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Gliding (flight)
Encyclopedia
Gliding flight is heavier-than-air flight
without the use of thrust. It is employed by gliding animal
s 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. However almost all powered aircraft are capable of gliding without engine power.
The main human application is currently recreational, though during the Second World War military glider
s were used for carrying troops and equipment into battle. The types of aircraft that are used for sport and recreation are classified as gliders (sailplanes)
, hang gliders and paragliders. These two latter types are often foot-launched. The design of all three types enables them to repeatedly climb using rising air and then to glide before finding the next source of lift. When done in gliders (sailplanes), the sport is known as gliding
and sometimes as soaring. For foot-launched aircraft, it is known as hang gliding
and paragliding
. Radio-controlled glider
s with fixed wings are also soared by enthusiasts.
In addition to motor glider
s, some powered aircraft are designed for routine glides during part of their flight; usually when landing after a period of a powered flight. These include:
Some aircraft are not primarily designed to glide except in an emergency, for example airliners that have run out of fuel. See list List of airline flights that required gliding flight.
s have separately evolved
gliding many times, without any single ancestor. Birds in particular use gliding flight to minimise their use of energy. Large birds are notably adept at gliding, including:
Like recreational aircraft, they too can alternate periods of gliding with periods of soaring in rising air
, and so spend a considerable time airborne with a minimal expenditure of energy. For similar reasons to birds, bat
s can glide efficiently.
Other mammals such as gliding possums and flying squirrel
s also glide, but with much poorer efficiency than birds and cannot gain height. For these creatures, gliding has mainly evolved to get from tree to tree in rainforest
s, most especially Borneo
, where the tree
s are tall and widely spaced. This mode of flight involves flying a greater distance horizontally than vertically and is therefore can be distinguished from a simple descent like a parachute. Some reptiles, amphibians and flying fish also glide.
As the aircraft or animal descends, the air moving over the wings generates lift. The lift force acts slightly forward of vertical because it is created at right angles to the airflow which comes from slightly below as the glider descends, see angle of attack
. This horizontal component of lift is enough to overcome drag
and allows the glider to accelerate forward. Even though the weight causes the aircraft to descend, if the air is rising faster than the sink rate, there will be a gain of altitude.
generated by a wing
or vehicle, divided by the drag
it creates by moving through the air. A higher or more favourable L/D ratio is typically one of the major goals in aircraft design; since a particular aircraft's needed lift is set by its weight, delivering that lift with lower drag leads directly to better fuel economy and climb performance.
The term is calculated for any particular airspeed
by dividing the measured lift by the measured drag at that speed. When measured against speed, the results can be plotted on a 2D graph. The lift curve proceeds in a straight line towards the critical angle, where it sharply drops off, and the drag curve forms a parabolic or U shape, the symmetry and shape depending on the effect of two main components of drag. The L/D curve normally forms a lopsided upside down U shape which peaks around the point of minimum drag.
As lift and drag are both proportional to the coefficient or Lift and Drag respectively multiplied by the same factor (1/2mv2S), the L/D ratio can be simplified to the Coefficient of lift divided by the coefficient of drag or Cl/Cd, and since both are proportional to the airspeed, the ratio of L/D or Cl/Cd is then typically plotted against angle of attack.
, this means that a component of the force is directed to the rear. The rearward component of this force is seen as drag. At low speeds an aircraft has to generate lift with a higher angle of attack, thereby leading to greater induced drag. This term dominates the low-speed side of the drag graph, the left side of the U.
Profile drag is caused by air hitting the wing, and other parts of the aircraft. This form of drag, also known as wind resistance, varies with the square of speed (see drag equation
). For this reason profile drag is more pronounced at higher speeds, forming the right side of the drag graph's U shape. Profile drag is lowered primarily by reducing cross section and streamlining.
As lift increases steadily until the critical angle, it is normally the point where the combined drag is at its lowest, that the wing or aircraft is performing at its best L/D.
Designers will typically select a wing design which produces an L/D peak at the chosen cruising speed for a powered fixed-wing aircraft, thereby maximizing economy. Like all things in aeronautical engineering, the lift-to-drag ratio is not the only consideration for wing design. Performance at high angle of attack
and a gentle stall
are also important.
Minimising drag is of particular interest in the design and operation of high performance glider (sailplane)
s, the largest of which can have glide ratios approaching 60 to 1, though many others have a lower performance; 25:1 being considered adequate for training use.
under these conditions; but is not necessarily equal during other manoeuvres, especially if speed is not constant. A glider's glide ratio varies with airspeed, but there is a maximum value which is frequently quoted. Glide ratio usually varies little with vehicle loading however, a heavier vehicle glides faster, but maintains its glide ratio.
