Go Back   EcoModder Forum > EcoModding > Aerodynamics
Register Now
 Register Now
 

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 05-24-2008, 01:47 PM   #1 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,267
Thanks: 24,392
Thanked 7,360 Times in 4,760 Posts
mods-data-%change Cd or drag(installment#3 surface drag)

Note from Darin (admin): this installment is part of a series posted by Phil (aerohead) about the effectiveness of various aero mods - with quotations and citations to source data.

See the aero mods data index here.

End note.

---

I figured this was going to come up at some point so I wanted to nip it in the bud before spammers started marketing "miracle" finishes for cars, promising higher mpg and we got a flurry of inquests.

This one's short and it's from Kelley and Holcombe at General Motors Research Laboratories:

"The nature of the boundary layer is such that a critical speed exists below which improvement of a particular body surface smoothness has no effect on reducing surface drag. For the finished portion of an automobile body the surface smoothness is of the order of 0.5 to 1.0 microns or 20 to 40 Mu in. Any improvement will not reduce surface drag,since the grain size of the surface ( 0.02-0.05 mils ) is below the critical diameter for any land vehicle operation."

Of interest to Bonneville racers whom will enter into transonic flow, Hot Rod Magazine's June,1962 issue published the following:

"By just waxing the surface of the C118 ( DC-6 ) airplane the Air Force was able to save an hour's time,or 370 gallons of avgas between Honolulu and Japan."

Bottom line, if you've washed and waxed your car,that's as good as you're going to do. Surface friction is still going to claim 9% drag from you.

__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 05-24-2008, 03:18 PM   #2 (permalink)
Master EcoModder
 
Big Dave's Avatar
 
Join Date: Jan 2008
Location: Steppes of Central Indiana
Posts: 1,319

The Red Baron - '00 Ford F-350 XLT
90 day: 27.99 mpg (US)

Impala Phase Zero - '96 Chevrolet Impala SS
90 day: 21.03 mpg (US)
Thanks: 0
Thanked 186 Times in 127 Posts
Good post!

Fuel economy is the most poorly understood (by the general public) parameters of auto preformance.

Thanks to high-priced gas we are seeing old charletans coming out of the woodwork hawking "solutions" that never worked before and counting on the public's short attention span.

As we know, there is little new in the world of engineering. Stuff works or doesn't work for fundamental engineering reasons.
__________________
2000 Ford F-350 SC 4x2 6 Speed Manual
4" Slam
3.08:1 gears and Gear Vendor Overdrive
Rubber Conveyor Belt Air Dam
  Reply With Quote
Old 05-24-2008, 04:17 PM   #3 (permalink)
Master EcoModder
 
tasdrouille's Avatar
 
Join Date: Jan 2008
Location: Mirabel, QC
Posts: 1,672

The Guzzler - '08 Hyundai Elantra GL
90 day: 33.12 mpg (US)

Got Soul? - '11 Kia Soul 2U
Thanks: 35
Thanked 86 Times in 57 Posts
Phil,

Have a look at this blog entry at AutoSpeed.

I haven't read the book yet, but from the article it looks like it's possible to deal with friction drag at our speeds.
__________________



www.HyperKilometreur.com - Quand chaque goutte compte...
  Reply With Quote
Old 05-24-2008, 10:50 PM   #4 (permalink)
Cd
Ultimate Fail
 
Cd's Avatar
 
Join Date: Feb 2008
Location: Austin,Texas
Posts: 3,585
Thanks: 2,872
Thanked 1,121 Times in 679 Posts
.
  Reply With Quote
Old 06-03-2008, 05:50 PM   #5 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,267
Thanks: 24,392
Thanked 7,360 Times in 4,760 Posts
friction drag

Quote:
Originally Posted by tasdrouille View Post
Phil,

Have a look at this blog entry at AutoSpeed.

I haven't read the book yet, but from the article it looks like it's possible to deal with friction drag at our speeds.
I looked at Barnes & Noble,and Hasting's for the book.No luck.I'll keep on trying.I did run across something of potential interest in Hermann Schlichting's Boundary Layer Theory involving laminar airfoils which may have significance to the book.I'm gonna chew on it for awhile and post when I think I've got a handle on it.P.S.,all of the Navier Stokes stuff is in Schlichting's book.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 06-03-2008, 06:41 PM   #6 (permalink)
EcoModding Lurker
 
Join Date: May 2008
Location: Central New Mexico
Posts: 18

Bun - '02 Ford Focus ZTS
90 day: 31.3 mpg (US)
Thanks: 0
Thanked 0 Times in 0 Posts
Would a car have more drag if it's dirty? I don't know that much about aerodynamics, but the original post suggests to me that it might. My very informal observations suggest that washing may improve mileage.
  Reply With Quote
Old 06-03-2008, 07:10 PM   #7 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 16,267
Thanks: 24,392
Thanked 7,360 Times in 4,760 Posts
dirty vs clean

Quote:
Originally Posted by Mr. Cheap View Post
Would a car have more drag if it's dirty? I don't know that much about aerodynamics, but the original post suggests to me that it might. My very informal observations suggest that washing may improve mileage.
The surface drag is only 9-percent of the total drag,however,as mentioned in the installment,the relationship to a clean and freshly-waxed finish is firmly established.It's picking nits but its one of the things we do have control over.When I get all my "pick and shovel " work done,I'd like to spray a nice finish on my monstrosities and keep 'em maintained.

__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Reply  Post New Thread




Similar Threads
Thread Thread Starter Forum Replies Last Post
CdA list Daox Aerodynamics 206 10-25-2023 07:32 PM
Aerodynamics Seminar #2 - by Phil Knox MetroMPG Aerodynamics 2 05-10-2013 06:34 PM
Mercedes modded C-class: Cd 0.25. Up 7.5 mpg over regular model (with other mods). MetroMPG Aerodynamics 25 04-08-2013 05:57 PM
Sources of Aerodynamic Drag in Automobiles and Possible Solutions SVOboy Aerodynamics 12 02-17-2010 03:09 PM
BMW cooling duct fabrio. Aerodynamics 19 09-27-2008 05:48 PM



Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2024, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com