Asymmetric vaned sections in a turboprop booster

A booster-compressor assembly (10, fig 1) for supercharging air into a core engine that powers propellers of a turboprop aircraft engine (20, fig 1) includes an asymmetric annular booster duct with at least one symmetric annular rotor section 24 with a row of rotor blades 26 disposed therein. The booster duct has a core flowpath to a core engine inlet (30, fig 1) and a bypass flowpath (34, fig 1) around the core engine inlet. A flow rate means may include bypass inlet guide vanes 50 angled in a flow closing direction A1 and core inlet guide vanes 52 angled in an open direction A2, such that a bypass flow rate per unit area is substantially less than a core flow rate per unit area. The exit guide vanes 70A,70B may also be angled B1,B2 to match the flow from the inlet vanes.