Originally Posted by
pattern_is_full
The PW901A uses a centrifugal compressor. Rather unusual in turbofans.
Centrifugal compressors are quite common on small turbine engines for a couple simple reasons. First off - with a small turbine engine and a ~30-1 compressor ratio - with an axial compressor you end up with such small parts in the high stages you need a watchmaker to put the thing together. Which leads directly to the second reason - centrifugal compressors - especially small ones - are cheaper to produce (usually by quite a bit). Although centrifugal compressors increase the frontal area of the engine, you need a large volume for the combustor (pressure loss through a combustor is proportional to the local Mach number
squared, so you want to slow the airflow way down - less than 0.1). As a result on smaller turbine engines there isn't much of a penalty.