AMCA News and Discussions

nachiket · Post by **nachiket** » 14 Feb 2013 21:53

Ah, the great "Professor" Das. I still remember his ridiculous article about how the LCA should have really been an upgraded Mig-21 etc. etc.

The fin shape – particularly the leading edge sweep is all wrong – perhaps not fit for a propellor driven trainer let alone a stealth aircraft.

So Prof. Das can confidently say this just by looking at the fin, while ADA engineers who have tested the model in their wind tunnel can't? Maybe he should join the ADA and educate them instead of pooh-poohing them whilst sitting on his musharraf.

Raman · Post by **Raman** » 14 Feb 2013 21:58

shiv wrote:
Eureka - I found it!

Our controversial friend Prof Prodyut Das has a great article in Vayu, but more to the point here is his comment on the AMCA model at Aero India
http://idrw.org/?p=18444
For the AMCA display model to have been built it must have gone up several layers of “top” management. The pity is that no one bothered to see and check the glaring errors in the configuration. The fin shape – particularly the leading edge sweep is all wrong – perhaps not fit for a propellor driven trainer let alone a stealth aircraft.

And what are those deep boundary layer diverters doing on a apparently fifth generation combat aircraft? Even the “Wang Lu laundry and Chop suey” aircraft companies – very respected incidentally for their track record -are using diverterless intakes. The Western Aviation companies must be laughing up their sleeves because if this is the best ADA can do then AMCA like Dilli is “dur ast”. A unsuitable configuration -if translated into a prototype can be the devil to develop- witness the LCA.

What ADA needs is more seriousness at the Project engineering level. Unfortunately in India “Good manager ” has always outweighed “Good Engineer” in the promotion sweepstakes and when the troops come up with a model that is suitable for Bankipore Fair there is no one there to make the simple corrections!
In fact I did think the AMCA fin looked stupid, but I could not say what was wrong. Click on image to enlarge.

India has virtually no scale model industry and we make among the worst models I have seen. Last week at a party in Sanjay Simha's house I saw a model of Mahindra's NM 5 made by HAL or someone. That is the ugliest model I have seen in my life - besides it would not stand on its three wheels and toppled tail down.

Is this "Prof" Prodyut Das for real? Edge sweep is "wrong"? And how did he determine this? An ignoramus amateur like me realizes that surface edge alignment is performed along a common projection plane. If one looks at the top-view of the AMCA, the front and rear edges of the fins exactly line up with the common angles established for the airframe.

The one way to increase the sweep of the fin while maintaining edge alignment is to mess with the dihedral angle, which will impact directional stability, which requires messing with tail volume coefficient, etc. etc. All these have been parameters have been established after a lot of modeling.

I can assure the professor (and this from personal experience) that Americans laugh much harder at what passes for "defense analysis" in India than they do at our design capability.

negi · Post by **negi** » 14 Feb 2013 22:06

The model which Shiv ji has linked definitely looks like out of scale ; the V stabilizers are actually out of proportion (One can clearly see the difference in Kanson's uploaded pic which looks more closer to proper scale; is it the actual wind tunnel model ?).
Prodyut Das is not much different from a jingo except that he probably knows a lot about aero stuff than average layman if his comments are specifically about the model in question then yeah I agree with him except for diverter less design part for both PAKFA and F-22 have the characteristic boundary layer diverter.

Indranil · Post by **Indranil** » 14 Feb 2013 23:32

Raman wrote: Is this "Prof" Prodyut Das for real? Edge sweep is "wrong"? And how did he determine this? An ignoramus amateur like me realizes that surface edge alignment is performed along a common projection plane. If one looks at the top-view of the AMCA, the front and rear edges of the fins exactly line up with the common angles established for the airframe.

Exactly, I had posted a picture about it a couple of pages back. I respect Prof. Das a lot. But on this one, he is all over the park. Perhaps somebody should show him the F-35's vertical stabs.

About the boundary layer separators, both F-22 and PAKFA are not 5th generation planes then.

P.S. Negi sir beat me to it.

negi · Post by **negi** » 15 Feb 2013 00:11

^ While going by an image of a model could be misleading but if you see the image of the model which Shiv ji has linked the vertical Stabs appear too big and their profile too does not match up with the ones on the model which Kanson has linked in his post. The V stabs on the model in Kanson's pic are much more ahead than the one in Shiv ji's pic , they are more swept back and imho much more canted than the one in Shiv ji's pic.

nachiket · Post by **nachiket** » 15 Feb 2013 00:18

negi wrote:^ While going by an image of a model could be misleading but if you see the image of the model which Shiv ji has linked the vertical Stabs appear too big and their profile too does not match up with the ones on the model which Kanson has linked in his post. The V stabs on the model in Kanson's pic are much more ahead than the one in Shiv ji's pic , they are more swept back and imho much more canted than the one in Shiv ji's pic.

