Thursday 5 June 2014

The Ails of the LCA

Professor Prodyut Kumar Das
Kolkata, June 2014

I wish I had a guinea every time ADA missed out on a Date. I would have been, if not rich, at least well –to-do. I say this because recently, this last December , I think, one of the key figures of the programme- one might say- the Father of the LCA- stating that we would have two LCAs more by March and, if I remember a right- half a dozen before the year is out. The Ides of March have come and gone, “April, the Cruellest of Months” has gone and now even “the Darling Buds of May” have wilted. “June is ready to bust out but nary a sign of them those Airplanes!
It is worrisome when ADA repeatedly fails on dates because these are symptoms of  cluelessness. The highly qualified gentleman in the above paragraph must have had access to the proverbial “Horses Mouth” and yet, not for the first time, he has been hopelessly wrong. Is it really so difficult to predict the future events?
 In India we have a culture of very accurate predictions based on informal methods and folklore. The apparently “stupid” farmer kicking the dust as he chews slowly on a dry rice stalk may predict the Weather quite accurately. The old Crone sitting under the Neem Tree as she berates her newest daughter- in -law will still be able to predict whose Bahu is going to be a Mother -sometimes even before the poor girl herself is aware! Neither the Farmer nor the Crone has any “scientific” qualifications but they still come pretty close to the truth. So why not try applying those techniques on the possible date for the LCA?
Let me say before I begin that I have no access to “inside” facts. I am a very seasoned Engineer and I like machinery. That is all. What I am writing is therefore a construct. Of course ADA may, (out of sheer spite!) come out with a squadron of LCAs by December along with a chorus of well trained mechanics and a well organized stream of spares etc just to prove me wrong. That would be quite nice. In any case if people speaking from the Augean stables are so repeatedly wrong I am in “eminent” company if my here predictions are wrong. Of, course, mark my word; I fear I shall be proved right!
Let me put down the more important tasks remaining for the LCA to get FOC.
a) Opening the full envelope of positive and negative ‘g’
b) weapons firing particularly of the 23 mm GSh.
c) Spin trials
d) Missile Launching.
e) Proving of remaining systems.
Missile Launching: Pakistan managed to jury rig the AIM9 onto the MiG19 in a matter of months there is no reason to expect that the same cannot be done onto the LCA. I am referring only to CCMs. It will be a brave Air Marshal who will refuse the LCA solely because the aeroplane cannot fire BVRs for the moment.
GSh 23 firing.
The problem of gun firing is “old hat”. The Chemistry is Class 9. The gun propellant gases are ingested by the engine and that affects the air fuel ratio as the propellants gases displace the oxygen in the air causing the engine to flame out through “over richness”. This is aggravated by the pulsations of firing which will tend to “blow out the candle”. This is particularly true at high altitudes where the air is “thin” causing both effects to be amplified. The old trick is to “dip” or reduce the fuel to the engine automatically when the gun is fired. In the LCA, a one second burst will release about five kilos of gun gases into a region of inlet flow of 4 kilos of air over the same period at high altitudes. Vibration is of course a problem but the GAST system (look up!) of the GSh 23 means the recoil loads are much less. I do not think the horrible memories of the HF24 -where I still believe the concerned German Engineer probably put a “bug” into the design- will be repeated here, especially if ADA has had the wit to use the forged aluminum cradle or its derivative the MiG Bureau used for the MiG 21M’s mounting.
240 AOA
This is the old Phantom joke now gone sour. I would like to meet the person who will refuse the LCA simply because the aircraft won’t do 240.
Proving of remaining systems
Thirteen years after the first flight there would be very few things that require major tweaks so there is very little that remains to be done.
Does that mean then we can see a FOC by December and a steady stream of LCAs from 2015. No, definitely not, because I guess the Mk1 is still a ”lemon”. It is not combat worthy. I am on shaky grounds here because I am making the previous statement entirely on what is available in “open source”. The LCA was “officially” declared to be about 1300 kilos overweight by ADA. Subsequently there has not been any announcement about the weight being corrected. Certainly the weight correction would have been noised about. If you have “inside” confirmation that the basic empty weight of the LCA is around 5100 kilos don’t read the remaining portion because everything written below is then irrelevant.
Why is weight important?
Airframes will tolerate a fair amount of abuse but they cannot tolerate excess weight. Let us take the MiG 21 Bison. Despite its age it is still relevantly “sprightly” as Cope India showed. The MiG 21 is of the same thrust to weight class as the LCA. Now imagine we poured in 1300 kilos of lead (Plumbum!) into the airframe. Immediately all critical parameters- take off run, acceleration, climb rate, radius of turn, range, ceiling and top speed will fall below current designed figures. In short the MiG 21 will not be fit to fight. In summer thrust and lift reduces by about ten percent and things would be worse! Exactly the same is happening to the LCA. Until the weight has been corrected the aircraft cannot even complete its flight test programme. My Farmer’s guess is that ADA should have an airframe weight of around 2300 kilos and an undercarriage weight of around 300 kilos to come out shouting winners. Mention has been made of the LCA requiring ballast. Aeroplanes sometime require ballast to get the CG right. The HF 24 needed 134 kilos about 2 % percent of the basic empty weight. This was in the days of wooden slide rules but evidently someone cared. How much ballast does the LCA need? Given the use of CAD it should perhaps be no more than half that figure.
