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India’s growing research potential in control theory and implications for flight control

amardeep mishra

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India’s growing research potential in control theory and implications for flight control



India has produced many giants in the field of control theory who have contributed immensely in various branches of this wonderful discipline. Three names that immediately come to my mind are:
(1) Kumpati Narendra (Citations ~ 44000)
‪Kumpati Narendra - ‪Google Scholar
and
(2) Shankar Sastry (Citations ~104899)
Shankar Sastry's Home Page (berkeley.edu)
‪Shankar Sastry - ‪Google Scholar
(3) M Vidyasagar (Citations ~37000)
‪Mathukumalli Vidyasagar - ‪Google Scholar

Out of these, Sastry has the honour and privilege of contributing the most in the field of adaptive control. He has authored several highly citated papers on stability proofs of various adaptive control formulations. Incidentally he is also an alumni of IIT Bombay, BT ’77 batch. Adaptive control has a lot potential benefit over several other control strategies as it renders the possibility of online learning/adaptation in the face of changing plant behaviour.
In recent times, reinforcement learning (RL) has gained enough traction within the controls community. In control theory, it is often implemented via what is known as “adaptive dynamic programming”. The fundamental benefit of this strategy is that approximately optimal policies could be learnt online under various actuator constraints while adhering to Lyapunov-like stability requirements. Several Indian researchers in recent times have made their contribution to this new field such as,
1) Rushikesh Kamalapurkar - ‪Google Scholar
2) ‪Shubhendu Bhasin - ‪Google Scholar
3) ‪Jagannathan Sarangapani or S. Jagannathan or sarangapani Jagannathan - ‪Google Scholar
4) ‪Nitin Sharma - ‪Google Scholar
5) ‪Balaraman Ravindran - ‪Google Scholar
6) ‪Amardeep Mishra - ‪Google Scholar

While several advancements have been made in reinforcement learning (from control theoretic perspective), the aerospace community in general hasn’t embraced the new control strategy. And this has got to do with MIL spec requirements of gain and phase margins. While RL in recent times has been made more rigorous via incorporating both stability and safety (control barrier Lyapunov functions), it still requires certain fundamental assumptions notably those associated with persistency of excitation condition. In addition, a pure adaptive controller requires large gain (learning rate) to adapt itself to lets say large error buildup, large abrupt variation in dynamics etc. It however can potentially destabilize the system by inducing unwanted oscillations especially in systems with significant noise and disturbances.

In Indian context, especially from aerospace industry, considerable effort has been paid to Gain Scheduling-based PID and Model Reference Adaptive Control (MRAC). The prime flight control system of LCA Tejas consists of these two techniques.
Designing And Testing Flight Control Laws Of Light Combat Aircraft [LCA] Tejas [Aero India 2013] - YouTube
The video describes some of the challenges CLAW faced while designing the flight control law for LCA tejas.
03 Challenge in flight control systems Dr Vijay V Patel , ADA Bangalore - YouTube

It could be noted that Dr. Deodhare (an alumni of IIT Bombay BT ’84 batch) has pioneered the flight control development at ADA. In the video below he explains how LCA is not just an aircraft for India, but it represents maturity in various facets of aerospace engineering notably aerodynamic design (wind tunnel testing under various regimes), flight control laws, composites and avionics.
Dr Girish S Deodhare : Distinguished Scientist - YouTube
He beautifully explains as to how ADA and CLAW have created a wealth of knowledge resource within the country to undertake complex aerospace developments that are coming up.
For instance, according to him, the ADA/CLAW team could undertake controls development task for various classes of aircrafts namely:
(1) Tejas Mk2 with canards.
(2) Tailess aircraft design.
(3) Stealth AMCA with twin engine configuration.

