Unpowered flight is the ability to stay airborne for a period of time without using any power source. There are several types of unpowered flight. Some have been exploited by nature, others by man, and some by both.

Unpowered aircraft are aerial vehicles that can fly without any propulsion mechanism.

The ability to fly short or long distances without power has evolved many times in nature. Many creatures capable of sustained wing-powered flight also soar unpowered for much of the time they are airborne.

Classification of flight methods

Pennycuick divides animal flight into three types: parachuting, gliding and powered. He observes however that these have no sharp boundaries. For example at one point he sees parachutes as unpowered and as a primitive form of soaring, while soaring itself he sees as being powered by air movement (wind). Other methods, such as lighter-than-air flight, are used only by man.

This article makes the following distinctions between types or methods of unpowered flight, based on their characteristics:

• Lighter than air - Sustained flight, buoyed by a density less than air with no forward motion required,
• Falling - Sustained free flight due to slow rate of descent compared to upward air-speed,
• Parachuting - Vertical descent slowed by high air resistance, though possibly with a minor horizontal motion (or sometimes defined as flight at an glide angle greater than 45 deg.),
• Gliding - Forward flight with smooth airflow (or sometimes defined as flight with a glide angle less than 45 deg),
• Soaring - Sustained free gliding flight, drawing energy from rising air,
• Kiting - Tethered flight using an angled plane to create an upward force from the wind.

These are summarised in the table:

colspan=5 | Flight characteristics and methods

		Flight mode
		Short duration	Sustained free flight	Tethered
Forward motion through the air	None	Not classified as flight	Lighter than air Falling	Lighter than air
	Slower than downward motion	Parachuting	Parachuting	Kiting
	Faster than downward motion	Gliding	Soaring	Kiting

Flight methods and usage

Some examples of usage are shown in the following table:

colspan=4 | Flight methods vs. usage

	Aircraft	Animals	Lower life forms
Lighter than air	Balloon Balloon A balloon is an inflatable flexible bag filled with a gas, such as helium, hydrogen, nitrous oxide, oxygen, or air. Modern balloons can be made from materials such as rubber, latex, polychloroprene, or a nylon fabric, while some early balloons were made of dried animal bladders, such as the pig...	—	—
Falling	—	Small insects	Spores, Orchid seeds
Parachuting	Parachute Parachute A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...	Spider kite Ballooning (spider) Ballooning is a term used for the mechanical kiting that many spiders, especially small species, as well as certain mites and some caterpillars use to disperse through the air. Many small spiders use gossamer or especially fine silk to lift themselves off a surface or use the silk as an anchor in...	Rotary wings (maple, sycamore) Hairs (dandelion)
Gliding	Glider Glider aircraft Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...	Flying squirrel Flying squirrel Flying squirrels, scientifically known as Pteromyini or Petauristini, are a tribe of 44 species of squirrels .- Description :...
Soaring	Sailplane	Albatross Albatross Albatrosses, of the biological family Diomedeidae, are large seabirds allied to the procellariids, storm-petrels and diving-petrels in the order Procellariiformes . They range widely in the Southern Ocean and the North Pacific...
Kiting	Kite Kite A kite is a tethered aircraft. The necessary lift that makes the kite wing fly is generated when air flows over and under the kite's wing, producing low pressure above the wing and high pressure below it. This deflection also generates horizontal drag along the direction of the wind... Rotor kite Rotor kite A rotor kite or gyroglider 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...

Lighter than air

Lighter than air flight is only used by man. An unpowered, lighter than air craft is called a balloon.

Balloons

A balloon

Balloon

A balloon is an inflatable flexible bag filled with a gas, such as helium, hydrogen, nitrous oxide, oxygen, or air. Modern balloons can be made from materials such as rubber, latex, polychloroprene, or a nylon fabric, while some early balloons were made of dried animal bladders, such as the pig...

 is a bag filled with a gas with a lower density

Density

The mass density or density of a material is defined as its mass per unit volume. The symbol most often used for density is ρ . In some cases , density is also defined as its weight per unit volume; although, this quantity is more properly called specific weight...

 than the surrounding air to provide buoyancy

Buoyancy

In physics, buoyancy is a force exerted by a fluid that opposes an object's weight. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus a column of fluid, or an object submerged in the fluid, experiences greater pressure at the bottom of the...

. The gas may be hot air, hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 or helium

Helium

Helium is the chemical element with atomic number 2 and an atomic weight of 4.002602, which is represented by the symbol He. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas that heads the noble gas group in the periodic table...

