起落架是飞机下部用于起飞降落或地面（水面）滑行时支撑飞机并用于地面（水面）移动的附件装置。起落架是飞机起飞、着陆、滑跑、地面移动和停放所必需的支持系统，是飞机的主要部件之一，其性能的优劣直接关系到飞机的使用于安全。
起落架是唯一一种支撑整架飞机的部件，因此它是飞机不可分缺的一部份；没有它，飞机便不能在地面移动。当飞机起飞后，可以视飞行性能而收回起落架。
视频源自Pilot Training System频道
参考原文：
Landing Gear
The landing gear forms the principal support of an aircraft on the surface. The most common type of landing gear consists of wheels, but aircraft can also be equiped with floats for water operations or skis for landing on snow.
The landing gear on small aircraft consists of three wheels, two main wheels, one located on each side of the fuselage, and a third wheel positioned either at the front or rear of the airplane.
Landing gear employing a rear-mounted wheel is called conventional landing gear. Airplanes with conventional landing gear are often referred to as tail wheel airplanes. When the third wheel is located on the nose, it is called a nose wheel, and the design is referred to as a tricycle gear.
A steerable nose wheel or tail wheel permits the airplane to be controlled throughout all operations while on the ground. A tricycle gear airplane has 3 advantages:
1) It allows more forceful application of the brakes during landings at high speeds without causing the aircraft to nose over.
2) It permits better forward visibility for the pilot during takeoff, landing and taxiing.
3) It tends to prevent ground looping (swerving) by providing more directional stability during ground operation since the aircraft CG is forward of the main wheels. The forward CG keeps the airplane moving forward in a straight line rather than ground looping.
Tail wheel landing gear aircraft have 2 main wheels attached to the airframe ahead of its CG that support most of the weight of the structure. A tail wheel at the very back of the fuselage provides a third point of support. This arrangement allows adquate ground clearance for a larger propeller and is more desirable for operations on unimproved fields.
With the CG located behind the main gear, directional control of this type of aircraft becomes more difficult while on the ground. This is the main disadvantage of the tail wheel landing gear.
For example, if the pilot allows the aircraft to swerve while rolling on the ground at a low speed, he or she may not have sufficient rudder control, and the CG will attempt to get ahead of the main gear, which may cause the airplane to ground loop.
Lack of good forward visibility when the tail wheel is on or near the ground is a second disadvantage of the tail wheel landing gear aircraft. These inherent problems mean specific training is required in tail wheel aircraft.
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