Landing gear

Landing gear is the undercarriage of an aircraft or spacecraft that is used for engaging the surface — typically land, but may also be the surface of a water body — when parking, taxiing, taking off or landing. It was also formerly called alighting gear by some manufacturers, such as the Glenn L. Martin Company. For aircraft, Stinton makes the terminology distinction undercarriage (British) = landing gear (US).

For aircraft, landing gear is the foundational part of the airframe that supports the craft's weight when it is not in flight, keeping the fuselage at a clearance off the ground so it can avoid sustaining frictional/collisional damages. Wheeled landing gear is the most ubiquitous, used in almost all aircraft that perform conventional and short takeoff and landing, while skids or floats are used in aircraft that can take off and land vertically or operate from snow/ice/water. Landing gears from early aircraft are usually fixed, and remain protruded under the aircraft during flight, with no or only partial fairing coverage to reduce drag; while most modern aircraft have retractable undercarriages that fold into the fuselage during flight, which maximizes aerodynamic streamlining and allows for faster airspeeds and smoother flight control.

Landing gear must be strong and robust enough to handle the stress of both the aircraft's weight and the touchdown shock during landing, and its design is crucial to the aircraft's operational safety. Most landing gears constitute a tricycle layout with three sets of wheels, each with a single wheel or a wheelset/bogie, either in a "1-2" delta-shaped layout (tricycle gears) or a "2-1" nabla-shaped layout ("conventional" gears, also called tail wheel-type gears or "taildragger"), while other atypical configurations such as bicycle (two gears in tandem layout), quadracycle (four gears in a "2-2" rectangular layout) and other multicycle arrangements (usually a single front gear with three or more rear gears, in a kite, dart or pentagonal layout). Some other anomalous landing gears have also been evaluated experimentally, including: no landing gear (e.g. on flying boats), made possible by operating from a catapult cradle and flexible landing deck: air cushion (to enable operation over a wide range of ground obstacles and water/snow/ice); tracked (to reduce runway loading).