[Part 3]
Kaveri Design Choice Rational: With this historical background in place, IMVHO, I’d speculate that what really happened in 1990 or thereabouts, while the performance and (also materials roadmap) design for Kaveri were being finalized , is the designers and technologists of the GTRE were faced with a major dilemma:
- 1) On the design front,
- a. is it sensible to aim for the various core design parameters (e.g. OPR, TET, BPR, Combustor efficiency, supersonic compressor regimes, ultra-low aspect ratio blades, blisk manufacturing etc) of the various modern engine development programs in R&D
OR
b. to stick to the basic already understood basic design layouts of the GTX-37U and 37UBs and try and introduce medium-level of improvements on these design parameters and still meet the Kaveri specs.
2) Similarly, on the materials front,
- a. Aim of the materials technology being worked on at various material design houses (e.g 2nd and 3rd Gen SCBs, DS based later-stage compressor blades, 1st gen SCB based , Ceramic and Polymer Matrix based combustors and static-engine parts etc etc) and provide a quantum jump in performance parameters that was being asked from Kaveri specs
OR
b. Provide a more conservative incremental advancement in material tech (e.g. introduce Dir Solidified blades for HPT, Ti and Ni based-equiaxed-casted Compressor blades, contemporary “bolted” disk and blade interfaces, annular combustor etc) and still achieve the Kaveri specs
It may be fashionable to attribute the GTRE folks as failures/worthless/losers etc , but the fact they had a fair idea about the contemporary advancements being carried out world-wide, to have made the design-choices that were made, then.
So the decision matrix then may have looked like:
1(a)2(b) ---|--- 1(a)2(a)
---------- Risk ------------>
1(b)2(a) ---|--- 1(b)2(b)
The GTRE technologists and designers chose 4th quadrant i.e. 1(b)2(b) – of course, with a hidden/inner ambition of getting to the 1st quadrant stuff concurrently and as the general technological level of the country advances in next 2 decades.
Overall Design Goals met/not-met: Pls, one word of caution towards over-emphasizing the success of dry-thrust, 90% wet thrust achievement (SFC, well, not sure) etc – yes those values are achieved, but at what weight (and maybe SFC also) penalty?
If you look at the chart above, a prev gen GTX-37UB also would have met these figures, isn’t it (with even more weight and SFC penalty).
So IMO right way of labeling Kaveri is to call it as qualified-success. As it, for the first time, if pursued with no let-up thru the flight-test-programme, will validate a flying turbofan engine – in technological terms it would
1) validate (and provide invaluable empirical data) the CFD and basic mechanical design of a twin-spool 80KN turbofan (90s level)
2) given enough design and manufacturing technological confidence of 80s level of material tech
Without these there’s no hope of leapfrogging technological gens etc (refer to epilogue section for a glimpse of that), and we're doomed to play catch-up forever.
Inference: But there-in lies the problem,
i.e. first, recall the findings of Engine evaluation study of 1985 which basically stated LCA engine specs are set high-enough to be met by a contemporary engine then. Now contrast that with the constraining technological choices (aka Conservative-Conservative) being made for Kaveri to achieve those.
This essentially means, there’s wafer-thin margin of error towards meeting both the core engine-design parameters and the enabling material/manufacturing design/technology. Even shortfall of one parameter may spell doom – and that’s precisely happened with Kaveri albeit shortfall in meeting almost all design parameters (admittedly, by small enough margin but big enough to all contribute to a compounding effect of the shortfall we see today).
But wait, before we start dishing out our advises, from our hindsight-is-20/20 vantage point, let’s try and think thru why would the GTRE folks not consider high-high risk of 1(a)2(a) approach.
Well, if you look at our national psyche of extremely naval-gazing, if-it’s-made-in-India-must-be-useless, pricing-of-tech-dev-in-terms-of-social-upliftment-missed-cost, 3-legged-cheetah-labelling-user-attitude etc. (Shivji will have a longer list), GTRE folks would be mortally scared of failures arising from such a high-risk endeavor.
Frankly, I’m not very sure if it mattered to the GTRE folks, if LCA flew or not, as long as they have met the Kaveri design parameters. So when the larger program, due to scope creep, necessitated a requirement growth of a next-gen powerplant, Kaveri in it’s present technological form is not even close to it.
Plus all this talk of new imported core etc means exactly that – a fully imported engine in terms of jet-engine tech, nothing more nothing else.
That’s the price to be paid for a pessimistic/stifling national outlook towards technological advancement with zero-tolerance towards failures and import at all cost attitude.
Epilogue: While we constantly continue to berate the GTRE folks for technological failure etc, a small bit of snippet needs understanding.
In mid-2000s, desperate to trying to reduce the overweight Kaveri (it’s still overweight by 150Kg or there-abouts), GTRE folks went ahead experimenting with the absolute cutting edge of material tech i.e. Ceramic Matrix Composites (CMC) and Polymer Matrix Composites (PMC) on some of the non-rotating-non-critical components. CMC was targeted towards a few hot-components like Nozzle divergent petals, exhaust cone etc – while PMC (high temp PMR-15 class) towards bypass duct, CD Nozzle cowls at the back etc.
The aim was to reduce weight by 30Kgs (i.e. approx. 20-25%).
In contrast, pls google around for CMC and PMC related R&D and, more importantly, it’s usage on various aero-engine by established western players (
Hint: some links are there couple of pages back on this very thread).
This confidence and attitude are the true by-products of the Kaveri engine development program.
[The End]