flight. The wing must have a long enough span that the lift will counter act the force of gravity. The wing must be shaped in a foil design so that it produces lots of lift and less drag. There are many different shapes of wings, and foil designs all serving different purposes. The most commonly used foil design is a wing with a flat bottom and the top must be curved upward more drastically towards the front and sloping down to a point towards the end (a diagram of a foil design is shown in page 10). DragAnother important aspect of flight is the opposite of forward motion called drag. Drag can be seen in almost everyday life. An example of drag would be swimming in a pool. As you dive in the water the water must displace around you therefore causing two kinds of friction and slowing you down. The two types of drag friction that aircraft deal with are pressure drag and skin friction drag. An example of pressure drag is the air that hits the frontal part of the wing, or the most forward flat part of the wing and causes the plane to slow down. An example of skin friction is the actual air moving over the wing and being slowed down by the skin of the wing. There are a few other types of drag called induced drag. Induced drag basically means that drag caused by lift. Since the plane moves upward during lift the plane also has to displace air above the wing. Another type of induced drag is the drag caused by the wing tips. As the aircraft lifts off the ground air wants to move onto the top of the wing rather than stay on the bottom (equalize pressure). The wing tips actually allow the air on the bottom of the wing to travel to the top in a sideward motion or around the wing tip. When this happens the air from the bottom of the wing pushes down on the wing forcing the airplane to want to go down. The only way to eliminate wing tip drag is to have a wing of infinite size, which is impossible because lift would not be effectiv...
