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What you are seeing is the effect of a huge vortice at the back of the cab. Vortices create big losses due to drag <snip>


I thought that "vortices" was the plural of "vortex". <img src="/forums/images/graemlins/confused.gif" alt="" />

Everything else you stated made perfect sense Frank. <img src="/forums/images/graemlins/bird.gif" alt="" />