“Opening up the envelope”.
This cannot happen safely because the “g”s to be applied requires acceleration and lift. Unfortunately lift means drag particularly in AR Deltas whose induced drag is almost double of comparable swept wings. Given the combination of excess mass and drag the F 404 just may not have enough “urge” to pull the little aircraft around a turn at 8.5 G i.e. the aircraft is power limited and lift limited to pull the required “Gs”. One could of course dive the aircraft and do pull ups but I think it would be a pointless exercise because one would have to do it again when the definitive airframe is available.
Spin Trials.
This is also held up because of weight. A spin is a combination of a stall and a turn at low airspeeds. The aircraft sinks because of the stall and it yaws and rolls (slowly) because of differential lift and drag caused by the different airflows due to the turn over the two wing panels. The forces at play are the above aerodynamics loads and the inertia of the aircraft which depends on the weight of the aircraft. Given these basics the LCA will be reluctant to spin because the Delta wing is usually difficult to stall. Given the excess weight/ inertia it will take a long time to stabilize the spin. Height loss in recovery will be “interesting”. It may be recalled that the Mc Donnell Phantom II was so difficult in spin recovery that if the crew had not recovered from the spin by 10,000 feet the drill was to eject. Well that is a precedent anyway!
So unless you have tackled the weight you can’t do the spin trials. What happens to the FOC? Please do try and not have FOC 1,2 etc.
Intake Problems
There have been persistent reports of “intake matching” problems. What happens is the take off requirements of the intake are in direct contradiction to those required in transonic flight. You either accept poor take off and climb or face high spillage drag and engine surge at transonic speed. The solution is conceptually and mechanically very simple. Aeromodellers flying ducted fan models (PE Norman’s ducted fan MiG 15 of happy memory!) used them. We used to call them “cheat intakes”) .Spring loaded “blow in” and “dump out” doors are generally used. Even the dear old Hunter of Good Queen Victoria’s times (well, almost!) had them. You could see them on the wing intake lips. As I write about this I realize that I have not seen any photos of such doors yet on the LCA . Perhaps some reader can post?
Aerodynamics
I have elsewhere mentioned that the LCA is aerodynamically blunt, its comparable equivalents being almost a meter longer. Any Aerophile will remind you the Douglas A4M with the 10% more power was actually 0.1 Mach slower than the less well powered Hunter Mk6 which had a longer fuselage and better entry Supersonic wave drag depends on the maximum cross sectional area and its position along the longitudinal axis as well as the entry aerodynamics i.e. from the radome tip to somewhere behind the rear cockpit bulkhead. ADA needs to go over the contour and the cross section centimeter by centimeter. I am not exaggerating because it is so easy to end up with excess weight and wetted area if one becomes too enthusiastic. It is not for me to dare suggest but for God’s sake use some “feel” along with the Analysis.
Maximum speed.
My betters have said that the aircraft has reached Mach 1.4 -(or was it Mach 1.6?).). Sorry, Guv’nor but the facts don’t tie up! We seem to have on our hands an overweight aeroplane that is significantly stubby and has inlet problems and yet it reaches its design speeds? Cap in hand, with fingers touching my forelocks (Alas! Long gone to happy hunting grounds!), I would say no, Sors, this bain’t true! What may have happened is that the claimed speed has been achieved in a dive of around 300.
The Prognosis
Common sense is that if the LCA Mk1 is reasonably well designed it should be in the same class as the early Gripens i.e. definitely superior as a replacement to the early Mig 21s which have begun to retire. The LCA Mk1 should be clear for super priority production. Somehow that is not happening and, going by precedent- not going to happen. The horrible suspicion is that we will see only “token” numbers of the LCA Mk1on v pretexts of manufacturing difficulties etc as a rearguard action until, hopefully, the LCA mk2- which will be an almost new airframe design, - is ready. We will, of course be relying on an organization, which could not correct an overweight problem it itself acknowledged in near twenty years (1996-2013). I am so glad I am not the Air Chief!
The interest expressed by the IAF in the AJTs is perhaps a corroboration of the above. The YAK 132 is a fairly useful LCA if you look at it carefully and indicates how little was actually wanted by the customer before ADA went gaga over Technology. Reminds one of Tacticus who had said so long ago “The enthusiasm for war is highest amongst those who have the least experience of it”. Replace “war” with “Technology” and you have the gist of the situation.

