Gliders

Gliders are aircraft with no internal powerplant. Model gliders are generally hand-launched or catapult-launched (using an elastic bungee.) The newer "discus" style of wingtip handlaunching has mostly supplanted the earlier "javelin" type of launch. Other launch methods include ground based power winches, hand-towing, and towing aloft using a second powered aircraft. As gliders are unpowered, flight must be sustained throughout exploitation of the natural wind in the environment. A hill or slope will often produce updrafts of air which will sustain the flight of a glider. This is called slope soaring, and when piloted skillfully, R/C gliders can stay airborne for as long as the updraft prevails. Another means of attaining height in a glider is exploitation of thermals, which are bubbles or columns of warm rising air created by hot spots on the ground. As with a powered aircraft, lift is obtained by the action of the wings as the aircraft moves through the air, but in a glider, height can only be gained by flying through air that is rising faster than the aircraft is sinking relative to the airflow.
Sailplanes are flown using available thermal lift. As thermals can only be indirectly experiential through the reaction of the aircraft to the invisible rising air currents, pilots find sailplane flying challenging yet rewarding.