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Date:         Wed, 26 Oct 2011 22:15:38 -0500
Reply-To:     John Rodgers <inua@CHARTER.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         John Rodgers <inua@CHARTER.NET>
Subject:      Re: Aerodynamics related to fuel consumption (for an 84 tin top)
Comments: To: Alistair Bell <albell@SHAW.CA>
In-Reply-To:  <AD65AAA3-B1D0-45A6-9366-9C4E386C50CC@shaw.ca>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

In conjunction with spoilers, vortex generators should be considered as well. Here is a link to some pretty interesting stuff regarding vortex generators. There are a couple of pictures showing the effects of vortex

generators coupled to the airflow that leads to the spoilers. They sure generate smoother air flow.

Maybe the more technical minded on this list will get some mileage from this PDF.

Research on Aerodynamic Drag Reduction by Vortex Generators

http://www.mitsubishi-motors.com/cor...004/16E_03.pdf <http://www.mitsubishi-motors.com/corporate/about_us/technology/review/e/pdf/2004/16E_03.pdf>

John

John Rodgers Clayartist and Moldmaker 88'GL VW Bus Driver Chelsea, AL Http://www.moldhaus.com

On 10/25/2011 7:33 PM, Alistair Bell wrote: > I've wondered about a horizontal splitter like that. I have also seen Vee shaped short fins (V in plan view) for use in similar situations. The wide part of the Vee at the rear of the roof. The Vees were also slightly askew. > > WIth the luggage rack I'd say (and Jake de Villiers has done it) put a filler piece or cover in it. It is the edges of the rack that mucks things up. > > alistair > On 2011-10-25, at 4:33 PM, Poppie Jagersand wrote: > >> Here is a rear spoiler design for vans that potentially reduces drag by 5% >> >> http://www.greencarcongress.com/2008/11/novel-spoiler-d.html >> >> Development of a rear spoiler of a new type for mini-vans >> by Inchul Kim, Xin Geng, Hualei Chen >> International Journal of Vehicle Design (IJVD), Vol. 48, No. 1/2, 2008

>> Abstract: To reduce aerodynamic forces on mini-vans, we have developed a rear >> spoiler of a new type based on the principles of fluid dynamics and >> through numerical computations. The aerodynamic drag as well as lift on >> vehicles having a bluff back can be reduced when the new spoiler is >> attached to them. Numerical simulations show that the aerodynamic drag

>> and lift on a mini-van moving at 30 m/s are reduced by 5% and more than >> 100%, respectively, when the new spoiler is attached to it. >> >> A challenge with using it on a Vanagon Westy might be that the flow towards the rear end of the roof is not clean enough for the spoiler above to work as designed. >> >> So in terms of potential improvements, the removal of the Westy luggage rack and replacement with the European 89-91 style gives an experimentally verified 12% improvement. The part is likely not to diffiuclt to find in European junkl yards, but shipping would be expensiove, unless some of the various dealers in Europeean engines and transmissions sticks a few of these in his next container shipment. >> >> >> Dealing with the rear end would entail downloading the above or other similar design papers and try to adapt the design to the Vanagon. >> >> >> Martin >> >> >> >> ________________________________ >> From: Alistair Bell<albell@shaw.ca> >> To: Poppie Jagersand<poppie.jagersand@YAHOO.CA> >> Cc: vanagon vanagon<vanagon@GERRY.VANAGON.COM> >> Sent: Monday, October 24, 2011 11:36:51 PM >> Subject: Re: Aerodynamics related to fuel consumption (for an 84 tin top) >> >> Of course both front and rear matter, but I maintain the rear matters more :) >> >> the luggage rack lip trips the airflow. >> >> your model for drag dos not indicate where the main areas of drag are. That needs much more empirical work. I can build a water tunnel for you if you want :0 >> >> alistair >> >> >> On 2011-10-24, at 10:17 PM, Poppie Jagersand wrote: >> >>> Both the front and the rear matter for air drag. The Westy luggage rack is a big culprit on campers as shown in wind tunnel testing is here: >>> >>> http://www.t3-infos.de/images/Luftwiderstand_1.jpg >>> Partial English translation: >>> >>> http://www.cs.rochester.edu/u/jag/vw/gen/pops/popsT3.htm >>> >>> An experimentally identified mathematical model for drag: >>> http://gerry.vanagon.com/cgi-bin/wa.exe?A2=ind9812E&L=vanagon&P=R3587 >>> >>> >>> Martin >>> >>> >>> >>> ________________________________ >>> From: Alistair Bell<albell@SHAW.CA> >>> To: vanagon@GERRY.VANAGON.COM >>> Sent: Monday, October 24, 2011 7:27:24 PM >>> Subject: Re: Aerodynamics related to fuel consumption (for an 84 tin top) >>> >>> It is not the frontal area that kills the aerodynamics of the van, it is the big low pressure area at the rear. Don 't get me wrong, reducing frontal area would improve things, but fairing the rear would work wonders :) >>> >>> I think my improvement in gas milage with canoe on top (which increases frontal area) is that the canoe modifies the airflow at the rear. >>> >>> alistair >>> >>> >>> >>> >>> On 2011-10-24, at 6:09 PM, Richard Koerner wrote: >>> >>>> 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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