AMCA - Advanced Medium Combat Aircraft (HAL)

Twinblade

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^^ It's not about simulations of models, it's about the imperfections resulting from production techniques (surface fastners, gaps and edge alignment issues in panels, surface undulations) that can be rectified and improved upon before production, perfection is easy to reproduce, real life imperfection, not. A field radar reading is corrupted with secondary and tertiary reflections from surrounding surfaces resulting in large margin of errors. The design will never be optimised to its potential. If you think it is necessary only for fifth generation aircraft and fourth generation aircraft can make do with simulation, think again.






Even SAAB has managed to create facilities to test a full sized Gripen E/F.
 

ersakthivel

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No doubt the chambers will improve and help a great deal in tweaking the design to iron out the minor glitches and optimize it .

But the basic design done using high powered software is never going to be proven as false in the chambers.A discussion on similar vain has already taken place in Tejas thread. So I don't want to repeat it more than once.

Also creeping wave magnification of RCS is fit only for perfect cylindrical shapes like Missile body , Not for tejas fuselage which has subtle angles all over deflecting the creeping waves all over.

And even this creeping wave RCS reflection is governed by Fock calculation which can be built into software simulation based on high power computers.

But it is the prediction of the mathematical model which forms the bedrock of the RCS calculation. for a LO design

That is the reason why the stealth formula invented by Dr. Ufimtsev have to wait for the higher computing power era to be transformed into production model like F-117 and f-22.
 
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Decklander

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^^ It's not about simulations of models, it's about the imperfections resulting from production techniques (surface fastners, gaps and edge alignment issues in panels, surface undulations) that can be rectified and improved upon before production, perfection is easy to reproduce, real life imperfection, not. A field radar reading is corrupted with secondary and tertiary reflections from surrounding surfaces resulting in large margin of errors. The design will never be optimised to its potential. If you think it is necessary only for fifth generation aircraft and fourth generation aircraft can make do with simulation, think again.
Even SAAB has managed to create facilities to test a full sized Gripen E/F.
Sometimes it is just impossible to have anykind of healthy debate with some people. Not only do you need a full size model and big enough anechoic chamber but you also need the ability to pitch and roll the model to simulate maneavers in flight and measure the RCS from various angles and frequencies from 1-18 ghz to have the 360* dbSM diagram for each frequency.
 

dvdiyen

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Sometimes it is just impossible to have anykind of healthy debate with some people. Not only do you need a full size model and big enough anechoic chamber but you also need the ability to pitch and roll the model to simulate maneavers in flight and measure the RCS from various angles and frequencies from 1-18 ghz to have the 360* dbSM diagram for each frequency.
Totally agreed. My simple question is is it not possible to simulate the same by taking full size model on a high end server?
I think this is totally possible.
 

SajeevJino

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I don't think so. The largest anechoic test facility that I have seen is for Arjun MBT. Test facility near AVADI (EMI/EMC Testing).
Are You Sure Sir

I think this one is in Madurai ..HW owned Building inside a Engg College
 
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Decklander

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Totally agreed. My simple question is is it not possible to simulate the same by taking full size model on a high end server?
I think this is totally possible.
It is very much possible. I had it done for my model using a software only. But that is not perfect way. You still need to get it perfect by using full scale actual model with all its openings and panels fitted to get the complete picture. Direct ray method will never give out the imperfections. It can at best be indicative and far from truth.
In my model, I initially had straight line bay doors for main as well as side bays but the RCS changed the moment I changed them to be serrated lines and repeated the analysis by creating nearly all panels and doors. The complete picture changed. what seemed an outstanding design suddenly seemed inadequate. We went back to drawing board. redesigned and reshaped a few areas and finally we had what we wanted from a software.
 

p2prada

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Who will know it better than I do? For last four months I have tried to get the RCS measured for my Model and went to everyone in India. Finally I got it done but from external agency software.
I agree with you. And I did state they are building it now. They are still half a decade away from an actual RCS facility.

Now tell me why are we making a fool of whole of India by stating that RCS of LCA is lowest of all fighters in IAF? When you can't calculate and have no such facility, than where did you do it and what is the basis of those claims? use of composites does not make an ac LO.
Sir, I remember the time you just entered the forum, you claimed the Rafale's RCS is actually bigger than LCA's and I said otherwise.

LCA is not designed with RCS in mind at all. It is just a fluke of sorts that it is detected much closer than a Mirage-2000.
 

Decklander

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I

Sir, I remember the time you just entered the forum, you claimed the Rafale's RCS is actually bigger than LCA's and I said otherwise.

LCA is not designed with RCS in mind at all. It is just a fluke of sorts that it is detected much closer than a Mirage-2000.
I did state that but I alsi stated that it is probably due to extensive use of composites which have much lower reflectivity and also due to size. The RCS of any surface is dependent on three things- geometric area, reflectivity & directivity.
the RCS equation is given by the formula RCS=geometric area x reflectivity x directivity.
LCA scores over all these ac based on first two factors. M2K is an all metal ac and also bigger in size compared to LCA.
 

p2prada

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Totally agreed. My simple question is is it not possible to simulate the same by taking full size model on a high end server?
I think this is totally possible.
Nope. In the end, a simulation is only a simulation. Real world test conditions need a real deal facility which we do not yet possess.
 

dvdiyen

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Nope. In the end, a simulation is only a simulation. Real world test conditions need a real deal facility which we do not yet possess.
I know that. What I am saying is a very rough idea of RCS can always be simulated.
 

