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I was looking for airfoils, and I came across an interesting design. It's called a KFm1 step airfoil. Those of you in model aircraft design might have heard of it. However, I've never really seen one of these in normal aviation.

My questions are:

  • Why don't they work for full sized aircraft?
  • Is there some way to make them work?
  • What gives this airfoil its properties?
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    $\begingroup$ From Wikipedia article you linked: "Poor lift-to-drag ratio performance in wind tunnel testing has meant that to date the KF airfoil has not been used on any full size aircraft." Are you asking why they have a poor L/D? $\endgroup$
    – Ron Beyer
    Commented Apr 19, 2017 at 20:35
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    $\begingroup$ Questions 1 & 2 are answered by the Wiki article, as pointed out. Question 3, however, seems to be a reasonable one to look for an answer to. $\endgroup$
    – FreeMan
    Commented Apr 19, 2017 at 20:53
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    $\begingroup$ @Ron Beyer Partly I'm asking why L/d is so poor, part of the question is whether modifying a different airfoil with a KFm step will also cause low l/d $\endgroup$
    – Nicholas
    Commented Apr 19, 2017 at 22:26
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    $\begingroup$ Related: aviation.stackexchange.com/questions/35063/… $\endgroup$
    – Peter Kämpf
    Commented Apr 20, 2017 at 6:49

1 Answer 1

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The idea works but only with active automated re-configuration of the shape of the step(s) during flight. Further testing has shown that this airfoil is effective in low Reynolds number flow.

source: Wikipedia

The Reynolds number is indicative of the speed of the airflow over the wing. The higher the speed, the higher the Reynolds number and vice versa. This is why they would be more suited for model aircraft rather than large aircraft which would experience higher Reynolds numbers.

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