Prodyut Das
Professor.



Prodyut Kumar Das is an Alumnus of St.Xaviers’ Hazaribagh, IIT Kharagpur, and IIM Kolkata. He started his career with Aircraft Design Bureau HAL and for twenty years worked and led various vehicle related Product Development Projects with leading Indian and multi National Companies.
He left Industry to join IIT Kanpur in 1993 as a Professor in the Department of Mechanical Engineering. There he won a prize of the Royal Aeronautical Society of UK for his design of a light sports aeroplane using grants given by ARDB. He also did a project study on “The design of a Light Car costing less than 1 Lakh” which was a Ministry of HRD funded project IDICM 36 and started his research on Stirling Engines in which the IN was keen.
When IIT Kanpur did not renew his 5 year tenure he returned to the  Industry as a Vice President Technical and finally retired as Advisor Aerospace in the e- Engineering Division of a Leading Indian Engineering Company.

He currently teaches Engineering in a Private Engineering College in his hometown and continues his Research as a Consultant. He has been writing on matters related to Defence Engineering since 1990s.

25 comments:

  1. Just want to comment on your portion with "Intake Problems". LCA does look like having spring loaded blow-in doors like Jaguar. Please refer the take off photograph below.

    http://defenceforumindia.com/jh4cz/assets/LCA-Tejas-10.jpg

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    1. Thanks. Seen. If the reports are right then perhaps they need enlargement.
      Thanks,once again.

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  2. The R-73 has been test fired from the LCA several times

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  3. Mr Das,

    Typhoon's fuselage length is 15.96 meter. rafale's fuselage length is 15.27 meter. Applying the same analogy you applied for tejas vs gripen, Do you think IAF selected a lemon as MMRCA winner because rafale is aerodynamically blunt compared to its contemporary Typhhon?

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  4. BARC: Bhabha Atomic Research Center: Computer Division[68]
    ANUPAM-860/16 Node parallel processor, used for CFD work related to LCA engine intakes
    Other versions of ANUPAM/16 Node (ex. ANUPAM-Pentium/16) are under development. This is a significant contribution to evolving field of Parallel Processing applications.

    Do you think that people at BARC gave a wrong CFD enabled design for ADA?

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    1. CFD will work only if you put in suitable"windage" factors. Was that done?
      I do not know

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  5. Tejas's s contemporary gripen C which is 300 Kg more empty weight than tejas. So it too must be too heavy and should perform poorer than tejas considering it has an engine which gives 4 Kn lesser thrust than tejas while also being 300 kg overweight in its gripen C/D airframe. Is it true?

    So what about gripen C/D's claim of mach 1.8 and supersonic at sea level?Is it correct or not?

    Also the release to service document of tejas mk-1 at IOC-2 says tejas has achieved 24 deg AOA till now within the 80 percent opened flight envelope.

