Propfan. Computer aided design screen display of a propfan power unit used in aviation. The propfan is comprised of a turbine (blue, lower right), two sets of blades (red and green), and an outer casing (blue, upper left). The outer casing has been cut away in this image to allow viewing of the turbine and blades. Air is drawn in by the blades. Part of this incoming air passes into the turbine, is compressed, mixed with fuel and ignited to provide power. The other part is partially compressed and passes between the turbine and casing, cooling the engine and reducing noise. All the air is then exhausted from the rear of the engine to provide thrust.