The helicopter pilot starts the engine. Its big blades spin-slowly at first, then faster and faster. But the helicopter is still on the ground. The pilot twists the big blades at an angle. This forces air down. Then the helicopter rises off the ground. The pilot tilts the blades back. The helicopter stops rising and moves forwards. A small propeller at the back of the helicopter keeps it from spinning while the big blades are turning. It also keeps the helicopter from spinning around when it is in the air.
Helicopters are very useful. Since they rise straight into the air, they can land and take off in very small spaces. They can also hover, or stay in one place. So they are often used to help people who are trapped on a mountain, at sea, or on top of a high building.
Picture Credit : Google