. The use of buoyant gases is unknown in the natural world.

A balloon may be tethered like a kite or drift with the wind in free flight. The pilot can control the altitude of a free-flying balloon, either by heating the gas or by releasing ballast, giving some directional control (since the wind direction changes with altitude).

Falling

A free-falling object without any adaptation to flight can only be sustained by the wind if it is very light and falls more slowly than the wind blows it upwards.

Many mould and bacterial spore

Spore

In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...

s, even live bacteria, are small enough to be carried long distances and to great heights on the wind.

Some plants also use the wind for seed dispersal

Seed dispersal

Seed dispersal is the movement or transport of seeds away from the parent plant. Plants have limited mobility and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors. Seeds can be dispersed away from the parent plant...

 in this way. Orchid seeds are very small and dust-like.

Parachuting

Parachuting is essentially falling but with an aerodynamic braking surface. The high ratio of surface area to weight reduces the rate of descent of the parachute

Parachute

A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...

, allowing it to stay airborne for longer periods. The aerodynamic surface may also allow a small amount of forward motion, but a parachute always falls faster than it can travel forwards. The airflow around a parachute is typically turbulent.

Small creatures and seeds that have evolved parachutes can be blown on the wind for long distances. Among the plants, Dandelion, milkweed and poplar

Poplar

Populus is a genus of 25–35 species of deciduous flowering plants in the family Salicaceae, native to most of the Northern Hemisphere. English names variously applied to different species include poplar , aspen, and cottonwood....

) seeds have hairs that act as parachutes. Some spiders cast parachutes

Ballooning (spider)

Ballooning is a term used for the mechanical kiting that many spiders, especially small species, as well as certain mites and some caterpillars use to disperse through the air. Many small spiders use gossamer or especially fine silk to lift themselves off a surface or use the silk as an anchor in...

 of thread. Although mostly done by small spiderlings, adults weighing over 100 mg and with a body size of up to 14 mm have been observed casting parachutes a meter across into a strong updraft.

Parachuting is also used by larger creatures and seeds to travel shorter distances. Maple

Maple

Acer is a genus of trees or shrubs commonly known as maple.Maples are variously classified in a family of their own, the Aceraceae, or together with the Hippocastanaceae included in the family Sapindaceae. Modern classifications, including the Angiosperm Phylogeny Group system, favour inclusion in...

, pine

Pine

Pines are trees in the genus Pinus ,in the family Pinaceae. They make up the monotypic subfamily Pinoideae. There are about 115 species of pine, although different authorities accept between 105 and 125 species.-Etymology:...

 and sycamore

Sycamore

Sycamore is a name which is applied at various times and places to three very different types of trees, but with somewhat similar leaf forms....

 seeds have one or two wings that act like parachutes to aid in seed dispersal

Seed dispersal

Seed dispersal is the movement or transport of seeds away from the parent plant. Plants have limited mobility and consequently rely upon a variety of dispersal vectors to transport their propagules, including both abiotic and biotic vectors. Seeds can be dispersed away from the parent plant...

. Flying frog

Flying frog

A "flying" frog is a frog that has the ability to glide. That is, it can descend at an angle of less than 45° relative to the horizontal. Arboreal frogs can also descend vertically, but only at angles greater than 45°, which is referred to as parachuting...

s use their webbed feet as parachutes.

Gliding

Gliding flight requires an initial launch giving the object enough energy to fly.

Aerodynamic lift

The principles of aerodynamic lift

Lift (force)

A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...

 are shared by both nature and man-made aircraft. As the aeronaut falls, outspread wing

Wing

A wing is an appendage with a surface that produces lift for flight or propulsion through the atmosphere, or through another gaseous or liquid fluid...

s are angled to the oncoming air to create a fast forward flow of air over the wing. This flow generates aerodynamic lift

Lift (force)

A fluid flowing past the surface of a body exerts a surface force on it. Lift is the component of this force that is perpendicular to the oncoming flow direction. It contrasts with the drag force, which is the component of the surface force parallel to the flow direction...

 which slows the rate of descent. The result is gliding flight as opposed to a simple descent like a parachute

Parachute

A parachute is a device used to slow the motion of an object through an atmosphere by creating drag, or in the case of ram-air parachutes, aerodynamic lift. Parachutes are usually made out of light, strong cloth, originally silk, now most commonly nylon...

.

