almost never be able to determine from video and it also will add to the error.

Ideally to measure AoA, we should have proper side view in the video. There will be still some error, since we would typically be seeing an a/c from the altitude lesser that of its own, we will never have true side view.

shaun · Post by **shaun** » 23 Jan 2016 22:00

SaiK wrote:^didn't work for me

By mistake made the video private, now rectified.

JTull · Post by **JTull** » 23 Jan 2016 22:36

Tejas - LCA FB update about Bahrain show

Q: If LCA Tejas will be testing Derby and Python on return from Bahrain, Captive flight trials of LCA Tejas carrying Derby and Python should have been completed by now. If so Can you please share a couple of pictures of LCA Tejas carrying Derby and Python.
A: yes, they are. The Derby and python can be carried simultaneously both in MB and IB. As of onw, underbelly pylons are for carrying a 725 ltr drop tank. The pylons for tandem bombs in the IB are in final stage for integration.
Q: Whats the max alpha that it will be hitting during the demo?
A: Around 22
Q: wasn't it cleared for 24?
A: Flight testing is done for 24. That's why it is cleared for 22.
Q: There was an unconfirmed report that the envelope is opened up till 26deg. Anyways. So we should be seeing even tighter turns once Tejas is cleared for 24deg. smile emoticon Can you divulge details of the loops Tejas is performing in BIAS, such as radius of loop, speed of Tejas while in the loop, total time taken for full 360 loop etc??
A: The square loop is appx 5500 feet in each leg and the hard turns are around 360 meters of ROT. Speed is in the band of 300-450'knots.
Q: can you please tell us if any Unguided/Guided Rockets/Missiles (air to ground) have been integrated or planned to be integrated and tested with LCA Tejas
A: As of now 1000lbs mk11, LGBs and PB500 have been successfully flight tested as air to ground weapons. The first one is non guided whereas the last two are guided.
Q:By looking at the LCA model pics which was installed in Bangalore recently where wing root section was visible, it looks like LCA wing uses supercritical airfoil with supersonic cambering. Can you confirm whether its right observation or wrong??
A: The cranked double delta configuration has an improved mach no -beta (sideslip angle) envelope than a pure delta. Plus the initial sweep acts as an added surface area similar to leading edge strakes. They certainly improve maneuverability in high subsonic and performance in transonic regime. Improvement in supersonic operations is a theory which needs lots flight testing to prove. This aircraft performs well in that high subsonic where the cooper harper rating has been always excellent. The double delta config is the prime contributor.
Q: just to be precise, this financial year means March-2016 ? And total 3 SPs will be be produced in this financial year (Apr-2015 to march-2016) ? OR just 2 as SP1 was already produced ?
A: Plan is to have SP2 first flight before march 16. The next financial year might see 3 or 4 SPs ready for flying.

Nick_S · Post by **Nick_S** » 23 Jan 2016 23:59

Indranil · Post by **Indranil** » 24 Jan 2016 00:35

The clean weight of LCA is 9.6 Tons. The MTOW is 13.5 tons. So external carriage with full internal fuel is ~4 Tons. Maximum external carriage capacity is 4.5 Tons.

member_29267 · Post by **member_29267** » 24 Jan 2016 01:17

New Photos on FB Page

member_29267 · Post by **member_29267** » 24 Jan 2016 01:21

chilarai · Post by **chilarai** » 24 Jan 2016 02:23

shiv wrote:
chilarai wrote: If the observer is directly below you can probably have a better approximation of the angle of attack , the aspect ratio ( wing tip to wing tip vs head to tail ) of the pic would change with the angle of attack and should be fairly accurate IMO.
Could you explain that please?

I was wrong I assumed the plane to be flying horizontally only then we could calculate only the aoa (in which case it would be the same as the pitch angle ) at fair degree of accuracy with a picture of Tejas directly above the camera

btw i think aoa is best explained here with a diagram

http://www.boeing.com/commercial/aeroma ... tisaoa.pdf

SaiK · Post by **SaiK** » 24 Jan 2016 02:52

krishAgain, the deb rana pics are simply scintillating.

jtull, wonderful q&a. so, the supersonics yet to be proven on the cranked delta is what i read.. would it do a super cruise with f-414 is a question for the future? or am I'm dumb asking this question on cranked-double delta?

member_29267 · Post by **member_29267** » 24 Jan 2016 03:43

Its a tremendous achievement and I would like to congratulate the whole team on getting bird till here. Sir, if I might ask, what mach numbers have been achieved by LCA at sea level and overall? Also, the GE414 for Mk2 were scheduled to start arriving by december 2015. Since Mk1A is the priority, will Mk2 be delayed or will work start parallely on Mk2? Will it be correct to assume Mk2 config has been finalized and all that's remaining is to start building the PVs?

