Angle of attack

Lee Dempsey/HowStuffWorks.com

Aerial Navigation: Wings, Slats and Flaps

Having covered the basic physics of flight and the ways in which an airplane uses them to fly, the next obvious step is to consider navigation. How does an airplane turn in the air? How does it rise to a higher altitude or dive back toward the ground?

First, let's consider the angle of attack, the angle that a wing (or airfoil) presents to oncoming air. The greater the angle of attack, the greater the lift. The smaller the angle, the less lift. Interestingly enough, it's actually easier for an airplane to climb than it is to travel at a fixed altitude. A typical wing has to present a negative angle of attack (slanted forward) in order to achieve zero lift. This wing positioning also generates more drag, which requires greater thrust.

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. However, when these airplanes are taking off or landing, their speeds can be reduced to less than 200 miles per hour (322 kilometers per hour). This dramatic change in the wing's working conditions means that a different airfoil shape would probably better serve the aircraft. Airfoil shapes vary depending on the aircraft, but pilots further alter the shape of the airfoil in real time via flaps and slats.

During takeoff and landing, the flaps (on the back of the wing) extend downward from the trailing edge of the wings. This effectively alters the shape of the wing, allowing it to divert more air, and thus create more lift. The alteration also increases drag, which helps a landing airplane slow down (but necessitates more thrust during takeoff).

Slats perform the same function as flaps (that is, they temporarily alter the shape of the wing to increase lift), but they're attached to the front of the wing instead of the rear. Pilots also deploy them on takeoff and landing.

Pilots have to do more than guide a plane through takeoff and landing though. They have to steer it through the skies, and airfoils and their flaps can help with that, too.