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6 Answers

Spin Procedure

Asked by: 2557 views Aerodynamics

AC 61-67 C pertains to stalls and spins and states that if you enter a spin with flaps extended( down) to leave flaps in the extended position until rotation stops . For reference, I found this statement at the end of this AC. Question: Assume you enter a spin with flaps extended ( you forget to retract flaps at the onset of the spin due to being distracted) how would a airplane respond if you retracted the flaps during the developed phase of a spin?  ( For those of you that respond, I am asking this question assuming the airplane is within the normal CG range and I realize that not all aircraft behave the same way during spins.)   Thank you for the feedback.

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6 Answers



  1. Wes Beard on Oct 23, 2013

    The definition of a spin requires two components. (1). Both wings must be stalled and (2) uncoordinated flight.

    The definition of a stall is where the wing exceeds the critical angle of attack. The definition of angle of attack is the angle between the chord line of the wing and relative wind. Lastly, the definition of chord line is a straight line from the leading edge to the trailing edge.

    If you were to retract flaps during a spin the chord line would change and cause a greater angle of attack than what you had before. This would cause the airplane to deepen the spin instead of allowing the pilot to exit out of it.

    The recovery procedure for a spin is P-A-R-E. Power to Idle, Aileron Neutral, Rudder to stop rotation and elevator pitch forward to break the stall. You will have to pitch the nose over considerably more if the flaps were retracted.

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  2. Sam Dawson on Oct 23, 2013

    I add a “D” to pared- dive recovery. Neutralize the controls, level the wings, then pull out of the dive. While giving spin instruction in my Super D I would have students forget to do this and go into a cross over spin during recovery.

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  3. Dan Chitty on Oct 24, 2013

    Thank you Sam and Wes for the feedback.

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  4. Brian on Oct 25, 2013

    Changing the flaps can do a whole slew of things. It may help or hurt the recovery. While what Wes notes is true, flaps also disturb the flow over the tail, how much depends on the airplane. Either way I’d go with what you read in part 23 over anything else. For a normal category airplane:

    Part 23.221 (iv) For the flaps-extended condition, the flaps may be retracted during the recovery but not before rotation has ceased.

    Read the entire part here: http://www.evolutionaryflighttraining.com/resources/fars/part-23#14:1.0.1.3.10.2.66.42

    In other words, flaps can be retracted in the normal category case, but only after the spinning has stopped.

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  5. Kris Kortokrax on Oct 25, 2013

    Dan,

    Spin recovery is addressed in paragraph 111 of AC 61-67C. There is no mention of flaps in that paragraph. The text to which you refer appears in Chapter 4 which discusses Airworthiness Standards. During certification spin testing, 23.221(a)(iv), the regulation to which Brian refers, is a certification regulation stating part of the procedure for demonstrating spin recovery.

    Wes,

    Retracting flaps, whether during a spin or not, decreases the angle of attack (i.e. a lesser angle of attack than before retraction).

    http://naca.central.cranfield.ac.uk/reports/1948/naca-tn-1643.pdf

    This link will take the reader to Technical Note 1643, which was developed by NACA in 1948. NACA is the predecessor to NASA. The aerodynamics have not changed since 1948. Their conclusions are that:

    1. “if a spin is entered inadvertently with the landing flaps extended, the flaps should usually be retracted immediately.”

    2. “Lowering flaps generally caused … an increase in the angle of attack”

    Take a look at the Type Certificate Data Sheets for different models.
    As an example, the Cessna 172 shows that the limit load factor is less with flaps extended than with flaps retracted. The POH also states that intentional spins must not be performed with flaps extended.

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  6. Dan Chitty on Oct 26, 2013

    Thank you Kris and Brian for the additional feedback.

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