standard cirrus comparative cruising vs. a superior PIK-20D
j...@oxaero.com
Much has been happening lately regarding the lower-surface 12mm wide leading edge tape modification.
The dust has yet to settle on this issue, but it is beginning to appear to me that the Transparent variant of Tesa 4104 tape does not work due to a different surface texture compared to the White variant of the same product.
To see if there was anything to this conjecture, I flew twice over the last weekend, once with the Transparent tape on the left wing and White on the right wing. I expected this to produce a left yaw if the left wing was flying normally and the right with less drag. Of course, there are other ways to understand a left yaw, but good measurements with the Transparent tape have shown no change in glider performance at all, so I choose to interpret a left yaw as indication that the right wing is flying better than normal. Well, there was a left yaw on lift off, against a right cross wind, but aloft there was a strong banking left that was consistent for two hours of flying in turbulent and relatively calm air. Part of the flight can be seen at http://youtu.be/0FIMWJ5orcI .
Then, two days ago, I flew again with White tape on both wings. The banking tendency was gone the ship seemed to be flying well. A PIK-20D was sharing the sky with me and we encountered each other climbing and cruising. In both cases, the taped Cirrus outperformed the PIK. Of course, there is more skill involved in climbing and a comparison is less meaningful. But comparative cruising is somewhat more meaningful, though it can be corrupted by dissimilar air. With those caveats, I point you to a YouTube video of the taped Cirrus following the PIK, then pushing the speed up to overtake it. The Cirrus climbed over the PIK throughout the whole process. See the video at http://youtu.be/i9RGL6smMP4 .
As a single incident, this does not mean much, but it is yet another in a growing number of reported good experiences with the lower-surface deturbulator mod on gliders with Wortmann airfoils (http://www.deturbulator.org/participants.asp).
If nothing else, you may share my excitement at overtaking a superior ship at a 15 kt closing speed and climbing above it at the same time.
Jim Hendrix
417 N. 11th Street
Oxford, MS 38655