PRINCIPLES Forces Acting on An Airplane
There are four forces acting on the airplane all the time during airplane is flying.The four forces are
(1) Lift, (2) Gravity force or Weight, (3) Thrust, and (4) Drag.
Lift and Drag are considered aerodynamics forces because they exist due to the movement of the Airplane through the Air.
Lift: is produced by a lower pressure created on the upper surface of an airplane's wings compared to the pressure on the wing's lower surfaces,causing the wing to be LIFTED upward. The special shape of the airplane wing (airfoil) is designed so that air flowing over it will have to travel a greater distance and faster resulting in a lower pressure area (see illustration) thus lifting the wing upward. Lift is that force which opposes the force of gravity (or weight).
Lift depends upon (1) shape of the airfoil (2) the angle of attack (3) the area of the surface exposed to the airstream (4) the square of the air speed (5) the air density.
Weight: The weight acts vertically downward from the center of gravity (CG) of the airplane.
Thrust: is defined as the forward direction pushing or pulling force developed by aircraft engine . This includes reciprocating engines , turbojet engines, turboprop engines.
Aircraft Flight Control
Drag: is the force which opposes the forward motion of airplane. specifically, drag is a retarding force acting upon a body in motion through a fluid, parallel to the direction of motion of a body. It is the friction of the air as it meets and passes over an airplane and its components. Drag is created by air impact force, skin friction, and displacement of the air.
An airplane is equipped with certain fixed and movable surfaces or airfoil which provide for stability and control during flight. These are illustrated in the picture.
Each of the named of the airfoil is designed to perform a specific function in the flight of the airplane. The fixed airfoils are the wings, the vertical stabilizer, and the horizontal stabilizer. The movable airfiols called control surfaces, are the ailerons, elevators, rudders and flaps.The ailerons, elevators, and rudders are used to "steer" the airplane in flight to make it go where the pilot wishes it to go. The flaps are normally used only during landings and extends some during takeoff.
Aileron: may be defined as a movable control surface attached to the trailing edge of a wing to control an airplane in the roll, that is , rotation about the longitudinal axis.
Elevator: is defined as a horizontal control surface, usually attached to the trailing edge of horizontal stabilizer of an airplane, designed to apply a pitching movement to the airplane. A pitching movement is a force tending to rotate the airplane about the lateral axis,that is nose up or nose down.
Rudder: is a vertical control surface usually hinged to the tail post aft of the vertical stabilizer and designed to apply yawing movement to the airplane, that is to make it turn to the right or left about the vertical axis.
Wing Flaps: are hinged or sliding surfaces mounted at the trailing edge of wings and designed to increase the camber of the wings. The effect is to increase the lift of the wings.