Abstract: An internal combustion engine, which is particularly adapted for vertical take-off and landing aircraft, has a plurality of fixed annularly arranged combustion chambers and an opening in each chamber. The chamber openings are arranged to define either a cylindrical surface or a plane surface. The combustion chambers are arranged in groups and the groups may be staggered either radially or axially with respect to each other. A rotatable distributor has a surface conforming to the surface defined by the chamber openings and closely spaced from these openings. The distributor has a plurality of slots and recesses therein arranged in zones so as to coregister with the combustion chamber openings.