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What about this, how would you read this 2 graphs?
Why Cd has negativ and positive numbers at first graph?
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What is delta Cd at first graph,why delta?
And why negative numbers?

In the first graph what is charted is a ratio of tail length over overall length. The numbers go negative because it is charting the delta, or difference for five test cases between included angle and length ratio.
This is all mooted by compound curve surfaces.