CYS-40F piston engine is a single cylinder two-stroke air-cooled aerial gasoline engine aimed at small-sized unmanned aerial vehicles. Its maximum output capability is 2.1 KW. This engine adopts carburetor of diaphragm pump type and improves power system’s adaptability at different altitudes. The engine can install forward pulling positive propeller or backward pushing propeller which is easy to use and operate. It is an ideal miniature aerial piston power.