Glider (sailplane) - AbsoluteAstronomy.com

A glider or sailplane is a type 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...

used in the sport of 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...

. Some gliders, known as 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 are used for gliding and soaring as well, but have engines which can, in some cases, be used for take-off

Takeoff

Takeoff is the phase of flight in which an aerospace vehicle goes from the ground to flying in the air.For horizontal takeoff aircraft this usually involves starting with a transition from moving along the ground on a runway. For balloons, helicopters and some specialized fixed-wing aircraft , no...

or for extending a flight. Foot-launched aircraft (such as hang gliders

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 paragliders

Paragliding

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

) are described in separate articles, though their differences from sailplanes are covered below. Gliders have also been used for purposes other than recreation, for example for military purposes

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...

and for research.

Sports gliders benefit from creating the least 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...

for any given amount of lift, and this is best achieved with long, thin wings

Aspect ratio (wing)

In aerodynamics, the aspect ratio of a wing is essentially the ratio of its length to its breadth . A high aspect ratio indicates long, narrow wings, whereas a low aspect ratio indicates short, stubby wings....

and a fully faired narrow cockpit. Aircraft with these features are able to climb efficiently in rising air and can glide long distances at high speed with a minimum loss of height in between.

Use of engines

Although most gliders do not have engines, there are a few that do. (see 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 ,...

). The manufacturers of high-performance gliders will list an optional engine with a retractable propeller that can be used to sustain flight, if required; these are known as 'self-sustaining' gliders. Some have enough thrust to launch themselves before the engine is retracted and are known as 'self-launching' gliders. There are also 'touring motor gliders' which can self launch and switch off the engine in flight without retracting their propellers.

History

Sir George Cayley's gliders achieved brief wing-borne hops from around 1849. Otto Lilienthal

Otto Lilienthal

Otto Lilienthal was a German pioneer of human aviation who became known as the Glider King. He was the first person to make well-documented, repeated, successful gliding flights. He followed an experimental approach established earlier by Sir George Cayley...

built (barely) controllable gliders in the 1890s using weight shift with which he could ridge soar. Wright Brothers

Wright brothers

The Wright brothers, Orville and Wilbur , were two Americans credited with inventing and building the world's first successful airplane and making the first controlled, powered and sustained heavier-than-air human flight, on December 17, 1903...

achieved full control in the early 1900s using movable surfaces, to which they successfully added an engine.

After World War I

World War I

World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

gliders were built for sporting purposes in Germany (see link to Rhön-Rossitten Gesellschaft

Rhön-Rossitten Gesellschaft

The Rhön-Rossitten Gesellschaft or Rhön-Rossitten Society was a German gliding organization, the first one in the world that was officially recognised...

) and in the United States (Schweizer brothers

Schweizer brothers

Paul, William , and Ernest Schweizer were three brothers who started building gliders in 1930. In 1937, they formed the Schweizer Metal Aircraft Company. Their first commercial glider sale was an SGU 1-7 glider to Harvard University's Altosaurus Glider Club. At that time, Eliot Noyes was a...

). Germany's strong links (continuing today) to gliding were to a large degree due to Post-WWI regulations forbidding the construction and flight of motorised planes in Germany, so the country's aircraft enthusiasts often turned to gliders and were actively encouraged by the German government.

The sporting use of gliders rapidly evolved in the 1930s and is now the main application. As their performance improved, gliders began to be used for cross-country flying and now regularly fly hundreds or even thousands of kilometers in a day if the weather is suitable.

Glider design

Early gliders had no cockpit and the pilot sat on a small seat located just ahead of the wing. These were known as "primary glider

Primary glider

Primary gliders are a category of aircraft that enjoyed worldwide popularity during the 1920s and 1930s as people strove for simple and inexpensive ways to learn to fly....

s" and they were usually launched from the tops of hills, though they are also capable of short hops across the ground while being towed behind a vehicle. To enable gliders to soar more effectively than primary gliders, the designs minimized drag. Gliders now have very smooth, narrow fuselage

Fuselage

The fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...

s and very long, narrow wings with a high aspect ratio

Aspect ratio (wing)

and winglet

Winglet

Wingtip devices are usually intended to improve the efficiency of fixed-wing aircraft. There are several types of wingtip devices, and though they function in different manners, the intended effect is always to reduce the aircraft's drag by partial recovery of the tip vortex energy...

