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3 Answers

Speed steep spiral

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Commercial Pilot

Does anybody have a rule of thumb for steep spirals speed. The Airplane Flying Handbook states: After the throttle is closed and GLIDING SPEED is established, a gliding spiral should be started and a turn of constant radius maintained around the selected spot on the ground. But for example if I use the glide speed on the cessna 150 (60 kts) in a 60 degree turn my stall speed will be 66. Since it‘s a 1-2 gs maneuver i don‘t want to end in a stall.

Regards.

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3 Answers



  1. Dan S. on Sep 25, 2015

    Daniel,
    The load factor you are referring to (2g’s at 60 degrees bank) would only occur if you were maintaining level flight in a 60 degree bank. Since with this maneuver, you will be descending, the load that the aircraft is supporting will be much less than if you were to try a 60 degree bank in level flight. This is because the aircraft will not be having to overcome gravity as it would at level flight, and because you are descending you aren’t having to add the large amount of back pressure which would put you closer to the critical angle of attack. Go practice the maneuver, and if you will find that it will not be an issue!

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  2. Daniel ENRIQUEZ EGUIGUREN on Sep 29, 2015

    Dan S.
    Please be careful! Your statements are WRONG, in fact if you are doing a 60 degree turn with power on you will have a much slower stall speed than with idle power, beacuse the wing load tend to be less with full power. You can experience load factors with and without power.

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  3. Kris Kortokrax on Oct 14, 2015

    Daniel,

    It is interesting that you ask a question and when someone gives you an answer (the right answer, by the way), you tell him that he is wrong. If you knew the answer, why did you ask the question?

    There are several problems with your assumptions.

    1. You assume that when the Airplane Flying Handbook states to establish gliding speed, that it means to use the speed for maximum range. Where does it say that you cannot pick a higher glide speed?

    2. You ignore the fact that on page 4-29 of the Pilot’s Handbook of Aeronautical Knowledge, it discusses the load factors encountered in a “constant altitude turn” as Dan stated. In a descending turn, you are not maintaining the same back pressure as you would in a constant altitude turn. When I do a wingover, I reach a bank angle of 90 degrees at the halfway point. There is no attempt to maintain a constant altitude and the airplane experiences no more than 1 G while banked 90 degrees.

    3. The stall speed chart in the POH shows that at a 60 degree bank, the flaps up stall speed at the most aft CG is 65 KCAS (51 KIAS). At most forward CG, it is 68 KCAS (57 KIAS).

    4. The maximum glide speed is 60 KIAS, so the indicated stall speeds 51-57 are below 60. The speed for maximum glide is 1.05 – 1,17 times Vs1.

    5. In your post, you correctly described the spiral as a constant radius turn. That means that you do not establish and maintain a 60 degree bank. You vary your bank angle to maintain the constant radius, as in turns around a point or S turns. You would only approach the 60 degree bank when headed downwind. The bank shallows as you encounter more of a headwind. So the amount of time during which you would even approach the stall would be minimal.

    6. You should to be at a speed below maneuvering speed (Va) to perform the maneuver. That speed is shown as 93-104 KIAS.

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