I found info on this offset plate test. Reseached by Hucho[1987] in the late 1970's. Full scale test's in 1988 at Nasa's Ames Research.[Lanser et. al 1991].
The results showed that the highest drag reduction came with a plate of 0.36w and inset of 0.06w, where w is the width of the trailer. For a full sized enclosed semi-trailer this translates to a plate length of 33 inches inset at approx. 7 inches form each edge. For this configuration the researches recorded an overall drag reduction of approx. 10% over a +/- 15 degress yaw range.
interestingly the tangent of 0.06/ 0.36 = 9 1/2 degrees. vs. the 10 to 12 degrees often quoted for the smooth boatail.
Last edited by diesel_john; 05-26-2008 at 11:44 PM..
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