Quote:
Originally Posted by orbywan
Anyone have any guild lines or suggestions for how much I should drop the lower part of the boat tail to achieve the right airflow down there?
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Hucho's book says maximum gains for a "short" diffuser are achieved at 3.66 degrees upward slope, and for a "long" diffuser it's 2.66 degrees. The long one has positive benefits (compared to a zero degree diffuser) up to about 6 degrees, and a short one sees benefits up to about 11 degrees. The 6 and 11 numbers may go further, but that's where the graphs stop.
I am guessing your diffuser qualifies as a "long" diffuser. If I were you, I would take a straight edge and try to not exceed the taper from your back wheel to your back bumper, that way you will not drag your diffuser on a steep driveway. On the other hand, your RV may be tall enough that this is of little concern, and you could get away with a more shallow angle.