The early gliders were made mainly of wood with metal fastenings, stays and control cables. Later fuselages made of fabric-covered steel tube were married to wood and fabric wings for lightness and strength. New materials such as carbon-fiber, fiber glass and Kevlar

Kevlar

Kevlar is the registered trademark for a para-aramid synthetic fiber, related to other aramids such as Nomex and Technora. Developed at DuPont in 1965, this high strength material was first commercially used in the early 1970s as a replacement for steel in racing tires...

have since been used with computer-aided design to increase performance. The first glider to use glass-fiber extensively was the Akaflieg Stuttgart FS-24 Phönix

Akaflieg Stuttgart FS-24

The Akaflieg Stuttgart FS-24 Phönix was a glider designed and built in Germany from .- Development :The Phönix was the first glider to use fibreglass in its construction...

which first flew in 1957. This material is still used because of its high strength to weight ratio and its ability to give a smooth exterior finish to reduce drag. Drag has also been minimized by more aerodynamic shapes and retractable undercarriages. 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...

are fitted to the trailing edges of the wings on some gliders to minimise the drag from the tailplane at all speeds.

With each generation of materials and with the improvements in aerodynamics

Aerodynamics

Aerodynamics is a branch of dynamics concerned with studying the motion of air, particularly when it interacts with a moving object. Aerodynamics is a subfield of fluid dynamics and gas dynamics, with much theory shared between them. Aerodynamics is often used synonymously with gas dynamics, with...

, the performance of gliders has increased. One measure of performance is the glide ratio. A ratio of 30:1 means that in smooth air a glider can travel forward 30 meters while losing only 1 meter of altitude. Comparing some typical gliders that might be found in the fleet of a gliding club - the Grunau Baby from the 1930s had a glide ratio of just 17:1, the glass-fiber Libelle

Glasflügel H-201

|-References:*Thomas F, Fundamentals of Sailplane Design, College Park Press, 1999*Simons M, Segelflugzeuge 1965-2000, Eqip, 2004*...

of the 1960s increased that to 39:1, and modern flapped 18 meter gliders such as the ASG29

Schleicher ASG 29

|-References:**...

have a glide ratio of over 50:1. The largest open-class glider, the eta, has a span of 30.9 meters and has a glide ratio over 70:1. Compare this to the infamous 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...

, a 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...

which ran out of fuel mid-flight and was found to have a glide ratio of only 12:1, or to the Space Shuttle

Space Shuttle

The 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...

with a glide ratio of 4.5:1.

Due to the critical role that aerodynamic efficiency plays in the performance of a glider, gliders often have aerodynamic features seldom found in other aircraft. The wings of a modern racing glider have a specially designed low-drag laminar flow

Laminar flow

Laminar flow, sometimes known as streamline flow, occurs when a fluid flows in parallel layers, with no disruption between the layers. At low velocities the fluid tends to flow without lateral mixing, and adjacent layers slide past one another like playing cards. There are no cross currents...

airfoil

Airfoil

An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....

. After the wings' surfaces have been shaped by a mold to great accuracy, they are then highly polished. Vertical winglets at the ends of the wings are computer-designed to decrease drag and improve handling performance. Special aerodynamic seals are used at the aileron

Aileron

Ailerons are hinged flight control surfaces attached to the trailing edge of the wing of a fixed-wing aircraft. The ailerons are used to control the aircraft in roll, which results in a change in heading due to the tilting of the lift vector...

s, rudder

Rudder

A rudder is a device used to steer a ship, boat, submarine, hovercraft, aircraft or other conveyance that moves through a medium . On an aircraft the rudder is used primarily to counter adverse yaw and p-factor and is not the primary control used to turn the airplane...

and elevator

Elevator (aircraft)

Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's orientation by changing the pitch of the aircraft, and so also the angle of attack of the wing. In simplified terms, they make the aircraft nose-up or nose-down...

to prevent the flow of air through control surface gaps. Turbulator

Turbulator

A turbulator is a device that turns a laminar flow into a turbulent flow. Turbulent flow can be desired on parts of the surface of an aircraft wing or in industrial applications such as heat exchangers and the mixing of fluids.-Airfoil turbulators:...

devices in the form of a zig-zag tape or multiple blow holes positioned in a span-wise line along the wing are used to trip laminar flow air into turbulent flow at a desired location on the wing. This flow control prevents the formation of laminar flow bubbles and ensures the absolute minimum drag. Bug-wipers may be installed to wipe the wings while in flight and remove insects that are disturbing the smooth flow of air over the wing.

