Amphibious aircraft

An amphibious aircraft or amphibian is an aircraft that can take off and land on both land and water. Fixed-wing amphibious aircraft are seaplanes (flying boats and floatplanes) that are equipped with retractable wheels, at the expense of extra weight and complexity, plus diminished range and fuel economy compared to planes designed for land or water only. Some amphibians are fitted with reinforced keels which act as skis, allowing them to land on snow or ice with their wheels up and are dubbed tri-phibians.

Floatplanes often have floats that are interchangeable with wheeled landing gear (thereby producing a conventional land-based aircraft) however in cases where this is not practical amphibious floatplanes, such as the amphibious version of the DHC Otter, incorporate retractable wheels within their floats.

Many amphibian aircraft are the flying boat type. These aircraft, and those designed as floatplanes with a single main float under the fuselage centerline (such as the Loening OL and Grumman J2F), require outrigger floats to provide lateral stability so as to avoid dipping a wingtip, which can destroy an aircraft if it happens at speed, or can cause the wingtip to fill with water and sink if stationary. While these impose weight and drag, amphibious aircraft also face the possibility of these getting hit when operating from a runway. A common solution is to make them retractable as those found on the Consolidated Catalina however these are even heavier than fixed floats. Some aircraft may have the tip floats removed for extended use from land. Other amphibians, such as the Dornier Seastar use stub wings called sponsons, mounted with their own lower surfaces nearly even with the ventral "boat-hull" shaped fuselage surface to provide the needed stability, while floatplane amphibians usually avoid the problem by dividing their buoyancy requirements between two floats, much like a catamaran.

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