Testing times ahead for HAL: ARDC prepares for dangerous Tejas and IJT flight tests - Broadsword by Ajai Shukla - Strategy. Economics. Defence.

Home Top Ad


Sunday 4 July 2010

Testing times ahead for HAL: ARDC prepares for dangerous Tejas and IJT flight tests

The first Limited Series Production version of the Sitara IJT. The vertical fin below the engine and the lateral fins at the front, ahead of the IAF roundel, are anti-spin devices.

The LSP-1, parked in the ARDC hangar in Bangalore. The IAF wants 73 Sitara trainers for Stage-2 training of its fighter pilots

by Ajai Shukla
HAL, Bangalore
Business Standard, 5th July 10

The Russian designers stared transfixed at the monitor as the model of India’s Sitara Intermediate Jet Trainer (IJT) went into a spin, rotating like a fan uncontrollably. Despite every attempt to straighten it out with the aircraft controls, the Sitara kept spinning. If this had been a real flight, rather than just a “spin tunnel” test in Russia, both pilots in the Sitara would have died as the uncontrollable trainer smashed into the ground.

Instead, Indian designers at the Aircraft R&D Centre (ARDC) in Bangalore --- which is designing and testing the Sitara --- have tweaked the Sitara’s aerodynamics until it has passed the “spin tunnel” test.

But now, Chief Test Pilot Baldev Singh has to actually test-fly the Sitara, deliberately throwing the trainer into a hair-raising spin and then coaxing it into level flight again.

Only after that can the Indian Air Force use the Sitara to teach rookie pilots the vital skills needed to recover an aircraft from a spin. During training, IAF instructors will put the IJT into a spin and then hand over controls to the trainee, allowing him or her to stabilise the aircraft.

These are literally testing times at the ARDC, a unit of Hindustan Aeronautics Limited, which is preparing for several risky test flights that will determine the success or failure of its key projects.

Although the Sitara has cleared the “spin tunnel” test in Russia, that is no guarantee that the Sitara will recover from its first real life spin. Therefore, to minimise the risk to the test pilot, a special parachute is being fitted on the aircraft’s tail, which the pilot opens if he is unable to recover from a spin. Acting as an aerodynamic drag, the parachute retards the spin, allowing the pilot to recover control.

“There are always uncertainties in testing something for the first time”, explains HRS Prasad, the General Manager of ARDC. “So we make doubly sure there is a system that will enable (the pilot) to recover from a potentially disastrous situation. But we are confident of demonstrating that the Sitara can recover from a spin… that is a basic requirement for a trainer.”

Even more dangerous are the flight tests ahead for the Tejas Light Combat Aircraft (LCA), to demonstrate its ability to handle higher angles of attack, or Alpha, as the designers call it. Simply put, a flying aircraft’s angle of attack is the angle it makes, nose to tail, with the horizontal. A high Alpha provides several benefits to a fighter, especially letting it fly slower to land on shorter runways.

The Tejas has currently tested an Alpha of just 22-24 degrees, and will go up gradually to 28 degrees. But flying a higher Alpha risks stalling the fighter; its engine could go off (or flame out, as pilots call it) leaving the Tejas --- without propulsion power, or electrical and hydraulic power for its fly-by-wire controls --- to fall out of the sky like a stone.

To guard against that, the ARDC is fitting a test Tejas with a fast-response power pack that US company, Honeywell, manufactures for such flight-testing. Within milliseconds of the Tejas main engine going off, the hydrogen-operated power pack starts up, providing power to the fighter’s hydraulic and electrical systems, and re-lighting the main engine.

“In flying a single-engine aircraft, there is no bigger emergency than a flame-out”, says a former Tejas test pilot. “But no fighter engine should flame out at just 28 degrees Alpha. However, the Tejas air intakes have not been well designed and, as the Alpha increases, the intakes constrict the airflow, and the engine dies for want of air.”

In contrast to the Tejas’ maximum Alpha of 28 degrees, India’s Sukhoi-30MKI can comfortably handle an Alpha of over 50 degrees. The US Navy F/A-18 Super Hornet can manage an Alpha of 58 degrees.

The Tejas flight test programme, India’s first such testing process, has been controversial, with critics charging that the slow speed of testing has delayed the Tejas’ induction into service. On the positive side, the Tejas testing has given birth to the National Flight Test Centre (NFTC), a test facility that is of global standard. The Aeronautics Development Agency (ADA), which oversees the Tejas’ development, has now engaged European aerospace giant, EADS, to advise on how to speed up testing.

“We have to proceed cautiously”, the Tejas programme director, PS Subramaniam told Business Standard while witnessing a test last year. “We have managed to come so far without a single mishap. An accident would seriously damage the credibility of the Tejas programme.”


  1. I hope Mahindra aerospace (or any private firm) would mature soon enough to enter the fighter jet stream and replace the "BSNL" LIKE HAL and its cousins...
    I know its a dream... but as MLK says... I have a dream...

