Glider (sailplane)
A glider or sailplane is a type of
In North America the term 'sailplane' is also used to describe this type of aircraft. In other parts of the English-speaking world, the word 'glider' is more common.
Types
Gliders benefit from producing very low
Sailplanes have rigid wings and either skids or undercarriage.[2] In contrast hang gliders and paragliders use the pilot's feet for the start of the launch and for the landing. These latter types are described in separate articles, though their differences from sailplanes are covered below. Sailplanes are usually launched by winch or aerotow, though other methods, auto tow and bungee, are occasionally used.
These days almost all gliders are sailplanes, but in the past many gliders were not. These types did not soar. They were simply engine-less aircraft towed by another aircraft to a desired destination and then cast off for landing. The prime example of non-soaring gliders were military gliders (such as those used in the Second World War). They were often used just once and then usually abandoned after landing, having served their purpose.
Motor gliders are gliders with engines which can be used for extending a flight and even, in some cases, for take-off. Some high-performance motor gliders (known as "self-sustaining" gliders) may have an engine-driven retractable propeller which can be used to sustain flight. Other motor gliders have enough thrust to launch themselves before the engine is retracted and are known as "self-launching" gliders. Another type is the self-launching "touring motor glider", where the pilot can switch the engine on and off in flight without retracting the propeller.[3]
History
After World War I gliders were first built for sporting purposes in Germany. Germany's strong links to gliding were to a large degree due to post-World War I regulations forbidding the construction and flight of motorised planes in Germany, so the country's aircraft enthusiasts often turned to gliders[5] and were actively encouraged by the German government, particularly at flying sites suited to gliding flight like the Wasserkuppe.[6]
The sporting use of gliders rapidly evolved in the 1930s and is now their main application. As their performance improved, gliders began to be used for cross-country flying and now regularly fly hundreds or even thousands of kilometres in a day[7][8] if the weather is suitable.
Design
Early gliders had no
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
With each generation of materials and with the improvements in
High aerodynamic efficiency is essential to achieve a good gliding performance, and so gliders often have aerodynamic features seldom found in other aircraft. The wings of a modern racing glider are designed by computers to create a low-drag
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
Most gliders are built in Europe and are designed to
Launch and flight
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The two most common methods of launching sailplanes are by aerotow and by winch.[10] When aerotowed, the sailplane is towed behind a powered aircraft using a rope about 60 metres (200 ft) long. The sailplane pilot releases the rope after reaching the desired altitude. However, the rope can be released by the towplane also in case of emergency. Winch launching uses a powerful stationary engine located on the ground at the far end of the launch area. The sailplane is attached to one end of 800 to 1,200 metres (2,600 to 3,900 ft) of cable and the winch rapidly winds it in. The sailplane can gain about 270 to 910 metres (900 to 3,000 ft) of height with a winch launch, depending on the headwind. Less often, automobiles are used to pull sailplanes into the air, either 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) 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 gliders can self-launch by using retractable engines or just retractable propellers. (see motor glider). These engines can use internal combustion or battery power.[11]
Once launched, gliders try to gain height using
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.
- Sideslipping
- A slipis 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 increasing drag. Early gliders primarily used slipping for glide slope control.
- Spoilers
- Spoilers 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. Spoilers significantly increase drag.
- Air brakes
- spin.
- Flaps
- stall speed. Another feature that some flapped gliders possess is negative flaps that are also able to deflect the trailing edge upward a small amount. This feature is included on some competition gliders in order to reduce the pitching momentacting on the wing and so reduce the downwards force that must be provided by the horizontal stabiliser; this reduces the induced drag acting on the stabilizer. On some types the flaps and ailerons are linked, known a 'flaperons'. Simultaneous movement of these allows a greater rate of roll.
- Parachute
- Some high performance gliders from the 1960s and 1970s were designed to carry a small drogue parachute because their air brakes were not particularly effective. This was 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
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
Auxiliary engines
Most gliders require assistance to launch, though some have an engine powerful enough to launch unaided. In addition, a high proportion of new gliders have an engine which will sustain the glider in the air, but is insufficiently powerful to launch the glider. Compared with self-launchers these lower powered engines have advantages in weight, lower costs and pilot licensing. The engines can be electric, jet, or two-stroke gasoline.
