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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 07-20-2008, 03:46 PM   #1 (permalink)
What? THIS IS MY GOOD CAR
 
justpassntime's Avatar
 
Join Date: Jun 2008
Location: Eastern Washington
Posts: 285

The Japillac - '87 Honda Accord LXi Sedan
90 day: 31.77 mpg (US)

Ranchero GT - '73 Ford Ranchero GT

Spaz - '83 Chevy S10 4X4 Tahoe
90 day: 27.53 mpg (US)
Thanks: 0
Thanked 0 Times in 0 Posts
Send a message via ICQ to justpassntime
Arrow Update! Are there any magic numbers? Updated!

I am doing a rear window extension, defuser, rear window spoiler. Seems like many names are being used for the same part.

Anyway, is there a magic number for the length or just what works or looks good?

I know the degrees from the flat roof line is 15 other than that I am just winging it.

Any contributions would be greatly appreciated. Comments work too but money is better.

__________________
Honda...the economical, renewable resource.



Last edited by justpassntime; 07-27-2008 at 10:49 PM.. Reason: Updated
  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 07-20-2008, 06:10 PM   #2 (permalink)
Mr. Blue Tape
 
azraelswrd's Avatar
 
Join Date: Jun 2008
Location: Fresno, CA
Posts: 345

AzxA - '06 Scion xA
90 day: 42.72 mpg (US)
Thanks: 0
Thanked 2 Times in 2 Posts
Experimentation and tuft testing may help in figuring out the size and angling, though an oft-cited resource is Hucho's book on aerodynamics. Search for it on Amazon.com. It's massive (both price and size) but it has those "magic numbers" you're looking for.

If you're lucky maybe your local free library has one....
__________________


My 5 pillars of fuel efficiency:
  • driving style
  • aerodynamics
  • tires
  • weight reduction
  • engine maintenance
  Reply With Quote
Old 07-20-2008, 06:24 PM   #3 (permalink)
What? THIS IS MY GOOD CAR
 
justpassntime's Avatar
 
Join Date: Jun 2008
Location: Eastern Washington
Posts: 285

The Japillac - '87 Honda Accord LXi Sedan
90 day: 31.77 mpg (US)

Ranchero GT - '73 Ford Ranchero GT

Spaz - '83 Chevy S10 4X4 Tahoe
90 day: 27.53 mpg (US)
Thanks: 0
Thanked 0 Times in 0 Posts
Send a message via ICQ to justpassntime
The 15 degrees came from Hucho's book originally but was posted here in this forum.

I am guess I am going to have to wing it I don't have access to such a book. I figure that anything is better on a sedan or coupe anyway. I think I will go with 6-7" range. It won't hurt to try. If it doesn't help, I'll take it off and sell it. It's going to look cool after I am done. Somebodies gonna want it.

Oh well back to work. Got one side of it done already. The other side will be faster, I know what I am doing now.
__________________
Honda...the economical, renewable resource.


  Reply With Quote
Old 07-21-2008, 04:39 AM   #4 (permalink)
Sequential
 
Concrete's Avatar
 
Join Date: Jun 2008
Location: Kansas
Posts: 177

The Truck - '00 Chevy S10 Extended Cab
90 day: 22.47 mpg (US)
Thanks: 0
Thanked 22 Times in 7 Posts
Not sure what you are building
if it is a Kamm back - just make it gently curved
metroMPG has a good thread going on this right now
no magic - just the longer the better

if you are building a spoiler and not a Kamm back
you might find this interesting

about a third of the way into the infomercial they show a back view of this concept SAAB
looks like it has active spoilers that extend behind the hatch and under the bumper - but they seem to indicate they are for low drag




been thinking of something similar myself
interested to see what you are building
__________________
Concrete
Start where you are - Use what you have - Do what you can.
  Reply With Quote
Old 07-21-2008, 05:20 AM   #5 (permalink)
What? THIS IS MY GOOD CAR
 
justpassntime's Avatar
 
Join Date: Jun 2008
Location: Eastern Washington
Posts: 285

The Japillac - '87 Honda Accord LXi Sedan
90 day: 31.77 mpg (US)

Ranchero GT - '73 Ford Ranchero GT

Spaz - '83 Chevy S10 4X4 Tahoe
90 day: 27.53 mpg (US)
Thanks: 0
Thanked 0 Times in 0 Posts
Send a message via ICQ to justpassntime
Here's a pic of what I am working on.

