Quote:
Originally Posted by aerohead
The xB is a "full-wake" vehicle.There is virtually no body taper underneath,along the sides,or at the roofline to the rear of the body.Consequently,the wake of the xB is as large as it's frontal area.Had the xB been shaped like Klemperer's "aero-brick" of 1922 (with Cd 0.16),the xB would see a 25% improvement in HWY mpg.The xB would probably benefit from any boat-tailing you could tolerate.A friend has a Toyota Highlander,getting 28-mpg HWY.I am to fabricate a 30-inch long tail for his car when the time avails itself.We are reasonably confident that the tail will deliver mpg comparable to his wife's Camry (34 mpg HWY).He's trying to wrap his brain around the length issue,and it will be receiver-hitch mounted for easy on-off and perhaps dedicated only for road trips.The difficulty of significant drag reduction with van-type rear vehicles is reflected in the comment about trading for a different type of vehicle.A full aero trailer could net you a 30% increase,but then you'd be pulling a trailer.Not very practical.
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Finally, thank you.
Not practical was the point I was trying to get across, not come across as an ass. It seemed to me this was going to be a question no one answered because they were trying to be nice. You wanted facts so I provided them, but did not realize it was only to keep dirt off the rear of the vehicle, not to increase mpg via aero. Some kind of boat tail that slipped into a hitch would probably be the best bet, but will render your "barn doors" in-accessable.
As mentioned before, probably the best bet is installing one of those turn down spoilers found on the back of some earlier suburbans and wagons. My 1990 Suburban had one and while not perfect it did force the air(and rain) to wash down the back window and keep things cleaner.