Did some more research. Pages 55-58, the conclusion on "rear roof garnish" is not exactly what I had in mind. Their "garnish" is set at a 12 degree downward angle, and I'm guessing about 6 inches deep.
PDF link:
http://csus-dspace.calstate.edu/xmlu...pdf?sequence=1
Quote:
Table 4.2.1 presents the overall effect of using rear roof garnish. It shows that by attaching Rear Roof Garnish to the baseline truck model, aerodynamic drag coefficient Cd was reduced by about 2.4%;
however, the lift coefficient Cl was increased by about 33%
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I think that if I were to bend my roof spoiler down 12 degrees and caulk or foil tape the joint/connection I could expect similar results.
Right now my spoiler/wing/garnish is flat, and allows boundary air under it. I should not get the same amount of lift, but that remains to be seen. I'll take safety over mpg gains any day of the week.
EDIT 11/21/11: This is pretty close to what I am first testing. Tonight I get to do some serious highway driving, will be doing more driving tomorrow as well (I work from home).
The Recumbent Bicycle and Human Powered Vehicle Information Center
Quote:
Additional mods for Vans and SUVs::
A new spoiler design has been shown to reduce drag and lift significantly on bluff-backed vehicles such as minivans and SUVs. Simulations showed that aerodynamic drag on a mini-van moving at 67 mph were reduced by 5% when the new spoiler was attached. This rear spoiler acts like a diffuser when it is attached to the back of a vehicle, making the pressure on the back of the vehicle higher than without it. That's a good thing!
Full technical paper ($22)
A Rear Spoiler of a New Type that Reduces the Aerodynamic Forces on a Mini-Van
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NOTE: Last night I added plastic automotive button head plugs to the open holes on the trailing wing edge. I snipped and did some grinding to make it flush on the bottom (they were too long). I used a butane torch lighter to soften the plastic plugs before inserting, as they were a bit tight and got stuck half way in a test fitting.