Why IAF Retained AL-31FP Engines for Su-30MKI Fleet Despite Superior Thrust AL-41F Offer from Russia? Logistics and Training Main Factors

In a decision with significant implications for the Indian Air Force (IAF), India has opted to retain the existing AL-31FP engines for its fleet of 84 Su-30MKI fighter aircraft, declining an offer from Russia to upgrade them with the more advanced AL-41F engines.

While the AL-41F offers superior thrust and improved Mean Time Between Overhauls (MTBO), the IAF's choice reflects a prioritization of logistical efficiency and training continuity.

An official from Hindustan Aeronautics Limited (HAL) confirmed that the decision to stay with the AL-31FP engines was primarily driven by the IAF.

Despite the AL-41F's proven compatibility with the Su-30MKI platform, as demonstrated by the Russian Air Force's transition to these engines on their Su-30SM aircraft, several factors influenced this decision.

Over the years, HAL, in collaboration with the Gas Turbine Research Establishment (GTRE), has successfully addressed early technical issues with the AL-31FP engines.

Furthermore, HAL has achieved the capability to manufacture these engines domestically from raw materials, enhancing India's self-reliance in engine production.

Logistical considerations also played a key role in the IAF's decision. While the AL-41F shares some commonalities with the AL-31FP in terms of service ground tools, transitioning to the new engine would necessitate significant reskilling of ground crew for maintenance and repairs.

Additionally, the higher thrust of the AL-41F could alter the flight dynamics of the Su-30MKI, requiring pilot reorientation and potentially new training modules.

Ultimately, the IAF chose to avoid the additional costs and time associated with transitioning to a new engine type, especially when the existing engines have been effectively localized and improved.

By sticking with the AL-31FP, the IAF can leverage its established supply chain and maintenance ecosystem without significant disruption.

However, this choice means forgoing the potential performance enhancements offered by the AL-41F, including increased thrust and engine longevity. The Su-30MKI, a cornerstone of the IAF's fighter fleet, will still undergo upgrades to become the "Super Sukhoi," but these will focus on avionics, radar systems, and weapon integration rather than a change in propulsion.

This decision reflects a strategic balancing act between technological advancement and operational continuity. The IAF has prioritized minimizing disruption to its existing infrastructure and expertise, even if it means forgoing potential performance gains.

 

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[Suddhasattwa Bandyopadhyay]

So you guys can have TOT for two different engines from GE - F404 and F414 at the same time, but not with Russia's AL-31 and AL-41? Have some sense, HAL! Tejas Mk-1A will be our lightweight fighter and Mk-2 will be medium weight, due to which both engines F404 and F414 will be made simultaneously, but for Sukhoi, on transition from AL-31 to AL-41, only the latter (AL-41) would be made! So what's wrong with switching engines, geniuses?

Please read the article. HAL doesn't make the decision which engine they'll use. It's IAF who decides it. It was IAF who wanted GE 404 director sourced from the US including its Maintenance and Overhaul also to be done by GE. And, Russia gave India ToT for AL 31 FP with various riders, especially with India sourcing its components and materials from Russia and other CIS countries. What we need to do is to build an upgraded engine with higher thrust and longer engine MTBF based on AL 31 FP drawings with materials and components sourced and manufactured entirely in India, incorporating all the indigenous solutions by GTRE to the AL 31 FP engine's technical issues.

 

[Shiva]

There are additional important reasons for this preference. India already purchased ToT of AL-31FP engines, but AL-41FP requires repurchase at an additional cost. Also, the improvement in the new engine is just about 10%. Paying 100% additional cost for such low improvement is detrimental to indigenization.

Additional enhancement should have been by increasing or reducing size significantly to alter performance or heat signature in a significant way. Also, India attained new technologies for stealth which can be added, thereby reducing the dependency on weight-to-thrust ratio for stealth and instead can comfortably take up higher weight/size engines.

So, putting additional cost on AL-31FP related engines with a higher size by simply scaling up with an additional size increase in critical components with super alloy metals. Importing these kinds of things, either from Russia or others, and developing a new engine similar to the AL-31FP engine could make Indian rights on the product more than how much Russia can have.

When HAL already acquired almost 100% to create AL-31FP engines and is capable of scaling up, design skills can easily create new engines with three times the thrust if size is ignored a little. This can lead ahead in looking at hypersonic variants of aircraft, either with or without a pilot.

