“A Discus Launch Glider (DLG) is a radio controlled model sailplane launched using a ‘discus launch’ in which the glider is held by a wingtip and rotated around the flyer by hand before release. Using this method of launching the average flier can achieve launch heights of greater than 140 feet (43 m), with the better throwers exceeding 200-foot (61 m) high launches.”
The discus method of hand launching has now in effect replaced the older ‘javelin style’ launch, where a hand launched model glider would be launched over-arm, like a javelin would be thrown. The discus launch is far easier, more efficient and less physically demanding than the javelin launch.
Although some DLG designs utilize a traditional built-up construction using balsa wood and covering film, most DLG models are generally now constructed from composite materials, in the form of Kevlar, carbon fiber and glass fiber. Fuselages are molded in Kevlar/carbon and epoxy, with wings either molded as a hollow composite shell, or vacuum bagged over a wire-cut foam core.
Most DLG models use aileron, rudder and elevator control, with the ailerons also being used as camber changing flaps for different modes of flight and also as air-brakes for landing. A modern DLG model weighs approximately 9 or 10 ounces (255-283 grams) and has sophisticated aerodynamics. Many pilots use computer radio transmitters with full mixing and flight mode capabilities in order to optimize performance and set up the models for flight as near perfectly as possible.
DLG models are used for both general fun/sport flying and also for contest flying.
F3K is the international contest class for radio controlled, hand-launched model gliders.
Although the roots of RC hand-launched gliders can be traced back to the late 1970s, F3K is a relatively new aeromodelling discipline, becoming officially recognized by the FAI (international body responsible for aeromodelling competition disciplines) in 2007.
F3K gliders are limited to a 1.5 meter wingspan. F3K competitions consist of a group of fliers completing a number of predefined flight tasks involving launching, flying and landing the model in a number of timed durations. Just the hand launch and thermal currents of rising air (thermals) are used to sustain the flight. Since thermals cannot be seen, F3K pilots 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.”