That's interesting Brian. Generally in multiple shaft turbine engines, combusted exhaust gasses pass into the turbine section driving N2. The expansion of combustion gasses drives N1 (free power turbine) which either has a fan or a prop attached to it.....
It's certainly the case with the jet engine I operate.
Last edited by Blueskymine; 15th Aug 2014 at 02:11.
Reason: Reworded for the pedantic