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 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.Hughes 1975, p. 181.
'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.Hughes 1975, p. 193.
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.Hughes 1975, p. 257. 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.Stringwell 1997, p. 17. 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 for a total distance of . 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.Hughes 1975, p. 105.
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 popular, as novices can learn to fly with a less fragile and cheaper model that can work as a stand-off scale model. Particularly popular combat gliders are World War II fighters, e.g. the Spitfire/Seafire, P-51 Mustang and P-47 Thunderbolt.
Ridge racing Ridge racing (or pylon racing where markers are present) 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.
PSS PSS, or Power Scale Soaring, 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 Bf 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
Dynamic soaring is a relatively new style of flying model gliders whereby the windshear just downwind of certain slopes can be used to create high speeds. It involves gaining altitude, then soaring into a patch of dead air, then back to the lift to gain speed.
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 airfoils 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 three axes of control (aileron, elevator, and rudder), and often use flaperons to extend the capabilities of the airfoils 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 fiber 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.
Thermal soaring 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 on man thermal soaring competition undertaken on a flat field site (ideally 1–2 miles from workable slope lift). Models are launched by a monofilament tow line, pulled by two towers who run with the line or a pulley. The method is similar to winch launching without any electrical equipment required. A group typically of from 6 to 10 pilots try to fly for as long as possible within a 10-minute period of time (known as a slot). Within the slot time they have to launch the glider, fly for as long as possible and land as close as they can to a predetermined spot, without overflying the end of the slot time. If the nose of the model comes to rest on the centre of the landing spot then 100 landing points are scored. Landing points are reduced by 1 point every 20 cm from the center of the landing circle. A combination of the flying time (as a percentage of the longest flight within the slot) and precision landing makes up scoring. A maximum of 1000 points is awarded to the winner of each group. Overflying the slot time results in a penalty and the withdrawal of any landing points bonus.
The models have evolved into predominantly all composite gliders of 3.4–4 m wingspan with full span flaps and ailerons, sufficiently strong to take a two-man tow in a wind of up to 20 mph. Advances in composite construction have reduced the flying weights of these models to less than 2 kg. Ballast weight is added to increase the flying speed during windy weather.
The individual winner of the competition is determined by a fly-off in which the top 10−12 competitors fly after the preliminary rounds. The fly-off task is 15 minutes, making the soaring task more difficult. Typical winning scores at a World Championships are 14:58 minutes of flight times and 98-100 landing points. The top places are separated by the smallest margins, often less than 5 points separate the winner from 5th place.
F3B