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Date:         Mon, 24 Oct 2011 21:44:20 -0700
Reply-To:     "Danny C." <bruiserbabie@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         "Danny C." <bruiserbabie@YAHOO.COM>
Subject:      Re: Aerodynamics related to fuel consumption (for an 84 tin top)
In-Reply-To:  <1319516317.589.YahooMailNeo@web33901.mail.mud.yahoo.com>
Content-Type: text/plain; charset=iso-8859-1

Here is my roof rack set-up and now Im loosing .000000000000001 MPG. Its pretty serious its now costing me around $0.0001 cents a year. Its going to break the bank!!!!   http://www.thesamba.com/vw/forum/album_page.php?pic_id=700868 Danny C. Portland, Oregon '84 Westy (Vanny)     ________________________________ From: Danny C. <bruiserbabie@YAHOO.COM> To: vanagon@GERRY.VANAGON.COM Sent: Monday, October 24, 2011 9:18 PM Subject: Re: Aerodynamics related to fuel consumption (for an 84 tin top) Seriously!!! your worried about what drag there is on a roof rack. WOW!!! Danny C. Portland, Oregon '84 Westy (Vanny)     ________________________________ From: Don Hanson <dhanson928@GMAIL.COM> To: vanagon@GERRY.VANAGON.COM Sent: Monday, October 24, 2011 9:02 PM Subject: Re: Aerodynamics related to fuel consumption (for an 84 tin top) > > > 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 > > >   Actually, the Quick N Easy rack system is probably one of the more aero ones out there, but anything that causes air turbulence is very harmful to overall aerodynamic efficiency.  A simple round tube metal crossbar rack on the roof of a vehicle....those will create a very significant airflow disruption all the way back along the vehicle.   Yes, a boat on the roof, that can really help.  The Vanagon's shape most likely causes turbulence to begin at the top of the windshield...and all back along the roof, there is no laminar flow (better for moving through the air)..Stick a boat up there, and the air remains attached to the boat...till it gets to the back...then the big suction.....  I recall 12degrees is the Magic number...If you can slope something down to a point with the slope never exceeding 12 degrees, the air will  remain attached...like a drop of water's shape... It is counter-intuitive (Unbelievable?) how significant even a small detail can influence the aerodynamic efficiency of a vehicle.  One time in the Pony Express open highway high speed event, my navigator and I were doing our 'practice run' where we had a short two-way 'pre-run' to test things before doing our 100 mile high speed run...We were limited to remain within 10mph of our stated 'target speed' which in that race was the Super Sport speed of  165mph....but we knew the radar gun guy was going to not be there to check...so I wanted to really try to break 200mph on one of our passes through a 15 mile section they'd given us for practice.  On our first pass, my navigator forgot to raise his window all the way and we could only run at 165, flat out.  I was appalled!  How could we average 165 if we could only max out at 165?...then the light went on..."Aha!...Put up your window on the return leg..."  Going back with the window up we easily hit 190 and still climbing.......At that speed, yes, a down window robbed us of 25+mph in speed...Those flag mirrors you see on street cars?....probably about 20mph at speed, easily.   The term "Streamline"...that came from the old days before windtunnels when guys would put dot's of oil or something else, all along the surface of the bodies of their vehicles or airplanes or trains....then go run them at speed and stop to check out how the liquid drops had been 'streamed' along the surface of the body...'streamlines'          I saw guys doing that still at the track, testing different wings and tail sections on racecars....kinda crude, but hey, we aren't F-1 when we race in the Sports Car Club of America events...And it really worked...You could see where there was turbulence because the oil was blown around in crooked lines or backwards or in an unpredicted way, while where everything was 'laminar' (smooth) the streamlines flowed smoothly along...   Don Hanson


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