While interacting with one of the senior controls engineer (A Ph.D. in flight dynamics and control from IISc Bangalore with more than a decade experience in flight controls), I was told that the Tejas comprises of many control loops for various purposes, some of which are, the primary 3-axis FBW, Mach hold autopilot, stability augmentation system (SAG), various other controllers to improve the damping characteristics etc. These control loops leverage some of the well-known control techniques from literature, for instance the primary 3-axis FBW uses gain scheduling. It entails finding best possible gains for linear state feedback controllers over all the possible operating points in the flight regime.
Similarly, there are certain other control loops that make use of model reference adaptive control (MRAC). In fact, there is a flight recovery controller that recovers the flight from edge case scenarios and bring it back to level flight. This one use sliding mode!

Development of proper flight controls is directly contingent upon extensive wind tunnel tests of various scale models under various mach regimes. These tests reveal the wealth of aerodynamic coefficients ranging from stability derivatives, damping derivatives to controls derivatives. A good mathematic model of an aircraft captures the variation of these coefficients with respect to angle of attack, mach no., side slip, various rates etc. Further, a good model replicates the true physics of flight in simulations thus paving way for controls design. It must be noted that wind tunnels alone are not sufficient, it must have requisite instrumentation setup to capture wide variety of aerodynamic data. India has a multitude of such wind tunnel tests ranging from subsonic, transonic, supersonic to now hypersonic with adequate instrumentation to capture these aerodynamic coefficients.
Wind tunnel test of tejas:

LCA tejas mk2 in wind tunnel tests
1648099724697.png


Wind tunnel tests of TEDBF:
1648099805209.png


Wind tunnel tests of AMCA:
1648099915594.png

1648099935238.png


In addition, India has developed a full fledged hardware in loop (HIL) system known as "iron bird test rig" that mimics the entire control system on the ground. Here is a brief video on the test rig:
The test rig makes the control development much more realistic as the response of the control signals could be realized on the ground over a real system.


One important challenge he spoke of was time delays. A well-behaved system could easily burst into oscillations and eventually instability if the time delays are not compensated well enough. For linear systems, the time delay compensation is well documented in literature and has been leveraged in the FBW design. However, for more fancy RL-based control strategies large time delays present a grave challenge.

@JamD , @Quwa , @SQ8
 
Last edited:

Raj-Hindustani

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India’s growing research potential in control theory and implications for flight control



India has produced many giants in the field of control theory who have contributed immensely in various branches of this wonderful discipline. Three names that immediately come to my mind are:
(1) Kumpati Narendra (Citations ~ 44000)
‪Kumpati Narendra - ‪Google Scholar
and
(2) Shankar Sastry (Citations ~104899)
Shankar Sastry's Home Page (berkeley.edu)
‪Shankar Sastry - ‪Google Scholar
(3) M Vidyasagar (Citations ~37000)
‪Mathukumalli Vidyasagar - ‪Google Scholar

Out of these, Sastry has the honour and privilege of contributing the most in the field of adaptive control. He has authored several highly citated papers on stability proofs of various adaptive control formulations. Incidentally he is also an alumni of IIT Bombay, BT ’77 batch. Adaptive control has a lot potential benefit over several other control strategies as it renders the possibility of online learning/adaptation in the face of changing plant behaviour.
In recent times, reinforcement learning (RL) has gained enough traction within the controls community. In control theory, it is often implemented via what is known as “adaptive dynamic programming”. The fundamental benefit of this strategy is that approximately optimal policies could be learnt online under various actuator constraints while adhering to Lyapunov-like stability requirements. Several Indian researchers in recent times have made their contribution to this new field such as,
1) Rushikesh Kamalapurkar - ‪Google Scholar
2) ‪Shubhendu Bhasin - ‪Google Scholar
3) ‪Jagannathan Sarangapani or S. Jagannathan or sarangapani Jagannathan - ‪Google Scholar
4) ‪Nitin Sharma - ‪Google Scholar
5) ‪Balaraman Ravindran - ‪Google Scholar
6) ‪Amardeep Mishra - ‪Google Scholar

While several advancements have been made in reinforcement learning (from control theoretic perspective), the aerospace community in general hasn’t embraced the new control strategy. And this has got to do with MIL spec requirements of gain and phase margins. While RL in recent times has been made more rigorous via incorporating both stability and safety (control barrier Lyapunov functions), it still requires certain fundamental assumptions notably those associated with persistency of excitation condition. In addition, a pure adaptive controller requires large gain (learning rate) to adapt itself to lets say large error buildup, large abrupt variation in dynamics etc. It however can potentially destabilize the system by inducing unwanted oscillations especially in systems with significant noise and disturbances.