Modern competition gliders carry jettisonable water ballast (in the wings and sometimes in the vertical stabilizer). The extra weight provided by the water ballast is advantageous if the lift is likely to be strong, and may also be used to adjust the glider's center of mass

Center of mass

In physics, the center of mass or barycenter of a system is the average location of all of its mass. In the case of a rigid body, the position of the center of mass is fixed in relation to the body...

. Moving the center of mass

Center of mass

toward the rear by carrying water in the vertical stabilizer reduces the required down-force from the horizontal stabilizer and the resultant drag from that down-force. Although heavier gliders have a slight disadvantage when climbing in rising air, they achieve a higher speed at any given glide angle. This is an advantage in strong conditions when the gliders spend only little time climbing in thermals. The pilot can jettison the water ballast before it becomes a disadvantage in weaker thermal conditions. Another use of water ballast is to dampen air turbulence such as might be encountered during ridge soaring. To avoid undue stress on the airframe, gliders must jettison any water ballast before landing.

Most gliders are built in Europe and are designed to EASA

European Aviation Safety Agency

The European Aviation Safety Agency is an agency of the European Union with offices in Cologne, Germany, which has been given regulatory and executive tasks in the field of civilian aviation safety. It was created on 15 July 2002, and it reached full functionality in 2008, taking over functions...

Certification Specification CS-22 (previously Joint Aviation Requirements

Joint Aviation Requirements

The Civil Aviation Authorities of certain European countries have agreed common comprehensive and detailed aviation requirements — referred to as the Joint Aviation Requirements — with a view to minimising Type Certification problems on joint ventures, and also to facilitate the export...

-22). These define minimum standards for safety in a wide range of characteristics such as controllability and strength. For example, gliders must have design features to minimize the possibility of incorrect assembly (gliders are often stowed in disassembled configuration, with at least the wings being detached). Automatic connection of the controls during rigging is the common method of achieving this.

Launch and flight

The two most common methods of launching sailplanes are by aerotow and by winch. When aerotowed, the glider is towed behind a powered aircraft using a rope about 60 meters (about 200 ft) long. The glider pilot releases the rope after reaching the desired altitude. However, the rope can be released by the towplane also. Winch launching uses a powerful stationary engine located on the ground at the far end of the launch area. The glider is attached to one end of 800–1200 metres (about 2,500-4,000 ft) of cable and the winch rapidly winds it in. The glider can gain about 1200-2000 feet of height with a winch launch (about 400 - 600 metres), depending on the head wind. Less often, automobiles are used to pull gliders into the air, by pulling them directly or through the use of a reverse pulley in a similar manner to the winch launch. Elastic ropes (known as bungees

Bungee cord

A bungee cord , also known as a shock cord, is an elastic cord composed of one or more elastic strands forming a core, usually covered in a woven cotton or polypropylene sheath...

) are occasionally used at some sites to launch gliders from slopes, if there is sufficient wind blowing up the hill. Bungee launching was the predominant method of launching early gliders. Some modern sailplanes can self-launch with the use of retractable engines and/or propellers, which can also be used to sustain flight once airborne (see motor glider

Motor glider

).

Once launched sailplanes try to gain height using 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....

or 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...

and can remain airborne for hours. This is known as 'soaring'. By finding lift sufficiently often experienced pilots fly cross-country, often on pre-declared tasks of hundreds of kilometers, usually back to the original launch site. Cross-country flying and aerobatics are the two forms of competitive gliding

Gliding competitions

Some 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:...

. For information about the forces in gliding flight, see lift-to-drag ratio

Lift-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...

Glide slope control

Pilots need some form of control over the glide slope to land the glider. In powered aircraft, this is done by reducing engine thrust. In gliders, other methods are used to either reduce the lift generated by the wing, increase the drag of the entire glider, or both. Glide slope is the distance traveled for each unit of height lost. In a steady wings-level glide with no wind, glide slope is the same as the lift/drag ratio (L/D) of the glider, called "L-over-D". Reducing lift from the wings and/or increasing drag will reduce the L/D allowing the glider to descend at a steeper angle with no increase in airspeed. Simply pointing the nose downwards only converts altitude into a higher airspeed with a minimal initial reduction in total energy. Gliders, because of their long low wings, create a high ground effect which can significantly increase the glide angle and make it difficult bring the glider to Earth in a short distance.

