A couple of years ago, Les Garber and I used the U of Minnesota Hydraulics Lab wind tunnel to evaluate a number of parameters governing the performance of model autogyro rotors. The tunnel at the U has a test cross section about 6' X 6' and can produce velocities from about 10mph to over 80mph.

Results are summarized in an article in RC Modeler, August 2001. The most remarkable finding was that one of Michael Selig's airfoils, the SG6042 produced significant great lift than almost any other airfoil tested. Further, the SG6042 is only slightly different than the good old Clark-Y.

Another interesting finding was the effect of "trips" placed at the 20% chord point. These were .005" thick, .125 wide automotive striping tapes. With trips the rotors would spin up quicker and produce larger lift at lower airspeeds.

For me this indicates that subtle differences in shape can make big differences in the performance of our models.

Bill