  2. Dear Ajay,

    Thank you for the wonderful blog,it is a staple diet for aerospace and defence enthusiasts like me.

    FYI Su 30 MKI of the Indian Airforce can easily do upto an angle of attack of 90-120 degrees, which enables its famous maneuver the Cobra.

  3. After 30 years, we come to know that intakes are not well designed...........wow HAL

  4. Hi Ajai,

    Can you please tell us what is the AOA required by IAF for LCA.

    I know the AOA for F-16 is 25 degrees.

    What is the AOA of the JF-17 and J-10 fighters developed by China.

    With the addition of new engine, will the problems in LCA be solved?



  5. Fundoo piece of reporting! Cheers!

  6. Ajai, your first pic is not clicking open. Same thing happened with your last story on the LUH.

  7. are they planning to increase angle of attack in mark 2?

  8. Sir,
    Waiting for more pictures, mainly of Tejas, Dhruv and LCH

    Thank You

  9. Angle of attack of Mirage2000 (same delta winged aircraft like LCA) is mentioned as 24 degrees in its wikipedia page. Also is written that that value is impressive for a delta winged aircraft. So going by this logic, LCA is better than Mirage 2000.

    Sukhoi, Super hornet cannot be compared to LCA as their wing design or configuration itself is different.

  10. "We have managed to come so far without a single mishap. An accident would seriously damage the credibility of the Tejas programme."

    What credibility is he talking about? Credibility of a weapon is established only after it is accepted and used by the customer, in this case the IAF. He better get this thing flying soon otherwise all the credibility will go down the drain of Bangalore like Rasam.

  11. Aken:

    "Can you please tell us what is the AOA required by IAF for LCA"

    My article mentions that it will gradually be raised to 28 degrees. That is what the IAF's Air Staff Requirements specify.

    HAL plans to achieve this with the Mk II Tejas.

    Anonymous 10:30:

    "After 30 years, we come to know that intakes are not well designed...........wow HAL"

    If you come to know this after 30 years, it says more about you than about HAL! Firstly, the air intake problem has been extensively written about for years.

    And, secondly, it is ADA, not HAL, that is responsible for the LCA's design.

    I know you are posting anonymously, but there must be some level of ignorance and stupidity below which Anonymous postings must not sink!!

  12. Ajai sir

    the F/A-18 Super Hornet you are referring is not the regular one used by US Defense forces but its actually a experimental one, F-18 High Alpha Research Vehicle (HARV). It was developed under a program that lasted from 1987 to 1996.

    F-18 High Alpha Research Vehicle (HARV)took the AOA to 70 degrees as against 58 degrees said by you.

  13. continued

    F/A-18 HARV is the only thrust vectoring aircraft with that kind of AOA. Next aircraft that is expected to have that kind of AOA is FGFA/PAK FA.

    I also support anonymous 13.31 that "Sukhoi, Super hornet cannot be compared to LCA as their wing design or configuration itself is different."

    By The Way does the HAL, DRDO, ADA has any plan to extend the LCA AOA to over 36 degrees.

  14. Sir,
    I have deep respect for you as a journalist. However, with this article you seem to be trying to dabble your hand in sensationalization as every other reporter. The spin test you mention in the beginning is nothing so serious that "Russian scientists would stare transfixed". It is a regular process which every a/c development goes through. Please detest trying to give cheap thrills in your future articles. We respect you too much to see you walk the same path as other journalists.
    Also, for "However, the Tejas air intakes have not been well designed and, as the Alpha increases, the intakes constrict the airflow, and the engine dies for want of air."
    Every intake of every supersonic a/c constricts airflow. It is the job of intake to slow down and smooth out the flow of airflow. What happens at high alpha is that the airflow entering the intakes becomes so turbulent that it becomes difficult for the intake to smooth it out.

  15. bravo for shutting down that idiot, unlike all the armchair aerospace/radar/marine/land systems engineers. there is much to still be learned about a system that a designer has not envisioned. the tejas airframe has its intakes designed as a single piece monocoque, airframe changes are difficult to make but modular construction makes it less tedious. This took 30 years to make because we had to develop all its tech in house. I would like to see its detractors do better. once some things are mastered the next incarnation comes at an accelerated pace, it is a fact.

  16. Ajai Sir,

    Thanks for answering one my quesitons.

    The other question, I have is:
    How does our LCA stack up against JF-17 and F-16?

    I couldnt find the AOA of JF-17 on any website.

    I am aware of F-16 AOA as to 25 degrees.

    If LCA has a higher AOA than F-16 does this mean the LCA will have a slight advantage in dogfights?




  17. Ajai Ji,
    You have not answered the question on JF-17, JF-10 angle of attack.
    I feel it is fair criticism of HAL/ADA that the intakes are defective. Do you not think that the capabilities of the fighter jet are effected and so the pilot? The present version of Tejas is defective and should not be put through countless, rigorous tests unless a good prototype free of critical errors can be tested. The habit of MK-II' ing everything is not what the enemy will consider with serious thought.
    I am sorry if I have offended you by not disclosing my profile but I do not write very often in your blog.
    You may have recognized me by my style of writing.
    Thank you, Ajai ji.

