Design
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 of 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), 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 to provide the needed stability while floatplane amphibians usually avoid the problem by dividing their buoyancy requirements between two floats, much like a catamaran.
Some non-amphibious seaplanes may be mistaken for amphibians (such as the Shin Meiwa PS-1) which carry their own beaching gear - usually this is a wheeled dolly or temporary set of wheels used to move a flying boat or floatplane from the water and allow it to be moved around on land but can also appear as a conventional undercarriage. These are not built to take the impact of the aircraft landing on them. An amphibian can leave the water without anyone getting in the water to attach beaching wheels (or even having to have any handy), yet a fully functional undercarriage is heavy and impacts the aircraft's performance, and isn't required in all cases, so an aircraft may be designed to carry its own.
Read more about this topic: Amphibious Aircraft
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