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A floatplane (float plane or pontoon plane) is a type of seaplane, with one or more slender pontoons (known as "floats") mounted under the fuselage to provide buoyancy. By contrast, a flying boat uses its fuselage for buoyancy. Either type of seaplane may also have landing gear suitable for land, making the vehicle an amphibious aircraft.
Floatplanes have often been derived from land-based aircraft, with fixed floats mounted under the fuselage instead of retractable undercarriage (featuring wheels).
All floatplanes tend to be less stable on water than flying boats. However, in small aircraft design, floatplanes offer an advantage over flying boats, as the hull (i .e. the lower part of the fuselage) of floatplanes does not make contact with water surfaces, permitting a conventionally mounted single piston engine, with a propellor, in the nose.
Floats inevitably impose extra drag and weight, rendering floatplanes slower and less manoeuvrable during flight, with a slower rate of climb, relative to aircraft equipped with retractable landing gear. Nevertheless, air races devoted to floatplanes attracted a lot of attention during the 1920s and 1930s, most notably in the form of the Schneider Trophy.
There are two basic float configurations on floatplanes:
- "single float" designs, in which a single large float is mounted directly underneath the fuselage, with smaller stabilizing floats underneath the wings and;
- "twin float" designs, with one float mounted beneath each wing.
The main advantage of the single float design is its capability for landings in rough water: a long central float is directly attached to the fuselage, this being the strongest part of the aircraft structure, while the smaller floats under the outer wings provide the aircraft with good lateral stability. By comparison, dual floats restrict handling, often to waves as little as one foot (0.3 metres) in height. However, twin float designs facilitate mooring and boarding, and – in the case of bombers – leave the belly free to carry a large bomb or torpedo.
The first aircraft to successfully take off from water was Henri Fabre's Fabre Hydravion, first flown on 28 March 1910. Although not a very successful aircraft, this inspired other aircraft designers to emulate him, and Fabre designed and built floats for a number of other aircraft, such as the Voisin Canard.
Floatplanes were widely used during World War I, and remained in naval use until World War II. Most larger warships of that era carried floatplanes - typically four for each battleship, and one to two for each cruiser - to be launched by catapults; their main task was to spot targets over the horizon for the big guns. Other floatplanes, sometimes carried on seaplane tenders, were used for bombings, reconnaissance, air-sea rescue, and even as fighters.
In the interwar period, civilian use of floatplanes was rare, given the larger fuselage (hence greater payload) of flying boats. However, floatplane racing aircraft were very popular, as exemplified by those that participated in the Schneider Trophy.
After World War II, the advent of radar and helicopters, and the advanced development of aircraft carriers and land-based aircraft, saw the demise of military seaplanes. This, coupled with the increased availability of civilian airstrips, have greatly reduced the number of flying boats being built. However, numerous modern civilian aircraft have floatplane variants, most of these are offered as third-party modifications under a supplemental type certificate (STC), although there are several aircraft manufacturers that build floatplanes from scratch. These floatplanes have found their niche as one type of bush plane, for light duty transportation to lakes and other remote areas, as well as to small/hilly islands without proper airstrips. They may operate on a charter basis (including, but not limited to, pleasure flights), provide scheduled service, or be operated by residents of the area for private, personal use.
See also 
- "Why Seaplanes Fly With Bullet Speed", December 1931, Popular Science excellent article on the different design features of the floats on floatplanes
- "Will a Lake Be Your Postwar Landing Field?" Popular Science, February 1945, pp. 134–135.