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Dr. Shyam Chetty was the Former Director of CSIR - National Aerospace Laboratories, Bangalore, and held additional responsibilities as Director CSIR-4PI, Bangalore, Project Director of the National Control Law team for LCA, and Chairman of the Systems Engineering Cluster of NAL. He has over 40 years of experience in the field of Aircraft Flight Mechanics & Control. His research interests include Flight Control System Design & Development, Aircraft Simulation & Modelling, Handling Qualities & Aircraft Pilot Coupling, Computer Aided Flight Control Design & Rapid Prototyping Techniques.

He also has the distinction of having served as the Chairman / Technical Expert of Review Committees on most of the Major National Aerospace Programmes of ISRO, DRDO and ADA. He has won several awards, prominent among them being the Jawahar Lal Nehru Memorial Award in 1976, Sir C.V. Raman Distinguished Young Scientist Award in 1998, DRDO Award for Path Breaking Research in 2002 and many more.

CSIR-NAL has also provided significant value-added inputs to all the Indian national aerospace programmes. Its contributions over the last five decades have enabled it to create a niche for itself in advanced aerospace research and technology development.



Question 5: The Flight simulator of the Tejas has been designed at Flight Mechanics & Control Division, NAL. It has been instrumental in validation and final implementation of LCA’s control law design. How does this technology help the Pilots who fly the Light Combat Aircraft?

As discussed earlier, since pilot in loop realtime simulation is a crucial step in the overall design, evaluation, verification and validation of the flight control laws, FMCD NAL developed a novel low cost Engineer in loop simulator (ELS) where the designer could bring in the pilots to evaluate and test the performance and handling of the aircraft at an early stage of design.
ELS being a design cum evaluation tool, control law versions under development can be easily ported and integrated with the rest of the simulation software. It also allows various flight motion parameters to be bled out and plotted in realtime as the simulator tests are progressing.

This allows the designer to make changes quickly if necessary to the control law gains, filter constants etc. based on the pilot comments and observations to get immediate feedback. The facility was also extensively used for not only refining the normal and reversionary mode control laws, autopilot functions / mode switching logic  and carefree maneuvering but also for  example finalizing  the Head Up Display parameter layout and formats.

The parameter id group along with the flight test crew also used the ELS facility to synthesize and finalise specific flight test maneuvers for generating input-output data which in turn enabled them to validate and then  update the aerodynamic data base to get a good match between simulator and flight.

As mentioned earlier extensive testing using pilot in loop simulation and getting their feedback at different stages of development is the only way to ensure that the overall performance of the closed loop aircraft is satisfactory both under normal and failure conditions.

Since the comments made by the pilots are qualitative in nature, and to refine the control laws one needs to identify and make quantitative changes in the respective control law parameters , special segmented  tests have to be planned to identify the exact cause and extract more precise feedback information from pilots ,  so that one can home on to the problem area and then make quantitative parameter changes. 

Questions 6: How far are we from making the Tejas completely Autonomous?

Even in the current version of the control laws once the aircraft crosses the safety height, the up and away flight can be flown autonomously. However, the two most critical phases are takeoff and landing where the margin for errors are very less, hence automating these phases is going to be complex and needs additional design effort. But since we already have very high fidelity flight validated models,  these two phases  can also be automated by incorporating two additional modes in the control laws leading to a fully autonomous aircraft. In fact in the lca naval variant we have already automated the ramp takeoff.

Question 7: CSIR-NAL successfully led the National Team for the composite wing development for Tejas. Forty percent of the Tejas airframe is fabricated at NAL. How has this helped the Tejas become the world’s smallest light weight fighter aircraft?

The extensive use of cocured cobonded carbon epoxy composite manufacturing technology  inidigenously developed by NAL  for realizing 150 plus high strength structural components for fuselage, wing, under carraige doors and empennage have not only helped in optimizing and reducing the overall weight of the aircraft but has significantly simplified the overall manufacturing of the airframe as very large components having complex curved shapes can be produced in one shot using this technology.  

It also reduces the part count and avoids the use of thousands of rivets that would be necessary if conventional metallic machined parts / technology were to be used for realizing these structures. Further it reduces the overall cost of the airframe as there is relatively less wastage of material due to subtractive manufacturing process adopted for realizing weight optimized metallic structural parts. The manufacture and assembly  are therefore  faster due to lower part count hence further reducing the manufacturing costs.