Kanson's pic is of the older model. It has evolved a lot since then as can be seen. And ADA engineers would not have reduced the sweepback angle unless it was for a reason.

NRao · Post by **NRao** » 15 Feb 2013 00:19

There is a huge diff in the wing design between the Kanson and Shiv pictures. I cannot say anything about the V-fin, but the two are not quiet the same planes. I recall posting - long time back - when the diamond design was introduced by the AMCA team. I think the Kanson picture is too old for consideration of this discussion - just/only based on the change in the wing design.

Karan M · Post by **Karan M** » 15 Feb 2013 00:23

Prodyut Das ji was the same gentleman who was touting the values of a "people's air force" sort of concept of a lot of light fighters to swarm an enemy, having minimal systems onboard but being sufficient in numbers. Apparently the much vaunted success of the Me163 and the Hs178, to be flown similarly, during the closing days of WW2 didn't enter his thoughts. Net, one can pretty much be sure that whatever Shri Das says, one would do well to take a large bag of salt with it.

negi · Post by **negi** » 15 Feb 2013 00:27

nachiket wrote:
negi wrote:^ While going by an image of a model could be misleading but if you see the image of the model which Shiv ji has linked the vertical Stabs appear too big and their profile too does not match up with the ones on the model which Kanson has linked in his post. The V stabs on the model in Kanson's pic are much more ahead than the one in Shiv ji's pic , they are more swept back and imho much more canted than the one in Shiv ji's pic.
Kanson's pic is of the older model. It has evolved a lot since then as can be seen. And ADA engineers would not have reduced the sweepback angle unless it was for a reason.

Well point is not about old or new; point is about if the model is upto scale and proportionate. The one in Kanson's image is a wind tunnel model here http://en.wikipedia.org/wiki/Advanced_M ... t_Aircraft while the one in Shiv ji's pic is not , it is just a display model we don't even know if it is upto correct scale.

hnair · Post by **hnair** » 15 Feb 2013 00:29

shiv wrote:This is the time for Tatas, Mahindras, Reliance, Infosys etc to come out and show how good they are at Blisk making.

SaiK · Post by **SaiK** » 15 Feb 2013 00:30

correct.. and we need to verify if the show model reflects the supposedly "changed wind tunnel model" accurately.

plus note the degraded stealth angles of the tail from frontal RCS point of view.. or is it my eyes?

NRao · Post by **NRao** » 15 Feb 2013 00:36

negi wrote:
nachiket wrote:
Kanson's pic is of the older model. It has evolved a lot since then as can be seen. And ADA engineers would not have reduced the sweepback angle unless it was for a reason.
Well point is not about old or new; point is about if the model is upto scale and proportionate. The one in Kanson's image is a wind tunnel model here http://en.wikipedia.org/wiki/Advanced_M ... t_Aircraft while the one in Shiv ji's pic is not , it is just a display model we don't even know if it is upto correct scale.

negi · Post by **negi** » 15 Feb 2013 00:39

^ Yep you see the leading edge of V fin where does it meet the fuselage ? It meets at a point well in front of the location where trailing edge of the main wing meets the fuselage and they are much more ahead of the H fins and that is how they are supposed to be to keep the v fin isolated from wash from the H stabs.

NRao · Post by **NRao** » 15 Feb 2013 00:47

Seems likes they have moved the diamond wing forward (as compared to previous pictures/models). There is a large gap (relatively) between the wing and the tail in the display model. In previous pictures/diagrams there were none.

negi · Post by **negi** » 15 Feb 2013 00:50

^Well for all we know the model might have undergone changes since we last saw the wind tunnel model but my point is that the model in AI 2013 is a display piece it does not look right to me. Here another view of the same thing.

http://img145.imageshack.us/img145/5317/76237717.jpg

Btw today is Valentine's day and what am doing discussing AMCA model ?

NRao · Post by **NRao** » 15 Feb 2013 01:05

negi wrote: Btw today is Valentine's day and what am doing discussing AMCA model ?

Just guessing, but, look at roundels with a binocular?

