The Kaveri Turbofan Project - an “open source” Assessment

If reports that the Kaveri has reached 90% of its Full Military power are true it represents a considerable achievement for the Engineers concerned. It also indicates no foreign collaboration is required to complete this project. The above numerator is unfortunately tarnished by the denominator of several decades of development with no engine flight cleared and a realistic date of completion is uncertain. Jet Engines development presupposes certain facilities as sine quo non: a) Test rigs for combustion chamber development   b) Test rigs for testing the compressor spools together at rated conditions, c) test rigs for testing the turbine blading for cooling, thermal and mechanical loads simultaneously and finally d) a flight test bed to test the engine in the air. Item d) is still not available in the country and there are reasons to believe that items a), b, c) were not available at the time of taking up the project and may not in fact be satisfactorily available even now. Recall that Egypt, developing the E300 engine under the guidance of Ferdinand Brandner, with much poorer traditions and resources, had a flying test bed , a modified AN12, in 1964,.

The lack of these basic test rigs and their exploitation would have had a significant effect on the programme. The present “problems” with the engine – lack of performance, unreliability and overweight can be traced directly to the lack of the above test rigs and indicates a lack of top leadership at the front line of problems. It was “disconnected thinking”, in 1987, to so confidently say that our engine would be “flat rated”. The basic tools needed for the job was nowhere there. The relatively low total running hours (< 2000hrs for the entire programme spread over about ten engines) would mean that the infantile “measles and mumps” kind of problems have not yet been exposed. If the engine hours are correct, it was surely premature to have air tested the engine in 2003 when it, quite expectedly, failed. “A part of the learning process” is not an adequate explanation for this kind of repeated self induced “failure”. The failure delayed the project and should not have been done at that point of time. I recall a former Director, in discussing the Kaveri pressure ratio, admitting privately “Yes. We did over reach ourselves”. He was being modest! The fault, dear Brutus, is in our stars! Pratt & Whitney (P&W) was not allowed to do Jet Engine work because of the War. GE was clearly ahead. Immediately after, in 1945 itself, P&W set up a Turbine Laboratory (WTL). Note that they named this critical survival asset after their Chief Engineer Andrew Wilgoos and not after Rentschler, their Founder & Chairman!)  WTL was fully integrated into P&Ws mission to be a prime player rivaling GE and had the skill and resources of P&W on tap. We set up GTRE but it was a completely different entity vis a vis HAL in terms of aims, service conditions and critical performance parameters. Yet GTRE was supposed to depend on HAL. We do things right but don’t or cannot do the right things! Even given the best of intentions results would be what they are.

The Good news is that an engine that is giving 90% of its cold thrust cannot be all that bad. The engineers who can achieve that also cannot be bad. What has been lacking has been the leadership over several “generations” of higher management. We will come to this point later. The Kaveri does not want more technology. It needs more care and analysis. Jet engines, though inherently simple, are extremely sensitive to detail as the following examples will illustrate. “Point one millimetre” (‘four thou’ if you are that old!) is the general unspecified tolerance in aerospace machinery. It is the average thickness of human hair. If the gap between the rotating blades and the casing varies by this “point one “ millimeter in a Kaveri sized engine it means a difference in the turbine tip/casing flow area of about the size of a 20mm hole. Imagine the differences in flows if you are dealing with pressures of around 20 bars! If the clearance is that amount too little, you will soon get very expensive sounds, blades being shed and possibly an engine fire. The tip clearance is a decider for TBOs. The current technique is to remotely sense the tip clearance and heat or cool the casing locally to keep the clearance constant. No wonder the grudgingly respected Chinese engineers still manage to stir fry their new engines with some regularity! The same “thickness” or (thinness, if you will!) in the engine casing will vary the weight of the engine by approximately 5-8 kg and an increase or decrease in engine length by about ten millimeter will affect engine weight by about 4 to 5 kgs due to casing and shaft weights. Of course a 0.1 mm variation in blade profile is unthinkable.  I cite these figures to show the “gearing” between cause and effect in Jet engine development and the need to go over details, components and results with a fine comb -and an engineering Sherlock Holmes by your side!

