The landing gear is the most common type of landing gear for aircraft and one of the most important components of the aircraft. It has a large bearing capacity and is more complicated to bear. It bears the ground reaction caused by landing impact, ground running and various maneuvering movements (such as braking, turning, etc.), and both the landing impact and the ground running impact load. There are obvious dynamic characteristics.
It usually consists of a force structure, a buffer, a wheel, a retracting mechanism, an upper lock and a lower lock, a turning control mechanism, and a brake system.
As part of the aircraft body, the landing gear should of course meet the general requirements of the structural design of the aircraft, that is, the lightest quality under the premise of ensuring the strength, rigidity and certain life of the landing gear structure; easy to use and maintain, easy to inspect, repair and replace; Aerodynamics and processability, economy and other requirements should be met. Under the complicated fatigue load, the landing gear is different from other structures of the aircraft in terms of its design criteria. At present, it is generally designed according to the principle of safe life (ie fatigue life), and is not designed according to the principle of damage tolerance. The main reason is that the landing gears are mostly made of high-strength or ultra-high-strength materials due to the large load. The critical crack length is small, the expansion life between the cracks from the detectable to the fracture is short, and the crack inspection in some parts is still difficult. In the past, the life of the landing gear was generally much shorter than the life of the aircraft body structure and therefore required regular replacement. However, both foreign countries have demanded and achieved the same life of the landing gear and the body structure, and this requirement has been basically met in China. In addition to these general requirements, the landing gear should also meet the following requirements related to its own function.