SaiK · Post by **SaiK** » 15 Feb 2013 01:56

perhaps they did a super plastic forming after they made the model and extended it.

nachiket · Post by **nachiket** » 15 Feb 2013 02:04

negi saar,I think this is a scale model. It has just changed a lot from the last AI. The LERX in the model NRao posted are gone. The wings are more diamond shaped and moved forward, the front nose and cockpit area is more PAK_Fa-ish. They have lengthened the fuselage behind the rear of the wing. And of course, they have changed the vertical fins. Prodyut Das' observation about the fins is correct, his conclusion is ridiculous. I wonder what he says about the F-35's vertical fins.

Indranil · Post by **Indranil** » 15 Feb 2013 02:14

The model shown at AI'13 is the correct representation of the latest iteration of the design. Raghuk had talked about this model a couple of pages back.

hnair · Post by **hnair** » 15 Feb 2013 02:16

And what are those deep boundary layer diverters doing on a apparently fifth generation combat aircraft? Even the “Wang Lu laundry and Chop suey” aircraft companies – very respected incidentally for their track record -are using diverterless intakes

Reminded one of how we sorely miss a certain kindergartner

Prof Das's comment on "deep boundary layer diverters" sound interesting. What did PakFA and F22 do to get such opprobrium?

negi · Post by **negi** » 15 Feb 2013 02:46

Nachiket If you would observe I am nowhere saying that model is not the AMCA model; I clearly stated my opinion i.e. it does not appear to be an appropriately scaled down model those v fins are out of proportion. It is not about where fins are placed etc etc they can change even as the first prototype makes it first flight. Look at the sweep on the trailing edge of v fins on the model in the image I posted those are not even in line with Indranil's image .

SaiK · Post by **SaiK** » 15 Feb 2013 03:32

planforms and wings, take a look at kfx
http://img809.imageshack.us/img809/830/kfx201.jpg

wags little, and straight forward design.. imho, perfect stealth characteristics.

Karan M · Post by **Karan M** » 15 Feb 2013 03:34

pankajs wrote:My understanding is that the TOT is very narrowly defined and can only be used to manufacture the product for which it was transferred and in approved numbers only. It is the reason that GTRE is floating tenders for collaborative effort on critical sections of the engine, even when the Russian tech is being used to produce the Russian engines in India under TOT.

TOT in the Indian context should be correctly defined as TOMT (Transfer of Manufacturing Tech.) which too can be shackled by restrictions on the raw material used. For instance, if specifications of the alloy used to mill a certain component are not given, we continue to be reliant on the TOMT nation for the raw material sourcing! And further, developing the technology further is shackled both by our lack of knowledge of first principles regarding its design and also IPR restrictions!!

The joke is some people still don't get this and keep complaining about "reinventing the wheel". What talk of making automobiles when one can't even understand how a wheel works & how to make them locally!! Bottomline, the forced sanctions on the LCA ensured a focus on indigenization & a 50% local LRU count despite an imported engine, and by the time it comes to service, that % will rise ensuring long term self determination!

shiv · Post by **shiv** » 15 Feb 2013 05:07

nachiket wrote: Kanson's pic is of the older model. It has evolved a lot since then as can be seen. And ADA engineers would not have reduced the sweepback angle unless it was for a reason.

No. Kanson's pic is a wind tunnel model. My aero India photo is of a display model made by someone else which I agree is horrible. That angle of sweep (in my pic) is unrealistic IMO for the leading edge of the vertical tail surface of a supersonic fighter.

Third party agencies are employed to make models - I will put up an image of an INSAS made by some unheard of model making firm in Gujarat - but that model did not look too bad and its butt color ws realistically orange and horrible

shiv · Post by **shiv** » 15 Feb 2013 05:12

indranilroy wrote:The model shown at AI'13 is the correct representation of the latest iteration of the design. Raghuk had talked about this model a couple of pages back.

http://img203.imageshack.us/img203/2181/amca1.jpg

The leading edge of the tailfin is like that of the Canberra but Canberra has more sweep back

SaiK · Post by **SaiK** » 15 Feb 2013 09:55

Well, it could that it was a model made by someone else, but my best guess is it should be someone from ADA/NAL/HAL body in-charge of AMCA. Wonder why would even some external model person (our ArmenT could make a better model) given a wind tunnel model as sample for a bit larger or smaller scale. It is better they come with many RC plane models for AMCA, and check it out just for modeling it alone. who knows, such models could be refined even with a miniature RC one.

pankajs · Post by **pankajs** » 15 Feb 2013 11:48

Lalmohan wrote:ToT is a waste of time - buy stuff outright and in the meantime start building desi products from scratch and start the long slow climb up the learning curve, will get to destination faster in the long run...