Tejas - LCA Sir, lots of questions and we are thrilled to receive them too. It has been the directive by the minstry to work in parallel for both Mark 1a and Mark 2. However, priority is with Mark 1A. The configuration for Mark2 is still under debate and will definitely be improved from Mark 1A. The aircraft has been flying in high subsonic mach no in sea level conditions. Barring a small pocket in the bottom right corner, the entire envelope has been flight tested.

It would be helpful to collect all the new info coming from FB in a repository thread or something of that sort. Will through a lot of light and will be useful later.

Cain Marko · Post by **Cain Marko** » 24 Jan 2016 04:43

Really great to see the active responses from team tejas on fb. To confirm, first 20 will be foc std bvr capable sans gun and ifr, aoa of 22 degs, payload of 4 tons. Remaining 100 will be mk1a std that will address above deficiencies with bonus aesa. Will foc std. have cobham radome?

Only disappointment is the small order...should be more..hal should be mandated to increase capacity to 24 pa for about 8 years and a total run of 10 years.need to do this if we are to arrest shortfall. Otherwise IAF still have 32 odd sqds, and it will take late 2020s to come anywhere close to 39 sqds let alone 42.

Viv S · Post by **Viv S** » 24 Jan 2016 04:53

Why 22 deg AoA at FOC when the envelope has already been opened up to 26 deg?

manjgu · Post by **manjgu** » 24 Jan 2016 06:16

Akshay Kapoor ji..if this is how science will be done..then god save this country. trying to calculate AoA from a hazy pic!!

manjgu · Post by **manjgu** » 24 Jan 2016 06:25

Angle of attack... http://www.boeing.com/commercial/aeroma ... tisaoa.pdf .... this will clear up some air

shiv · Post by **shiv** » 24 Jan 2016 07:00

manjgu wrote:Akshay Kapoor ji..if this is how science will be done..then god save this country. trying to calculate AoA from a hazy pic!!

At least two people have gracefully said they don't know (that is also a mark of good science) and a few others have given answers. But for you it is hilarity and bad science. But you still don't want to admit that you don't know why it can't be done or what is necessary for it to be done. Please don't try and shake that off by saying science is bad in the country or that asking a question is hilarious. To me that is like our DDM. Don't know and don't want to know. If you spend 2 minutes thinking there is even more data that can be inferred from that "hazy pic" - I will probably post that and ask the same question of those who actually think rather than give smart non replies.

member_20067 · Post by **member_20067** » 24 Jan 2016 07:07

shiv wrote:
manjgu wrote:Akshay Kapoor ji..if this is how science will be done..then god save this country. trying to calculate AoA from a hazy pic!!
At least two people have gracefully said they don't know (that is also a mark of good science) and a few others have given answers. But for you it is hilarity and bad science. But you still don't want to admit that you don't know why it can't be done or what is necessary for it to be done. Please don't try and shake that off by saying science is bad in the country or that asking a question is hilarious. To me that is like our DDM. Don't know and don't want to know. If you spend 2 minutes thinking there is even more data that can be inferred from that "hazy pic" - I will probably post that and ask the same question of those who actually think rather than give smart non replies.

Spot on---.. very good retort...

member_29172 · Post by **member_29172** » 24 Jan 2016 07:14

manjgu wrote:Akshay Kapoor ji..if this is how science will be done..then god save this country. trying to calculate AoA from a hazy pic!!

what does Shivji's comment has anything to do with science in India? god needs to save you, the country is just fine

Sid · Post by **Sid** » 24 Jan 2016 07:27

Maybe looking at the AoA sensor orientation during flight can provide better idea about current AoA of LCA, but we need to have high resolution closeup to analyze it. In LCA it's on right side of cockpit.

member_29089 · Post by **member_29089** » 24 Jan 2016 07:33

NRao wrote:
shiv wrote:Someone please tell me why it would be erroneous to calculate AoA from this image? So what is the AoA of the Tejas in this low speed high AoA pass (Screen grab of display in Bahrain)

NRaoJi drew two lines. But seems if the camera is at an angle then the vapour-trail will be photographed at an angle shown. If you tilt the pic clock-wise and make the vapour-trail horizontal then the angle can be approximated.

