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Rear Three-point Landing Gear Business Advantages And Disadvantages
Oct 09, 2018

The rear three-point landing gear was widely used in propeller aircraft early on. It is characterized in that two main wheels (main landing gear) are arranged in front of the center of mass of the aircraft and close to the center of mass, and the tail wheel (tail support) is arranged away from the center of mass at the tail of the aircraft. In the shutdown state, 90% of the aircraft's mass falls on the main landing gear, and the remaining 10% is shared by the tail support. The weight of the last three-point landing gear is lighter than the first three points, but the ground turning is not flexible enough. When the brakes are too strong, the aircraft has the danger of “taking a big top”, which is rarely used in modern aircraft.


advantage

(1) The overall structure of the rear three-point landing gear is relatively simple and the weight is light.

(2) Easy to configure on a propeller aircraft. It takes a lot of propeller blades to produce large thrust blades, which has forced the aircraft to increase the height of the propeller engine when it is designed and installed, and the aircraft with the rear three-point landing gear is lifted at a high angle of attack when the aircraft is on the ground. Very big.

(3) It is easy to install the tail wheel on the aircraft. Compared with the front wheel, the tail wheel has a simple structure and a small size and quality;

(4) At the time of normal landing, the three wheels touch the ground at the same time, which means that the attitude of the aircraft at the time of falling (the fourth stage of the landing process) is the same as that of the ground running and stopping. That is to say, the ground has a large angle of attack when it is slid, so it is possible to use a large aircraft resistance to decelerate, thereby reducing the landing time and the running distance. Therefore, most of the early aircraft were in the form of a rear three-point landing gear.


Disadvantage

(1) When running at a large speed, encountering a frontal impact or a strong brake, it is prone to an inverted phenomenon (commonly known as taking a big top). Therefore, in order to prevent the inverted position, the rear three-point landing gear does not allow strong braking, thereby increasing the running distance after landing.

(2) Landing speed requirements are high. If the landing speed is too large, the impact force of the main wheel grounding will increase the aircraft's head-on angle of attack, which will cause the aircraft's lift to increase and then “jump” from the ground. Even after jumping, the stall will occur and an accident will occur.

(3) The direction stability is poor when the ground is running. If during the sprinting process, some disturbances (side winds or uneven road surfaces make the resistance of the two wheels unequal) cause the aircraft to rotate a certain angle with respect to its axis, then the friction formed on the struts will produce relative At the moment of the airplane's centroid, it turns the airplane to a larger angle.

(4) When the machine is stopped, started or dropped, the front fuselage is raised, so the downward view is not good.


Based on the above shortcomings, the dominant position of the rear three-point landing gear was gradually replaced by the first three-point landing gear, and only a small number of small and low-speed aircraft still used the rear three-point landing gear.


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