If birds, insects and airplanes want to fly, they must bear upward pressure and compete with their own weight. The wings of an eagle are very similar to those of an airplane. The top has a certain curvature and the bottom is flat. When flying in this way, the upper air flow is faster than the lower one, and the air pressure is also lower. Then the lower side of the wing (wing) can generate greater pressure than the upper side, and the eagle (aircraft) can be lifted. But bees' wings are almost flat, so they have to keep flapping their wings to generate upward pressure and make themselves fly.