Sideslipping - A slip
Slip (aerodynamic)
A slip is an aerodynamic state where an aircraft is moving somewhat sideways as well as forward relative to the oncoming airflow. In other words, for a conventional aircraft, the nose will not be pointing directly into the relative wind .A slip is also a piloting maneuver where the pilot...

is performed by crossing the controls (rudder to right with ailerons to left, for example) so that the glider is no longer flying aligned with the air flow. This will present one side of the fuselage to the air-flow significantly increased drag. Early gliders primarily used slipping for glide slope control.
Spoilers - Spoilers
Spoiler (aeronautics)
In aeronautics, a spoiler is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly...

are movable control surfaces in the top of the wing, usually located mid-chord or near the spar which are raised into the air-flow to eliminate (spoil) the lift from the wing area behind the spoiler, disrupting the spanwise distribution of lift and increasing lift-induced drag
Lift-induced drag
In aerodynamics, lift-induced drag, induced drag, vortex drag, or sometimes drag due to lift, is a drag force that occurs whenever a moving object redirects the airflow coming at it. This drag force occurs in airplanes due to wings or a lifting body redirecting air to cause lift and also in cars...

. Spoilers significantly increase drag.
Air brakes - Air brakes
Air brake (aircraft)
In aeronautics, air brakes or speedbrakes are a type of flight control surface used on an aircraft to increase drag or increase the angle of approach during landing....

, also known as dive brakes, are devices whose primary purpose is to increase drag. On gliders, the spoilers act as air brakes. They are positioned on top of the wing and below the wing also. When slightly opened the upper brakes will spoil the lift, but when fully opened will present a large surface and so can provide significant drag. Some gliders have terminal velocity dive brakes, which provide enough drag to keep its speed below maximum permitted speed, even if the glider were pointing straight down. This capability is considered a safer way to descend without instruments through cloud (or to descend vertically in confined terrain), than the only alternative, an intentional spin
Spin (flight)
In aviation, a spin is an aggravated stall resulting in autorotation about the spin axis wherein the aircraft follows a corkscrew downward path. Spins can be entered intentionally or unintentionally, from any flight attitude and from practically any airspeed—all that is required is sufficient yaw...

.
Flaps - 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...

are movable surfaces on the trailing edge of the wing. The primary purpose of flaps is to change the camber
Camber (aerodynamics)
Camber, in aeronautics and aeronautical engineering, is the asymmetry between the top and the bottom surfaces of an aerofoil. An aerofoil that is not cambered is called a symmetric aerofoil...

of the wing and so change the lift-to-drag ratio of the wing. This reduces the 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...

speed and so allows reduced landing speeds. It was possible to lower the flaps on some older gliders by up to 90 degrees to increase drag significantly as well as increasing lift coefficient
Lift coefficient
The lift coefficient is a dimensionless coefficient that relates the lift generated by a lifting body, the dynamic pressure of the fluid flow around the body, and a reference area associated with the body...

when landing. Another feature that flapped gliders possess are negative flaps that are also able to deflect the trailing edge upward. This feature is included on some competition sailplanes in order to reduce the pitching moment
Pitching moment
In aerodynamics, the pitching moment on an airfoil is the moment produced by the aerodynamic force on the airfoil if that aerodynamic force is considered to be applied, not at the center of pressure, but at the aerodynamic center of the airfoil...

on the wing and allowing better glide ratios at higher speeds (a particularly desirable characteristic for racing sailplanes).
Parachute - Some high performance gliders from the 1960s and 1970s were designed to carry a small drogue parachute
Drogue parachute
A drogue parachute is a parachute designed to be deployed from a rapidly moving object in order to slow the object, or to provide control and stability, or as a pilot parachute to deploy a larger parachute...

because their air brakes are not particularly effective. This is stored in the tail-cone of the glider during flight. When deployed, a parachute causes a large increase in drag, but has a significant disadvantage over the other methods of controlling the glide slope. This is because a parachute does not allow the pilot to finely adjust the glide slope. Consequently a pilot may have to jettison the parachute entirely, if the glider is not going to reach the desired landing area.

