Difference between Cd and Cda? - Fuelly Forums

Android Users - Coming Soon! - Migrating from aCar 4.8 to 5.0

Reply
 
Thread Tools Display Modes
 
Old 07-19-2008, 09:20 PM   #1
Registered Member
 
Hasbro's Avatar
 
Join Date: Dec 2007
Posts: 16
Country: United States
Difference between Cd and Cda?

Does Cd consider more factors? My 04 Civic Si has a Cda of .33 but would Cd be different and why?
__________________

Hasbro is offline   Reply With Quote
Old 07-20-2008, 03:40 AM   #2
Registered Member
 
Join Date: Jul 2008
Posts: 9
Country: United States
CdA actually considers more factors, as it is Cd (drag coefficient) multiplied by A (the frontal area of the object in question). The value you found has to be Cd...it's far too small to be the CdA value of a vehicle that size unless it has a Cd value of <0.15 (which it doesn't )

For example: Car A has great aerodynamics (Cd=0.25), but a very tall roofline and, consequentially, a large frontal area of 3.0m^2. Car B is less slippery (Cd=0.35), but is smaller overall and has a frontal area of only 2.0m^2. At any speed, Car B will cause less aerodynamic drag and waste less energy overcoming it.

Just in case you're interested, the formula for aerodynamic drag is:

1/2 * rho * velocity^2 * Cd * A where rho is air density (which changes with temperature, altitude, etc)
__________________

SteveX82 is offline   Reply With Quote
Old 07-20-2008, 09:04 AM   #3
Registered Member
 
thornburg's Avatar
 
Join Date: Jun 2008
Posts: 162
Country: United States
Quote:
Originally Posted by SteveX82 View Post
1/2 * rho * velocity^3 * Cd * A where rho is air density (which changes with temperature, altitude, etc)
I thought it was v^2, not v^3 ?
__________________
thornburg is offline   Reply With Quote
Old 07-20-2008, 09:38 AM   #4
Registered Member
 
Join Date: Jul 2008
Posts: 9
Country: United States
Quote:
Originally Posted by thornburg View Post
I thought it was v^2, not v^3 ?
You're right....I was thinking of the power consumed by the aero drag. The appropriate change has been made! Thanks for noticing
SteveX82 is offline   Reply With Quote
Old 07-21-2008, 07:58 AM   #5
Registered Member
 
Join Date: Oct 2006
Posts: 557
Country: United States
Think of CdA as Cd times A. It's a coefficient times an area. If the car were doubled in size the coefficient would not change, but the area would.
A jet aircraft has a lower Cd than a motorcycle, but the much smaller area of the bike gives it lower total air drag or CdA.
Lug_Nut is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
GreenSwitch GasSavers_DaX General Discussion (Off-Topic) 10 11-30-2007 12:13 PM
Woo! Tripminder! Any 80's ford EFI, take a look. Wyldesoul General Fuel Topics 6 06-17-2007 07:43 PM

Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 11:50 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2017, vBulletin Solutions, Inc.