Rotorcraft Flying Menu >General Aerodynamics >Airfoil > Angle of Attack

When the angle of attack is increased, air flowing over the airfoil is diverted over a greater distance, resulting in an increase of air velocity and more lift. As angle of attack is increased further, it becomes more difficult for air to flow smoothly across the top of the airfoil. At this point the airflow begins to separate from the airfoil and enters a burbling or turbulent pattern. The turbulence results in a large increase in drag and loss of lift in the area where it is taking place. Increasing the angle of attack increases lift until the critical angle of attack is reached. Any increase in the angle of attack beyond this point produces a stall and a rapid decrease in lift. [Figure 2-5]

Figure 2-5. As the angle of attack is increased, the separation point starts near the trailing edge of the airfoil and pro-resses forward. Finally, the airfoil loses its lift and a stall condition occurs.

Angle of attack should not be confused with pitch angle. Pitch angle is determined by the direction of the relative wind. You can, however, change the angle of attack by changing the pitch angle through the use of the flight controls. If the pitch angle is increased, the angle of attack is increased, if the pitch angle is reduced, the angle of attack is reduced. [Figure 2-6]

Figure 2-6. Angle of attack may be greater than, less than, or the same as the pitch angle.