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Do flaps or leading edge devices change an airfoil’s critical angle of attack?

Asked by: 5345 views Aerodynamics

Do flaps or leading edge devices change the angle of attack at which the airfoil will stall?  My research online seems to favor a decrease in critical AOA when flaps are extended, and an increase in critical AOA when leading edge devices are extended.  I just can't quite grasp why that is.  Can someone verify whether or not that is correct, and if so, why? 

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2 Answers

  1. Vidura Asanka Jayawardene on Jun 07, 2014

    From what I know that is correct. The angle of attack is the angle between the cord line and relative airflow, extending the flaps will change the cord line in such a way that the normal angle of attack of the wing relative to the airflow is increased, so now the change in angle required to reach the critical AOA is less hence the critical AOA is deceased. The whole opposite occurs when leading edge devices are deployed. I wish I could draw this out then I can show you whats happening….

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  2. Brian on Jun 11, 2014

    It depends on the type of flap. The definition of chord line is a line drawn from the leading to the trailing edge of a clean airfoil. Since flaps increase this angle (called the virtual chord line) and slats decrease this angle the critical AOA is decrease when flaps are introduces. Conversely, slats decrease the angle of the chord line (again referred to as the virtual chord line) so the actual stalling AOA is greater than in an clean configuration. I will try to get some pictures posted tomorrow.

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