 

[EMD XD41/06MAC]

Please read the article. HAL doesn't make the decision which engine they'll use. It's IAF who decides it. It was IAF who wanted GE 404 director sourced from the US including its Maintenance and Overhaul also to be done by GE. And, Russia gave India ToT for AL 31 FP with various riders, especially with India sourcing its components and materials from Russia and other CIS countries. What we need to do is to build an upgraded engine with higher thrust and longer engine MTBF based on AL 31 FP drawings with materials and components sourced and manufactured entirely in India, incorporating all the indigenous solutions by GTRE to the AL 31 FP engine's technical issues.

So who will give increased thrust? AL-31FP gives only 28K lbf per engine (totally 56K), giving a slower takeoff speed. AL-41F1S gives the same thrust vectoring, but 32K lbf per engine (totally 64K), which gives a better takeoff speed! Grow up IAF!!! I've seen in every Aero India that Su-30MKI takes off too slow and late compared to every other fighter jet - Tejas, Rafale, Gripen, F-16, etc.

 

[Sandeep]

While the AL-41 might give slightly better performance than the current AL-31 engine, the problem we face is that we will have to make another expensive deal to manufacture them in India, and they still won't transfer any critical technology, like the core, or allow us to manufacture it all in India with Indian content.

So the best and most affordable option is to improve the performance and longevity of the current AL-31 engines, as HAL has made some improvements and changes already. We should take more of a risk and increase the indigenous content rate from raw materials from India rather than Russia, as that is what increases the cost. Also, if we know that we can manufacture more parts of the engines, then we should go ahead and quietly do it. Russia won't make too much of a fuss as it's busy with its war and grappling with funding issues.

 

[Anant]

GTRE, DRDO, and the industry needs to collaborate to create it's own AL31F derived AL51 type engine. Research needs to go in materials, and redesign of sub-components, including possibly engine core.

You do realise that what you are suggesting is, in effect, a new engine, right?

 

[Rajesh]

Thrust might be a bit more than AL-31, but the reliability of AL-41 over AL-31 must have promoted the IAF to stick with AL-31, and they might be waiting for the new AL-51, which is still under development. A lot of talks on these things will be going on which will not come out in the media, and we will have to wait a bit more, especially when talks with the West are still going on as usual.

 

[Anant]

There are additional important reasons for this preference. India already purchased ToT of AL-31FP engines, but AL-41FP requires repurchase at an additional cost. Also, the improvement in the new engine is just about 10%. Paying 100% additional cost for such low improvement is detrimental to indigenization.

Additional enhancement should have been by increasing or reducing size significantly to alter performance or heat signature in a significant way. Also, India attained new technologies for stealth which can be added, thereby reducing the dependency on weight-to-thrust ratio for stealth and instead can comfortably take up higher weight/size engines.

So, putting additional cost on AL-31FP related engines with a higher size by simply scaling up with an additional size increase in critical components with super alloy metals. Importing these kinds of things, either from Russia or others, and developing a new engine similar to the AL-31FP engine could make Indian rights on the product more than how much Russia can have.

When HAL already acquired almost 100% to create AL-31FP engines and is capable of scaling up, design skills can easily create new engines with three times the thrust if size is ignored a little. This can lead ahead in looking at hypersonic variants of aircraft, either with or without a pilot.

Um, you can't just scale up or scale down an engine in size and get a commensurate increase or decrease in thrust, heat signature, etc. Doesn't work that way, and there is far, far more nuance involved in it.

Regardless, as it stands today, we cannot build a new AL-31FP solely by ourselves even if we had the raw materials handy. Russia still provides some subcomponents we can service (which technically indigenises them as per the government's definitions) but cannot manufacture. Therefore, the question of having a larger share of (or complete) IP rights over an engine developed from the AL-31 is difficult to answer, since developing such an engine to begin with is not exactly straightforward.

 

[Anant]

Any aeronautical engineer here on this blog to let me know if the AL-31FP themselves can't be improved, obviating the need for on-paper technically superior engines?

I am not an aeronautical engineer by training, but I do know for a fact that there is only so much you can do to any engine to improve various aspects of performance before you fundamentally need to change it.

For instance, the Kaveri, in its present form, can, atleast in theory, manage between 75-80 kN of thrust depending on the kind of afterburner you integrate. Said integration would impact a number of performance parameters too. However, in order to get something like 90 kN of wet thrust, you essentially need a new core in the engine, which is a fundamental change.

Similarly, to bring massive changes in engine life would necessitate changes in the materials used, which will again affect the engine enough for major modifications to be required.

 

[Varaaah]

Good decision. Russians want to make useless the expertise India gained with the AL31. Russians will make less money so they push for the AL41.