However creditable the performance of the “troops” the present situation reflects on the higher direction of the programme.  There are two management issues involved. The first was to undertake the project without having the physical resources ready. Everything is always wanted yesterday. It appears the then leaders, (assuming they knew clearly what was involved) either wanted to “make someone happy” or wanted the project “at any cost”. Honesty about the situation-so disdained by the “clever”-   is an essential requirement –and a mark of leadership. In 1962 Lt. Gen Kaul, by acceding to political pressure gave us the Himalayan Blunder .Nine years later Sam Manekshaw by stubbornly (but charmingly!) refusing to move until he was ready, delivered Bangladesh! The second area of failure of Leadership was a failure of knowledge. There was a lack perhaps of a holistic view of what the engine was supposed to do. They apparently wanted an engine “just like the F404” rather than thinking more systemically about an adequate engine which would do the job. By these two fatal lacunae-one physical and the other mental- GTRE fell into “mission impossible” mode.

Rebooting our mindset

Let us look at the above in a bit more detail. Modern Western Military engines are, perhaps surprisingly, strongly injected with technologies developed for competing in the civilian markets. It makes sense for the West to use these thoroughly proven technologies in their military programmes- it helps to amortize costs! An opposite corollary was the USSR where Technology Development was always led by Military requirements and USSR civil engines were the dregs in terms of Sfc and TBO!  For a civilian engine a TBO of 4000 hrs is “essential”. The plane flies fourteen hours per day. One cannot yank the engine off the pylon every 6 weeks as a R29B style of 550 hour TBO would entail. Every gram of fuel saved per hour is of consequence given the huge number of hours flown per year. This entails engines having compression ratio s of 20:1 to 30:1 with current research exploring 70:1. (Want to play catch up with the Technology, any one!) One could go on but the drift is that before we follow someone’s lead we have to stop and think of our task and the cloth we have for our coat. What are these?

a)    Slash the engine ‘to begin with’ TBO to around 400-500 hours .Insist the Air Force declare what is their attrition rate for single engine close support fighters. I know we lost about 30 Hunters out of 96 active in the six squadrons in the nine years between inductions to just before the ’65 war. Very few if any of these could have approached 1000 hours. It would be interesting to have a histogram of the number of engine hours of all the MiG 21s at the time of their write off. If this figure is pretty low as I suspect it to be, there is no need to make a 2000 TBO or 4000hr technical life an immediate target. A 250 hrs TB0 (Incoming! Incoming! Duck! Duck!) would last a couple of years on a fighter airframe. Reduction of TBO time will significantly reduce the development task without affecting the operational efficiency. The ‘problem” of low TBO-replacing engines- can be ameliorated by designing for easy installation and removal. In the Mig 15 two men could do it in one hour!  Engines are more “plumbed” nowadays but that is where the challenge of good engineering comes in! Incidentally, an Indian Engine built with Indian materials in Indian factories would be formidably competitive against all comers even with these low TBOs and TTLs.

b)    Do we really need 20:1 CRs (compression ratio) given the engine becomes heavier and more surge prone as we jack up the CR? Higher CRs mean more stages and the compressor and combustor casings being open ended pressure vessels, mostly in heavy alloys add much to the weight. Remember that a 0.1 mm thicker casing will add 8 kg to the weight! We know the benefits of high compression ratios are subjected to diminishing returns. The Orpheus with a CR of 6:1had a sfc  1.03, the R 25 had a CR of 12:1 and had a sfc of 0.9 and an engine with 20:1 CR will have an sfc of around 0.8. This “high compression ratio” led improvement in sfc does not pay in our typical low duration sorties. For an IAF standard fighter sortie the weight of engine plus fuel required (for the same level of technology in other areas) disfavours the high compression engine. Also because the compressor passage areas are fixed, the resistance to compressor flows at part throttle (where the wretched engine will be spending most of its life, anyway!) the proneness to surging will cause problems. Finally to remember is that high CRs in themselves are a partial contributor to the sfc figures. Burners, combustor and turbine blade technology being the others.

