The landing gear (also referred to as undercarriage) of an aircraft supports the aircraft on the ground, provide smooth taxiing, and absorb shocks of taxiing and landings. It has no function during flight, so it must be as small and light as possible, and preferably easily retractable.
Due to the weight of the front (containing cabin and equipment) and rear parts (where the empennage is located) of the aircraft, large bending moments occur on the centre section of the fuselage. Therefore, to withstand these bending moments, a strong beam is located. This reduces the space in which the landing gear can be retracted.
When an aircraft lands, a large force is generated on the landing gear as it touches the ground. To prevent damage to the structure, this shock must be absorbed and dissipated as heat by the landing gear. If the energy is not dissipated, the spring system might just make the aircraft bounce up again.
After touchdown, the aircraft needs to brake. Disc brakes are primarily used. The braking of an aircraft can be supplemented by other forms of braking, such as air brakes, causing a large increase in drag, or reverse thrust, thrusting air forward.