Glider (sailplane)

[1][2] This unpowered aircraft can use naturally occurring currents of rising air in the atmosphere to gain altitude.

Gliders benefit from producing very low drag for any given amount of lift, and this is best achieved with long, thin wings, a slender fuselage and smooth surfaces with an absence of protuberances.

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.

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.

These were known as "primary gliders" 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.

Later fuselages made of fabric-covered steel tube were married to wood and fabric wings for lightness and strength.

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.

Flaps are fitted to the trailing edges of the wings on some gliders to optimise lift and drag at a wide range of speeds.

The wings of a modern racing glider are designed by computers to create a low-drag laminar flow airfoil.

Special aerodynamic seals are used at the ailerons, rudder and elevator to prevent the flow of air through control surface gaps.

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.

Although heavier gliders have a slight disadvantage when climbing in rising air, they achieve a higher speed at any given glide angle.

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.

[11] Once launched, gliders try to gain height using thermals, ridge lift, lee waves or convergence zones and can remain airborne for hours.

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.

Simply pointing the nose downwards only converts altitude into a higher airspeed with a minimal initial reduction in total energy.

Ideally, should circumstances permit, a glider would fly a standard pattern, or circuit, in preparation for landing, typically starting at a height of 300 metres (1,000 ft).

The ideal landing pattern positions the glider on final approach 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.

If such control devices are not sufficient, the pilot may utilize maneuvers such as a forward slip to further steepen the glider slope.

In addition to an altimeter, compass, and an airspeed indicator, gliders are often equipped with a variometer and an airband radio (transceiver), each of which may be required in some countries.

An Emergency Position-Indicating Radio Beacon (ELT) may also be fitted into the glider to reduce search and rescue time in case of an accident.

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

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.

Conversely, descending air is announced with a lowering tone, which advises the pilot to escape the sink area as soon as possible.

Electronic variometers make the same calculations automatically, after allowing for factors such as the glider's theoretical performance, water ballast, headwinds/tailwinds and insects on the leading edges of the wings.

Fibreglass resin loses strength as its temperature rises into the range achievable in direct sun on a hot day.

[15] Non-fibreglass gliders made of aluminum or wood are not so subject to deterioration at higher temperatures and are often quite brightly painted.

Elsewhere in the world, there are other manufacturers such as Jonker Sailplanes in South Africa, Sportinė Aviacija in Lithuania, Allstar PZL in Poland, Let Kunovice and HpH in the Czech Republic and AMS Flight in Slovenia.