    It also says supersonic at all altitudes. but you are saying it is supersonic only in dives. So what is the meaning of ADA's claim supersonic at all altitudes?

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    1. I will normally not reply to "Unknown" commentators.
      One enduring confusion is that SAAB Gripen weight is the operational empty weight. The LCa's is the basic empty weight. B
      But that is missing or obfuscating the point on which I hinge my doubt.
      The LCA, by ADA's own admission is 1300 kilos overweight.
      My simple contention is that an aeroplane that is 20% over the design weight CANNOT achieve Design performance. QED.

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  6. If a 6.8 ton empty weight 80 Kn engine Gripen C can achieve supersonic speed at sea level, why couldn't 6.5 ton empty weight 84 kn engine tejas mk-1 achieve supersonic speeds of mach 1.6 and mach 1.1 at sea leve(achieved while pulling out of a powerless(not powered dive) dive from 4 km to sea level altitude during flutter test in hot goan skies )

    Also ADA has stated record in their website that tejas was modelled on F-16 XL with a vortex generating compound delta design instead of canard delta design with a view of reducing weight and having far lower wing loading for high altitude operations from himalayan forward bases.

    they stated that they chose the compound delta design after it was conclusively proved in wind tunnel tests that canard delta design has not given them any agility advantage considering the weight penalty it imposed.

    is it wrong or right?

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  7. Well No offence sir!!!I respect your knowledge and but you need to update yourself with latest happening in LCA. Now you are saying it is supersonic only in dives,that I must say is pure BS. When LCA navy can goes supersonic on hot goan sea with weight 400-500kg more than airforce version then how come you say that? http://www.dnaindia.com/india/report-light-combat-aircraft-navy-goes-super-sonic-1978347
    C'mon LCA fired dozens of R73 in trails and even in IRON fist exercise,it shows it swing rolecapbality with droping LGB,fired R73 and shoots chaff and flare,all within 50 secs.

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    1. I am a little sceptical about the ADA's claims on the speeds for reasons given in the article. I also did a fuel burn analysis and certainly the aircraft would be fuel limited if it has to be back over base with enough fuel for a diversion of 70-80 n.m.,overshoot and landing.

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    2. Now you are sceptical Sir. You are ignoring plethora of media reporting and ADA june newsletter where they said that LCA Navy Crossed important milestone for going Supersonic over Goan sea.You are comparing Fuel burn analysis but you ignored simple things that LCA tejas touched transonic in 2013 AERO India in matter of few seconds.While the Engine you are talking about is same as Gripen Engine however its more powerful and efficient then RM 12.

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  8. Basic empty weight of gripen C is given as 6250 Kg in the following link.

    http://indiandefence.com/threads/saab-gripen-news-and-discussions.18472/page-29.

    tejas mk-1 comes in at 6500 Kg. So the difference is just 250 Kg. And Tejas has a significantly larger wing area and more volume for internal fuel.

    SO there tejas mk-1 weighs just 250 Kg more than its very successful contemporary (just around 4 percent more), but has an engine that is 5 percent more powerful than gripen C. SO on the whole no reason to call it a heavy obsolete design that wont meet the specs.

    For that 250 Ke extra basic empty weight it has a higher wing area giving it an advantageous lower wing loading which will help in Instantaneous turn regime.

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  9. The Thrust to weight ratios of gripen C and its contemporary tejas mk-1 in half fuel internal fuel weight and with just two close WVR missiles config are almost the same(both in the 1.07 region, if I am right).

    So tejas mk-1 performance wont fall significantly from gripen C performance on the reason of weight alone. Tejas mk-1 has a max take off weight of 13.2 tons where the engine thrust and lift drops close to 12 percent as per your old estimate.

    Gripen C whose max take off is given as 14 tons is for cold climate conditions. So it wont lift as much in indian hot climate conditions based on your estimate. So tejas mk-1 doesnot compare unfavourably with its contemporary Gripen C.

