In aeronautical engineering, a nacelle is a separate streamlined enclosure mounted on an aircraft to house an engine, cargo, or crew.
The V-22 Osprey has a feature unique in production aircraft: nacelles that swivel from the horizontal to the vertical, allowing fixed-wing and helicopter operation.
Lighter-than-air Zeppelin aircraft had their engine nacelles attached, by struts, to the rigid skeleton over which the gas bag was stretched. In the LZ1 prototype, the flight path was adjusted in pitch by sliding a weight between the engine nacelles.
It is also used to describe the part between the tower and rotor of a wind turbine.