The Tejas LCA: improving performance with the current F-404 engine - Broadsword by Ajai Shukla - Strategy. Economics. Defence.

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Wednesday 16 July 2008

The Tejas LCA: improving performance with the current F-404 engine

(Concluding part of a two-part series on the Tejas LCA's engine)

by Ajai Shukla

The selection of the Tejas LCA’s new engine in October --- the choice (as the previous post deals with) is between the Eurojet EJ200 and the GE F-414 --- will provide an extra 10 KiloNewtons of thrust to the Tejas. The new engines, however, will start being fitted onto the third Tejas squadron; the first two squadrons, comprising 40 aircraft, would already be in service with the GE F-404 IN-20 engines.

And so the Indian Air Force (IAF) has asked the Aeronautical Development Agency (ADA) and Hindustan Aeronautics Limited (HAL) to urgently improve the performance of Tejas LCAs fitted with the GE F-404 IN-20 engines. These will power the first two LCA squadrons consisting of 40 fighters.

I visited HAL’s Bangalore Complex to see how that is being done. HAL has adopted a three-fold strategy:

1.  Improving the air intake. 

Top HAL decision-makers pooh-pooh the IAF’s contention that the LCA’s air intakes are incorrectly designed, resulting in oxygen starvation and incomplete burning and, therefore, sub-optimal engine power from the F-404s. At the same time, however, steps are being taken to improve air intake, without getting into major redesign that could set back the programme by years. Instead, auxiliary air intakes are being provided on the sides of the Tejas engine housing --- similar to those on the Jaguar (see photos).

These auxiliary air intakes comprise of spring-loaded panels that open when engine suction is very high and provide an additional route for airflow into the engine intakes. As you can see in the photos, the spring-loaded panels can be pushed in by manual pressure.

At critical stages in the flight envelope, such as during take-off, rapid climb, sustained turn… and in any case, when afterburners are on… the heavy suction from the engines would open the auxiliary air intakes. When the demand for air goes down, such as in level flight, the auxiliary air intakes would close.

HAL designers aver that this would improve the engine performance only in some portions of the flight envelope. They say that during the most critical moments --- which are during sustained turns, in aerial combat --- the auxiliary air intakes would provide only marginally improved performance, if any at all.

A top HAL designer told me, “There is some merit in [the IAF’s idea]… the designers are considering it. There has been a debate for quite some time… will it really improve to that extent. Where it really matters it may not give added thrust.. in other places it will give.”

Nevertheless, the fitment of auxiliary air intakes is going ahead, partly because this does not require major re-engineering, nor will it delay the Tejas induction in any way. According to HAL, this will take six months to engineer; later LSPs will incorporate the auxiliary air intakes.

2.  Reduction of Tejas' weight. 

The LCA’s designers say that the removal of telemetry instrumentation, which is essential during flight testing, will bring the Tejas’ weight down by as much as 300-400 kilos. Re-engineering some of the displays and sub-systems within the cockpit will lop off another 300 kilos; the weight reduction of 600-700 kilos is expected to allow the carriage of more weapons.

There is a lack of understanding about what the Tejas’ weight is, since all kinds of figures are bandied about. Let me clarify: The 10.5 tons that I wrote about in my last post is the total weight of the Tejas, with full fuel on board; all 7 pylons fitted but not carrying weapons; and two outboard missiles being carried. The maximum payload of the Tejas is 3.5 tons… carried on its pylons. This could be armament or external fuel tanks; if external fuel tanks are fitted, the weight of fuel will correspondingly bring down the weapons load carried.

But there’s a catch! The maximum take-off weight of the Tejas is 13 tons. So if you load the maximum payload of 3.5 tons onto the 10.5 ton fighter, your weight of 14 tons is beyond the maximum take-off weight. So you’ll have to shed one ton… or either internal fuel or external fuel/armaments. That’s what happens when a fighter’s weight goes beyond what was originally planned.

So the reduction of 600-700 kilos may not actually go into making the Tejas more manoeuvrable. This shaved off weight may be made up by allowing the Tejas to carry (close to) its full capacity of external fuel-cum-armament.