Glide ratio is also known as glide number, finesse and is the cotangent of the downward angle- the glide angle. Alternatively it is also the forward speed divided by sink speed (unpowered aircraft):
).
Pilots sometimes fly at the aircraft's best L/D by precisely controlling airspeed and smoothly operating the controls to reduce drag. However the strength of the likely next lift and the strength of the wind also affects the optimal speed to fly
. To achieve higher speed across country, gliders (sailplanes)
are often loaded with water ballast
to increase the airspeed and so reach the next area of lift sooner. This has little effect on the glide angle but increases rate of sink (and speed over ground in proportion) because the heavier aircraft achieves optimal L/D at a higher airspeed.
If the air is rising faster than the rate of sink, the aircraft will climb. At lower speeds an aircraft may have a worse glide ratio but it will also have a lower rate of sink. A low airspeed also improves its ability to turn tightly in centre of the rising air
where the rate of ascent is greatest. A sink rate of approximately 1.0 m/s is the most that a practical hang glider or paraglider could have before it would limit the occasions that a climb was possible to only when there was strongly rising air. Gliders (sailplanes) have minimum sink rates of between 0.4 and 0.6 m/s depending on the class
. Aircraft such as airliners may have a better glide ratio than a hang glider, but would rarely be able to thermal because of their much higher forward speed and their much higher sink rate. (Note that the Boeing 767
in the Gimli Glider
incident achieved a glide ratio of only 12:1.)
During landing, a high lift/drag ratio is desirable. Some aircraft therefore employ flaps
, to increase their performance at lower speeds. Experiments with lifting bodies show that a lift/drag ratio below about 2 makes landing very difficult because of the high rate of descent.
The loss of height can be measured at several speeds and plotted on a "polar curve
" to calculate the best speed to fly in various conditions, such as when flying into wind or when in sinking air. Other polar curves can be measured after loading the glider with water ballast. As mass increases, the best glide ratio is achieved at higher speeds. (The glide ratio is not increased.)
. Five principal types of lift are used: thermal
s, ridge lift
, lee waves
, convergences
and dynamic soaring
. Dynamic soaring is used predominately by birds, and some model aircraft, though it has also been achieved on rare occasions by piloted aircraft.
Examples of soaring flight by birds are the use of:
For humans, soaring is the basis for three air sports
: gliding
, hang gliding
and paragliding
.
Flight
Flight is the process by which an object moves either through an atmosphere or beyond it by generating lift or propulsive thrust, or aerostatically using buoyancy, or by simple ballistic movement....
without the use of thrust. It is employed by gliding animal
Flying and gliding animals
A number of animals have evolved aerial locomotion, either by powered flight or by gliding. Flying and gliding animals have evolved separately many times, without any single ancestor. Flight has evolved at least four times, in the insects, pterosaurs, birds, and bats. Gliding has evolved on many...
s 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. However almost all powered aircraft are capable of gliding without engine power.
Aircraft ("gliders")
Most winged aircraft can glide to some extent, but there are several types of aircraft designed to glide:- GlidersGlider (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...
, also known as sailplanes - Hang gliders
- Paragliders and ram-air parachutes
- Rotor kiteRotor kiteA 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...
s, if untethered, these are rotary gliders. Also known as gyrogliders. - Military gliders
- Paper aeroplanePaper AeroplanePaper Airplane is an EP by American singer-songwriter Rosie Thomas, released in 2002.-Track listing:All songs written by Rosie Thomas unless otherwise stated.#"Wedding Day " – ?:??#"Feeding Off The Love Of The Land" – 4:24...
- Radio-controlled gliderRadio-controlled gliderA radio-controlled glider is a type of radio-controlled aircraft that normally does not have any form of propulsion. They are able to sustain continuous flight by exploiting the lift produced by slopes and thermals, controlled remotely from the ground with a transmitter...
