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5 Answers

Why is Vso lower than Vs (why does extending flaps allow for a lower stalling speed)?

Asked by: 4221 views General Aviation

Lowering the flaps changes the AoA to be greater, so wouldn't the critical AoA be reached quicker? Does extending the flaps also change the wing's critical AoA?

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5 Answers



  1. BJ Miller on Oct 29, 2015

    Allow me to be “that guy” and answer your question with a question…or two.

    What have you changed about your airfoil by lowering the flaps? How does this affect the airfoil diagram?

    The answer lies in the answer to these two questions and the definition of critical AoA.

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  2. Drew on Oct 30, 2015

    Lowering the flaps increases lift and drag and increases the angle of the camber in relation to the relative wind. I’m still unsure…

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  3. KenW on Oct 31, 2015

    You are corrrect that the camber of the wing is increased when flaps are deployed, although camber is not measured in relation to relative wind. As a result of the increased camber the wing with flaps extended will generate a greater amount of lift at a given AOA. At a given airspeed, Vs for example, a no flap wing will need to be at a higher AOA to maintain the same lift as a wing with flaps deployed. As a result, at a given airspeed, the no flap wing will reach critical AOA before the wing with flaps extended.

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  4. Brian on Oct 31, 2015

    You’re problem is you’re using lift and lift coefficient interchangeably. They are not synonymous. Lift coefficient increases, lift returns to be equal to wait after a short transient phase. AoA winds up being lower than when flaps were deployed (assuming you maintain the same speed) and maximum lift coefficient is increased due to the camber change.

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  5. Brian on Oct 31, 2015

    Weight**** doh! I wish I could edit with this darn thing…

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