Helicopters:

The genius of helicopters: There are two parts to how an ordinary airplane flies. Engines push it forward through the air, which forces air over curved and tilted wings. The wings direct the air downward and that makes the plane lift upward. The engines are less important than the wings: a plane can fly (for a time) without engines but not without wings. In a helicopter, the spinning rotors serve as wings: they have a curved (airfoil) shape similar to airplane wings. With a plane, you get lift only when the craft moves forward, as air rushes past the wings. With a helicopter, spinning the rotors at high speed means you can generate lift even when you're hovering in one place. Spinning rotor blades through the air (in a still helicopter) is exactly the same as moving still wings quickly through the air (in a moving plane). By changing the angle ("pitch") of the rotors as they rotate, you can generate more lift in one direction than another, which makes a helicopter steer in any direction you like. It all seems simple to us now, but this invention is a work of genius. The inventor? Ikor Sikorsky. And here's his first practical helicopter design from 1931.