  18. At this stage, we can only hope that Tejas mk1 achieves its maximum possible AoA safely and efficiently.

    Any further issues on this matter can be resolved only on Tejas mk2.

  19. Why not compare single-engined aircraft for the Angle of Attack? Sukhoi, F-18 are all twin-engined, and have a very different wing design. There is no reason for you to bring in the angle of attack to denigrate the LCA. It reflects badly on the research conducted. Google might be my friend, but he could be your saviour.

    Paul Virani

  20. wish all the sucess to HAL and tejas team........

  21. and you wonder why the iaf likes foregin fighters....they know they will have a fight on their hand with jf/j10...we cannot expect them to fight in a fighter that even the very experienced test pilot says has severe flight issues....

  22. Sir,
    That means the AOA of tejas will be limited to just 28 degrees in the mark 2 versn also? Can you please inform us what is the AOA of jf-17 & j-10 with their socalled f-35 like DSI inlets . Is it possible to improve the AOA of TEJAS further by incorporating any such features like DSI inlets in the mark 2 versn(rather than just meeting ASQR) or is their exist any such program to do so & if it is, then how much time consuming technically difficult it will be.
    with regards

  23. It is unfair to compare AoA of TVC engine planes(MKI and F18-HARV) and wing-designs with rotatable elevators/canards with a fixed delta only type wing design.

    Blame the person who set the requirements as a delta wing design for Tejas for lapses in AoA and not ADA. Flawed requirement setting cannot be blamed on developer agency

  24. What will be the AOA of N-LCA with LEVCON? Is there any plan to integrate LEVCONs in AF variant?

  25. The spin test is a critical part of the certification program of any fighter aircraft.
    Yes it is somewhat dangerous but HAL pilots have been at it for decades and I am sure they will clear the Sitara spin trials.
    Congratulations on a well defined program but I think the IAF is getting a bit impatient waiting for the deliveries.

  26. @ anon @ 0542. "Blame the person who set the requirements as a delta wing design for Tejas for lapses in AoA and not ADA. Flawed requirement setting cannot be blamed on developer agency"

    The ASR for the LCA does not specify a delta wing design. The choice of wing planform was the design agency's and the design agency's alone. Having said that, the AOA limit is laid down / implied, and is fairly robust. AOA alone does not turn performance make.

  27. Col Shukla,
    Aircraft flies because of lift generated by the control surfaces. This lift is generated because the airflow speed is higher on top surface than the lower surface. This is because air has to travel more distance in the same time when covering upper surface (due to curvature). This creates pressure difference which creates lift. Well I don't think you are qualified to report on Aircrafts. Let me tell you that nothing changes with the intakes and they "constrict" the airflow just as in normal flight, it is just that the airflow is now distorted and for any plane, there are strict flight limits within which the intakes are designed. Even something like a Mig29 which has very high tolerance to distorted air flows in the intakes will flame out if those are exceeded.

    Also, I do think that 28deg alpha that you have quoted, is a misunderstanding. The designed alpha always is higher than the actual or real life possibilities ( may be around 32 to 35 deg), but in actual operating conditions, it would be limited by the FCS to 28deg. The 58deg alpha in a F-18 is the max possible alpha, but kind of alpha would be done in only a specially instrumented prototype test vehicle like NASA' F-18 High Angle test vehicle and not be done with an in service F/18 A/B/C/E with any Navy/Air force in the world. The alpha limits will be much less,closer to the 28 to 30deg in real life.

    Every a/c is has a restricted alpha. It is simple physics and no a/c can escape that. When the airflow pressure both above and below the wing becomes the same, the a/c "will" stall.Beyond an alpha of 35deg or so, it is nearly impossible to sustain such maneuvers with any degree of stability with normal control surfaces. You need thrust vectoring in all probability.

    So, you can naturally expect that when the wing will be at a high certain angle to the ariflow, the distance needed by the air to travel will become same for both upper and lower surfaces. So, at that angle, no lift will be created.

    Also, the intakes are designed to decrease the speed and smoothen out the airflow but they are hardpressed to do so at high alphas because of high turbulance in the airflow.

    Please write on Tanks and armor - your strength and experience.

  28. Ajay, either you have an error in the comments section or you are continuously deleting any comments afte the 15th one because in the list it says '27 comments' but on opening the article only 15 are displayed.

  29. IJT flight tests -- what happened
    Did it Fail

  30. Frankly lets get over with LCA.. start something new .. with the experince(mistakes) we gained from LCA. I am sure when it goes into service we will have another HAL Marut!!

  31. I want to ask anyone here who is expert on this field,what will be the maximum possible alpha and sustained turn rate for the tejas mk1?? Really want to knw


Recent Posts

Page 1 of 10412345...104Next >>Last