This is just the one end cap. It ended up being three pieces.

Two end caps and the center visor part. Going to get welded together when it's done. The two ends are done and the center is done just have to put it together and make a couple of supports for the center.

It basically snaps into and around the rear window molding. I made it out of steel because that's what I had and know how to work with.

It is 15 degrees from the flat of the roof. and is 7" in depth and 2" from the rear lip to the rear window.

I also have in the plans a trunk lip extension.

I would have finished it if it hadn't been for that damn weed wacker I had to fix. Got it going too.
Attached Thumbnails
Click image for larger version

Name:	rearwindowsp.jpg
Views:	140
Size:	27.9 KB
ID:	1203  
__________________
Honda...the economical, renewable resource.



Last edited by justpassntime; 07-21-2008 at 05:34 AM..
  Reply With Quote
Old 07-21-2008, 04:20 PM   #6 (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
angles

Lots of pages in the aero forum now.If you can find my installment on "Rooflines",it may answer your questions.It's not a matter of "angles",its a matter of curvature,and it all depends on where the Accord's roofline begins it's downward slope.Do the research before you jump in.At 15-degrees,I think your headed for trouble and disappointment.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 07-21-2008, 05:15 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
justpassntime,if you'll go to the top of the forum page,at ecomodder search,Advanced,and type in, mods-data-% change or Cd change ( installment # 5- roofline data ),that should get you some material to chew on.
__________________
Photobucket album: http://s1271.photobucket.com/albums/jj622/aerohead2/
  Reply With Quote
Old 07-21-2008, 08:20 PM   #8 (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
It’s always a tradeoff between minimizing wake area and having an excessively steep slope. My bed cover does a nice job of minimizing wake area – a 47% wake area reduction – but does so at the price of having a seventeen degree slope.

It is time for me to revise my wake cover to make it handier to use. What I am thinking of is to reduce the slope to 11 degrees (1-in-5). This will mean my wake area reduction will be only 27%.

Going to a 1-in-4 slope (14 degrees) would result in a 37% reduction in wake area.

Does Hucho have a graph showing the effects of wake area reduction on drag?

I can’t do a full boattail. That would result in a thirteen foot long “tail” if one stuck to the one-in-five slope I’m planning. The truck is enough of a bear to park as is. The other extreme is simply a flush commercial cap. Zero degree angle but zero wake area reduction.
__________________
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 07-22-2008, 01:39 AM   #9 (permalink)
Master EcoModder
 
FastPlastic's Avatar
 
Join Date: May 2008
Location: Ames, IA
Posts: 419

98 Cherokee - '98 Jeep Cherokee
90 day: 17.18 mpg (US)

ZX7R Ninja - '99 Kawasaki ZX7R Ninja
90 day: 42.45 mpg (US)
Thanks: 4
Thanked 13 Times in 12 Posts
Nice job on the metal work, Looks good.
__________________

Adjusted for my driving habits. 80%city/20%Highway.
20mpg city/30mpg highway or bust! Check out my mods so far
  Reply With Quote
Old 07-22-2008, 01:57 AM   #10 (permalink)
Sequential
 
Concrete's Avatar
 
Join Date: Jun 2008
Location: Kansas
Posts: 177

The Truck - '00 Chevy S10 Extended Cab
90 day: 22.47 mpg (US)
Thanks: 0
Thanked 22 Times in 7 Posts
yep, it is going to look cool either way
drag wise it looks pretty clean too
but I'm with Aerohead if you are 15 degrees below the roof line
who knows, at this point tack it together and do some tuff test
you will figure out if it is a drag reducer pretty quick

interested in the outcome
looking at this for my truck - but only virtually for now


need to get my wheel covers and skirt done first

Big Dave - like your bed cover
spent my money on a cheap flat one before I knew any better

__________________
Concrete
Start where you are - Use what you have - Do what you can.
  Reply With Quote
Reply  Post New Thread




Similar Threads
Thread Thread Starter Forum Replies Last Post
Electric Motorcycle conversion bennelson Fossil Fuel Free 315 01-27-2018 04:51 PM
Racing discs-worth it? rjacob Aerodynamics 43 09-10-2008 12:28 AM
New EPA numbers rsx2002 EcoModding Central 7 07-18-2008 08:34 PM
Scangauge II Question (suddenly seeing inflated MPG numbers) awillard69 Instrumentation 7 04-17-2008 01:04 AM



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