title_body: What is the typical glide ratio of Kline-Fogleman airfoils?
upvoted_answer: This paper (AE-74-1054-1) from the University of Tennessee has a graph on page 15 showing the best they managed was 1:17 with the step on top and 1:8 with the step on the bottom but these were at a very specific angle of attack, and about half that was more typical.
  
  
    The wind tunnel results show that for this new airfoil the lift/drag ratio is lower  than for the flat plate, and the pressure data show that the airfoil derives its lift the same way as the inclined flat plate. This airfoil offers no discernable advantages over the conventional airfoil. 
  
  
  Anecdotally, that matches my experience with KFm gliders. They work about as well as a flat plate. Ok for a light-wieght park-flier with loads of thrust but no good for a glider.