1.      

The GTRE engine presentation at the 27th Subroto Memorial lectures               Prof. Prodyut Das

15 /01/2025

“See how the Winter of our discontent is made Glorious by the Sun of York"

That the present Government is making efforts to clean the Augean stables of our  “Weapons Development” is like the Sun in Winter. Most, rather than much, remains to be done. Recently a Conference was held under the aegis of the Society for Aerospace Studies and the statements of the Air Chief Marshal and the Defense Secretary. the Customer and the Banker respectively were like a breath of fresh air. They showed that at least two of the pillars of our archaic Socialist state- controlled and inefficient weapons development edifice publicly acknowledge that problems exist. It is a small but important first step because without acknowledgment of the problem there can be no solutions. It remains for the developing agencies under the DRDO to acknowledge their fairly major contribution to the situation The solutions are easy but it is not the DRDO prescription of pouring more “ghee” of funds into the embers will work. References to Chinese defence R&D budgets by DRDO should only go with concurrent mention of Chinese export earnings and sticking to schedules, let alone in Chinese persistence, especially after Deng Xiao Ping, in solving development problems- the J7’s intake cone positioning system problems comes to mind- before attempting new ones.

As an example of how off track our thinking is below is an analysis of the presentation by GTRE about their plan to develop a 115kN engine with a foreign collaboration which will need Rs. 50,000 crores. GTRE will fail, with delays, because they have proposed “Scientist’s” rather than simpler, “engineered to the situation” solutions.

The presentation I am referring to is at  https://t.co/MoSJi2LQdp  by Dr. SV Ramamurthy, Director of GTRE and their plan to develop a 115 kN with foreign collaboration. It is presumed the presentation reflects the collective wisdom of GTRE and that is what makes this presentation so depressing because if GTRE is thinking along these lines then failure is guaranteed. We will end up with yet another half-baked GTRE product which is of no earthly use to anybody.

It is GTRE- struggling with the Kaveri since 1985s which is nowhere near full certification- is stepping over the carcasses of the Marut reheat, GTX 10, GTX 10-32 and even the “until recently written off” Kaveri to propose yet another, more challenging engine with the following aims;

Pressure Ratio 30.

TET 2200K,

TTL 3000hrs.

T/W ratio is 10:1

Thrust 115 kN

 These parameters, a copy paste of US engine specification, necessarily drag along with them advanced technology that GTRE wants funds for such as SCB, Blisk, sintered metal turbine disks (which require non- existent 50,000 tons presses) Fadec and other such impressive acronyms all of which cost a great deal of money and very considerable technical risks. In short DRDO has proposed a “Scientists” engine developable only in an ideal work environment. What is needed is an “Engineers” proposal. This means not looking at the lack of 50, 000-ton press, and Rs.50,000 crore funds as yet another affliction hurled upon toiling Scientists but more maturely just another constraint in the search for a solution.

Let us take a look at the implications of the proposed DRDO engine.

Compression ratio

GTRE wants a CR of 30:1. Every engineer knows from his 3^rd year that the higher the compression ratio the higher the efficiency.  I have tabulated the rise of thermal efficiency with compression ratio.

Table1

Table under construction but the figures shows that the laws of diminishing returns apply in Turbine engine design.

Sl.no	Compression Ratio	Thermal efficiency	Typical Engine	Sfc	TET0 K	T/w
1	4	0.327	Orpheus	0.98-1.06	950	6
2	6	0.4
3	8	0.44	Avon RA7	0.92		6.0
4	10	0.48	R25	0.95	1360	8.34*
5	14	0.53		0.9
6	20	0.57
7	24	0.596	F 404
8	30	0.62	GTRE proposal		2200	10:1

 

*R 25 Contingency rating for 3 minutes but required engine examination on return. Mainly boost came from the 3- stage afterburner. Typical “Soviet” solution!

The table shows that increasing the pressure ration by 4 units i.e. from 4 to 8 increase the thermal efficiency by 11.3 percentage points whereas the same increase in CR from 20 to 24 improves the thermal efficiency by only 2.6%. i.e. a severe case of diminishing returns. The question to discuss is why should we aim for CR of 30;1 and what are other possibilities in -other than CR in increasing Thermal efficiency.

These thermal efficiencies are available fully only at full throttle. In turbo machinery much of the difference achieved after so much developmental pain will be lost at part throttle which is where the engine will spend most of its time. Have we generated data on this or are we blindly following a given figure?

What are the challenges in engine design for achieving the 30:1 compression ratio proposed in the presentation. Some of the commonest are

1.      For a given level of engine technology it usually means a bigger, heavier or a very tricky compressor. The risk of the compressors behaving badly increases, surging, leading to component damage, flameouts and blade shedding being quite common a development problem.

