1. A flying machine, or a small plane for experiments on flying, which floats in the air only when propelled through it.
2. 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; hence, a flying machine using such a device. These machines are called monoplanes, biplanes, triplanes, or quadruplanes, according to the number of main supporting planes used in their constraction. Being heavier than air they depend for their levitation on motion imparted by one or more propellers actuated by a gasoline 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. There are many varieties of form and construction, which in some cases are known by the names of their inventors.