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  • Is defined as a surface that can obtain a lift from the air through which it moves, and  may state that any part of aircraft that transfer air resistance into a lift that is an airfoil.
  • There is a difference between the upper and lower surface of the wing builds up the lift force and that is shown in air flowing, the air flowing on  the top of the wing must reach the trailing edge at the sometimes air is flow underwing.
  • It’s important to know that the air pass on top the surface of the wing moves at greater velocity more than air pass below the wing because there greater distance and is taken along travel on the top surface and this must high velocity.
  • The principle of Bernoulli says that pressure differential creating between the upper and the lower surface of the wing is forcing the wing to upward in the the direction of the low pressure in the air.


The angle of Incidence :

  • Is defined as an acute angle wing chord that makes with the longitudinal axis of aircraft , is also called the angle of wing setting, and usually, this angle is fixed is built angle, this angle is positive when the leading edge of the wing is higher than the trailing edge and is negative when leading-edge is lower than the trailing edge.

The Angle of Attack (AOA) :

  • Is defined as the angle between the chord line of the wing and the direction of the relative wind, another mean is the angle between the chord line and a longitudinal axis, we can define a chord line as a straight line is pass through the section from the leading edge to the trailing edge.

Boundary-Layer :

  • Is defined as a layer of fluid in the immediate vicinity of bounding surface, and have relation with aircraft that is part of the airflow closet to the surface of aircraft is used to minimize pressure drag and skin friction drag on the aircraft.


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