2.      Usually, a great deal of the work done in compressing the air is wasted by dumping at part throttles.  

3.      Variable angle stator vanes and dump valves are needed to tame the ill tempered compressor adding complexity and weight.

4.      The higher amount of compressor power needed means a greater amount of energy has to be extracted from the gas stream to drive the compressor. This pushes up the TET whose technology we are lacking at the level required.

5.      Everyone talks about “blisk” but it is another technology that has to be inducted to shave off a little of the fuel consumption. It is extremely expensive but makes mandatory sense in airliners. How much sense it will make in a continuous environment of bird hits needs quantification.

6.      In sum at any given level of technology we need a big heavy complicated engine if we go for increasing the CR. There are other ways of getting the benefits of a high cycle efficiency than relying on a highly advanced turbo compressor; One common one is to concentrate on the inlet and duct design which can even at subsonic speeds, say at M 0.8, give a 1,52 x multiplication of the overall compression ratio i.e. a CR of 15 will give an actual CR of 23 in flight. Then there are coatings which can be the same purpose as compression and these are recommended because they involve no pumping/dumping losses. Let us think of what engine we can do ‘as is”  

TTL of 3000 hours

Again a “nice rather than “necessary” feature. It requires unavailable super alloy and powder metallurgy technology and massively push up engine material and machining costs.

Who has confirmed, based on hard facts, the 3000 hrs Total Technical Life is necessary. The Hunters at Kalaikunda in the 60s used to go for an overhaul after 500 hrs. intervals. Very few airframes would come back for the third being written off in accidents of various sorts. Things may have improved but a quick study of the in- field life of a combat engine in IAF service will show that the engine life due to all causes not necessarily due to the fault of the engine barely exceed 2000 hours. So fixing TTL on the basis of actual data would help everyone to get a cheaper, more sensible product.  

Thrust to weight ratio of 10:1

For the proposed 115 kN engine the weight of the engine for 6:1, 8:1 and 10:1 the engine weights will be 1900kgs, 1450 kgs and 1150 kgs, obviously it is a worthwhile gain. There are two ways to tackle this shortcoming.

1.      A more careful weight improvement programme will bring the Kaveri weight down from 1200 kgs to 1100 kgs. Th difficulty is not in the technology but the lack of josh and confidence in GTRE’s repertoire of skills. 

2.      A particular to case solution, is to reduce the airframe weight of the Tejas or the AMCA by that proportionate amount e.g. even the Tejas 1A by my estimate, is about 6-800 kilos overweight.

The academic question arises as to why does the US have such advanced specification. Up to a certain point it is their necessity. As a global policeman it needs long range aircraft and this means highly fuel- efficient engines. They have both the technology and the need and their weapons exports make economic sense so why not. There is also the case that much of the US specifications are influenced via politicians and by the bankers who would naturally like to have returns on their investments. The highly specified Raptor only action in 22 years of service has been the shooting of a Chinese Balloon over continental US. The US specifications are to be envied but not copied.

A question of attitude

The attitude reflected in the presentation is also cause for misgiving. From the days when a Socialist Pattern of Society was inflicted on us the idea sold by our leaders was that a government organization is expected to be dependable, responsible and scrupulously honest. The GTRE presentation reflected that somehow this organization has not been able to accept that it needs to change for the better and clings to an unacceptable sense of victimhood. I will cite a few examples which jarred:

Test bed: It is not the Government’s job to provide the Flight test Bed. Mr. Rajnath Singh or the defence secretary may need a fairly lengthy briefing of WHAT is a flight test bed. It is the GTRE’s job to “do the needful” and continue to wheedle the Government until it gets its FTB. Dhawan, Kurien, VS Krishnamurthy were people who would not take no for an answer. So why did GTRE/ DRDO not persist if they realized that the FTB was sine qua non or should one conclude that something as elementary as the need for a FTB is also a part of the now famous “learning process”?

Reliability of stated facts; No matter how damning the situation, after a time delay, Honesty brings respect and trust for the future just as to justify a mess by subtle distortion of facts cause misgivings.The speaker mentioned that GTRE spent 250 million USD and that a similar US engine would cost 2.5 billion USD. This statement smacks of a case of supressio veri i.e. a suppression of truth.

i)                  It is a comparison from two very different bases. The US costs are always TOTAL costs where every expenditure including Manpower and every incidental is accounted. In India the project cost does not include the manpower cost.

ii)                 The US always gives costs in present USD i.e. present-day value costs. DRDO adds up costs over decades and stating that as the sum spent e.g. in the DRDO (INSDOC) book on the Tejas the development costs is given as 14000 crores whereas the corrected figure is Rs.1,69,000 crores 2024 value.

