Speaking as someone who has done a lot of aerodynamics reaseach in the past, inculuding wind tunnel tests, I would say you most likely would get a lot of lift from a kayak on the roof of a car. The "up" flow field from the front, hood and windsheild would cause large vortexes to form off the gunwales causeing a lot of lift. This would occur either way you mount the kayak [right side up, or upside down]. You also can not ignor the effects of the rack or straps since these could have a large spoiler effect, disrupting the flow. There would be no effective down force on the car from the "bernulli" effect between the car roof the the kayak, whatever low pressure that occures in this space would have equal and opposite effect on the roof of the car, as the kayak, cancelling each other. More likely the rack would totally spoil this flow any way, and since it is not contained the low pressurre area would just draw in air from the sides, causing more lift generating vortexes. The vast majority of the effect would be drag, very noticable on smaller cars in terms of fuel economy. As well as in cross winds. Perhaps dangerouly so in very light cars. I carry my lightweight skin on frame kayaks directly on the roof with a thin foam pad, with bow and stern lines, and at least one circumference strap. This reduces the drag, and the lift, as much as possible and does not affect the fuel economy much. This is much less expensive than a rack, and you are not as likely to drive off without securing the kayak. Peter *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Mon Jan 28 2002 - 20:00:39 PST
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