c)      Are we worrying too much about smoke and NOx? Western “standards” are again derived from already existing and already proven and available low risk “Civilian” technology which we do not have. A short combustor means a lighter engine because the shaft and casing becomes shorter. Shorter combustors will require focused research on getting the spray pattern “tighter” in the spread of droplet size. How much work has been done in this area before we set our targets?

d)      Western aircraft design philosophy believes that VG intakes don’t make sense below M1.3. Our designers follow the same track. This, I believe, is a “frozen” thought from the ‘60s and the days of electromechanical sensors and actuators. Given developments in sensor technology  and computer controls we should look at new variable geometry intake configurations to maximize pressure recovery. Even if we can save the equivalent of one or two stages on the compressor it would help in reducing the length of compressor, ergo a lighter engine.

e)      Also to be examined is the total thrust /fuel flow requirement profile and optimize the engine’s weight and fuel consumption in relation to the task. A typical LCA type engine will have the following profile. A/B thrust approx 2⅟2-3 minutes, Full military 6 minutes, 60% thrust 20 minutes, 45% thrust 25 minutes, and flight idle about 5 minutes. The figures are illustrative but the idea that we must reduce the Total fuel burn/sortie rather than optimize for a rarely used “best” figure. The intake, the engine and the afterburner   together have to be seen as a system which will give optimum performance in the 0.6-o.8M at low level with all other conditions being seen as “special” cases for the system.

f)       A consequent question to the point made above is given that relatively small duration of operation of the max. Installed thrust how much of the thrust should come from the engine and how much from the A/B? The Tyumanskii/Gavrilov R 25  of the MiG 21bis is an example of alternative thinking. The dry thrust is 59kN, with A/b it is 69kN but with a “boosted” a/b it gives 97kN (from Russian sources!) which thrust wise would be ample even for the LCA! The use of the boosted A/b reduced engine life at the rate of one hour per three minutes but it works! Anyway as said before a “totally Indian engine” will be cheaper.

There are several more such issues but the point I am trying to make is that we have to see the task not as an engine “just like” something else, as I suspect, had been done. Let us move from mere Information to Knowledge and, hopefully, from Knowledge to Wisdom! GTRE   hamstrung itself by trying a “drop fit” replacement for the F404. The saner approach would have been to have a dialogue with ADA so that ADA would be prepared to “rebore” (Not, please, literally as one irate reader seemed to think!) the LCA airframe to accept the slightly different engine.  We must therefore come to a state of mind where we read the book and then throw it away to chart our own course. So what needs to be done?

If you have ten hours to chop a tree…

Spend nine sharpening your axe! Build up and “sophisticate” our test rigs so that the key problems can be solved in detail. For example the test rig for the turbine blade should not only be able to handle a mass flow of around  5kg/sec @ 1400⁰ C- for a cascade of four or five blades but also will be able to simulate the creep loads on the blade whilst a separate air source will  supply cooling air through the internal passages. Similarly for the compressor test rigs it is necessary to have rigs powerful enough to test the two spools together irrespective of what may be the practice in other countries. A short combustion chamber will need research on droplet uniformity, spray pattern, burner types and configurations. Turbulence and uniformity of temperature at Turbine entry are other areas to study. The test rigs help to break down the problem before synthesizing the solution. These test rigs are the axes for the problem and in future we must emphasize test rigs and their roles in any project. Normally the evolution, design, fabrication, and operation of productive test rigs will require the same quality of ingenuity and good engineering as the engine itself.

The obvious thing to do-don’t!
Perhaps there is a need to review the Jet engine programme as a “National” programme rather than a DRDO baby. No single organization can do the job alone. In England Bristol Engines starting Jet development from scratch but let Lucas focus on the critical fuel systems and combustion. Team work has to be enforced by getting GTRE back to what it really was set up to do and HAL has to be forced to pick up “GTRE’s baby” and bring it up to some state of civil behaviour. It is possible that a team of HAL ‘s best designers and fitters from Koraput and Engine Division are transferred to lead the Kaveri programme. Unfortunately, whilst administratively such action is possible it won’t work in peacetime. Internal priorities would change; the organizations concerned would become creative. We would see tribal warfare the Pathans would relish! As things stand GTRE must find a way out from the difficulties it has created for itself!