iii)              The manpower costs are the highest single item in development costs. If GTRE had to pay US salaries our expenditure on the Kaveri- even to its present half- baked state would exceed the US spend of $2.5 bn by several times.  No real comparison can be made because US costs are for an exportable equipment whereas DRDO has given a FOC certificate to a fighter which has 87 major concessions and has not fired its guns. The figures I have is that the Tejas at IOC1 cost us 20% more than what the US spent on developing the F16 Bl.10- which was used in combat- our much cheaper engineering salaries notwithstanding.

iv)               DRDO’s repeated questionable statements erodes its credibility. Given the business of the Tejas certification can DRDO complain of prolonged trials of it’s products by the Army? I am sure that the Air Force people talk to the Army at the United Services or whatever is its current avatar.

 

v)                 I will close this dismal list by mentioning that whilst DRDO fans have generously accused everyone of being Import Lobbyists we have to find out whose decision it was to close down the very promising programme in 2008 when it was just suffering from “measles and mumps”. Was it from within DRDO that the case was made for closing down the project? Fool or Knave?       

An assessment of GTRE capability- an inability for undefined problems.

The Kaveri is actually quite a remarkable achievement. Despite its present shortcomings the engine is close to its design cold thrust. It also turns the glare on GTRE’s lacunae.

a)      GTRE has proved that it can tackle the defined problems of engine design.

b)      In not being able to close the small gap in dry thrust performance, in not running the engine as is “to the death” as it were, in not getting a flight test bed first thing, GTRE - and this reflects not on the line engineers but the GTRE leadership- has proved it is unable to tackle the “ill-defined” problems of engine design.

c)       there has been elementary failures of simple common sense. It did not require funds to engage with the Customer and insist on going through with the Customer clause buy clause on every point. Every Engineering sale- and the Engine development is an engineering sale- requires.  It does not require funds and sanctions for GTRE asked for actual engine life or has it merely gone like a PWD clerk. It does not require huge funds to run the engine- a minimum statistical batch of 3 but ideally 5 -to the specified TTL so that we would have had by now perhaps 10,000 hrs of just test bed runs. We still don’t know what hidden problems of reliability are there in the Kaveri because a total of 3000 hours spread over five prototypes is simply ridiculous as regards establishing design maturity. Where is the concern and the care?

Benefits of the proposed collaboration.

Going by the what are we going to benefit? The GTRE /SAFRAN plan has a fatal flaw. GTRE will get to design the LP spool i.e. the fan and the LP turbine. My objection is that we will get to work for TETs at perhaps 15-1700^oK TET whereas the 2200 K technology will be at the mercy of the French and we will be lucky to get the scraps.So our learning will be marginal.

Administrative action     

Weapons development has a political angle always. Sanction proofing is a must, GTRE must not have an off shore collaboration with any vendor anywhere.

GTRE has a long history of “Project Jumping” and leaving a trail of half- baked products. It probably has reasonable competence in tackling defined or identified problems but it’s habitual project jumping has built up into a large portfolio of “non competence”. As an example, had it gone through with the afterburner development of the Marut it would not have been all at sea with the Kaveri reheat.

 Since the Chinese are frequently quoted let us adopt the least of all Chinese “totka” (fix) – never leave an engineering problem undeveloped. It must develop and certificate the Kaveri to international standards before it can be allowed to venture into new designs or else it will continue to fail at the last mile because of past neglects. Weight, cold thrust and A/B thrust must be met along with a reasonable engine life. Only if GTRE can do that will it can be considered for any collaboration. A Rs.50,000 crore must have reasonable prospects of returns but it can’t be the habitual learning experience.   

DRDO is failing because it is aiming to achieve figures rather than aiming to attain capability. We should not aim to obtain a certain figure of s.f.c. By doing so we are restricting our options for a solution. Given our political restrictions we should rather we should aim at how many sortie minutes will we get from a certain weight of fuel. So if a certain compression ratio is needed it instead of putting all the onus on GTRE then becomes necessary to collaborate with ADA so that a highly efficient inlet system is co- developed. Equally a parallel dialogue must be held with the IAF if they can relax the super-cruise requirements for the AMCA because it probably is unnecessary in our context and may even even be unnecessary in the US context. This means that we have to evolve a different style of problem solving where the considerable experience of all the stakeholders are pooled to obtain a politically independent solution.

GTRE must abjure foreign collaborations and start with the existing Kaveri Technology to scale up to the required thrust. It will be a large engine to begin with- about 1400 mm dia if 115 kN cold is required but then in collaboration with the airframe designer and the IAF the size can be whittled down and examine how far this horse will trot. It is certainly illogical of those at the helm to both damn American perfidy in holding up GE Engine supply and seek foreign collaboration for the AMCA engine in the same breath..