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

balloon A balloon is a flexible bag that can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, and air. For special tasks, balloons can be filled with smoke, liquid water, granular media (e.g. sand, flour or rice), or lig ...

s and tethered

kite A kite is a tethered heavier-than-air or lighter-than-air craft with wing surfaces that react against the air to create lift and drag forces. A kite consists of wings, tethers and anchors. Kites often have a bridle and tail to guide the fac ...

s. This requires a trajectory that is not merely a vertical descent such as a

parachute A parachute is a device used to slow the motion of an object through an atmosphere by creating drag or, in a ram-air parachute, aerodynamic lift. A major application is to support people, for recreation or as a safety device for aviators, w ...

. 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 Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the ...

and the balloon may or may not be tethered. Free balloon flight has little directional control. Gliding aircraft include

sailplanes A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding (also called soaring). This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplan ...

hang glider Hang gliding is an air sport or recreational activity in which a pilot flies a light, non-motorised foot-launched heavier-than-air aircraft called a hang glider. Most modern hang gliders are made of an aluminium alloy or composite frame covered ...

s, and

paraglider Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure. The pilot sits in a harness or lies supine in a cocoon-like ...

s 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 The Montgolfier brothers – Joseph-Michel Montgolfier (; 26 August 1740 – 26 June 1810) and Jacques-Étienne Montgolfier (; 6 January 1745 – 2 August 1799) – were aviation pioneers, balloonists and paper manufacturers from the commune A ...

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 Sir George Cayley, 6th Baronet (27 December 1773 – 15 December 1857) was an English engineer, inventor, and aviator. He is one of the most important people in the history of aeronautics. Many consider him to be the first true scientific aer ...

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 balloon A barrage balloon is a large uncrewed tethered balloon used to defend ground targets against aircraft attack, by raising aloft steel cables which pose a severe collision risk to aircraft, making the attacker's approach more difficult. Early barra ...

s were made and deployed in large numbers. Military assault gliders were also developed during World War II, while the

rotor kite A rotor kite or gyrokite is an unpowered, rotary-wing aircraft. Like an autogyro or helicopter, it relies on lift created by one or more sets of rotors in order to fly. Unlike a helicopter, gyrokites and rotor kites do not have an engine power ...

was used by the

German Navy The German Navy (, ) is the navy of Germany and part of the unified ''Bundeswehr'' (Federal Defense), the German Armed Forces. The German Navy was originally known as the ''Bundesmarine'' (Federal Navy) from 1956 to 1995, when ''Deutsche Mari ...

for seaborne observation. Modern applications include experimental High altitude wind power generation.

Gliders

Sailplanes A glider or sailplane is a type of glider aircraft used in the leisure activity and sport of gliding (also called soaring). This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude. Sailplan ...

s and

s 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" aircraft. A small foot-launched glider is launched by running downhill or stepping off a high location. Forward speed is then maintained by a gradual descent through the surrounding air, with the wings angled slightly down so that their lift also provides a small forward thrust to counter the drag of the wing. If the air is rising faster than the aircraft is descending through it, the glider will gain height and additional

potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potenti ...

. Sources of such rising air include warm

thermal A thermal column (or thermal) is a rising mass of buoyant air, a convective current in the atmosphere, that transfers heat energy vertically. Thermals are created by the uneven heating of Earth's surface from solar radiation, and are an example ...

s and hill ridges. In the past, unpowered

military glider Military gliders (an offshoot of common gliders) have been used by the militaries of various countries for carrying troops ( glider infantry) and heavy equipment to a combat zone, mainly during the Second World War. These engineless aircraft wer ...

s have been used for military applications. Today, the majority of use of all types of glider aircraft is recreational.

Balloons

Free-flying

Balloons A balloon is a flexible bag that can be inflated with a gas, such as helium, hydrogen, nitrous oxide, oxygen, and air. For special tasks, balloons can be filled with smoke, liquid water, granular media (e.g. sand, flour or rice), or light s ...

drift with the wind. The pilot controls the altitude either by heating the air more or by releasing ballast weight. The wind direction usually changes with altitude, so crude directional control can be obtained by changing altitude. A round tethered balloon is unstable in any significant wind. A kite balloon is streamlined to make it stable in strong winds. Today, the majority of manned balloon flights are recreational, whereas unmanned and usually free-flying balloons are widely used for meteorological measurement.

Kites

Kites are aircraft that are tethered to some other object (fixed or mobile) or other means that maintain tension in the

kite line In kiting, a line is the string made of cotton, nylon, silk or wire, which connects the kite to the person operating it or an anchor. Kites have a set of wings, a set of anchors, and a set of lines coupling the wings with the anchors. Kite lines p ...

; and rely on virtual or real wind blowing over and under them to generate lift and drag.

Kytoon A kytoon or kite balloon is a tethered aircraft which obtains some of its lift dynamically as a heavier-than-air kite and the rest aerostatically as a lighter-than-air balloon. The word is a portmanteau of kite and balloon. The primary advantage ...

s are balloon kites that are shaped and tethered to obtain kiting deflections, and can be lighter-than-air, neutrally buoyant, or heavier-than air. Kites have been developed for commercial applications using

kite control systems Kite types, kite mooring, and kite applications result in a wide variety of kite control systems. Contemporary manufacturers, kite athletes, kite pilots, scientists, and engineers are expanding the possibilities. Single-line kite control system ...

, including the airborne wind energy systems of high altitude wind power.

References

External links

Fédération Aéronautique Internationale
This is the world organisation for air sports such as gliding, hang gliding and paragliding {{DEFAULTSORT:Unpowered Aircraft