In order to meet the needs of aircraft take-off, landing run and ground taxiing, the bottom of the landing gear is equipped with pneumatic tires.
Wheel. In order to shorten the landing run distance, the wheel is equipped with brakes or automatic brakes. In addition, it also includes bearing strut, shock absorber (common load strut as shock absorber outer cylinder), retracting mechanism, front wheel reducer and turning control mechanism. The bearing strut connects the wheel and the shock absorber to the body and transmits the impact load during landing and taxiing to the body. The front wheel damper is used to eliminate the shimmy of the front wheels in high speed taxiing. The front wheel steering mechanism increases the flexibility of the aircraft's ground turn. For airplanes that land on snow and ice, the wheels on the landing gear are replaced by skids.
When the aircraft is grounded at the moment of landing or on the uneven runway at high speed, it will strike sharply with the ground. Except for the small part of the cushioning effect of the pneumatic tire, most of the impact energy is absorbed by the shock absorber. The most widely used on modern aircraft is the oil-air damper. When the shock absorber is compressed by impact, the air acts like a spring to store energy. The oil passes through the small holes at a very high speed, absorbs a lot of impact energy, converts them into heat energy, and makes the aircraft settle down quickly after the impact, so as not to bump.
The retracting system generally uses hydraulic pressure as the normal retracting power source, and uses cold air and electric power as the backup power source. Typically the nose gear is forwarded to the front fuselage, while the front landing gear of some heavy transport aircraft is laterally stowed. The main landing gear retractable form can be roughly divided into two types: retracting in the spanwise direction and retracting in the chord direction. The retractable position lock is used to lock the landing gear in the stowed and lowered positions to prevent the landing gear from automatically retracting when it is automatically lowered during flight and impacted. For retractable systems, there are generally position indication and warning systems.
Wheel and brake system
The main function of the wheel is to support the weight of the aircraft on the ground, reduce the resistance of the aircraft's ground motion, and absorb part of the impact kinetic energy of the aircraft landing and ground motion. The main landing gear is equipped with brakes, which can be used to shorten the landing distance of the aircraft and make the aircraft have good maneuverability on the ground. The wheel is mainly composed of a wheel hub and a tire. Brakes are mainly available in curved, capsule and disc styles. The most widely used is the disc type, which is characterized by large friction area, large heat capacity and easy maintenance.
There are two ways to steer the aircraft on the ground. One is to make the airplane turn by the main wheel single brake or to adjust the push and pull of the left and right engines. The other way is to turn the airplane by turning the front wheel deflection through the front wheel turning mechanism. Light aircraft generally adopt the former method; while medium and above aircraft are difficult to turn, most of them are equipped with front wheel turning mechanism. In addition, when some heavy aircraft are turning, the main wheel will also cooperate with the front wheel deflection to improve the turning performance of the aircraft.