In Indian context, especially from aerospace industry, considerable effort has been paid to Gain Scheduling-based PID and Model Reference Adaptive Control (MRAC). The prime flight control system of LCA Tejas consists of these two techniques.
Designing And Testing Flight Control Laws Of Light Combat Aircraft [LCA] Tejas [Aero India 2013] - YouTube
The video describes some of the challenges CLAW faced while designing the flight control law for LCA tejas.
03 Challenge in flight control systems Dr Vijay V Patel , ADA Bangalore - YouTube

It could be noted that Dr. Deodhare (an alumni of IIT Bombay BT ’84 batch) has pioneered the flight control development at ADA. In the video below he explains how LCA is not just an aircraft for India, but it represents maturity in various facets of aerospace engineering notably aerodynamic design (wind tunnel testing under various regimes), flight control laws, composites and avionics.
Dr Girish S Deodhare : Distinguished Scientist - YouTube
He beautifully explains as to how ADA and CLAW have created a wealth of knowledge resource within the country to undertake complex aerospace developments that are coming up.
For instance, according to him, the ADA/CLAW team could undertake controls development task for various classes of aircrafts namely:
(1) Tejas Mk2 with canards.
(2) Tailess aircraft design.
(3) Stealth AMCA with twin engine configuration.

While interacting with one of the senior controls engineer (A Ph.D. in flight dynamics and control from IISc Bangalore with more than a decade experience in flight controls), I was told that the Tejas comprises of many control loops for various purposes, some of which are, the primary 3-axis FBW, Mach hold autopilot, stability augmentation system (SAG), various other controllers to improve the damping characteristics etc. These control loops leverage some of the well-known control techniques from literature, for instance the primary 3-axis FBW uses gain scheduling. It entails finding best possible gains for linear state feedback controllers over all the possible operating points in the flight regime.
Similarly, there are certain other control loops that make use of model reference adaptive control (MRAC). In fact, there is a flight recovery controller that recovers the flight from edge case scenarios and bring it back to level flight. This one use sliding mode!

Development of proper flight controls is directly contingent upon extensive wind tunnel tests of various scale models under various mach regimes. These tests reveal the wealth of aerodynamic coefficients ranging from stability derivatives, damping derivatives to controls derivatives. A good mathematic model of an aircraft captures the variation of these coefficients with respect to angle of attack, mach no., side slip, various rates etc. Further, a good model replicates the true physics of flight in simulations thus paving way for controls design. It must be noted that wind tunnels alone are not sufficient, it must have requisite instrumentation setup to capture wide variety of aerodynamic data. India has a multitude of such wind tunnel tests ranging from subsonic, transonic, supersonic to now hypersonic with adequate instrumentation to capture these aerodynamic coefficients.
Wind tunnel test of tejas:

LCA tejas mk2 in wind tunnel tests
View attachment 826769

Wind tunnel tests of TEDBF:
View attachment 826770

Wind tunnel tests of AMCA:
View attachment 826771
View attachment 826772

In addition, India has developed a full fledged hardware in loop (HIL) system known as "iron bird test rig" that mimics the entire control system on the ground. Here is a brief video on the test rig:
The test rig makes the control development much more realistic as the response of the control signals could be realized on the ground over a real system.


One important challenge he spoke of was time delays. A well-behaved system could easily burst into oscillations and eventually instability if the time delays are not compensated well enough. For linear systems, the time delay compensation is well documented in literature and has been leveraged in the FBW design. However, for more fancy RL-based control strategies large time delays present a grave challenge.

