​​What Is Downwash? How Does It Happen?

If you’ve ever stood near a helicopter, you’ll know exactly how it stays in the sky: it creates a huge “downwash” of air that balances its weight. Helicopter rotors are very similar to airplane airfoils, but spin around in a circle instead of moving forward in a straight line, like the ones on a plane. Even so, airplanes create downwash in exactly the same way as helicopters, it’s just that we don’t notice. That happens because the wings aren’t perfectly horizontal, as you might suppose, but tilted back very slightly so they hit the air at an angle of attack. The angled wings push down both the accelerated airflow (from up above them) and the slower moving airflow (from beneath them), and this produces lift. Since the curved top of the airfoil deflects (pushes down) more air than the straighter bottom (in other words, alters the path of the incoming air much more dramatically), it produces significantly more lift. Now we can see that wings are devices designed to push air downward, it’s easy to understand why planes with flat or symmetrical wings can still safely fly. As long as the wings are creating a downward flow of air, the plane will experience an equal and opposite force-lift that will keep it in the air. In other words, the upside-down pilot creates a particular angle of attack that generates just enough low pressure above the wing to keep the plane in the air.