People made wings and strapped them to their arms. They flapped their arms but couldn't fly. They built gliders(滑翔机), light aircraft with wings. Some didn't work, but some did.
The gliders that worked had special wings. These wings were arched on both the top and the bottom. The air pulled the wings from above and pushed the wings from below. When the wings went up, so did the glider! Arched wings help create a force called lift. Lift is the force that keeps the gliders in the air.
Most gliders have long, thin wings. The wings create enough lift to carry the aircraft and its passengers. Gliders usually ride currents of air the same way a hawk soars(飞翔).
Gliders are very light, and long wings and air currents can give them enough lift to fly. But to carry more than just a passenger or two, an aircraft needs a lot more lift. The question is: How do you create more lift?
The engine is the answer!
The engine is a machine that changes energy into movement. The forward movement that an airplane needs to fly is called thrust. More thrust makes an airplane move forward faster. Moving faster creates more lift. And with more lift, an airplane can carry more weight so an aircraft with an engine can carry passengers or cargo.
In 1903 the Wright brothers figured out how to get wings and an engine to work together in order to give an airplane enough thrust to fly. They made the first powered flight at Kitty Hawk, North Carolina.
Since then people have made airplanes that can fly faster than sound can travel. They have made airplanes that can fly all the way around the world without stopping.
Today, thousands of people travel in airplanes every day. People really have learned how to fly!