@JamD , @Quwa , @SQ8

very nice..... HAL Tejas helped to build such infrastructure in India,

Otherwise, India was doing nut boult, paint, and manufacturing jobs for many decades. India has assembled the aircraft (JV products) but now needs to move forward...

SAAB Aircrafts are a great example - Import the critical few parts if needed but try to build everything as possible.
 

amardeep mishra

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Joe Shearer

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How is cloud relevant to India's research effort in control/flight dynamics? Since when did politicians start designing flight controls? Let politicians do their thing and for now focus on the primary topic of this thread.
It isn't.

You, of all people, should know better than to react.

This is a type 3 response. I've been working on these.

Type 1 takes information on board, sometimes with an approving comment, sometimes with a wish to be able to keep up as a nation. About 10% by volume (sound volume, not post volume).

Type 2 takes information on board, puts it in context, and usually pokes gentle fun at it from 35,000 feet. Taking this as an attack is a very shallow response; it has to be taken as an acknowledgement at a high level, and a statement of intent to keep up or to surpass the efforts mentioned, couched in humorous form. About 5% by volume.

Type 3 goes into frenzied denial, mostly with zero understanding of the issues mentioned. About 85% by volume.

You have learnt over the years where to spend mental effort; don't worry about Type 3 responses, and - in the spirit of doing as I say, not as I do - ignore them in the conversation, but take care to preserve the precious gems that emerge. They will prove to be the core of a priceless collection over the years.

Before you ask, you already have all the evidence you need, after ten years of experience in this forum, to affirm that we Indians respond in much the same fashion. In that colonial swine Kipling's words,

"Judy O'Grady and the colonel's lady,
Are sisters under their skin!"
 

Joe Shearer

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Anyways, I dont think I will ever comment again.
That will be a terrible shame! I hope you reconsider. I can assure you that besides the swarms of pests, there are some real heavyweights*, and they will absorb your posts with great attention.

However the decision is yours.

* I am referring to Pakistani gentlemen; we know that there are knowledgeable Indians as well, who tend to get distracted by silly interventions.
 
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I said the opposite of what you think I said in that thread. Also, I’m not an active mod anymore, can’t do anything at all here. Report the trolls.

I understand your point there. Sorry to bother you but I was talking about the Pakistani trolls complaining for Indians and see what they did here. @waz @LeGenD could you please clean it up and have your say on the subject. @Quwa @gambit what do you think of the subject. Better to have your view to learn a thing or two and having a fruitful discussion.
 

.King.

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The state of PDF is such, that a post discussing flight control systems is derailed by pakistani and chinese sh*tposters. How and why is it relevant, whether china got kicked, if china hid casualties etc with flight controls?


Those who started the derailment should get warnings here.
 

Joe Shearer

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I understand your point there. Sorry to bother you but I was talking about the Pakistani trolls complaining for Indians and see what they did here. @waz @LeGenD could you please clean it up and have your say on the subject. @Quwa @gambit what do you think of the subject. Better to have your view to learn a thing or two and having a fruitful discussion.
You're doing it wrong.

There's a report button; it invokes a blank space for your report. I've used it, once or twice a day (which is a lot). Action is taken within that 24 hour period.

If you write this kind of post, some poor guy has to plough pages and pages of sewage sludge trying to pick up reportable stuff.

Just use the button. It works; that doesn't mean that whatever you think is wrong is wrong. I have also got a very polite message back saying that xyz report I made could not be dealt with as it wasn't what I interpreted it to be.

The state of PDF is such, that a post discussing flight control systems is derailed by pakistani and chinese sh*tposters. How and why is it relevant, whether china got kicked, if china hid casualties etc with flight controls?


Those who started the derailment should get warnings here.
Don't worry about who should get what.

Just use the report button and move on.

Sometimes I practice what I preach; however, very often, I wade in. It is always better to report using the button, and moving on.

Man a technical thread has become a troll fest. WTH

@waz bro thread needs clean up.

@amardeep mishra Hey, happy to see you around. Keep posting.
@amardeep mishra
You and your posts are wanted. Stay on and keep cool.
 

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