There are some advantages to this so called TOT.

Firstly, they provide us with valuable manufacturing process and techniques which otherwise we couldn't have obtained. This should help the AMCA project to that extent.

Secondly, Assuming the manufacturing is 100% localized and we keep an adequate stockpile of the special/exotic alloy imported from Russia, it helps us with the spares. You will remember the issues we had with the Russians. Even in the case of Rafale, local production makes us less reliant on the French for every piece of spare.

Yagnasri · Post by **Yagnasri** » 15 Feb 2013 12:06

But we were local manufacturing this for decades. how for this helped us is the question. May be we need the production handled fully by the private sector which shold also be allowed to export things to identified frindly nations with full freedom.

vic · Post by **vic** » 15 Feb 2013 12:14

I think AMCA team may have applied the lessons learnt from the difficulties being faced by JSF and PAKFA team. Also the vertical tail fin may be radar transparent.

Lalmohan · Post by **Lalmohan** » 15 Feb 2013 13:24

it is clear that we are good at the science, we have not yet reached maturity with the engineering

SaiK · Post by **SaiK** » 15 Feb 2013 20:07

vic wrote:I think AMCA team may have applied the lessons learnt from the difficulties being faced by JSF and PAKFA team. Also the vertical tail fin may be radar transparent.

you have point.. but if you are saying is right, and we have broke da vincible code, then assuming wave forms are scattered by internal frame, then external stealth shape takes least priority surrendering total aerodynamic qualities. but there are exposures where deflection might be required, as we have no clue to internal deflection frame shapes. all magick onlee for now. but theoretically possible.

shiv · Post by **shiv** » 15 Feb 2013 20:33

Its not about composite fins. See the image below. All supersonic and near supersonic aircraft have tailfin leading edges that are swept back like their mainwings - mostly far more so than the AMCA model. Why?

For comparison (click on image)

Indranil · Post by **Indranil** » 16 Feb 2013 00:23

Shivji,

ADA must have calculated that the vertical stabilizer is behind the mach cone. And as long as it is behind the mach cone, it will see subsonic airflow. Since it is placed so far aft, you see that they have gone for a lower sweep. This gives them better stability at low speeds.

The other thing why supersonic planes have such a large sweep in the vertical stabilizer is to take care of the wave drag. This can be handled by using "waisting" the strake where the stabilizer is mounted. Now check the model carefully. you will be able to see the waisting.

Indranil · Post by **Indranil** » 16 Feb 2013 00:25

My questions are of a different kind ... why are the edges rounded on the stabilizers?

By the way, I did not like the AMCA design initially, but it is starting to grow on me

.

Misraji · Post by **Misraji** » 16 Feb 2013 02:21

Has the forum discussed anything about why the vertical stabilizers are so wide?

-Ashish

PS: As an aside, I needed some information from resident aerospace engineers.
what branch of aerospace engineering deals with what we usually discuss with respect to fighter design?
(Say) Discussions of aerodynamics, ITR and STR, lift, service ceiling?
Is it CFD or is Airframe Design a separate field?

Indranil · Post by **Indranil** » 16 Feb 2013 03:47

Misraji wrote:Has the forum discussed anything about why the vertical stabilizers are so wide?

You find them too wide? Why?

Misraji · Post by **Misraji** » 16 Feb 2013 04:33

indranilroy wrote:You find them too wide? Why?

Just going by the photos and relative dimensions, I suppose.
It could be that they are not very tall and that gives them a stubby look.
Speaking looks-wise (apologies, I am not an aerospace engineer) and relative dimension-wise, they seem like PAKFA's all moving tail + a rudder.

I understand the part about low-sweep and better stability. Plus waisting.
Thank you for that.

--Ashish

Indranil · Post by **Indranil** » 16 Feb 2013 05:16

They are slanted. Hence they don't look tall. They are actually quite tall. Also the rudder is of the right size. For control authority you would need that size. Compare them with F-22 and F-35.

I agree with you and Shivji, the shape looks weird, somewhat out of place. Because we are used to seeing really sleek wings and winglets on fighter planes.

SaiK · Post by **SaiK** » 16 Feb 2013 05:34

did they reduce the angles for an increased/decreased frontal RCS on the tail fins? meaning, if you take the side view, the angles of the wind tunnel model is greater than the air show model.

shiv · Post by **shiv** » 16 Feb 2013 07:06

Tarmak's software generated image of the tailfin looks better than the Aero India model which I think is probably not a good representation of the original.