What ails thee Knight?

Over the decades our betters have replaced in our Engineering colleges “practice based” engineering with “science based” engineering-even at the undergraduate level!  Consequently GTRE, as with other scientific research establishments in India, has unquestioningly adopted the rather large assumption that possession of an engineering degree confers the abilities of an engineer to the holder. The natural consequence of this assumption is that the more the degree the more the “qualification” of the person to take engineering decisions -never mind that one of the most esteemed and successful engineering leaders in the country, who has unfailingly delivered, Mr. E Sreedharan of Pamban Bridge, Delhi Metro et al ( the list be long!) is a “mere” B.E. The reality is that Engineering is a practioner’s   art and the “qualification”- irrespective of its degree -is merely a license to enter the area.  Possibly, as in education, in selecting “leaders”, possessions of qualifications have outweighed other parameters. The result is a lack of engineering leaders who enjoy being “at the front”.  I could cite several examples (looking back, quite amusing!) of the effect of lack senior “engineering leadership at the “frontline” .That will have to wait. However I will give an “unrelated” example. Rommel won his battles often with inferior forces, because he had much more direct knowledge of the tactical situation “real time” and was personally judging the situation with his great experience and technical skills-apparently he was an IC engine “nut”-rather than relying on what some inexperienced Feldwebel thought of the situation. This undistorted, experienced, assessment of realties came from being right at the front when his opponents were at their HQ way back from the action. How many “Top” Scientist work side by side with the fitters? The administrative problem is that passionate engineers often tend to be “enfants terrible” of the organization and are often ACR’d  ( quite validly, depending on your priorities!) “Not quite mature” or “good but simple minded”! The net result of all this is that GTRE probably has excellent administrators- and they are also needed -but it does not have excellent practical engineers who can calmly “think things through” and yet have the authority to get thing s done.

There be hope yet…

Despite the clouds above the situation is ripe for rapid rectification which should enable us to have- without foreign collaboration- a flight cleared engine within a predictable and short time scale Foreign collaboration, if available, may not hurt but I believe the here the demand for collaboration is a  bureaucratic “failsafe” decision; no one can be blamed. It is this lack of “the right stuff” – people who will work on the engine rather than eat their dinner-which is why we are where we are at present. Instead of commercial collaboration what we can do is however is to get retired engine designers over as a Teacher or a guide. The Chinese not only regularly had Hooker over as an honoured Guest they also had Ferdinand Brandner over as a Professor in their top University.  I don’t think Brandner simply taught the prescribed course! The other reason for rejecting foreign collaboration for the Kaveri is the nature of the present need. The answer to the Kaveri’s performance problems cannot be yet more technology-there is no magic in Technology- but more care and thought and listening to what the engine is trying to tell us- yes it talks! Assuming the basic design (barring, apparently the A/B) was sound, what is needed is a hundred small improvements - improving the surface finish of the compressor casing bore or the blades, working on cleaning up flows near the roots, stressing the components down to closer margins, tightening technology processes and so on rather than introducing “blisks” or “shrouded blading” or SCBs which everyone seems to talk about. We put in certain Technology. It was put in to do a job. Why is it not then doing it? It is here that GTRE is, by its charter, subtly handicapped. Being a R&D set up it does not have those seasoned practiced people whose hands can “read “the engine even with their eyes closed. A R&D organization, anywhere on the Globe will not have the skills common in a production unit. 

