Welcome Guest. Sign in or Signup

5 Answers

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

Asked by: 1215 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?

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

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.

    0 Votes Thumb up 1 Votes Thumb down 1 Votes



  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…

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  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.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes



  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.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes



  5. Brian on Oct 31, 2015

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

    0 Votes Thumb up 0 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.