These include: Motor glider – a conventional glider or sailplane with an auxiliary power plant that may be used when in flight to increase performance. Powered hang glider – a hang glider with a power plant added. Powered parachute – a paraglider type of parachute with an integrated airframe, seat, undercarriage and power plant hung beneath. Powered paraglider or paramotor – a paraglider with a power plant suspended behind the pilot. Ground effect vehicle A ground effect vehicle (GEV) is a craft that attains level flight near the surface of the earth, making use of the ground effect – an aerodynamic interaction between the wings and the earth's surface. Some GEVs are able to fly higher out of ground effect (OGE) when required – these are classed as powered fixed-wing aircraft. Glider A glider is a heavier-than-air craft that is supported in flight by the dynamic reaction of the air against its lifting surfaces, and whose free flight does not depend on an engine. A sailplane is a fixed-wing glider designed for soaring – the ability to gain height in updrafts of air and to fly for long periods. Gliders are mainly used for recreation, but have also been used for other purposes such as aerodynamics research, warfare and recovering spacecraft. A motor glider does have an engine for extending its performance and some have engines powerful enough to take off, but the engine is not used in normal flight. As is the case with planes, there are a wide variety of glider types differing in the construction of their wings, aerodynamic efficiency, location of the pilot and controls. Perhaps the most familiar type is the toy paper plane. Large gliders are most commonly launched by a tow-plane or by a winch. Military gliders have been used in war to deliver assault troops, and specialized gliders have been used in atmospheric and aerodynamic research. Rocket-powered aircraft and spaceplanes have also made unpowered landings. Gliders and sailplanes that are used for the sport of gliding have high aerodynamic efficiency. The highest lift-to-drag ratio is 70:1, though 50:1 is more common. After launch, further energy is obtained through the skillful exploitation of rising air in the atmosphere. Flights of thousands of kilometers at average speeds over 200 km/h have been achieved. The most numerous unpowered aircraft are paper airplanes, a handmade type of glider. Like hang gliders and paragliders, they are foot-launched