Landing gear

Landing gear is the undercarriage of an aircraft or spacecraft and may be used for either takeoff or landing. For aircraft it is generally both. It was also formerly called alighting gear by some manufacturers, such as the Glenn L. Martin Company.Me 163B Komet with its two-wheel takeoff 'dolly' in placeThe landing gear of a Boeing 767 retracting into the fuselageSchematic showing hydraulically operated landing gear, with the wheel stowed in the wing root of the aircraftA Boeing 737-700 with main undercarriage retracted in the wheel wells without landing gear doorsA Ju 87D with a wheel spat on its right wheel, absent on its leftWheel arrangements of large airlinersOleo strut rear landing gear of an Antonov An-124 (24 wheel landing gear)The A340-600 has an additional main undercarriage on the fuselage bellyWing and fuselage undercarriages on a Boeing 747-400, shortly before landingCessna 208 floatplane with amphibious floatsde Havilland Canada DHC-2 on non-amphibious floatsAmphibious Consolidated PBY Catalina with landing gear loweredNon-amphibious Short Solent flying boat with beaching gear Landing gear is the undercarriage of an aircraft or spacecraft and may be used for either takeoff or landing. For aircraft it is generally both. It was also formerly called alighting gear by some manufacturers, such as the Glenn L. Martin Company. For aircraft, the landing gear supports the craft when it is not flying, allowing it to take off, land, and taxi without damage. Wheels are typically used but skids, skis, floats or a combination of these and other elements can be deployed depending both on the surface and on whether the craft only operates vertically (VTOL) or is able to taxi along the surface. Faster aircraft usually have retractable undercarriages, which fold away during flight to reduce drag. For launch vehicles and spacecraft landers, the landing gear is typically designed to support the vehicle only post-flight, and are typically not used for takeoff or surface movement. Aircraft landing gear usually includes wheels equipped with simple shock absorbers, or more advanced air/oil oleo struts, for runway and rough terrain landing. Some aircraft are equipped with skis for snow or floats for water, and/or skids or pontoons (helicopters). It represents 2.5 to 5% of the MTOW and 1.5 to 1.75% of the aircraft cost but 20% of the airframe direct maintenance cost; each wheel can support up to 30 t (66,000 lb), reach over 300 km/h, roll up to 500,000 km (310,000 mi) ; it has a 20,000 hours time between overhaul and a 60,000 hours or 20 years life time. The undercarriage is typically 4–5% of the takeoff mass and can even reach 7%.