3.  Increasing control surfaces. 

The designers say they are considering adding an auxiliary wing (similar to the Eurofighter) to the front portion of the fuselage to increase the control surfaces, and therefore manoeuvrability. This involves major re-engineering, which cannot be done for the first two squadrons. However, it will be grouped along with the re-design that will be necessary for fitting in the new engine for Tejas No 41 onwards.

The Tejas designers are not unanimous about the utility of an auxiliary wing. Some are of the opinion that the added power that will come from the new engine might make the additional control surfaces superfluous. But the option remains on the table.


  1. More pictures please. Very informative article.

  2. Damn, even a layman like me was enlightened. Very nice explanation. Makes me appreciate both your textbook style narration and the LCA load shedding dilemma. The jag example was fantastic.

  3. good article; luv the progress on the lca. hope you get to visit gtre soon and are able to explain just as clearly on what is going on with kaveri

    once the first squadron of tejas has rolled out, i also expect a detailed 10 part writeup on how we got from zilch to one of the finest light combat aircrafts in the world :)

  4. Hi ajai

    Thanks for the clarification. One more question is the weapon payload 3.5 tonne as per HAL officials? Because till now all HAL presentations show the payload as 4 tonne. ALso whats the weight of the internal fuel carried?

  5. The extra control surface is canards or LEVCONs (Leading Edge Vortex CONtrollers)? Naval LCA is supposed to have LEVCONs, so that is going to come with the Naval prototype. Or is this something else?

  6. is there any a/c in the world where

    i thought the amount of fuel and weapons or extra fuel payload depended on the mission and trade-offs are made...

  7. Sir Thank you to the power 1000+ for all your post on LCA rest i am keeping for LCH.

    Your broadsword is becoming a LCA encyclopedia.

    One Qn. Will 41th LCA have all new air-intake?

  8. More comedy

    First DODO brushed aside the genuine IAF concerns about Airintake and then went to suggest Jaguar airintake example. These shameless DODO guys have the audacity to say it will only have marginal difference. Hell, they don't know what marginal difference is to IAF Pilots --it is life and death, failure of mission or success. But then again we are talking of scam artist disguised as Scientist.

    Weight issue, Ajai, I thought you gave some reason of the incompetence of these buffoons, rather than telemetry equipment. Do you think anyone include the flight instruments necessary for testing in the final weight of the plane??? C'mon you are not writing to junta here, but aviation nuts. It would be better you provide the actual empty weight, rather it come up again when IAF, criticism. Again the dodo-rakshak take ii on IAF, like they do to Army for Arjun.

    Increase control surface, so finally it is dawning on these experts the need for additional control surface- only after 25 years. Great going. take a lemon now we will give the masala after.

  9. Additional control surface like one in EF. It clearly refers to CANARD..........
    WOW LCA-NG is going to come. Great!

  10. Oh oh sweet innocent wishes...

    Alas when you have a new engine, you need new airintake to take care of that, more fuel to satisfy the higher powered engine.......additional control surface........all will essentially be a new plane.

    Do the scam artist pull off succesfully, with the given time and budget? Will it again be another scam TD, PV, LSP stretching for another 2 decade?? each with its own budget..

  11. Hello Shukla ji, thanks for explaining on weight issue. But what distance it will cover when fully loaded(10.5 tons with full fuel+ 2.5 tons of weapons).--- Puneet Shukla

  12. to troll @ 17 July 2008 17:10

    please go crawl back into the dirty hole you came from. maybe the scientists at pakdef can respond to your inane comments.

  13. Ajaiji, thanks for this article. you've clarified something that's been heavily debated on internet fora for a while now..

    But here's another question for you. if the ADA knew that the LCA needed a canard or LEVCON, why did'nt they start working on that earlier? The N-LCA has always had the LEVCON and ADA has known that it adds to the maneuverability of the basic LCA.

    Looking forward to more of your articles of this type on the LCA. Really informative. :)

  14. Won't adding adding additional air intakes increase the RCS? The hinges on these look crude!

  15. Could you please take a tripod with you and use it the next time you take pictures of Tejas. We would all appreciate the increased clarity. Thanks, in advance.

