n. [ aëro- + plane. ] (Aëronautics) 1. A light rigid plane used in aërial navigation to oppose sudden upward or downward movement in the air, as in gliding machines; specif., such a plane slightly inclined and driven forward as a lifting device in some flying machines. Also called airfoil. [ Webster 1913 Suppl. ]

2. Hence: A heavier-than-air flying machine using such a device to provide lift; an airplane. In a modern aeroplane, the airfoils are called the wings, and most of the lift is derived from these surfaces. In contrast to helicopters, the wings are fixed to the passenger compartment (airframe) and do not move relative to the frame; thus such a machine is called a fixed-wing aircraft. These machines are called monoplanes, biplanes, triplanes, or quadruplanes, according to the number of main supporting planes (wings) used in their construction. After 1940 few planes with more than one airfoil were constructed, and these are used by hobbyists or for special purposes. Being heavier than air they depend for their levitation on motion imparted by the thrust from either propellers driven by an engine, or, in a jet plane, by the reaction from a high-velocity stream of gases expelled rearward from a jet engine. They start from the ground by a run on small wheels or runners, and are guided by a steering apparatus consisting of horizontal and vertical movable planes, which usually form part of the wings or tail. There are many varieties of form and construction, which in some cases are known by the names of their inventors. In U.S., an aeroplane is usually called an airplane or plane. [ Webster 1913 Suppl. +PJC ]