A radio-controlled glider is a type of radio-controlled aircraft that normally does not have any form of propulsion. They are able to sustain continuous flight by exploiting the lift produced by slopes and thermals, controlled remotely from the ground with a transmitter. They can be constructed from a variety of materials, including wood, plastic, polymer foams, and composites, and can vary in wing loading from very light to relatively heavy, depending on their intended use. International radio-controlled glider competitions are regulated by the Fédération Aéronautique Internationale (FAI) although many countries have their own national classes.
Launching methods
Hand launch
Hand launching is the simplest way to get a model glider into the air. Depending on craft design and the conditions at launch—the pilot or an assistant need only to gently 'throw' it into the wind, at an angle deemed best suited, usually between horizontal and 45 degrees of zenith. In this manner a successful launch is possible with very little effort. This method is usually utilised when slope soaring, where with a little experience, it is possible to simply hold the craft above the head at the correct angle and let go.
Towline launch In this method another person runs along the ground pulling a 50-to-150-metre (160 to 490 ft) line with the glider attached to the end, while the pilot steers it. It can be performed on any flat piece of terrain, as the glider is given sufficient altitude during the launch. A variation of this method uses a pulley with the line staked to the ground and the line passing around it before going to the glider. The tow man runs with the pulley (still running away from the pilot) which doubles his effective speed. A variation of this is used in F3J competition when two tow men run with the pulley to generate much faster launches (although the models have to be sufficiently strong to handle the loads placed upon them by this method) which allows the model to use the energy to "zoom" (the model is pointed downwards briefly to convert the stored energy in the stretched monofilament line into airspeed, and once the airspeed exceeds the towline speed the line is released, before being rotated into a nose high attitude and the speed being converted back into additional height).
Bungee/Hi-start launch This launch is a variant of the towline launch performed alone. The running person is replaced by a combined length of elastic cord or rubber tubing and line which is attached to the ground upwind of the pilot, often using a 'corkscrew' dog stake. Variations in rubber diameter, model weight and headwind determine the launch height.
'Piggyback' launch A second, powered radio-controlled aircraft lifts the model glider into the air, attached to a special cradle which is, in turn, mounted to either the top or the bottom of the carrier aircraft. Although this method is spectacular, it requires an experienced pilot to steer the carrier aircraft as the addition of the glider can significantly affect the handling of their model. Special care must be also taken by the pilots of both models to avoid a collision after the release of the glider.
Discus launch
This method of launching can be performed only on a special type of glider - a Discus Launch Glider (DLG). To launch the model into the air, the pilot holds the model by the tip of a wing, spins 360°, rotating the model around their body and then releases hold of the model allowing it to launch at high speed and climb to height. Although DLGs are a fairly new type of model glider, they are gaining popularity due to their ease of launching and efficient flight characteristics. DLG models are used in the F3K contest class, as defined by the FAI.
Aerotow launch As full-size aerotowing using a radio-controlled tug, often used for launching larger scale gliders.
Winch launch As full-size winch launching but using a small electric motor (usually based on a car starter motor) and a reverse pulley staked to the ground upwind. The launch speed is controlled by the pilot using a foot pedal. A parachute is used (pulled shut by the launch tension) to assist in preventing the winch spool overrunning when the model is released. Variations have included multiple batteries and motors but regulations were put in place in the late 1980s by the FAI to limit the winch power used in FAI class competitions.
Forms of flight
Slope soaring Slope soaring refers to unpowered aircraft sustaining flight on the lift produced by wind blowing up the face of a steep slope on hills, mountains, and cliffs. See the Ridge Lift page for more information on the lift mechanism of "frontside" flying. Dynamic soaring, utilizing the leeward or "backside" of a hill, has recently become very popular.
Disciplines
F3F Another form of slope R/C glider racing is called F3F. The F3F is one of many competition categories for model and full scale aircraft that are defined by the Fédération Aéronautique Internationale (FAI). In F3F racing, the pilot is timed on the course for 10 legs of 100 metres (330 ft) for a total distance of 1 kilometre (0.62 mi). All pilots fly a timed run for each round. The fastest pilot receives 1,000 points for the round and all others are given a percentage which is determined by the ratio of their time to the fast time for the round. At the end of the competition, the pilot with the most points wins.
Combat Combat is usually flown with expanded polypropylene (EPP) foam models due to their impact resistance. Each pilot tries to knock the other's aircraft physically out of the air. A "kill" is scored only when the opponents aircraft hits the ground. If a hit occurs and each aircraft recovers and remains airborne, the hits generally do not count. Often this activity includes extreme maneuvers and aerobatics. This particular class of slope glider is extremely popular, as novices can learn to fly with a model that is practically indestructible. There is also a wide appeal in owning an inexpensive glider that is also a stand-off scale model, particularly of favorite World War II fighters, e.g. the Spitfire/Seafire, P-51 Mustang and P-47 Thunderbolt.
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