airplanes can fly because of lift. According to Bernoulli's principle, the higher the fluid velocity, the lower the pressure. When the lift is greater than the weight of the plane, the plane can fly. When the flow decreases, the pressure increases and the lift is less than the weight of the aircraft, the aircraft can descend and land. So when the plane takes off, it must go forward at high speed. The faster the plane moves, the greater the lift. Aircraft take-off principle: The aerofoil of aircraft wing is specially designed. When air flows over the upper and lower surfaces of the wing, the distance of the upper surface is longer than that of the lower surface, and the air flow speed of the upper surface is faster than that of the lower surface. According to Bernoulli's theorem, where the speed is high, the pressure is low, and where the speed is low, the pressure is high. So the pressure on the lower surface is higher than that on the upper surface, resulting in a pressure difference, which is the lift force that makes the plane fly. Aircraft power source: the aircraft power device is used to generate pulling force (propeller aircraft) or pushing force (jet aircraft) to push the aircraft forward. Power plant with thrust vector can also be used for maneuvering flight. Most modern military aircraft are jets. The power plant of jet aircraft is mainly divided into turbojet engine and turbofan engine. Aircraft structure 1. The fuselage fuselage is mainly used to load personnel, cargo, fuel, weapons and airborne equipment, and through it, the wing, tail wing, landing gear and other components are connected into a whole. In light aircraft, fighters and attack aircraft, engines are usually installed on the fuselage. 2. Wings Wings are the main components used to generate lift on an airplane, which are generally divided into left and right wing surfaces. Wings usually have flat wings, swept wings and delta wings. The front and rear green wings are basically flat, and the front and rear edges of the wings are swept back, which is called swept back wing. The plane shape of the wing is triangle, which is called delta wing. The former is suitable for low-speed aircraft, while the latter two are suitable for high-speed aircraft. Recently, advanced aircraft have adopted plane shapes such as strake wings and forward swept wings.