Undercarriage – (plus Wheels, tyres and brakes) Overview The undercarriage or landing gear is the structure (usually wheels) that supports an aircraft and allows it to move across the ground or water. The assembly usually has wheels and shock absorber apparatus, but sometimes skis for snow or floats for water, and skids or or pontoons (helicopters). (helicopters). To decrease drag drag in flight some undercarriages retract into the fuselage. Aircraft with at least partially retractable landing gear did not appear until 1917, and it was not until the late 1920s and early 1930s 1930s that such aircraft became became common. By then, aircraft performance was improved to the point where the aerodynamic advantage of a retractable undercarriage justified the added complexity and weight. Wheeled undercarriages come in two types: taildragger, where there are two main wheels towards the front of the aircraft and a single, much smaller, wheel or skid at the rear; or tricycle undercarriage where there are two main wheels (or wheel assemblies) under the wings wings and a third smaller wheel in the nose. nose. Most modern aircraft have tricycle undercarriages. undercarriages. Taildraggers are considered considered harder to land and take off, and usually usually require special pilot training. Sometimes a small tail wheel or skid is added to aircraft with tricycle undercarriage, in case the tail strikes the ground during take-off. The Concorde, for instance, had a retractable tail "bumper" wheel. As aircraft grow larger, they employ more wheels to cope with the increasing weights. The Airbus A340-500/-600 A340-500/-600 has an additional four-wheel undercarriage undercarriage bogie on the fuselage centreline. centreline. The Boeing 747 has five sets sets of wheels, a nosewheel assembly and and four sets of four-wheel bogies. A set is located under each wing, and two inner sets are located in the fuselage, a little rearward of the outer bogies. Tricycle undercarriage aircraft are usually steered by the leading leading wheel(s) when taxiing. On the Boeing 747 the two inner bogies, bogies, and on the Boeing 777 the last two wheels on each leg, are also steerable with the nose wheels in order to reduce the lateral stresses on the undercarriage. Some planes use wheels only for take off and drop them afterwards to gain the improved streamlining without the complexity, weight and space requirements of a retraction mechanism. In this case, landing is achieved achieved on skids or similar simple simple devices. Historical examples include the Messerschmitt Messerschmitt Me 163 and the Messerschmitt Me 321.
An unusual undercarriage configuration is found on the Hawker-Siddeley Harrier, which has two mainwheels in line astern under the fuselage (called a bicycle or tandem layout) and a smaller wheel near the tip of each wing. On second generation Harriers, the wing is extended past the outrigger wheels to allow greater weapon loads to be carried. A multiple tandem layout was used on some military jet aircraft during the 1950s such as the Lockheed U-2, Myasishchev M-4, Yakovlev Yak-25, Yak-28 and the Boeing B-47 because it allows room for a large internal bay between the main wheels. A variation of the multi tandem layout is also used on the B-52 Stratofortress which has four main wheel bogies underneath the fuselage and a small outrigger wheel supporting each wing-tip. The B-52's landing gear is also unique in that all four pairs of main wheels can be steered. This allows the landing gear to line up with the runway and thus makes crosswind landings easier (using a technique called crab landing). For light airplanes, a landing gear which is economical to produce is a simple wooden arch laminated from ash, as used on some homebuilt aircraft. A recent addition to this type of gear is the fixed-gear RJ.03 IBIS canard homebuilt aircraft.
A-380 Nose U/C
A-319 – Main U/C
Executive Jet Nose U/C
Antonov 225 Main U/C
Shuttle Atlantis
Piper Cherokee
Boeing 777
A-380
Boeing 747
B-52
Harrier
Boeing 747
A-340
A-330
Vulcan
Vulcan
Valiant
Valiant
Valiant
Valiant
TSR-2
Wessex
Me-109G
Spitfire
Spitfire
DH Chipmunk
Avro Lancaster
