Blown Surfaces

Let's take our cylindrical wing from the above examples and find another way to create lift with it. If you've ever held the back of your hand vertically under the faucet, you may have noticed that the water did not simply run down to the bottom of your hand and then drip off. Instead, the water actually runs back up and around the side of your hand (for a few millimeters) before falling into the sink. This is known as the Coanda Effect (after Henri Coanda), which states that a fluid will tend to follow the contour of a curved surface that it contacts.

In our cylinder example, if air is forced out of a long slot just behind the top of the cylinder, it will wrap around the backside and pull some surrounding air with it. This is a very similar situation to the Magnus Effect, except that the cylinder doesn't have to spin.

The Coanda Effect is used in specialized applications to increase the amount of additional lift provided by the flaps. Instead of just altering the shape of the wing, compressed air can be forced through long slots on the top of the wing or the flaps to produce extra lift.

Believe it or not, in 1990, McDonnell Douglas Helicopter Co. (now known as MD Helicopters, Inc.) removed the tail rotors from some of its helicopters and replaced them with cylinders! Instead of using a conventional tail rotor to steer the aircraft, the tail boom is pressurized and air is blown out through long slots exactly like the figure above.