Details of the Silent Flight Technical Committee can be found here.

A radio-controlled glider is a type of radio-controlled aircraft that normally does not have any form of propulsion, they are often referred to as "Silent Flight". 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.

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.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. 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 manoeuvres 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 favourite World War II fighters, e.g. the Spitfire, P-51 Mustang and P-47 Thunderbolt.

Pylon racing

Slope Pylon racing is essentially using the slope lift to race along the "lift zone"—generally parallel to the slope. This can be MoM (man-on-man) racing, in which 2 to 4 gliders compete against each other on the same course. Scoring is similar to match racing in the sport of sailing - the first pilot to complete the course receives one point, the second two points and so on. At the end of the competition, the pilot with the fewest points wins.

Power Scale Soaring

PSS is all about building and flying scale model gliders of full-sized jet-, rocket- or piston-powered aircraft. World War II prop planes such as the P-51, Supermarine Spitfire and Me 109 are common subjects for PSS planes, however PSS aircraft produced to date have ranged from the early biplanes through to modern jet fighters and even commercial airliners.

The challenge with Power Scale Soaring is to build a model as close to scale as possible whilst at the same time ensuring the model has good flying characteristics.

Model EPP jet fighter slope soarers have become extremely popular, usually either 1950s and some 1960s designs e.g. the MiG-15, the P-80 Shooting Star, and the F-86 Sabre, and the Northrop F-5 and F-20. More ambitious modellers are experimenting with more recent jet fighters such as the F-16, F-15, MiG-29 and Su-27.

Dynamic soaring
Slope Aerobatics

Slope aerobatics involves flying aerobatic figures and sequences on the slope with gliders that have been optimized for aerobatic flight. These gliders typically using aerofoils that allow identical upright and inverted performance, as well as unique fuselage shapes that permit some amount of sustained knife edge flight. Most gliders feature 3 axes of control (aileron, elevator, and rudder), and often use flaperons to extend the capabilities of the aerofoils for maximum aerobatic performance. Some of the most advanced slope aerobatics gliders feature all-moving elevators and rudders capable of 180* rotation, allowing them to perform "flips" around the pitch or yaw axis, respectively. Airframes are constructed of any material, with wood, fiberglass and/or carbon fibre being preferred for gliders intended for precision aerobatics, and EPP (expanded polypropylene) being popular for low altitude aerobatics where interactions with the ground - like wingtip and/or inverted fin drags, or touch-and-goes off of obstacles - are commonly performed and desired.

Thermal soaring

Thermal soaring uses columns of warm, rising air called thermals to provide lift for a glider. Thermal soaring gliders are normally launched with a bungee cord catapult, a winch or towed by a powered model aircraft. A discus launch glider (DLG) is simply launched into the air with a spinning motion much like a discus throw.

Discus launching is often combined with slope soaring. Thermals from elsewhere can drift in over the hill to combine with the hill lift or they can be formed by the hill itself, if the slope is angled to the sun causing the slope to heat up faster than in the surrounding areas. The resulting warm air will then flow upwards pulling in air from the valley below, causing a wind up the slope. The lift is thus a combination of ridge lift and thermal. This has produced a new term, "slermal", to describe the mixture of both slope lift and thermal activity coming up the hill face.

F3J

F3J is one of many competition categories for model and full scale aircraft that are defined by the Fédération Aéronautique Internationale (FAI). F3J is a man of man compettition where a group typically of 6 to 10 pilots launch the glider at the same time from a flat field and compete to keep the model flying for 10 minutes. Then they have to land the closest as possible to a predetemined spot. A combination of the flying time and precision landing is made for the scoring. Flying longer and landing far from the spot has penalties.

F3B

F3B is a competition category defined by the Fédération Aéronautique Internationale (FAI). It is a flat field soaring category where the glider is launch with help of a winch. There are three tasks to perform. Thermal duration, that is to keep flying for 10 minutes and land in the spot; distance, maximum number of legs in three minutes; and speed, minimum time to cover six legs of 150 metres (490 ft) each. The three tasks have to be done with the same plane. F3B gliders are of the type of multitask glider, similar to F3F gliders with a composite layout lighter.

F3K

F3K is the competition category for discuss launched models where the competition is divided in different tasks and combined tasks in a way that the pilot may launch several times within a task, for example adding consecutive flying times as long as the time of the last flight is longer than the previous one.

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 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.

Discus launch

Aero tow launch

As full-size aero towing 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.