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Forward Slip with or without Flaps?

Asked by: 1081 views Aerodynamics

I've read articles and personal accounts of doing forward slips on purpose without using flaps. I was taught to always reduce the power and use full flaps prior to forward slipping (in a C172). On one of my flights, I was too high and fast on approach and decided to idle and forward slip, forgetting to put down the flaps, and I ended with the same high airspeed with the steep descent. So, are forward slips more appropriate with flaps down or up? What are the reasons for both? Is it aircraft dependent? Thank you.

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1 Answers



  1. Kris Kortokrax on Jul 31, 2016

    First, a forward slip is employed to control your descent path, not your airspeed. The Glider Flying Handbook contains a little better description of the maneuver, in that, it recommends raising the nose so that excess speed does not develop. The new ACS for Private pilot (which replaced the PTS on June 15th) has a requirement to maintain an airspeed that will result in minimum float on landing. With power at idle, you control your airspeed with pitch.

    Now to the flap issue. You need to look at the limitations section of the POH for the model you are flying. For instance, the 172S model contains a limitation against slips with one tank dry in excess of 30 seconds. The 172N has a requirement for a placard that states “Avoid slips with flaps extended.” Note that this is not a prohibition, but a recommendation. In the section on normal landings, both contain language stating that slips with greater than a 20 degree flap extension can cause a slight tendency for the elevator to oscillate. Again, not a prohibition, just a caution. In the same way that there is no prohibition concerning using flaps during a slip, there is also no directive that they shall be used. This is why we should seek out knowledgeable instructors, so that we don’t end up slaves to Old Wive’s Tales.

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