Landing

Early glider designs used skids for landing, but modern types generally land on wheels. Some of the earliest gliders used a dolly with wheels for taking off and the dolly was jettisoned as the glider left the ground, leaving just the skid for landing. A glider may be designed so the center of gravity (CG)

Center of gravity of an aircraft

The center-of-gravity is the point at which an aircraft would balance if it were possible to suspend it at that point. It is the mass center of the aircraft, or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated. Its distance from the reference datum is...

is behind the main wheel so the glider sits nose high on the ground. Other designs may have the CG forward of the main wheel so the nose rests on a nose-wheel or skid when stopped. Skids are now mainly used only on training gliders such as the Schweizer SGS 2-33. Skids are around 100mm (3 inches) wide by 900mm (3 feet) long and run from the nose to the main wheel. Skids help with braking after landing by allowing the pilot to put forward pressure on the control stick, thus creating friction between the skid and the ground. The wing tips also have small skids or wheels to protect the wing tips from ground contact.

In most high performance gliders the undercarriage can be raised to reduce drag in flight and lowered for landing. Wheel brakes are provided to allow stopping once on the ground. These may be engaged by fully extending the spoilers/air-brakes or by using a separate control. Although there is only a single main wheel, the glider's wing can be kept level by using the flight controls until it is almost stationary.

Pilots usually land back at the airfield from which they took off, but a landing is possible in any flat field about 250 metres long. Ideally, should circumstances permit, a glider would fly a standard pattern

Airfield traffic pattern

An airfield traffic pattern is a standard path followed by aircraft when taking off or landing, while maintaining visual contact with the airfield....

, or circuit, in preparation for landing, typically starting at a height of 300 metres (1,000 feet). Glide slope control devices are then used to adjust the height to assure landing at the desired point. The ideal landing pattern positions the glider on final approach

Final approach (aviation)

A final approach is the last leg in an aircraft's approach to landing. In aviation radio terminology, it is often shortened to "final".In a standard airport landing pattern, which is usually used under visual meteorological conditions , aircraft turn from base leg to final within one to two miles...

so that a deployment of 30-60% of the spoilers/dive brakes/flaps brings it to the desired touchdown point. In this way the pilot has the option of opening or closing the spoilers/air-brakes to extend or steepen the descent to reach the touchdown point. This gives the pilot wide safety margins should unexpected events occur.

Instrumentation and other technical aids

In addition to an altimeter

Altimeter

An altimeter is an instrument used to measure the altitude of an object above a fixed level. The measurement of altitude is called altimetry, which is related to the term bathymetry, the measurement of depth underwater.-Pressure altimeter:...

, compass

Compass

A compass is a navigational instrument that shows directions in a frame of reference that is stationary relative to the surface of the earth. The frame of reference defines the four cardinal directions – north, south, east, and west. Intermediate directions are also defined...

, and an airspeed indicator

Airspeed indicator

The airspeed indicator or airspeed gauge is an instrument used in an aircraft to display the craft's airspeed, typically in knots, to the pilot.- Use :...

, gliders are often equipped with a variometer

Variometer

The term variometer also refers to a type of variable transformer or an instrument for measuring the magnitude and direction of a Magnetic field....

, turn and bank indicator

Turn and bank indicator

In aviation, the turn and bank indicator shows the rate of turn and the coordination of the turn. The rate of turn is indicated from a rate gyroscopically and the coordination of the turn is shown by either a pendulum or a heavy ball mounted in a curved sealed glass tube. No pitch information is...

and an airband

Airband

Airband or Aircraft band is the name for a group of frequencies in the VHF radio spectrum allocated to radio communication in civil aviation, sometimes also referred to as VHF, or phonetically as "Victor"...

radio (transceiver

Transceiver

A transceiver is a device comprising both a transmitter and a receiver which are combined and share common circuitry or a single housing. When no circuitry is common between transmit and receive functions, the device is a transmitter-receiver. The term originated in the early 1920s...

), each of which may be required in some countries. An Emergency Position-Indicating Radio Beacon

Emergency Position-Indicating Radio Beacon

Distress radio beacons, also known as emergency beacons, ELT or EPIRB, are tracking transmitters which aid in the detection and location of boats, aircraft, and people in distress. Strictly, they are radiobeacons that interface with worldwide offered service of Cospas-Sarsat, the international...

