HAL Bangalore: Structural Coupling Test on Tejas - Broadsword by Ajai Shukla - Strategy. Economics. Defence.

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Saturday 15 March 2008

HAL Bangalore: Structural Coupling Test on Tejas

(Photos: Ajai Shukla)
Tejas LSP being prepared for a Structural Coupling Test)

HAL, Bangalore
January 2008

Here’s one of the LSP Tejas fighters undergoing the Structural Coupling Test. Structural coupling is the disturbance that is caused by the flexibility in a fighter’s airframe to the aircraft’s inertial sensors. The frequencies that are generated by vibrations in the airframe structure interfere with the frequencies within the Flight Control Systems (FCS). If these frequencies are not neutralised (by introducing phase delays, or by dampers) they can cause serious malfunctions in the flight control systems of modern fighters.

The Structural Coupling Test involves suspending the aircraft by the flexible hangers that can be seen in the pictures. Then the airframe is made to vibrate in the manner in which it would during actual flight… and then the avionics sensors are checked one by one in order to see how they are responding.

Basically, the Structural Coupling Test Facility checks whether the airframe frequencies have been sufficiently neutralised or not.

Incidentally, the two-seater version is about to be taken for this test in a month or so.


  1. excellent work!! how do u get access?

  2. Thats LSP-2, I thought you said it was out "flying". Anyways, nice pictures and keep them coming

  3. I can never get enough of LCA pictures. Ever.

  4. How do u get these pics mate???

    Do u work there??

  5. Do u have idea when are each of these aircrafts rolling out??


    And is PV-4 gonna roll out??? I heard PV-4 was canceled?? Is it true??

  6. Hi "m"... you're absolutely right... I stand corrected. That's LSP-2 on the Structural Coupling Test rig.

    anonymous, LSP-3 is slated to fly this month. Don't know about the others.

    And in the prototype series, I can confirm that there is no P-4. The four aircraft in that series are P-1, 2, 3 and 5.

    I also hear that metal cutting has begun for the IAF's order of 20 series production aircraft.

  7. Hey Ajay,

    Very nice explanation of the test...


    But a question, how did they allow photography, given that they are so paranoid about such things.


  8. Hi Sathya,

    They're not really paranoid. I found them forthcoming with facts as well as permissions for photography.

    Organisations like HAL and DRDO are beginning to realise the importance of image projection. And as they gain in confidence, they are becoming less defensive about failures as well. It was when there was very little success to point out that they felt... any coverage was bound to be negative!

  9. Thank U Sir.
    I can see a LCA in background in second picture. Can you/any body let me know, is it LSP-3 or PV-5 or any other LCA????

  10. Anonymous, it's the same Tejas which is in the photos of the MAST test. Alas, I did not ask or observe which of the ones it is.

    But by elimination, it cannot be LSP-2... which is undergoing the structural coupling test in the same photo (Heh, heh... just call me Sherlock!). To digress, LSP-2 is also the first aircraft fitted with the GE IN-20 engine.

    It also cannot be LSP-3, which is the first aircraft in which the radar is being integrated. LSP-3 is dedicated to radar integration and validation... a huge task by itself.

    Also, it cannot be P-2, which is the aircraft on which the Laser Designator Pod has been integrated. That has already been flown after integrating.

    Any more clues from anyone?

  11. Thanks for ur reply Sir. Does not matter whichever LCA is that, good news is one more added. I m dieing to know some thing abt LCH. Plz give a look.

  12. a few questions
    1)Has the engine fitting been completed in LSP-2?
    2)Has the Radar integration started in LSP-3?
    3)When are the LGB carrying and dropping going to be carried out by LCA?
    4)PV2= LDP integration and PV3= drop tanks? can any of the prototype do both?
    5)Has night flying been completed, if not when is it going to happen?
    6)Any more news on Naval LCA, except that the front fuselage is getting ready?
    7)Last but most important, DO you have more photos? Of anything in HAL's production/assembly line such as WSI dhruv, LCH, IJT, More Hawks, Jaguars, Sukhois, LCA. The list is not complete but I guess you get the idea, any i repeat any photo that you have taken will do. Even of a chidiya flying at HAL.

  13. okay, will post an article on IJT status, along with lots of hangar photos!

    But first, I've got four articles to write on the private sector in defence... that takes priority.

    Stand by!

  14. Good work Ajai, thanks for all the beautiful pics. When you get a chance, do write up on the the future of Arjun and which Shikhandi it needs to pair up with to take care of Bhishma.

  15. Any updates on LCA Tejas?


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