There was a mistake in my earlier reply. What I thought I was typing is not what I typed
. Happens to me when I type on a flight.
What I wanted to type was that HAL always wanted to design the LUH around the a derivative of the Shakti engine. And it did so, Shakti is Ardiden 1H1. LUH uses the Ardiden 1U which has slightly better power performance especially in emergency modes.
Safran just jacked up the price for the transmission development. HAL tried to find other developers, but it would have been very difficult for anybody else to just come in and generate a result starting from ground zero (engines and transmissions are very close coupled). So, they even considered going for an alternate engine transmission combo. But, the Ardiden is such a well-proven solution for the high altitude situations that this was a tough choice. This stalled the program for two odd years.
Thankfully, they solved the problem by going with the Ardiden 1U engine and a transmission designed at home. The (3-stage sun plenary) transmission designed for LUH is a more conservative design than the cutting-edge 2-stage transmission used in the ALH. The ALH transmission is a thing of beauty and was a major cause for worry which took decades to master. The LUH transmission is not as compact, but can get the job done.
If you are interested, you can find details of its testing here