What's the point of the centrifugal compressor stage in the P&W PT6A?
Hi everyone,
I've recently been reading into free-turbine turboprops and by extension, the PT6. I understand the maintenance advantages of doing away with any mechanical link between the power shaft and gas generator and in turn, why the engine must be reverse-mounted and airflow rotated through 180 degrees by the intake and again at the exhaust. What I don't understand is the advantage of reciprocating direction of airflow twice more in the gas generator; once following compression by the centrifugal, 4th stage, after it passes through the diffuser ducts and again as it exits the combustion chamber. The only potential benefit I could think of would be that it shortens the overall length of the engine, as it allows some of the combustion chamber to extend beyond the turbine. I would however have thought that the additional friction that comes about by virtue of this would have a severely negative effect upon efficiency and not be a worthwhile trade-off.
Kind regards,
Charlie Reed