Cutting your coat

We need to:

i)                    Enter into a dialogue with the customer about TBO, engine change procedures, TTL et al.
ii)                   Back off from trying to build something “same as the GE F XYZ”. It is not necessary or even the best solution.  The Airframe boys should be ready to rebore their fuselage. Everyone does it all the time.
iii)                 Flog the engines on the test beds even if they are developing no more thrust than kerosene stove. If 550 hrs TBO is technical target one would expect 5500 hours on a batch of ten engines anyway. That way at least the infantile mechanical problems are exposed and can be corrected.
iv)      Prioritize the acquisition of more than one flying test bed. Do you know Harry Folland’s last design was a large test bed to test the 2000 hp class Bristol engines that were supposed to be coming up in the 40s. A large simple multi engine aircraft an enlarged Canberra using the AL31 would be a lovely project for “people building”.

If we were to do it again
In future the task has to be bifurcated with GTRE contributing by providing experimental data and HAL Engine plant doing all the nitty gritty mechanical detail design stuff in which HAL is arguably, by far and away is better placed to do. Let me illustrate by one example: The Kaveri accessories drives gear box. HAL Helicopter Division has years of experience designing and making lightweight gear boxes for helicopters. For reasons possibly of “unease with HAL”, ADA gave the contract to CVRDE, a sister organization but with no aerospace collaboration and no direct access to the technology. My bet is that HAL Helicopter Division would have given a better gearbox in shorter time simply because the HAL’s supply chains of know how, information, machinery and process technology  and human resources were shorter than CVRDE. With every “license manufacture” agreement comes  a wealth of information- materials, processes, heat treatments, machining methods, testing methods and parameters, even how and where to mark the part no and how to store the part. Over the years, at HAL this “know how” has been subconsciously processed into Know why. To CVRDE it would be new territory.  The difference may or may not have been much but “look after the days and the years will look after themselves”.  This is why RAE and it’s cousins at AMES or Zhukovsky do not design engines and aircraft.

What are the areas on which DRDO/GTRE is particularly well equipped to focus on and what will be necessary for us to develop for a future Indian Engine programme?

1)      Carbon fibre fan casings: TETs, engine efficiencies and thrust are in symbiosis. Given modern TETs a pure jet is no longer efficient and some degree of bypass is inescapable. The fan shroud operating at relatively low pressures and temperatures is an ideal case for (carbon) composites. DRDOs appropriate unit should develop expertise on fabricating and proving fan shrouds of approximate 900mm dia. and capable of handling pressures of 2-5 bars.

2)      Short Length combustors: Excellence in combustion is a key to fuel efficiencies and light weights. GTRE must focus on a target of the shortest combustor length. Dual spray nozzles optimized for cruise and max thrust as used in modern civilian engines may be explored if found imperative.

3)      Compressor Aerofoils: The R11 achieved a 9:1 compression ratio using just six stages with consequent savings in weight. Could this be “the starting block” for a new development programme aimed at high pr. rise per stage with stable operations?

4)      Carbon fibre fans capable of sustaining bird hits.

5)      Turbine cooling technology: GTRE must further improve its capability to simulate actual working conditions faced by turbine blades.

6)      Production technology for precision cast “ready to use” turbine blades.

7)      Expansible thermal coatings to minimize “heat losses” through compressor casings.

8)      Technology for “milling” combustor surfaces to very close limits.

9)      Fan gearing systems. The future engines will all be geared so that the fan drive turbine can run at its happiest speed. This will give us useful freedom in fan design.

10)   Blisks. The Centrifugal Compressors, carved from an aluminum “cheese”, was an early form of Blisk. If HAL has the Goblin compressors process sheets these could be the starting point for our “Blisk” programme. Why not give HAL the contract?

It is tempting to suggest that the actual bench testing should be done by a different and independent group. Honda used to test all their engines at a different and independent test site. This is merely good Industrial practice and should be worth replicating here.

The flying test bed is of course an imperative. “Outsourcing” this function is simply not on. Apart from the problem of logistics there is also the subtle question of security of the engine itself when abroad. Countries adopt or build their own special aircraft for acting as a flying test bed. It is just a pipedream that if a few airworthy C119G airframes were available today one could toy with the idea of an interim test bed for the Kaveri! The old thing was configurationally ideal for a test bed. Of course an “enlarged” Canberra (ref “The Haft of the Spear” Vayu) would be another option. These would be simple aeroplanes capable of being designed, built and maintained by simple people and would need a simple budget!

