Why can planes fly in the blue sky?

Because the two wings of the plane are streamlined, when the plane is moving forward, due to the different air speeds above and below the wings, it will produce upward lift. When the lift is large enough, the plane will fly. As for the difference in air velocity between the two sides, it will produce a force flowing to the side with a larger velocity. It is suggested to do an experiment, that is, put two pieces of paper together in parallel and vertically and blow air from top to bottom through the mouth. Unless something goes wrong, the two pieces of paper will meet in the middle.