PW wrote:

Paul,

  How do I go about getting the wind drag numbers for two different cars?

One is the Ford Focus (the ZX3 hatchback) the other is the Ford Escort (ZX2).

  The Focus is about 150 lbs. over the Escort so I'm trying to figure out how much power it would take to overcome this.

Take care

Phil Williamson

You take them out on a nice flat road on a windless day and let them cost.
Drag = mass (in slugs) X deceleration in FPS^2.

slugs = weight/32.2 <<< check me on this number.

Or Drag = weight X deceleration in G's.

Get a Vbox to record the coast down deceleration as a function of speed.

http://www.racelogic.co.uk/vbox.htm

You can get a crude curve with stop watch and speedometer.

Rolling drag is directly proportional to speed while aero drag is a function
of speed squared. The two are roughly 50 50 at 50 mph.

Do a little trial and error curve fit to those two functions.
Then you will be able to separate the rolling drag from the aero drag.
The Cd will be around .3 based on the max cross sectional area of the car.

Paul Lamar
 
The AirCraft Rotary Engine NewsLetter.              Powered by Linux.
ACRE NL web site.
http://home.earthlink.net/~rotaryeng/            http://www.linux.org