Gliders or sailplanes are aircraft that do not have motors for propulsion, they use updrafts of warmer air to provide lift or the air moving over a physical barrier, such as a range of mountains. The glide ratio is the distance traveled horizontally divided by the distance traveled vertically. Gliders may have glide ratios of 30:1 or better.
A glider has similar controls to a conventional aircraft but instead of flaps it has spoilers. Flaps alter the geometry of the wing to provide greater lift while spoilers interrupt airflow over the wing to reduce lift. Spoilers do not alter the attitude of the aircraft, they simply steepen the glide angle.
Gliders are launched by winch or by towing behind a powered aircraft. There are a few gliders that have engines, so they can be self-launched or fly under power to the destination if conditions for gliding are not good.
Gliders were used in World War II to deliver troops to a battlefield. These gliders were towed behind other aircraft until released to glide to their destination.
The Blanik glider is a two-seat trainer with a forward swept wing. The pilot flies from the front seat with the passenger or instructor in the rear. The schliecher sailplanes such as the ASW-24 are examples of high performance gliders.