The invention discloses a UAV (unmanned aerial vehicle) which comprises a vehicle body, a rotor spindle and a rotor holder pin shaft. The UAV further comprises an engine, an air filter, a rotor connecting assembly and a dynamic balance part, wherein the engine is fixed in the vehicle body and comprises at least one cylinder, a cylinder body and an air inlet valve, an exhaust port is formed in one side surface of each cylinder, the cylinder body is detachably connected with the cylinder; the air inlet valve is detachably connected with the valve body, and an included angle between flowing direction of airflow into the air inlet valve and the exhaust direction of tail gas from the exhaust port ranges from 0 to 90 degrees; the air filter is fixed at the bottom of the vehicle body; the rotor connecting assembly movably connects the rotor spindle with the rotor holder pin shaft; and the dynamic balance part is nested on the rotor spindle and movably connected with the rotor holder pin shaft. The UAV solves or partially solves the technical problem of influence on UAV flight work due to insufficient gas combustion of the traditional engine.