-
Glider showing propeller of front electric sustainer. -
Small retractable jet engines are on some types such as this HPH Shark -
Retractable turbo two-stroke sustainer engine -
Turbo engine retracting 1 -
Turbo engine retracting 2 -
Turbo engine retracting 3
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Instrumentation and other technical aids
Gliders in continental Europe use metric units, like
In addition to an
Much more than in other types of aviation, glider pilots depend on the
Variometers are sometimes fitted with mechanical or electronic devices to indicate the optimal
Soaring flight computers running specialized soaring software, have been designed for use in gliders. Using
- Provide the glider's position in 3 dimensions by a moving map display
- Alert the pilot to nearby airspace 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.
Markings
So that ground-based observers may identify gliders in flight or in gliding competition, registration marks ("insignias" or "competition numbers" or "contest ID") are displayed in large characters on the underside of a single wing, and also on the fin and rudder. Registration marks are assigned by gliding associations such as the US Soaring Society of America, and are unrelated to national registrations issued by entities such as the US Federal Aviation Administration.[14] This need for visual ID has somewhat been supplanted by GPS position recording. Insignias are useful in two ways: First, they are used in radio communications between gliders, as pilots use their competition number as their call signs. Secondly, to easily tell a glider's contest ID when flying in close proximity to one another to alert them of potential dangers. For example, during gatherings of multiple gliders within thermals (known as "gaggles"), one pilot might report "Six-Seven-Romeo I am right below you".
Comparison of types
There is sometimes confusion about gliders/sailplanes, hang gliders and paragliders. In particular, paragliders and hang gliders are both foot-launched. The main differences between the types are:
Paragliders
|
Hang gliders
|
Gliders/Sailplanes | |
|---|---|---|---|
| Undercarriage | pilot's legs used for take-off and landing | pilot's legs used for take-off and landing | aircraft takes off and lands using a wheeled undercarriage or skids |
| Wing structure | entirely flexible, with shape maintained purely by the pressure of air flowing into and over the wing in flight and the tension of the lines | generally flexible but supported on a rigid frame which determines its shape (note that rigid-wing hang gliders also exist) | rigid wing surface which totally encases wing structure |
| Pilot position | sitting in a harness | usually lying prone in a cocoon-like harness suspended from the wing; seated and supine are also possible | sitting in a seat with a harness, surrounded by a crash-resistant structure |
| Speed range (stall speed – max speed) |
slowest – typically 25 to 60 km/h for recreational gliders (over 50 km/h requires use of speed bar),[16] hence easier to launch and fly in light winds; least wind penetration; pitch variation can be achieved with the controls | faster than paragliders, slower than gliders/sailplaines | maximum speed up to about 280 km/h (170 mph);[17] stall speed typically 65 km/h (40 mph);[17] able to fly in windier turbulent conditions and can outrun bad weather; good penetration into a headwind |
| Maximum glide ratio | about 10, relatively poor glide performance makes long distance flights more difficult; current (as of May 2017[update]) world record is 564 kilometres (350 mi)[18] | about 17, with up to 20 for rigid wings | open class sailplanes – typically around 60:1, but in more common 15–18 meter span aircraft, glide ratios are between 38:1 and 52:1;[19] high glide performance enabling long distance flight, with 3,000 kilometres (1,900 mi) being current (as of November 2010[update]) record[20] |
| Turn radius | tightest turn radius[citation needed] | somewhat larger turn radius than paragliders, tigher than gliders/sailplanes[citation needed] | widest turn radius but still able to circle tightly in thermals[21] |
| Landing | smallest space needed to land, offering more landing options from cross-country flights; also easiest to pack up and carry like a bag to the nearest road | 15 m to 60 m length flat area required; can be derigged by one person and carried to the nearest road | landings can be performed in ~250 m length field. Aerial retrieve may be possible but if not, specialized trailer needed to retrieve by road. Some sailplanes have engines that remove the need for an out-landing, if successfully started on time |
| Learning | simplest and quickest to learn | teaching is done in single and two-seat hang gliders | teaching is done in a two-seat glider with dual controls |
| Convenience | packs smaller (easier to transport and store) | more awkward to transport and store; longer to rig and de-rig; often transported on the roof of a car | often stored and transported in purpose-built trailers about 9 metres long, from which they are rigged. Although rigging aids allow a single person to rig a glider, usually the rigging involves 2 or 3 people. Some frequently used sailplanes are stored already rigged in hangars. |
| Cost | cost of new is €1500 and up,[22] cheapest but shortest lasting (around 500 hours flying time, depending on treatment), active second-hand market[23] | cost of new glider very high (top of the range 18 m turbo with instruments and trailer €250,000) but it is long lasting (up to several decades), so active second-hand market; typical cost is from €2,000 to €145,000[24] |
Competition classes
Eight competition classes of glider have been defined by the FAI.[25] 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, so the scores have to be adjusted by handicapping. Water ballast is not allowed).
