978. How do different airplane wings help or hurt the airplane?
An airplane wing's main job is to generate a large upward lift force while experiencing as little backward drag force as possible. To obtain the lift force, a wing must make the air flowing over its top to speed up while the air flowing under its bottom slows down. The wing must also avoid introducing turbulence into the main airstream because that will result in severe pressure drag. There are many cross sectional shapes for wings that achieve both large lift forces and small drag forces, but some are better suited to each style of airplane than others. For example, private propeller-driven planes travel relatively slowly and need broad, highly curved wings to obtain enough lift to support them. In contrast, commercial jets have much narrower, less curved wings because they travel faster and produce lift more easily. But during takeoff and landing, even jets need to increase the curvatures of their wings. That's why many jets have slats and flaps that extend from the leading and trailing edges of their wings to increase the wings' breadths and curvatures for low-speed flight.