Unpowered aircraft
Unpowered aircraft can remain airborne for a significant period of time without onboard propulsion. They can be classified as fixed-wing gliders, lighter-than-air balloons and tethered kites. This requires a trajectory that is not merely a vertical descent such as a parachute. In the case of kites, lift is obtained by tethering to a fixed or moving object, perhaps another kite, to obtain a flow of wind over the lifting surfaces. In the case of balloons, lift is obtained through inherent buoyancy and the balloon may or may not be tethered. Free balloon flight has little  directional control. Gliding aircraft include sailplanes, hang gliders, and paragliders that have full directional control in free flight. History. The first manned aircraft were kites, balloons and gliders. Man-lifting kites were used in ancient China and Japan, often as a punishment for prisoners. Unmanned hot-air balloons and toy "bamboo-copters" are also recorded in Chinese history. The first manned free flight was in a hot-air balloon built by the brothers Joseph-Michel and Jacques-Etienne Montgolfier in Annonay, France in 1783. The hydrogen balloon appeared at about the same time and proved more practical. The first practical , controllable glider was designed and built by the British scientist and pioneer George Cayley who many recognise as the first aeronautical engineer. It flew in 1849. Tethered balloons and, to a lesser extent, kites were developed for military and meteorological observation, however the use of kites has remained largely recreational. Free-flying ballooning using coal gas (which has about half the lifting power of hydrogen) became a popular sport. Gliders were used mainly for aerodynamic research until their sporting use was developed in the 1920s. During the two World Wars, tethered barrage balloons were made and deployed in large numbers . Military assault gliders were also developed during World War II, while the rotor kite was used by the German Navy for seaborne observation. Modern applications include experimental High altitude wind power generation. Gliders. Sailplanes, hang gliders and paragliders are all types of glider aircraft. For a glider to generate lift, it must first gain and then maintain sufficient forward air speed. Launching a glider gives it the initial forward airspeed to start flying. This is often done by towing the aircraft into the air on a long line, using either a ground-based winch or vehicle, or a powered "tug