- Rocket gliderRocket gliderA rocket glider, also known as rocket-propelled glider, is a glider aircraft that is powered by rocket power that glides to an unpowered landing...
s
The main human application is currently recreational, though during the Second World War military glider
Military glider
Military gliders have been used by the military of various countries for carrying troops and heavy equipment to a combat zone, mainly during the Second World War. These engineless aircraft were towed into the air and most of the way to their target by military transport planes, e.g...
s were used for carrying troops and equipment into battle. The types of aircraft that are used for sport and recreation are classified as gliders (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. These two latter types are often foot-launched. The design of all three types enables them to repeatedly climb using rising air and then to glide before finding the next source of lift. When done in gliders (sailplanes), the sport is known as gliding
Gliding
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.Gliding as a sport began in the 1920s...
and sometimes as soaring. For foot-launched aircraft, it is known as hang gliding
Hang gliding
Hang gliding is an air sport in which a pilot flies a light and unmotorized foot-launchable aircraft called a hang glider ....
and paragliding
Paragliding
Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure...
. Radio-controlled glider
Radio-controlled glider
A radio-controlled glider is a type of radio-controlled aircraft that normally does not have any form of propulsion. They are able to sustain continuous flight by exploiting the lift produced by slopes and thermals, controlled remotely from the ground with a transmitter...
s with fixed wings are also soared by enthusiasts.
In addition to motor glider
Motor glider
A motor glider is a fixed-wing aircraft that can be flown with or without engine power. The FAI Gliding Commission Sporting Code definition is: A fixed wing aerodyne equipped with a means of propulsion ,...
s, some powered aircraft are designed for routine glides during part of their flight; usually when landing after a period of a powered flight. These include:
- Experimental aircraftExperimental aircraftAn experimental aircraft is an aircraft that has not yet been fully proven in flight. Often, this implies that new aerospace technologies are being tested on the aircraft, though the label is more broad....
such as the North American X-15North American X-15The North American X-15 rocket-powered aircraft/spaceplane was part of the X-series of experimental aircraft, initiated with the Bell X-1, that were made for the USAAF/USAF, NACA/NASA, and the USN. The X-15 set speed and altitude records in the early 1960s, reaching the edge of outer space and...
, which glided back having used their fuel - SpacecraftSpacecraftA spacecraft or spaceship is a craft or machine designed for spaceflight. Spacecraft are used for a variety of purposes, including communications, earth observation, meteorology, navigation, planetary exploration and transportation of humans and cargo....
such as the Space ShuttleSpace ShuttleThe Space Shuttle was a manned orbital rocket and spacecraft system operated by NASA on 135 missions from 1981 to 2011. The system combined rocket launch, orbital spacecraft, and re-entry spaceplane with modular add-ons...
s, SpaceShipOne and the Russian Buran
Some aircraft are not primarily designed to glide except in an emergency, for example airliners that have run out of fuel. See list List of airline flights that required gliding flight.
Animals
A number of animalAnimal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...
s have separately evolved
Evolution
Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...
gliding many times, without any single ancestor. Birds in particular use gliding flight to minimise their use of energy. Large birds are notably adept at gliding, including:
- AlbatrossAlbatrossAlbatrosses, 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...
- CondorCondorCondor is the name for two species of New World vultures, each in a monotypic genus. They are the largest flying land birds in the Western Hemisphere.They are:* The Andean Condor which inhabits the Andean mountains....
- VultureVultureVulture is the name given to two groups of convergently evolved scavenging birds, the New World Vultures including the well-known Californian and Andean Condors, and the Old World Vultures including the birds which are seen scavenging on carcasses of dead animals on African plains...
- EagleEagleEagles are members of the bird family Accipitridae, and belong to several genera which are not necessarily closely related to each other. Most of the more than 60 species occur in Eurasia and Africa. Outside this area, just two species can be found in the United States and Canada, nine more in...
s - Storks
Like recreational aircraft, they too can alternate periods of gliding with periods of soaring in 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 so spend a considerable time airborne with a minimal expenditure of energy. For similar reasons to birds, bat
Bat
Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...
s can glide efficiently.
Other mammals such as gliding possums and flying squirrel
Flying squirrel
Flying squirrels, scientifically known as Pteromyini or Petauristini, are a tribe of 44 species of squirrels .- Description :...
s also glide, but with much poorer efficiency than birds and cannot gain height. For these creatures, gliding has mainly evolved to get from tree to tree in rainforest
Rainforest
Rainforests are forests characterized by high rainfall, with definitions based on a minimum normal annual rainfall of 1750-2000 mm...
s, most especially Borneo
Borneo
Borneo is the third largest island in the world and is located north of Java Island, Indonesia, at the geographic centre of Maritime Southeast Asia....
, where the tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
s are tall and widely spaced. This mode of flight involves flying a greater distance horizontally than vertically and is therefore can be distinguished from a simple descent like a parachute. Some reptiles, amphibians and flying fish also glide.
