The "standard" airfoil shape that we examined above is not the only shape for a wing. For example, both stunt planes (the kind that fly upside down for extended periods of time at air shows) and supersonic aircraft have wing profiles that are somewhat different than you would expect:
The upper airfoil is typical for a stunt plane, and the lower airfoil is typical for supersonic fighters. Note that both are symmetric on the top and bottom. Stunt planes and supersonic jets get their lift totally from the angle of attack of the wing.
Angle of Attack
The angle of attack is the angle that the wing presents to oncoming air, and it controls the thickness of the slice of air the wing is cutting off. Because it controls the slice, the angle of attack also controls the amount of lift that the wing generates (although it is not the only factor).
Zero angle of attack
Shallow angle of attack
Steep angle of attack
In general, the wings on most planes are designed to provide an appropriate amount of lift (along with minimal drag) while the plane is operating in its cruising mode (about 560 miles per hour for the Boeing 747-400). However, when these airplanes are taking off or landing, their speeds can be reduced to less than 200 miles per hour. This dramatic change in the wing's working conditions means that a different airfoil shape would probably better serve the aircraft.
To accommodate both flight regimes (fast and high as well as slow and low), airplane wings have moveable sections called flaps. During take-off and landing, the flaps are extended rearward and downward from the trailing edge of the wings. This effectively alters the shape of the wing, allowing the wing to turn more air, and thus create more lift. The downside of this alteration is that the drag on the wings also increases, so the flaps are put away for the rest of the flight.
Slats perform the same function as flaps (that is, they temporarily alter the shape of the wing to increase lift), but they are attached to the front of the wing instead of the rear. They are also deployed on take-off and landing.
Given what we know so far about wings and lift, it seems logical that a simple cylinder would not produce any lift when immersed in a moving fluid (imagine a plane with wings shaped like cardboard paper-towel tubes). In a simplified world, the air would just flow around the cylinder evenly on both sides, and keep right on going. In reality, the downstream air would be a little turbulent and chaotic, but there still would be no lift created.
However, if we were to begin rotating the cylinder, as in the figure below, the surface of the cylinder would actually drag the surrounding layer of air around with it. The net result would be a pressure difference between the top and bottom surfaces, which deflects the airflow downward. Newton's Third Law states that if the air is being redirected downward, the cylinder must be deflected upward (sounds like lift to me!). This is an example of the Magnus Effect (also known as the Robbins Effect), which holds true for rotating spheres as well as cylinders (see any similarities to curveballs here?)
Believe it or not, in 1926, Anton Flettner actually built a ship, named the Bruckau, using huge spinning cylinders instead of sails to power the boat across the ocean (click here for an article).
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 will actually run 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.