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

Reply  Post New Thread
 
Submit Tools LinkBack Thread Tools
Old 07-28-2012, 05:34 PM   #31 (permalink)
Master EcoModder
 
Diesel_Dave's Avatar
 
Join Date: May 2011
Location: Indiana
Posts: 1,194

White Whale - '07 Dodge Ram 2500 ST Quad Cab 2wd, short bed
Team Cummins
90 day: 37.68 mpg (US)
Thanks: 112
Thanked 508 Times in 211 Posts
Yes, technically, Cd does depend on Reynold's number, surface roughness, etc, etc., but those effects are pretty small. It's a fairly common assumtion that Cd is constant for a given shape, however. That's why there can be a Cd quoted for a given car. Technically a car will have different Cd's at different Reynold's numbers (and other factors), but often just assumed to be constant because those effects are fairly small.

__________________
Diesel Dave

My version of energy storage is called "momentum".
My version of regenerative braking is called "bump starting".

1 Year Avg (Every Mile Traveled) = 47.8 mpg

BEST TANK: 2,009.6 mi on 35 gal (57.42 mpg): http://ecomodder.com/forum/showthrea...5-a-26259.html


  Reply With Quote
Alt Today
Popular topics

Other popular topics in this forum...

   
Old 07-28-2012, 05:51 PM   #32 (permalink)
...beats walking...
 
Join Date: Jul 2009
Location: .
Posts: 6,190
Thanks: 179
Thanked 1,522 Times in 1,123 Posts
...except for the Mythbuster idjiots, nobody I know of has "dimpled" their car's body-panels in an effort to reduce its Reynolds Number!
  Reply With Quote
Old 07-28-2012, 06:06 PM   #33 (permalink)
GRU
Master EcoModder
 
GRU's Avatar
 
Join Date: Oct 2011
Location: Windsor ON Canada
Posts: 373

silver bullet - '00 Honda Civic
90 day: 34.41 mpg (US)
Thanks: 21
Thanked 36 Times in 31 Posts
This is why i thind Cd is pointless advertising about fuel economy....Take any car and make it twice the size without increasing the weight... The Cd will be the same yet the original (smaller car) will have less wind resistance and get better fuel economy
__________________

  Reply With Quote
Old 07-29-2012, 09:11 AM   #34 (permalink)
Master EcoModder
 
NeilBlanchard's Avatar
 
Join Date: May 2008
Location: Maynard, MA Eaarth
Posts: 7,887

Mica Blue - '05 Scion xA RS 2.0
Team Toyota
90 day: 42.48 mpg (US)

Forest - '15 Nissan Leaf S
Team Nissan
90 day: 156.46 mpg (US)

Number 7 - '15 VW e-Golf SEL
TEAM VW AUDI Group
90 day: 155.81 mpg (US)
Thanks: 3,413
Thanked 2,908 Times in 1,823 Posts
If you are comparing two very similarly sized cars, then the one with a lower Cd is likely to get better mileage. More information is better. And lowering the Cd is the best way to improve the efficiency, after improving the drivetrain.
__________________
Sincerely, Neil

http://neilblanchard.blogspot.com/
  Reply With Quote
Old 07-29-2012, 12:20 PM   #35 (permalink)
Deadly Efficient
 
Tango Charlie's Avatar
 
Join Date: Jun 2008
Location: Goshen, Indiana
Posts: 1,234

Olivia - '03 Pontiac Vibe base
90 day: 36.01 mpg (US)

R2-D2 - '00 Honda Insight
90 day: 58.81 mpg (US)
Thanks: 132
Thanked 175 Times in 91 Posts
Advertising a car's Cd is an indication that they've at least paid attention to it. Nothing but good can come of manufacturers producing more aerodynamic vehicles, bragging about it, and thus making the public aware of its impact on efficiency.
__________________
-Terry
  Reply With Quote
Old 08-02-2012, 06:20 PM   #36 (permalink)
Master EcoModder
 
aerohead's Avatar
 
Join Date: Jan 2008
Location: Sanger,Texas,U.S.A.
Posts: 12,963
Thanks: 20,775
Thanked 6,340 Times in 3,936 Posts
worthless

Quote:
Originally Posted by drmiller100 View Post
what you wrote makes no sense to me.

I don't compare fish to birds. I don't compare tractor trailers to hatchbacks.

Comparing Cd is worthless between the two.

Cda is what matters, because if you combine speed, Cda, and weight, you can KNOW the drag of the car.

Cd is a way to sort of calculate Cda, but it is kind of worthless by itself.
The Cd of a car would give a potential consumer the same information as the thermal R-Factor for doors,windows,walls,and ceiling in a prospective home purchase,as the inverse of R-Factor is the Heat Transfer Coefficient for the home.A thermal Cd if you will.
The square footage of the home wood give an overall sense of energy efficiency as would the frontal area in a vehicle.
It is quite proper to compare Cds of aircraft,birds,submarines,bullets,fish,radomes,'n such,as they are all subject to the same forces and we can learn from their performance vs shape.

  Reply With Quote
Reply  Post New Thread


Thread Tools




Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.
Content Relevant URLs by vBSEO 3.5.2
All content copyright EcoModder.com