Other posters are going through unnecessary trouble teaching basic geometry. In the photo there are so many unknowns that it can not be "calculated" precisely (which you know).

Big assumption is that the plane in flight is moving orthogonality to the camera.

NRao · Post by **NRao** » 24 Jan 2016 07:35

trying to calculate AoA from a hazy pic!!

There is entire branch in Artificial Intelligence - Pattern Recognition, that is based exactly on nailing the result based on a fuzzy picture. Do you really think that radars, IR, etc provide clear pictures? That is what threat libraries are about - they actually have people spending a long time getting hold of every signature there is out there and build a picture so that during conflicts they are able to identify based on very fuzzy inputs. It is a science - essentially math. Been there for 40+ years.

NRaoJi drew two lines. But seems if the camera is at an angle then the vapour-trail will be photographed at an angle shown. If you tilt the pic clock-wise and make the vapour-trail horizontal then the angle can be approximated.

Other posters are going through unnecessary trouble teaching basic geometry. In the photo there are so many unknowns that it can not be "calculated" precisely (which you know).

Big assumption is that the plane in flight is moving orthogonality to the camera.

I did not draw the lines, but it does not matter. The question still stands: Can you use that picture (NOT the two lines in teh picture) to determine the angle of attack. And, the answer is simple: yes, you can.

manjgu · Post by **manjgu** » 24 Jan 2016 08:00

bhai log..pl check defn of AoA before trying to calculate AoA from the hazy pic !! atleast i will not try to calculate AoA from this pic.

manjgu · Post by **manjgu** » 24 Jan 2016 08:02

NRao..thanks for educating us abt AI. I didnt know calculating AoA from such pic is another branch of Science. i stand educated.

shiv · Post by **shiv** » 24 Jan 2016 08:04

Anyone want to try this?

I have given length, wingspan (from Google) and some angles

ABCD is a plane, a parallelogram. The idea is to find the angle at A. Is it possible with the given data?

Sid · Post by **Sid** » 24 Jan 2016 08:13

well a simple take on AoA based on AoA sensor orientation.

Orange line indicates AoA sensor lines.

chilarai · Post by **chilarai** » 24 Jan 2016 08:21

it would help if there is a picture which has a building or a pole also in it to approximate the true vertical ..now we also have to assume that the cameraman is holding the camera upright and not rolling it somehow to get a better view of the plane in his frame , though i think in a video grab the cameraman would not concern himself too much with composition and such .

shiv · Post by **shiv** » 24 Jan 2016 08:21

Sid wrote:well a simple take on AoA based on AoA sensor orientation.

Orange line indicates AoA sensor lines.

LOL Brilliant! Thanks!!

NRao · Post by **NRao** » 24 Jan 2016 08:30

shiv wrote:
Sid wrote:well a simple take on AoA based on AoA sensor orientation.

Orange line indicates AoA sensor lines.

LOL Brilliant! Thanks!!

True.

Also, puttering around, found that the wing tip is at a slight angle, seems to tilt a wee bit forward. So, it would be decent indicator, but it would still not be a degree or so out of wack.

sivab · Post by **sivab** » 24 Jan 2016 09:06

Seems people are trying to measure AoA with respect to horizontal

AoA is motion of air foil (wing) with respect to relative air flow. Relative air flow is not same as horizontal/parallel to earth. It could be, but not true most of the time.

disha · Post by **disha** » 24 Jan 2016 09:13

shiv wrote:Anyone want to try this?

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I have a different take on this., since there is no frame of reference other than the smoke to indicate the jet's flight path., it is difficult to draw a line along that imaginary flight path and come up with an AoA.

Since this was taken when the jet was making a slow pass, or rather the slowest pass it could muster safely AND since Tejas is cleared to 22* AoA it follows that the slow pass was done at max cleared AoA which is at 22*. Could I be wrong., possibly and the AoA maybe 18* and Tejas is still making a very slow pass (at mere 117 knots). As I see it., it is already incredible at 22* and more incredible if I am wrong.

We know by now that Tejas has been tested to 24* AoA. So it can go further slow on its slow pass.

Here is a URL for F-35 http://www.lockheedmartin.com/us/news/f ... ttack.html

The first photo allows one to draw a line along the flight path (an approximation that too) and an approx. AoA can be derived.

PS: The imaginary flight path for the above foot is projecting out of the screen.

manjgu · Post by **manjgu** » 24 Jan 2016 10:00

sivab...correct. measuring to the horizontal is pitch not AoA.