Forces
Three principal forces act on aircraft and animals when gliding:- weight – gravity acts in the downwards direction
- lift – acts perpendicularly to the vector representing airspeed
- drag – acts parallel to the vector representing the airspeed
As the aircraft or animal descends, the air moving over the wings generates lift. The lift force acts slightly forward of vertical because it is created at right angles to the airflow which comes from slightly below as the glider descends, see angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
. This horizontal component of lift is enough to overcome drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
and allows the glider to accelerate forward. Even though the weight causes the aircraft to descend, if the air is rising faster than the sink rate, there will be a gain of altitude.
Lift to drag ratio
The lift-to-drag ratio, or L/D ratio ("ell-over-dee" in the US, "ell-dee" in the UK), is the amount of liftLift (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...
generated by a 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...
or vehicle, divided by the drag
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
it creates by moving through the air. A higher or more favourable L/D ratio is typically one of the major goals in aircraft design; since a particular aircraft's needed lift is set by its weight, delivering that lift with lower drag leads directly to better fuel economy and climb performance.
The term is calculated for any particular airspeed
Airspeed
Airspeed is the speed of an aircraft relative to the air. Among the common conventions for qualifying airspeed are: indicated airspeed , calibrated airspeed , true airspeed , equivalent airspeed and density airspeed....
by dividing the measured lift by the measured drag at that speed. When measured against speed, the results can be plotted on a 2D graph. The lift curve proceeds in a straight line towards the critical angle, where it sharply drops off, and the drag curve forms a parabolic or U shape, the symmetry and shape depending on the effect of two main components of drag. The L/D curve normally forms a lopsided upside down U shape which peaks around the point of minimum drag.
As lift and drag are both proportional to the coefficient or Lift and Drag respectively multiplied by the same factor (1/2mv2S), the L/D ratio can be simplified to the Coefficient of lift divided by the coefficient of drag or Cl/Cd, and since both are proportional to the airspeed, the ratio of L/D or Cl/Cd is then typically plotted against angle of attack.
Drag
Induced drag is caused by the generation of lift by the wing. Lift generated by a wing is perpendicular to the wing, but since wings typically fly at some small angle of attackAngle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
, this means that a component of the force is directed to the rear. The rearward component of this force is seen as drag. At low speeds an aircraft has to generate lift with a higher angle of attack, thereby leading to greater induced drag. This term dominates the low-speed side of the drag graph, the left side of the U.
Profile drag is caused by air hitting the wing, and other parts of the aircraft. This form of drag, also known as wind resistance, varies with the square of speed (see drag equation
Drag equation
In fluid dynamics, the drag equation is a practical formula used to calculate the force of drag experienced by an object due to movement through a fully enclosing fluid....
). For this reason profile drag is more pronounced at higher speeds, forming the right side of the drag graph's U shape. Profile drag is lowered primarily by reducing cross section and streamlining.
Designers will typically select a wing design which produces an L/D peak at the chosen cruising speed for a powered fixed-wing aircraft, thereby maximizing economy. Like all things in aeronautical engineering, the lift-to-drag ratio is not the only consideration for wing design. Performance at high angle of attack
Angle of attack
Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...
and a gentle stall
Stall (flight)
In fluid dynamics, a stall is a reduction in the lift coefficient generated by a foil as angle of attack increases. This occurs when the critical angle of attack of the foil is exceeded...
are also important.
Minimising drag is of particular interest in the design and operation of high performance glider (sailplane)
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...
s, the largest of which can have glide ratios approaching 60 to 1, though many others have a lower performance; 25:1 being considered adequate for training use.
Glide ratio
When flown at a constant speed in still air a glider moves forwards a certain distance for a certain distance downwards. The ratio of the distance forwards to downwards is called the glide ratio. The glide ratio is numerically equal to the Lift-to-drag ratioLift-to-drag ratio
In aerodynamics, the lift-to-drag ratio, or L/D ratio, is the amount of lift generated by a wing or vehicle, divided by the drag it creates by moving through the air...
under these conditions; but is not necessarily equal during other manoeuvres, especially if speed is not constant. A glider's glide ratio varies with airspeed, but there is a maximum value which is frequently quoted. Glide ratio usually varies little with vehicle loading however, a heavier vehicle glides faster, but maintains its glide ratio.
Glide ratio is also known as glide number, finesse and is the cotangent of the downward angle- the glide angle. Alternatively it is also the forward speed divided by sink speed (unpowered aircraft):
Importance of the glide ratio in gliding flight
Although the best glide ratio is important when measuring the performance of a gliding aircraft, its glide ratio at a range of speeds also determines its success (see article on glidingGliding
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.Gliding as a sport began in the 1920s...