If the air is rising faster than the object is descending, it will be carried upwards. In this way a gliding object can gain additional potential energy

Potential energy

In physics, potential energy is the energy stored in a body or in a system due to its position in a force field or due to its configuration. The SI unit of measure for energy and work is the Joule...

 from sources such as thermal

Thermal

A thermal column is a column of rising air in the lower altitudes of the Earth's atmosphere. Thermals are created by the uneven heating of the Earth's surface from solar radiation, and are an example of convection. The sun warms the ground, which in turn warms the air directly above it...

s and ridge lift.

Glider aircraft

Glider aircraft

Glider aircraft

Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...

 include sailplanes

Glider (sailplane)

A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...

, hang glider

Hang gliding

Hang gliding is an air sport in which a pilot flies a light and unmotorized foot-launchable aircraft called a hang glider ....

s and paraglider

Paragliding

Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure...

s. They must gain their initial energy of motion from a launch process. The launch may be by pulling the aircraft into the air with a tow-line, with a ground-based winch or vehicle, or with a powered "tug" aircraft. For foot-launched aircraft, there is also the option of merely stepping off a high location.

Sailplanes

Glider (sailplane)

A glider or sailplane is a type of glider aircraft used in the sport of gliding. Some gliders, known as motor gliders are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off or for extending a flight...

, hang gliders and paragliders have complete directional control and fly freely.

Gliding animals

Creatures able to launch themselves into the air and glide short distances include:

• Flying squirrel
  Flying squirrel
  Flying squirrels, scientifically known as Pteromyini or Petauristini, are a tribe of 44 species of squirrels .- Description :...
  
  s
• Petaurus
  Petaurus
  The genus Petaurus contains flying phalangers or wrist-winged gliders, a group of arboreal marsupials. There are six species, Sugar Glider, Squirrel Glider, Mahogany Glider, Northern Glider, Yellow-bellied Glider and Biak Glider, and are native to Australia or New Guinea.Flying phalangers are...
  
   marsupials
• Flying snakes
• Flying dragon lizards
• Flying fish

Soaring

Unpowered flights of longer duration and distance are possible if rising air

Lift (soaring)

Gliding flight is heavier-than-air flight without the use of thrust. It is employed by gliding animals and by aircraft such as gliders. The most common human application of gliding flight is in sport and recreation using aircraft designed for this purpose...

 is used to gain energy. This can further reduce the rate of descent or even increase height, which is known as soaring.

Soaring is where the object/animal obtains additional energy from rising air

Lift (soaring)

Gliding flight is heavier-than-air flight without the use of thrust. It is employed by gliding animals and by aircraft such as gliders. The most common human application of gliding flight is in sport and recreation using aircraft designed for this purpose...

 without exerting any power to remain airborne. An example is the albatross

Albatross

Albatrosses, of the biological family Diomedeidae, are large seabirds allied to the procellariids, storm-petrels and diving-petrels in the order Procellariiformes . They range widely in the Southern Ocean and the North Pacific...

, which is a large seabird renowned for its ability to stay aloft by soaring above the waves for days at a time. Many other birds such as raptor

Bird of prey

Birds of prey are birds that hunt for food primarily on the wing, using their keen senses, especially vision. They are defined as birds that primarily hunt vertebrates, including other birds. Their talons and beaks tend to be relatively large, powerful and adapted for tearing and/or piercing flesh....

s and stork

Stork

Storks are large, long-legged, long-necked wading birds with long, stout bills. They belong to the family Ciconiidae. They are the only family in the biological order Ciconiiformes, which was once much larger and held a number of families....

s also deliberately soar to extend their time aloft. Insects are often caught by rising air and so can be dispersed by it.

Many types of glider aircraft

Glider aircraft

Glider aircraft are heavier-than-air craft that are supported in flight by the dynamic reaction of the air against their lifting surfaces, and whose free flight does not depend on an engine. Mostly these types of aircraft are intended for routine operation without engines, though engine failure can...

 are designed to exploit rising air

Lift (soaring)

Gliding flight is heavier-than-air flight without the use of thrust. It is employed by gliding animals and by aircraft such as gliders. The most common human application of gliding flight is in sport and recreation using aircraft designed for this purpose...

and can therefore also soar.

Kiting

An airflow over a tethered object can gain it height up to a maximum determined partly by the length of the tether, and then enable it to maintain height while there is sufficient airflow. Such a tethered flying object is called a kite.

If there is a wind, the tether may be attached to a fixed point, or the motion of an object such as a speedboat can be used to create an airflow or to augment the wind. The mobile object can even be another kite.