Why an airplane lands on his behind wheels?

Answer 1

Most airplanes today have a set of landing gear under their wings and one under the nose. Earlier planes had wheels under the wings and a rear wheel on the very tail. So, I'm not sure what your question relates to. But aircraft are designed to land on their main landing gear. These are built stronger to take the impact loads of landing and stopping the aircraft descent. Also, the airplane is usually approaching at a slight Nose Up angle, so it would seem natural to have the gear at the center of the airplane or a little aft as that will be the first part to touch the ground. Finally, the gear is designed to hold the weight of the aircraft. The center of gravity of the aircraft is at the front part of the wing or at the center of where the wing attaches to the fuselage. The landing gear needs to be close or exactly on the center of gravity of the airplane. As stated above, these are usually the rear wheels.