rely on ground signs such as surface wind velocity, temperature and direction; signs such as circling birds, bugs, or rising particulates; and changes of direction or attitude of the glider due to the thermal itself. The pilot uses these signs to resolve the approximate location of the thermal. For F3K tasks where longer durations are needed, positioning and maintaining the model glider in thermal rising air is paramount. Contest strategy includes determining the location of thermals before the pilot launches. Discus launched gliders can be made from a combination of foam, balsa, carbon fiber, kevlar, and other materials. Prices of these models range from $100 to $900 plus. See also Model aircraft Radio-controlled aircraft References External links The Art of Discus Launch gliders DLG The British Association of Radio Control Soarers (BARCS) Charles River Radio Controllers - where detailed DLG plans and related articles can be found Radio-controlled aircraft