(ELT) may also be fitted into the glider to reduce search and rescue

Search and rescue

Search and rescue is the search for and provision of aid to people who are in distress or imminent danger.The general field of search and rescue includes many specialty sub-fields, mostly based upon terrain considerations...

time in case of an accident.

Much more than in other types of aviation, glider pilots depend on the variometer

Variometer

The term variometer also refers to a type of variable transformer or an instrument for measuring the magnitude and direction of a Magnetic field....

, which is a very sensitive vertical speed indicator, to measure the climb or sink rate of the plane. This enables the pilot to detect minute changes caused when the glider enters rising or sinking air masses. Both mechanical and electronic 'varios' are usually fitted to a glider. The electronic variometers produce a modulated sound of varying amplitude and frequency depending on the strength of the lift or sink, so that the pilot can concentrate on centering a thermal, watching for other traffic, on navigation, and weather conditions. Rising air is announced to the pilot as a rising tone, with increasing pitch as the lift increases. Conversely, descending air is announced with a lowering tone, which advises the pilot to escape the sink area as soon as possible. (Refer to the variometer
Variometer
The term variometer also refers to a type of variable transformer or an instrument for measuring the magnitude and direction of a Magnetic field....

article for more information).

Gliders' variometers are sometimes fitted with mechanical devices such as a "MacCready Ring" to indicate 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...

for given conditions. These devices are based on the mathematical theory attributed to Paul MacCready

Paul MacCready

Paul B. MacCready, Jr. was an American aeronautical engineer. He was the founder of AeroVironment and the designer of the human-powered aircraft that won the Kremer prize...

though it was first described by Wolfgang Späte

Wolfgang Späte

Major Wolfgang Späte was a German World War II Luftwaffe flying ace. He was also a recipient of the Knight's Cross of the Iron Cross with Oak Leaves...

in 1938. MacCready theory solves the problem of how fast a pilot should cruise between thermals, given both the average lift the pilot expects in the next thermal climb, as well as the amount of lift or sink he encounters in cruise mode. Electronic variometers make the same calculations automatically, after allowing for factors such as the glider's theoretical performance

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:...

, water ballast, headwinds/tailwinds and insects on the leading edges of the wings.

Soaring flight computers, often used in combination with PDAs

Personal digital assistant

A personal digital assistant , also known as a palmtop computer, or personal data assistant, is a mobile device that functions as a personal information manager. Current PDAs often have the ability to connect to the Internet...

running specialized soaring software, have been designed for use in gliders. Using GPS technology in conjunction with a barometric device these tools can:

Provide the glider's position in 3 dimensions by a moving map display
Alert the pilot to nearby airspace
Airspace
Airspace means the portion of the atmosphere controlled by a country above its territory, including its territorial waters or, more generally, any specific three-dimensional portion of the atmosphere....

restrictions
Indicate position along track and remaining distance and course direction
Show airports within theoretical gliding distance
Determine wind direction and speed at current altitude
Show historical lift information
Create a GPS log of the flight to provide proof for contests and gliding badges
Provide "final" glide information (i.e. showing if the glider can reach the finish without additional lift).
Indicate the best speed to fly under current conditions

After the flight the GPS data may be replayed on computer software for analysis and to follow the trace of one or more gliders against a backdrop of a map, an aerial photograph or the airspace.

Because collision with other gliders is a risk, the anti-collision device FLARM

FLARM

FLARM is an electronic device to selectively alert pilots to potential collisions between aircraft. It is not formally an implementation of ADS-B, as it is optimised for the specific needs of small aircraft such as gliders, not for long-range communication or ATC interaction.FLARM obtains its...

is becoming increasingly common in Europe and Australia. In the longer term, gliders may eventually be required in some European countries to fit transponders

Transponder (aviation)

A transponder is an electronic device that produces a response when it receives a radio-frequency interrogation...

once devices with low power requirements become available.

Markings

To distinguish gliders in flight, very large numbers/letters are sometimes displayed on the fin and wings. Registrations on narrow fuselages are difficult to read. These numbers were first added for use by ground-based observers in competitions, and are therefore known as "competition numbers" or "contest IDs". They are unrelated to the glider's registration number, and are assigned by national gliding associations. They are useful in radio communications between gliders, so glider pilots often use their competition number as their call-signs.