With such a list of activities to do GTRE would be busy and happy. I am reminded of the fact that TsAGI “discovered” that the tailed delta configuration was the best layout for the supersonic combat role and such was the quality and reliability of its findings that both Mikoyan and Sukhoi   OKBs were not too proud to rely on Ts AGI data for the MiG 21 and Su9 aircraft plan forms. Perhaps the proud traditions of high quality fundamental research continue till today; the similarity of aerodynamic layout of the Su 27 and the MiG 29 is no coincidence.

Give unto Caesar….

We must give unto HAL that the logical house for development of actual engines is HAL Engine Division. The reason is that they are organized, experienced and their supply chains are shorter. What then will they do? For my money they should engage in the development of three “core” engines using not tomorrow’s technology, not today’s technology but yesterday’s technology. By yesterday’s technology I mean technology that has been in production at HAL BLR or KPT for the last five years at least and we are all exposed to it thoroughly. The three cores will be of sizes 10kN, 25 kN and 60kN. They should all be single shaft turbojets and the stress will be on timeliness, reliability and technology security above all the other necessary aims. It is a sedulous myth that advanced features “teach”. If advanced features are a cause of such delay as enabling the proposer (s) to retire without delivering, then “advanced features” is de facto an accessory to a swindle. Maximum stress will be put on using  Midhani materials. The Orpheus, the work of a Master, has a few interesting features which could be replicated. The shaft is a thin walled large diameter tube; it easily permits the insertion of the second spool’s shaft as was done in the case of the Pegasus which gave three times the thrust even in its earliest version (despite VTOL configuration!). We can expect more. The second Orpheus feature I find desirable is that it has a limited number of stages (7+1) on a short shaft and so can use just two bearings thus avoiding the third bearing and jointed shaft with its attendant proneness to whirling vibrations and ,who knows,  blade shedding. In fact starting point for the 25 kN could well be the Orpheus since large quantities of partly used engines must be with ED Sulur (?) following the retirement of the Kiran! The purpose of these core engines is they will over time form a family of fan and “leaky” engines for a variety of military and civil applications ranging from 10kN to 250 kN. They will incorporate the certificated advanced technology GTRE will no doubt develop. In fact GTRE’s contribution will be essential to the success of the programme. A side effect of the development of these small  “cores” is that any of the Embraer’s can be rigged up as a 3 engine flying test bed either DC10 or Lockheed Tri star style or even in place of the AEW pack and the tail arrangement changed to a twin fin arrangement-good project with a “bite” for our young engineers in collaboration with Embraer.

In a lighter vein, GTRE should quietly examine its press statements carefully before clutching in the “tongue”. Talks about Marine Kaveri are allowable but to talk of a Kaveri powered locomotive is to betray “Ivory Tower” disconnection. Not only will the engine choke in the Indian dust but also the power would be so enormous the train length would exceed the loop line (siding!) length used by the Railways. Marine and Power versions are completely different animals using different materials and operating in different ambient conditions. These derivatives will in no way help the Aircraft Engine programme and recalls Northkote  Parkinsons’s story about how a big Government funded project  to make a hyper rocket fuel failed miserably but said the Chief of the project at a press conference “I am afraid we have failed to have a useful rocket fuel but fortunately we find it is an excellent paint remover!” The UACV Kaveri idea is much better and on the right track.

Nil desperandum!

The Kaveri is in no way worse off than the LCA programme. What is needed, as with the LCA, is not more technology but more care and attention to detail. That will transform both projects if not into outstanding stupor mundi (wonder of the world) products as so tiresomely claimed but at least in to serviceable and affordable equipment.  I take this opportunity to thank Shri Ashok Baweja, (Chairman HAL2004-2009)  for suggesting during a casual conversation why I did not do a piece on the Kaveri. This piece had its genesis in his suggestion and is by way of thanks for the same.

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.