Airplane

The term airplane generally denotes the landplane, or landbased airplane, but it applies also to several other categories of aircraft, including the carrierbased plane, the seaplane, and the amphibian. The principal variation in structure can be found in the landing apparatus. The carrierbased plane, a type of landplane designed for use on an aircraft carrier, is fitted with a tail hook that engages a cable stretched across the deck to arrest the plane after landing. The seaplane employs pontoons instead of the wheel gear of the landplane. In the variety of seaplane known as the flying boat, the fuselage is constructed as a hull, similar to that of a seagoing vessel, and serves to keep the plane buoyant. The amphibian is equipped with both wheel gear and hull or pontoons to permit operation with equal effectiveness on land and water.
Before World War II, flying boats were used for military transports and for intercontinental commercial service. These planes were limited to low flying speeds and to low landing speeds in water. With the advent of planes that fly and land much faster, large planes have been limited to landbased operation. The amphibian, even slower because of its double undercarriage, is less commonly employed than the landplane. For light sportplanes, amphibious floats are available. Generally resembling conventional pontoons, they have a recessed wheel located at the center of balance of the seaplane; the wheelwell is waterproof. The wheel tire does not extend far enough to add much drag to the float in the water, but it protrudes far enough to enable wheeled landings to be made on hardsurfaced runways or shortcut grass.
More successful types of heavierthanair craft include the VTOL craft, the STOL craft, and the convertiplane. The VTOL (vertical takeoff and landing) craft is an airplane that can rise up vertically, fly horizontally, and then reverse the procedure for a landing. The term VTOL is limited to describing aircraft with performances similar to those of conventional airplanes but with additional vertical takeoff and landing ability. Several means are used to lift VTOL aircraft off the ground. The direct downward thrust of jet engines is used in several designs. Enormous power is needed to lift a craft in this manner, much more than is required to propel it horizontally. Rotating wings and ducted fans are also used for direct lift, but they tend to introduce drag into the horizontal flight. Convertiplanes, combining the rotating wings of helicopters with the fixed wings of airplanes, have been used for shortdistance commercial VTOL operation. They compete directly with helicopters, however.
The STOL (short takeoff and landing) craft is an airplane that takes off and lands very steeply, thus requiring little runway. For a given payload, it is much more efficient in terms of fuel consumption and power requirements than a VTOL craft. It is also capable of higher speeds and longerrange flights than a helicopter. For lighterthanair craft, see AIRSHIP,; BALLOON.