Introduction

Many years ago I got interested in finding a mathematical model that describes the polar curves of the sailplanes we fly. The idea being that if a simple equation could be found then it would be relatively easy to collect sink rate data for the local sailplanes and fit the data to the model. Why? Do you really believe those nice polar curves found in your aircraft operators manuals. Those are for perfect aircraft under ideal conditions. What about that club Blanik you’re flying with all the dings in the leading edges?

I did some work on the problem and tried to get the local club members interested but nothing came of it. The initial results were very promising so I wanted some real data to test. I contacted Dick Johnson who had tested over 100 sailplanes for his Flight Test Evaluation series in Soaring Magazine. He declined to share any of his data stating that his methods were sufficient. At this point I dropped the project.

Well, I’M BACK! For the usual variety of reasons (time, money, family commitments) I haven’t been active in more than a few years but am considering returning to flying again. So, in an effort to get my brain back in soaring mode I went back and looked at what I had done with this problem. I’ll present it all here for your approval, disapproval, and comments.

Next: The Polar

(EDITORIAL NOTE: Anything that looks like text from a math book was rendered with LaTeX, the graphs were produced with the R mathematics program, and the initial figures showing the vector analysis were drawn with the iDraw vector drawing program on OS X.)

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