).
Pilots sometimes fly at the aircraft's best L/D by precisely controlling airspeed and smoothly operating the controls to reduce drag. However the strength of the likely next lift and the strength of the wind also affects the optimal speed to fly
Speed to fly
Speed to fly is a principle used by soaring pilots when flying between sources of lift, usually thermals, ridge lift and wave. The aim is to maximize the average cross-country speed by optimizing the airspeed in both rising and sinking air...
. To achieve higher speed across country, gliders (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...
are often loaded with water ballast
Sailing ballast
Ballast is used in sailboats to provide moment to resist the lateral forces on the sail. Insufficiently ballasted boats will tend to tip, or heel, excessively in high winds. Too much heel may result in the boat capsizing. If a sailing vessel should need to voyage without cargo then ballast of...
to increase the airspeed and so reach the next area of lift sooner. This has little effect on the glide angle but increases rate of sink (and speed over ground in proportion) because the heavier aircraft achieves optimal L/D at a higher airspeed.
If the air is rising faster than the rate of sink, the aircraft will climb. At lower speeds an aircraft may have a worse glide ratio but it will also have a lower rate of sink. A low airspeed also improves its ability to turn tightly in centre of the 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...
where the rate of ascent is greatest. A sink rate of approximately 1.0 m/s is the most that a practical hang glider or paraglider could have before it would limit the occasions that a climb was possible to only when there was strongly rising air. Gliders (sailplanes) have minimum sink rates of between 0.4 and 0.6 m/s depending on the class
Glider Competition Classes
Competition classes in gliding, as in other sports, mainly exist to ensure fairness in competition. However the classes have not been targeted at fostering technological development as in other sports...
. Aircraft such as airliners may have a better glide ratio than a hang glider, but would rarely be able to thermal because of their much higher forward speed and their much higher sink rate. (Note that the Boeing 767
Boeing 767
The Boeing 767 is a mid-size, wide-body twin-engine jet airliner built by Boeing Commercial Airplanes. It was the manufacturer's first wide-body twinjet and its first airliner with a two-crew glass cockpit. The aircraft features two turbofan engines, a supercritical wing, and a conventional tail...
in the Gimli Glider
Gimli Glider
The Gimli Glider is the nickname of the Air Canada aircraft that was involved in a notable aviation incident. On 23 July 1983, Air Canada Flight 143, a Boeing 767-200 jet, ran out of fuel at an altitude of ASL, about halfway through its flight from Montreal to Edmonton via Ottawa...
incident achieved a glide ratio of only 12:1.)
During landing, a high lift/drag ratio is desirable. Some aircraft therefore employ flaps
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
, to increase their performance at lower speeds. Experiments with lifting bodies show that a lift/drag ratio below about 2 makes landing very difficult because of the high rate of descent.
The loss of height can be measured at several speeds and plotted on a "polar curve
Polar curve (aviation)
A polar curve is a graph which contrasts the sink rate of an aircraft with its horizontal speed.-Measuring a glider's performance:...
" to calculate the best speed to fly in various conditions, such as when flying into wind or when in sinking air. Other polar curves can be measured after loading the glider with water ballast. As mass increases, the best glide ratio is achieved at higher speeds. (The glide ratio is not increased.)
Soaring
Soaring animals and aircraft may alternate glides with periods of soaring in rising airLift (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...
. Five principal types of lift are used: 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, ridge lift
Ridge lift
Ridge lift is created when a wind strikes an obstacle, usually a mountain ridge or cliff, that is large and steep enough to deflect the wind upward....
, lee waves
Lee waves
In meteorology, lee waves are atmospheric standing waves. The most common form is mountain waves, which are atmospheric internal gravity waves...
, convergences
Convergence zone
Convergence zone usually refers to a region in the atmosphere where two prevailing flows meet and interact, usually resulting in distinctive weather conditions....
and dynamic soaring
Dynamic soaring
Dynamic soaring is a flying technique used to gain energy by repeatedly crossing the boundary between air masses of significantly different velocity...
. Dynamic soaring is used predominately by birds, and some model aircraft, though it has also been achieved on rare occasions by piloted aircraft.