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  10. Please give us the operational and basic empty weight of both tejas mk-1 and gripen C. It will clear lot of things,

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    1. The basic empty weight of the Gripen C is 5650 kg as per William Green which is pretty near what ADA was trying to achieve for the LCA with 5500 kg. Gordon Swanborough puts the operational empty weight at 6622 kgs. The two figures can be reconciled by the fact that Green was talking about the "LSP" Gripens and some more equipment went on board -say about 200-250 kilos at most- on the definitive Gripen C which would have an empty weight of 5800-5900 kgs. All other sources I have seen just put empty weight at 6622 without specifying what type of empty weight it is.Getting back, The rest was due to all the other stuff that goes to make aircraft operational including the unusable fuel that an aircraft must have when it is coming in to land should it be required to fly to another airfield ,carry out an overshoot and land and taxi back.
      But to get back: The basic question is : Is the LCA overweight by 1300 kilos? If so then it cannot meet TO, range , climb, turn rate and acceleration and top speed parameters.

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  11. sir, i hope as an ex-HAL ADB man you might be following HJT-36 program. what do you think about the stall spin recovery problem as per press reports? Does this a/c has some inherent flaw in the design? is it correctable? pleaseg ive your valuable comments. Regards!!!

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  12. The empty weight of tejas as mentioned in IOC is 6.8 tons.

    It must be operational empty weight.

    because internal fuel is close to 2.7 tons. take off clean includes 2 R-73 missiles with pylons, which comes close to 200 Kg. And the ammo and other misc stores can come close to 300 KG. Adding 2.7+0.2+0.3=3.3 tons approx.

    Take off clean weight is mentioned as 9.8 tons.

    SO 6.5 + 3.3 =9.8 tons.

    These are the weight figures for early LCA prototype,

    TD-1 ------ 6,780 kg with Flight Test Instrumentation
    TD-2 ------ 6,670 kg with Flight Test Instrumentation
    PV-1 ------- 6,430kg (reduced 350kg of weight, with with Flight Test Instrumentation)

    These figures are for the weight reduction effort carried out by ADA from an earlier article called Radiance of tejas by B. harry.

    So by all evidence the 6.8 tons must be operational empty weight.

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  13. http://ajaishukla.blogspot.in/2008/07/concluding-part-of-two-part-series-on.html

    According to the above interviwe of Ajai Shukla's with HAL people,

    this flight test equipment weighs around 300 to 400 Kg. And in the same article it was clearly mentioned that further redesign of avionic mounts can shave off another 300 Kg weight.

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  14. http://ajaishukla.blogspot.in/2008/07/concluding-part-of-two-part-series-on.html

    The 10.5 tons 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.

    SO if we add 3.5 tons of weapon load it will come to 14 tons and exceed the 13.2 ton mtow.

    So this 700 Kg weight reduction with removal of telemetry instruments (400 Kg) + redesigning of display subsystems will bring down the weight of tejas(with full fuel on board; all 7 pylons fitted but not carrying weapons; and two outboard missiles being carried) to 9.8 tons,

    Which is what mentioned as take of clean by ADA in IOC. SO 9.8-3.3(fuel 2.6 tons+ seven pylons with two R-73 missiles on outboard pylons 400 Kg+misc stores like ammo 300 Kg) gives us an operational empty weight of close to 6.8 tons.

    So by all available evidence the excess empty weight must have been rationalized and now the operational empty weight must be around 6.8 tons as declared by ADA.

    SO please check with HAL and ADA and clarify. thanks.

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  15. http://ajaishukla.blogspot.in/2008/07/concluding-part-of-two-part-series-on.html

    Tejas weighs 10.5 tons with all seven pylons fitted, two outboard pylons carrying two R-73 missiles with full internal fuel and ammo loaded in take off clean.

    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.

    SO 10.5 ton-700 Kg= 9.8 tons is what was given by ADA in IOC releases.

    Fuel -2.65 tons,
    allseven pylons +2 R-73 missiles =400 Kgs(approx)
    Ammo+ misc stores=300 Kg. Total= 3.3 tons.

    So clean config take off weight 9.8 tons- 3.3 tons = 6.8 tons.It could only be operational empty weight and not basic empty weight.

    It

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  16. Prof. Pradyut Das
    Have you conducted any study regarding suitability of the Saturn AL-41F-1S engine on a modified LCA Tejas airframe? What is you take in this case?

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