PISTON ENGINES today are used mainly to power the vast numbers of light aircraft and microlights, as well as crop-sprayers and crop-dusters, small helicopters, and firebombers (which dump water on large fires). Virtually all heavier aircraft are now powered by jet engines. Modern piston aero-engines work on the same basic principles as the engine used by the Wright brothers in the first powered flight in 1903. However, today’s engines are more sophisticated than earlier engines. For example, modern aero-engines may use a two-stroke or a four-stroke combustion cycle; they may have from one to nine air- or water-cooled cylinders, which may be arranged horizontally,
in-line, in V formation, or radially; and they may drive the aircraft’s propeller either directly or through a reduction gearbox. One of the more unconventional types of modern aero-engine is the rotary engine shown here, which has a trilobate (three-sided) rotor spinning in a chamber shaped like a fat figure-eight.