Examples of soaring flight by birds are the use of:
- Thermals and convergences by raptorBird of preyBirds 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 such as vultureVultureVulture is the name given to two groups of convergently evolved scavenging birds, the New World Vultures including the well-known Californian and Andean Condors, and the Old World Vultures including the birds which are seen scavenging on carcasses of dead animals on African plains...
s - Ridge lift by gullGullGulls are birds in the family Laridae. They are most closely related to the terns and only distantly related to auks, skimmers, and more distantly to the waders...
s near cliffs - Wave lift by migrating birds
- Dynamic effects near the surface of the sea by albatrossAlbatrossAlbatrosses, 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...
es
For humans, soaring is the basis for three air sports
Air sports
The term Air sports covers a range of aerial activities such as:* Aerobatics* Ballooning* General aviation including Air racing* Gliding* Hang gliding* Human powered aircraft* Model aircraft* Parachuting* Paragliding...
: gliding
Gliding
Gliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.Gliding as a sport began in the 1920s...
, hang gliding
Hang gliding
Hang gliding is an air sport in which a pilot flies a light and unmotorized foot-launchable aircraft called a hang glider ....
and paragliding
Paragliding
Paragliding is the recreational and competitive adventure sport of flying paragliders: lightweight, free-flying, foot-launched glider aircraft with no rigid primary structure...
.
See also
- Approach slope
- Colditz CockColditz Cock|-See also:-External links:*****...
- a glider built to escape from ColditzColditzColditz is a town in the Free State of Saxony, Germany, near Leipzig, located on the banks of the river Mulde. The town has a population of 5,188 .... - Gimli GliderGimli GliderThe Gimli Glider is the nickname of the Air Canada aircraft that was involved in a notable aviation incident. On 23 July 1983, Air Canada Flight 143, a Boeing 767-200 jet, ran out of fuel at an altitude of ASL, about halfway through its flight from Montreal to Edmonton via Ottawa...
- a passenger jet aircraft that ran out of fuel - GlidingGlidingGliding is a recreational activity and competitive air sport in which pilots fly unpowered aircraft known as gliders or sailplanes using naturally occurring currents of rising air in the atmosphere to remain airborne. The word soaring is also used for the sport.Gliding as a sport began in the 1920s...
(sport) - Gliding competitionsGliding competitionsSome of the pilots in the sport of gliding take part in gliding competitions. These are usually racing competitions, but there are also aerobatic contests and on-line league tables.-History of competitions:...
- Gliding mammal
- Gravity dragGravity dragIn astrodynamics and rocketry, gravity drag is a measure of the loss in the net performance of a rocket while it is thrusting in a gravitational field...
rocketRocketA rocket is a missile, spacecraft, aircraft or other vehicle which obtains thrust from a rocket engine. In all rockets, the exhaust is formed entirely from propellants carried within the rocket before use. Rocket engines work by action and reaction...
s can have an effective lift to drag ratio while maintaining altitude - Gyroglider
- Hang Glider
- InductrackInductrackInductrack is a passive, fail-safe electrodynamic magnetic levitation system, using only unpowered loops of wire in the track and permanent magnets on the vehicle to achieve magnetic levitation. The track can be in one of two configurations, a "ladder track" and a "laminated track"...
maglev has a higher lift/drag ratio than aircraft at sufficient speeds - Military gliderMilitary gliderMilitary gliders have been used by the military of various countries for carrying troops and heavy equipment to a combat zone, mainly during the Second World War. These engineless aircraft were towed into the air and most of the way to their target by military transport planes, e.g...
- Paraglider
- Foot-Launched Powered Hang GliderPowered Hang GliderA foot-launched powered hang glider , also called powered harness, nanolight, or hangmotor, is a powered hang glider harness with a motor and propeller in pusher configuration...
- Range (aircraft)Range (aircraft)The maximal total range is the distance an aircraft can fly between takeoff and landing, as limited by fuel capacity in powered aircraft, or cross-country speed and environmental conditions in unpowered aircraft....
range depends on the lift/drag ratio - Sailplane - rigid wing soaring gliders
- Specific fuel consumptionSpecific fuel consumptionThrust specific fuel consumption or sometimes simply specific fuel consumption, SFC, is an engineering term that is used to describe the fuel efficiency of an engine design with respect to thrust output...
the lift to drag determines the required thrust to maintain altitude (given the aircraft weight), and the SFC permits calculation of the fuel burn rate - thrust to weight ratio
- Underwater glidersUnderwater glidersAn underwater glider is a type of autonomous underwater vehicle that uses small changes in its buoyancy in conjunction with wings to convert vertical motion to horizontal, and thereby propel itself forward with very low power consumption...