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5 Answers

Flap setting for Soft field take off, Cessna 172P

Asked by: 10633 views Student Pilot

POH does not specify, it says 10 degree for short field take off though.

I searched several internet, census is 10 degree. However, my CFI feels 20 is right.


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5 Answers

  1. Nathan Parker on Feb 05, 2012

    Every 172 I’ve ever flown had an operating limitation of 0 or 10 degrees of flap, which moves 20 degrees out of the realm of legal flight.  Check your AFM.
    But as a theoretical proposition, optimal flap setting will vary with the condition of the runway, because you’re essentially trying to balance the drag of the field with the drag of the flaps.  For very muddy fields, full flaps might be optimal, because the drag of the flaps pales when compared with the drag of the surface.  But as the condition of the runway improves, the optimal flap setting would decrease.  (This analysis is based on NASA (NACA) research conducted in the 1930’s.)

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  2. Brian on Feb 05, 2012

    “This analysis is based on NASA (NACA) research conducted in the 1930′s.”

    Happen to have the particular document? I’d love to add it to my folder. 

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  3. Bill Trussell on Feb 06, 2012

    Given the type of flap system on a C172 (Fowler) I have always thought of the first 10 degrees being more positive for lift than drag ( hence the pitch up and need for forward pressure on application).  Anything after the first 10 degrees is mostly drag and therefor not recommended for performance enhancements.
    Remember to check the notes in the peformance tables before concluding that the POH does not mention anything about flap settings.  It is sometimes hidden.

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  4. Mike LaForest on Feb 07, 2012

    In section 4 Normal Procedures – Amplified Procedures – Wing Flaps it says “Wing flap settings greater than 10 degrees are not approved for takeoff” in the POH for the Cessna 172N, 172P & 172R.
    The 172R amplified procedures states “Soft or rough field takeoffs are preformed with 10 degrees of flaps ….”
    The amplified procedures sections of the POH are rarely explored and contain a ton of great information that fills in many blanks that the check lists leave out.

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  5. Derek Schwalenberg on Feb 08, 2012

    I say test it. AFM says 10 then go with that if you are unsure. If you have a place with plenty of runway though you could always see which gets you off the ground quicker [or in less distance I should say], which gets you above your obstacle in less distance.. etc.. etc.. In many of the Piper’s 20+ degrees is the optimal setting but that’s a whole different airplane with different characteristics. Test it with plenty of room for error so when you don’t have room for error (although ideally one would never put themselves in such a situation) you know for sure which is the best choice.

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