Gliders or Sailplanes
Sailplanes are another popular part of R/C aircraft involvement. They are engineless airplanes that rely on rising air currents to keep them aloft. Compared to airplanes they are usually much lighter for the same wing area and are very streamlined to reduce drag. A typical sailplane will have a larger wingspan than a typical airplane, with 60 inches being considered small. Wingspans of over 100 inches are considered normal with even larger examples being quite common. Sailplanes are constructed with much the same materials as airplanes with wood being more common in beginner's models and fiberglass and other composites used on higher performance aircraft.
A typical beginner's glider will have a 2 meter wingspan and weigh between 2 and 3 pounds. All that is needed for control is a 2 channel radio for rudder and elevator. Most beginner models will fly very slowly and are best suited for non-windy conditions. They do however respond very well to "lift" or rising air and can stay aloft for very long periods of time making them very enjoyable to fly.
More advanced gliders will usually have more fuctions than rudder and elevator, with ailerons, flaps, and spoilers being the most common additions. They will be capable of very fast speeds when necessary, which is useful for getting out of poor areas of lift in a hurry. With higher speeds comes the ability to fly in very windy conditions without any trouble. A good sailplane is also capable of many aerobatic manuevers and should not be thought of as something for "inexperienced" or "beginner" pilots.
There are basically two types of "soaring", thermal and slope. In thermal soaring the sailplane depends on rising currents of warm air called thermals to stay aloft. The challenge to the pilot is to find these invisible air currents while staying out of areas of "sink". When in a thermal the pilot will circle the glider until a satisfactory altitude is reached or until they unwittingly exit the thermal and then have to look for another one. It is not at all uncommon to keep a glider up for over an hour at a time, riding several different thermals in the process. Of course some days you can't find lift to save your life! Slope soaring involves flying the glider over a slope or cliff which has wind blowing into it, such as on a lakeshore. When the wind hits the slope it is deflected upward providing a source of lift for the sailplane. This is nice for the pilot as he or she doesn't have to wonder where the lift is. As long as the wind is blowing you can stay up all day. Pilots many times have very fast and aerobatic gliders . Racing and combat are common activities on the slopes.
You may be wondering how people get their gliders up in the air if there is no engine on them. For slope flyers you just toss the thing off the cliff and away you go. For thermal flyers it requires a winch or "high-start". A winch usually consists of an electric motor with a spool of string (very strong string!) on it. The string or line is run along the ground to the opposite end of the field and through a pulley or "turn-around" and then back to the motor again. The pilot, standing at the motor end of this arrangement, connects the glider to the line with a small "tow hook" mounted to the bottom of the glider. The motor is then started via a foot controlled on/off switch and that quickly winds up the line, pulling the glider through the air in the process. The glider will climb very steeply as it heads towards the turn-around. When it is obvious that the line will not let the glider get any higher the pilot will point the nose first slightly down and then back up again which allows the line to slip off of the tow hook. The glider is now free to look for lift. Winch launches can get the glider several hundred feet into the air. A high-start consists of a length of string up to several hundred feet which is then attached to a length of surgical tubing which is staked into the ground at the other end. The pilot attaches the glider to the string with the tow hook and then walks away from the stake which stretches the rubber tubing. When the glider is released it surges forward and climbs as on the winch and can also reach several hundred feet of altitude depending on the length of the tubing and string.
If all of this sounds interesting to you then you're going to need more information on how to get started in model gliders!