Lift and drag are two of the four forces that act on an airplane in flight. The remaining forces include gravity and
thrust. Under normal operating conditions, lift is opposed by gravity (the total weight of the aircraft including
occupants, fuel, baggage, etc.). Drag is a force generated during the production of lift and when an object passes
through the atmosphere. The force of thrust is opposed by drag. There are various kinds of drag. Some of the
more well known forms of drag include induced drag, parasite drag, profile drag, and interference drag.1
The production of lift involves the dynamic reaction of air passing over specially-shaped surfaces known as
airfoils or wings. The shape of an airfoil is designed to generate the requisite amount of lift to support the weight of
the aircraft throughout a variety of flight parameters. Most airfoils have a pronounced camber or curved surface that
causes the mass of air flowing over the surface to accelerate in terms of velocity. As a consequence, the pressure
along the cambered surface is reduced. With a reduction of pressure on one side of the airfoil and near-ambient
pressure on the other, a pressure differential is established that acts on the surface area of the airfoil. The
magnitude of this force equals the amount of induced lift.
Another element in the production of lift is the downward deflection of air as it passes away from the airfoil. This
movement of air provides a Newton action/reaction component to the production of lift. The downward action of the
air provides an upward reaction to the wing. This lift is known as dynamic lift. The total lift of the airfoil is the
combination of induced and dynamic lift.
Several factors affect the quantities of lift and drag produced as the airfoil experiences relative wind. The shape
of the wing, the total surface area of the airfoil, the velocity of the flowing air mass (airspeed), and the angle at which
the air strikes the airfoil (angle of attack) are key factors in the generation of lift and drag. In this unit, several
examples demonstrating the shape of the airfoil, speed of flowing air mass, and angle of attack are presented.
0 التعليقات:
Post a Comment