Fibreglass gliders are white in color after manufacture. Since fibreglass resin softens at high temperatures, white is used almost universally to reduce temperature rise due to solar heating. Color is not used except for a few small bright patches on the wing tips; these patches (typically bright red) improve gliders' visibility to other aircraft while in flight (and are a requirement for mountain flying in France). Non-fibreglass gliders (those made of aluminum and wood) are not subject to the temperature-weakening problem of fibreglass, and can be painted any color at the owner's choosing; they are often quite brightly painted.

Comparison of gliders with hang gliders and paragliders

There is sometimes confusion about gliders, hang gliders and paragliders. In particular paragliders and hang gliders are both foot-launched. The main differences between the types are:

Competition classes of glider

Eight competition classes

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...

of glider have been defined by the FAI

Fédération Aéronautique Internationale

The Fédération Aéronautique Internationale is the world governing body for air sports and aeronautics and astronautics world records. Its head office is in Lausanne, Switzerland. This includes man-carrying aerospace vehicles from balloons to spacecraft, and unmanned aerial vehicles...

. They are:

Standard Class (No flaps, 15 m wing-span, water ballast allowed)
15 metre Class (Flaps allowed, 15 m wing-span, water ballast allowed)
18 metre Class (Flaps allowed, 18 m wing-span, water ballast allowed)
Open Class (No restrictions except a limit of 850 kg for the maximum all-up weight)
Two Seater Class (maximum wing-span of 20 m), also known by the German name "Doppelsitzer"
Club Class (This class allows a wide range of older small gliders with different performance and so the scores have to be adjusted by handicapping
Handicapping
Handicapping, in sport and games, is the practice of assigning advantage through scoring compensation or other advantage given to different contestants to equalize the chances of winning. The word also applies to the various methods by which the advantage is calculated...

. Water ballast is not allowed).
World Class (The FAI Gliding Commission
FAI Gliding Commission
The International Gliding Commission is a leading international governing body for the sport of gliding.It is one of several Air Sport Commissions of the Fédération Aéronautique Internationale , or "World Air Sports Federation"...

which is part of the FAI and an associated body called Organisation Scientifique et Technique du Vol à Voile
Organisation Scientifique et Technique du Vol à Voile
Organisation Scientifique et Technique du Vol à Voile is a body associated with the FAI Gliding Commission . The FAI IGC oversees the sport of gliding worldwide and is a department of the Fédération Aéronautique Internationale ....

(OSTIV) announced a competition in 1989 for a low-cost glider, which had moderate performance, was easy to assemble and to handle, and was safe for low hours pilots to fly. The winning design was announced in 1993 as the Warsaw Polytechnic PW-5
Politechniki Warszawskiej PW-5
|- References :InlineGeneral* * Carswell D, The Low Time Pilot in the PW-5 World Class Sailplane, Soaring, April 1997* Thomas F, Fundamentals of Sailplane Design, College Park Press, 1999* Simons M, Segelflugzeuge 1965-2000, Eqip, 2004* * * * * * * *...

. This allows competitions to be run with only one type of glider.
Ultralight Class, for gliders with a maximum mass less than 220 kg.

Major manufacturers of gliders

A large proportion of gliders have been and are still made in Germany the birthplace of the sport. The principal German manufacturers are:

DG Flugzeugbau GmbH
Schempp-Hirth GmbH
Schempp-Hirth
Schempp-Hirth Flugzeugbau GmbH is a glider manufacturer based in Kirchheim unter Teck, Germany.-History:Martin Schempp founded his own company in Göppingen in 1935, with the assistance of Wolf Hirth. The company was initially called "Sportflugzeugbau Göppingen Martin Schempp"...
Alexander Schleicher GmbH & Co
Alexander Schleicher GmbH & Co
Alexander Schleicher GmbH & Co is a major manufacturer of sailplanes located in Poppenhausen, near Fulda in Germany. It is also the oldest sailplane manufacturer in the world....

though there are other specialist manufacturers in Germany, Poland and in other eastern European countries.

External links

Information about all types of glider:
- Sailplane Directory - An enthusiast's web-site that lists manufacturers and models of gliders, past and present.
- KANJA Ultra Light Glider Eight Aeronautical Engineering students build a Glider, Kanja.
FAI webpages
- FAI records- sporting aviation page with international world soaring records in distances, speeds, routes, and altitude
- Links to all national gliding federations

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.