- World Class (The Warsaw Polytechnic PW-5. 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
A large proportion of gliders have been and are still made in Germany,[26] the birthplace of the sport. In Germany there are several manufacturers but the three principal companies are:
- DG Flugzeugbau GmbH
- Schempp-Hirth GmbH
- Alexander Schleicher GmbH & Co
Germany also has
See also
- History
- Gliding as a sport
- Other unpowered aircraft
- Unpowered flying toys and models
References
- ^ "FAA Glider handbook" (PDF). Archived (PDF) from the original on 25 August 2017. Retrieved 11 September 2014.
- ^ a b Definition of gliders used for sporting purposes in FAI Sporting Code
- ISBN 978-0-11-790501-6.
- ^ "Flight magazine 1954". Archived from the original on 9 May 2011. Retrieved 20 February 2009.
- ^ "History of Gliding & Soaring" (PDF). United States Soaring Team. 7 August 2004. Archived from the original (PDF) on 6 June 2011. Retrieved 23 February 2010.
- ^ "Gliding Magazine | Features". Archived from the original on 26 July 2011. Retrieved 23 February 2010.
- ^ "List of FAI claimed and ratified records". Archived from the original on 16 March 2015. Retrieved 11 September 2014.
- ^ "On-line contest web page". Archived from the original on 10 February 2010. Retrieved 3 April 2010.
- ^ "Space Shuttle Technical Conference pg 258" (PDF). Archived (PDF) from the original on 17 December 2008. Retrieved 19 February 2009.
- ISBN 978-0-7136-6148-4.
- ^ "SFPE Europe Digital Issue 30". www.sfpe.org. Archived from the original on 13 July 2023. Retrieved 13 July 2023.
- ^ "MacCready Theory". Archived from the original on 17 September 2007. Retrieved 24 August 2006.
- ^ Pettersson, Åke (October–November 2006). "Letters". Sailplane & Gliding. 57 (5). British Gliding Association: 6.
- ^ Reference to competition numbers on FAI web site Archived 7 October 2008 at the Wayback Machine
- ^ "Gliding In France". Archived from the original on 2 February 2010. Retrieved 23 February 2010.
- ^ "Technical data for Advance Omega 8". Advance AG. Archived from the original on 30 May 2013. Retrieved 22 October 2011.
- ^ a b Flight Manual of Scheicher ASW27b. Alexander Schleicher GmbH & Co. 2003.
- ^ "FAI Paragliding record". Fédération Aéronautique Internationale. Archived from the original on 9 May 2011. Retrieved 30 November 2010.
- ^ "Handicap list 2008" (PDF). Deutsche Meisterschaft im Streckensegelflug. Deutscher Aero Club. Archived from the original (PDF) on 24 February 2009. Retrieved 7 August 2008.
- ^ "FAI records". Fédération Aéronautique Internationale. Archived from the original on 11 September 2011. Retrieved 30 November 2010.
- ISBN 1-85310-504-X.
- ^ "Brochures Ozone". Ozone France. Archived from the original on 27 October 2013. Retrieved 21 October 2011.
- ^ "Typical set of classified ads for paragliders". Archived from the original on 30 March 2012. Retrieved 22 October 2011.
- ^ "Typical set of classified ads for gliders". Archived from the original on 6 December 2010. Retrieved 18 January 2011.
- ^ Competition classes as defined by FAI
- ^ Francis Humblet (November–December 2011). "World Glider Production". Gliding International.
- ISBN 978-3-9808838-1-8.
External links
- Information about all types of glider
- Sailplane Directory at the Wayback Machine (archived 21 April 2016) – An enthusiast's web-site that lists manufacturers and models of gliders, past and present.
- FAI webpages
- FAI records Archived 17 October 2021 at the Wayback Machine – sporting aviation page with international world soaring records in distances, speeds, routes, and altitude
- National Gliding Federations at the Wayback Machine (archived 23 November 2010)
