For clarity, I would like to add two words to the first paragraph in
my last post. I have wrapped these two words in *** to highlight the
edit.

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Alrighty -- following is a simple energy/force analysis for a small
propeller equipped DDWFTTW vehicle. In this analysis, we show that
in a 27.5ftsec wind, and with the vehicle traveling ***directly
downwind*** over the ground at 55ft/sec, the retardant force on the
wheels needed to drive the propeller is less than the propeller needs
to keep the vehicle at that speed.

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