Date: Mon, 24 Oct 2011 18:09:08 -0700
Reply-To: Richard Koerner <rjkinpb@SBCGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Richard Koerner <rjkinpb@SBCGLOBAL.NET>
Subject: Re: Aerodynamics related to fuel consumption (for an 84 tin top)
In-Reply-To: <CAHTkEu+4AP0Ohy74oRwCctZAgtJmGN6Fig=3g4aATpRG99s9hw@mail.gmail.com>
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Thanks Don, very good info. I've been thinking about building my own Quick-N-Easy roof rack for my 85 tin top and wanted to factor in aerodynamics into the decision. Of course, it might "blow" off all the empirical data by making a (sortof) aerodynamic box (maybe 10" tall or something) to hold lightweight floppy things like inflateable kayaks and paddles and even camp chairs and whatever. Maybe the large Vanagon frontal area pushes the slipstream high enough above the roofline and potential homemade "Rocket Box" or whatever they call them....hence no apparent decline in mileage. Anyway, it's not a huge outlay of cash and effort to give it a try for extended cross-country expeditions. Would be bummed by a -5 MPG result, but a couple MPG reduction would be acceptable. Still thinking about my design....rounded frontal end on my "box" seems appropriate. Also a factor is garageability with the higher roof.
Any perceptable increase in wind noise? Whistling and that sort of thing?
Rich
San Diego
--- On Mon, 10/24/11, Don Hanson <dhanson928@GMAIL.COM> wrote:
From: Don Hanson <dhanson928@GMAIL.COM>
Subject: Aerodynamics related to fuel consumption (for an 84 tin top)
To: vanagon@GERRY.VANAGON.COM
Date: Monday, October 24, 2011, 5:29 PM
For appx. 3 weeks I ran with my Quick-N-Easy roof rack on my vanagon,
having to carry some long stuff. It's a full width two-bar rack, with the
cross bars made from Alaskan yellow cedar, appx. 2x4" and just a little
narrower, side to side, than my stock mirrors. The 'bars' have large radius
corners. I was working about 60mi round trip from home, but otherwise
driving in the same area and at the same speeds I do in 'real life' (when I
am doing what I want, not working for pay)
My vanagon is a 5sp with a 2.0 liter Jetta inline gas motor and I've
always kept track of my fuel mileage, every tank for about 4 years now.
I've averaged ~23mpg really consistently. If I use premium fuel without
corn, I get almost 2 mpg more. If I drive at 75 all day, I get a few mpg
less. On my 4 or 5 fill-ups while sporting that roof rack, my gas mileage
declined by almost 2 miles per gallon.
Then, two tanks ago I took the rack off...it is Quick and Easy, so why
not, plus I'm out of work again so no need...The gas consumption again is
22.++ or 23 and 'small change'.... So there it is, a statistical sample of
one, but it is accurate. I fill at the same pump, letting the same auto
shut off stop the flow (and spew some backwash out on the station's
driveway) each time. I fill at about 275 miles run. I had the same weight
load aboard. I only carried a long ladder one time (30 miles) on the roof.
In case anyone is interested in how aerodynamic drag sucks down the gas...
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