Decklander

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I know that. What I am saying is a very rough idea of RCS can always be simulated.
All you get is very strong hot spots which show up. It also gives a complete spherical analysis. But that can only be used to refine the shape which again may need refinement during CFD analysis stage. Finally you can create least return only within a very small arc and particuler frequency band. All round stealth and all across the spectrum is probably not possible at all.
 

dvdiyen

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=Decklander;793557]All you get is very strong hot spots which show up.
Agree

It also gives a complete spherical analysis.
Depends on the planes that you select

But that can only be used to refine the shape which again may need refinement during CFD analysis stage. Finally you can create least return only within a very small arc and particular frequency band.
Depends on the solver you use (second part of the sentence)

All round stealth and all across the spectrum is probably not possible at all.
Agree
 

Decklander

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Agree

Depends on the planes that you select

Depends on the solver you use (second part of the sentence)

Agree
The software we used, gave us complete picture in whichever manner we wanted in whichever frequency we wanted. That software uses the autocad design of the object to calculate the RCS. Infact it uses the full scale digital model and not a scaled model.
 

dvdiyen

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The software we used, gave us complete picture in whichever manner we wanted in whichever frequency we wanted. That software uses the autocad design of the object to calculate the RCS. Infact it uses the full scale digital model and not a scaled model.
That is what is expected. Most of the present day solvers have all the features. Using a full scale model requires better computing facility more RAM and GPU cores (since more meshes are required).
 

p2prada

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I know that. What I am saying is a very rough idea of RCS can always be simulated.
There is no point in that. Rough RCS is not true RCS. There is a heaven and sea difference between the two.

It is the "micro" areas that give away everything. Sure, your wing may have the perfect stealthy design, but that ding the maintenance crew decided to leave behind because one guy was careless with his spanner will kill the aircraft's stealthy properties. That little aberration in your paint job will increase your RCS by many times.

The macro areas will be all right, like nose, wing, tail etc, but without a full scale aircraft being tested in real world conditions where the aircraft is subjected to dust, ice and bird grime settling on your canopy, intakes etc, it is pointless to talk about RCS measurements on a model.

As a matter of fact, the macro issues of RCS will be taken care of during the design stage itself. Even the biggest experts on the planet cannot measure RCS by eyeballing the aircraft, but they know whether an aircraft is designed with stealth in mind or not. LCA, for one, was never designed with stealth in mind, neither was Su-27, F-15, F-16, Mirage-2000, EF-2000, Rafale or Gripen. They can, "maybe," reduce RCS by a certain degree, perhaps decrease detection range by half or more compared to a F-16/Mirage-2000, but that's not what's considered "stealthy."
 

dvdiyen

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There is no point in that. Rough RCS is not true RCS. There is a heaven and sea difference between the two.
I agree there is a large difference but I think you are exaggerating to much. Do you think the people who make the software simply charge millions for a completely junk result? I don't think so.


As a matter of fact, the macro issues of RCS will be taken care of during the design stage itself. Even the biggest experts on the planet cannot measure RCS by eyeballing the aircraft, but they know whether an aircraft is designed with stealth in mind or not. LCA, for one, was never designed with stealth in mind, neither was Su-27, F-15, F-16, Mirage-2000, EF-2000, Rafale or Gripen. They can, "maybe," reduce RCS by a certain degree, perhaps decrease detection range by half or more compared to a F-16/Mirage-2000, but that's not what's considered "stealthy."
As a matter of fact the concept of stealth itself is a flaw. There are experiments that has proved the so called RAS/RAM does not absorb radiation in the UHF band. This UHF counter stealth measures are still in development stage. A PhD thesis on this also exists from NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA.


In fact one of the thesis from Ohio state university working for LM says "There has been much media interest in stealth and stealthy aircraft in the past ten years or so, and claims are made that such targets are 'invisible to radar'. Not surprisingly, much of this is rubbish !"
 
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p2prada

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I agree there is a large difference but I think you are exaggerating to much. Do you think the people who make the software simply charge millions for a completely junk result? I don't think so.
You mean the softwares will cater for manufacturing defects, maintenance defects and bird poop? No.

As a matter of fact the concept of stealth itself is a flaw. There are experiments that has proved the so called RAS/RAM does not absorb radiation in the UHF band. This UHF counter stealth measures are still in development stage. A PhD thesis on this also exists from NAVAL POSTGRADUATE SCHOOL MONTEREY, CALIFORNIA.


In fact one of the thesis from Ohio state university working for LM says "There has been much media interest in stealth and stealthy aircraft in the past ten years or so, and claims are made that such targets are 'invisible to radar'. Not surprisingly, much of this is rubbish !"
If you look at "actual" LM works, they never claimed invisibility. It is the media which created that word for the layman to understand.

F-22/F-35 etc are not capable of being stealthy under UHF. But what can you do with UHF? Can you generate enough information to send a missile out? No. Most aircraft don't even carry any protection against UHF frequencies onboard.

The F-22 design not working against UHF is true. But tell me which fighter in the world carries a UHF emitter for use against other fighters. That's the reason why the F-22 design works best against X band radars which is the standard fit on fighters and to an extent on S and L bands which are used on AWACS.
 

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