A paper airplane is, technically speaking, one type of gliding airplane. A parasail, which is a combination kite and parachute system designed to lift a passenger into gliding flight, can also be described as a glider. The space shuttle, when returning to earth, utilizes all the principles of gliding flight. However, the term airplane glider most often refers to a passenger-carrying aircraft with no motor or power of any kind. Like standard airplanes that do have engines, an airplane glider has a fuselage and wings but in many ways is an entirely different craft to fly.
To lift into the air, an airplane glider must move at a speed greater than the power of gravity. Greater speed than the force of gravity is what produces the lift. This can be achieved in a variety of ways that include speeding into a strong headwind, launching from a great height, or being towed and released by a powered aircraft.
To be effective in sustained flight, airplane gliders share common characteristics. First, they are built to be light in order to require as little energy as possible to attain lift. Second, their seamless construction in both shape and materials allows for less drag. Third, the wings of an airplane glider are much longer in relationship to the fuselage than standard airplanes and are also much thinner in order to result in less drag. Such engineering results in effective gliding but allows for less speed and less precise maneuverability.
Lack of an engine or motor means that an airplane glider is not capable of producing thrust to increase speed, which, in turn, increases lift. Therefore, an airplane glider must incorporate different techniques to increase speed. One method is descent. By descending at an angle, the airplane glider exchanges altitude for speed, thereby producing lift, which is able to prolong flight. Another method to increase speed involves the managing of ballast. Water tanks, carrying upwards of several hundred pounds of water, make the plane heavier and can result in increased speed in both the sinking of altitude and forward airspeed which can be used to create lift. At the right time, the pilot can opt to jettison the ballast to lighten the plane and obtain a greater lift.
There are updrafts, known as thermals, that can help keep an airplane glider in flight, but the glider will eventually lack sufficient altitude, updraft or headwind to prolong flight. The result will be a descent to land atop landing gear usually consisting of one or two small wheels.