The most widely used on modern aircraft is the first three-point landing gear. The two main wheels are arranged symmetrically at a certain distance from the center of mass of the aircraft, and the front wheels are arranged below the head of the aircraft. When the aircraft is taxiing and parking on the ground, the fuselage floor is basically in a horizontal position, which is convenient for passengers to board the plane and load and unload the cargo. Heavy aircraft use the method of increasing the number of wheels and fulcrums to reduce the pressure on the runway to improve the aircraft's ability to take off and land on the frontline dirt track.
(1) It has stability in the running direction. When the fuselage axis deviates from the running direction, the resultant force of the main wheel friction will generate a recovery torque, which will return the aircraft to the original direction of motion. It is safer when landing on a crosswind. When the ground slides, the steering turns are more flexible.
(2) When the aircraft landed at a small angle of attack with a large speed, the main wheel landing impact force produces a head moment on the aircraft's center of mass, reducing the angle of attack, allowing the aircraft to continue to slide along the ground without causing a "jump" phenomenon, so landing control comparison easy.
(3) Because the nose gear is far away from the center of mass, it can be braked when landing without causing the aircraft to “turn over”, thus shortening the landing distance.
(4) Because the aircraft axis is close to the horizontal level, the take-off and running resistance is small, the acceleration is fast, the take-off distance is short, and the driver's front view is good and the ride is comfortable.
(5) Jet jet jets do not spray directly onto the runway and therefore have less impact on the runway.
(1) The arrangement of the nose gear is difficult, especially for a single-engine aircraft, and the remaining space in the front of the fuselage is small.
(2) The front landing gear is subjected to large loads, large size, and complicated structure, and thus has high quality.
(3) At the small angle of attack when landing, it is not possible to fully utilize the air resistance for braking. When sliding on an uneven runway, the ability to overcome obstacles (ditches, mounds, etc.) is also poor.
(4) The front wheel will produce a shimmy phenomenon, so equipment and measures to prevent the shock are required, which increases the complexity and weight of the front wheels.
Nevertheless, due to the large landing speed of modern aircraft and the guarantee of landing safety, it is the primary determinant in determining the form of the landing gear. The first three points have obvious advantages compared with the latter three points in this respect, and thus the most extensive application.