The hangers under the wings of an airplane are designed to reduce interference drag.
Some parts of an airplane wing (mainly the leading and trailing edges) are movable. Pilot manipulation of these parts can change the shape of the wing and control the distribution of lift or drag on the wing for the purpose of increasing lift or changing the attitude of the aircraft.
The commonly used movable airfoils on an airplane wing include various leading and trailing edge augmentation devices, ailerons, spoilers, speed reducers, elevating and lowering ailerons, and so on. The interior of the wing is often used to hold fuel.
When the thickness of an aircraft wing permits, the main landing gear is also often stowed wholly or partially within the wing. In addition, the engines of many airplanes are either fixed directly to the wing or suspended below the wing.
Expanded information:
The main geometrical parameters describing the shape of an aircraft's wing are the wingspan, the wing area (the area of the wing's pitch projection), the angle of swept-back (mainly leading edge swept-back, 1/4 chord swept-back, etc.), the upward angle of inversion, and the shape of the wing profile (the airfoil shape).
Commonly used
Commonly used basic airfoils are low-speed airfoils, spiked airfoils, supercritical airfoils, and supersonic airfoils with sharper leading edges. The wing has a 1/4 chord swept back angle of about 20° or less.
Flat wings are mostly used on subsonic airplanes and some supersonic fighter planes. In subsonic aircraft, the chord ratio is about 8 to 12, and the relative thickness is 0.15 to 0.18. In supersonic aircraft, the chord ratio is 3 to 4, and the relative thickness is 0.03 to 0.04. The chord ratio is about 1 to 4, and the relative thickness is about 1 to 2.
Baidu Encyclopedia - Wings