  16. The maximum take-off weight of the Tejas is 13 tons. So if you load the maximum payload of 3.5 tons onto the 10.5 ton fighter, your weight of 14 tons is beyond the maximum take-off weight. So you’ll have to shed one ton… or either internal fuel or external fuel/armaments. That’s what happens when a fighter’s weight goes beyond what was originally planned.

    c'est à ordures, monsieur!

    all aircraft have that sort of trade-off. hardly any modern fighter can take off with a full fuel load at max payload.

    next, you'll hear the iaf complaining about how the tejas cannot pull 9 gs at full payload with full tanks while going supersonic.

  17. too late parikshit, that is already part of the iaf gsqr for lca mk 2 :)

  18. anon @ 17 July 2008 17:10

    i suppose the "life and death" argument doesn't apply when you buy cheap mig-21 spares from bulgaria.

    its only when it comes to drdo that everything becomes a life and death issue. redisgn this, change that, increase this, decrease that... jump through this hoop... no wait.. jump through that one...


  19. Looks like the paki vermin buradiah is still trolling around trying to hide his massive inferiority complex. Go and teach the paki scientists that they can double their share of work in JF-17 blundaar by applying 2 coats of green paint instead of one.

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  22. Hello shukla ji,

    Your article has raised many questions.


    Part - I

    Initial projected/design weight of LCA is 5,500 kg

    The design MTOW of the aircraft from the very beginning has been 13.5 tons. 13 ton MTOW as stated by you is wrong.

    It has been claimed by ADA (during the first flight of PV2) that PV2 weight (5,685 kg) was very close to the initial design weight of 5,500 kg. Later it has been reported that further weight reduction has been achieved.

    Some thing has changed after that which increased the empty weight by 1,000 kg to 6,500 kg by recent Singapore air show.

    (Empty weight + 2 R73 Missiles) 6500 kg + 3,000 kg internal fuel + 1,000 kg for 7 pylons = 10,500 kg (10.5 tons)

    13,500 kg - 10,500 kg = 3,000kg for Weapons/External stores.


    Part - II

    The big question that ADA/HAL needs to be asked is what caused nearly 1000 kg increase in empty weight after the design weight was almost achieved by first flight of PV2 (5,685 kg againest 5,500 kg goal).

    What is the mystery with 1,000 kg additional weight? Is it really increase in empty weight?

    It must also be noted that ADA/HAL has always stated (even during recent Singapore airshow) that LCA payload/external stores is > 4,000 kg.


    Part - III

    I think HAL and ADA are upto some thing here. Why else would thay need a > 95 KN engine for this little bird? I'm guessing that LCA's final configuration will be close to that of Gripen NG.

    I suspect that the MTOW has been increased and will be some where between 14.5 tons and 15.5 tons

    Please correct me if I'm wrong.

  23. Have they considered an inflight refueling probe?

    Would that be relatively "easy" to add?

    That would allow the aircraft to take off with lower fuel..though obviously that will be a limitation...

    Now if only you could get us pictures of the new Frigates being built...

  24. All LCA airframes since PV-1 already have auxillary intakes.

  25. Samudragupta, you'd better tell the LCA's designers that. They don't seem to know it.

  26. Shukla ji,

    What Samudragupta is saying is true. HAL/ADA's PR is at least 2 years behind ground reality in this case.

    The above link has a National Geographic video on LCA which was done some time in mid 2006.

    If you look at the video @ 1:15, 1:45, 2:30 you can clearly see the auxiliary air intake (similar to Jaugar auxillary intake) behind the main intake with three rows of small groves shaped like arrow leading towards the auxiliary air intake.

  27. This comment has been removed by a blog administrator.

  28. Sir
    Can you please give the stated timelines for the induction of the first 40 Tejas in IAF..
    The MiG 35's (these upgraded Mig 29s are most likely to win the tender - political reality) will in all likelihood be inducted by 2015 approx..
    Also, would appreciated if you could write on how would the performance of the Tejas with the 404 as well as new engine compare with the current crop of 4.5 to 5th Generation fighters..

  29. India has Su MKI which is a derivative of Su MK. Su MK did not have canards. IAF wanted canards therefore it was added later to the MKI design. So same can be done for LCA. Chinese Su MKK does not have canards.


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