Here's a link I found to calculate the drag coefficient for FD, FC, FB Etc...

http://www.gtechprosupport.com/support/AeroDragCalc.htm

and to save you the troubble of looking up the numbers for the FD:

Drag Coefficient (Cd) 0.290
Frontal Area 1.796 Ft.2
Add Speed you'd like to know HP loss for and PRESTO !

Pretty impressive.....

-DC

 

Drag coefficient for a base model or touring FD is 0.29. For the R1, it's 0.31, thanks mostly to the rear spoiler.

Also, the frontal area is 19.2 sq. ft., not 1.796.

 

Good to know, then their site is miss informed....

 

1.796 is in m^2

 

What's the Cd if my dog's head is out the window?

 

 

Not when he expresses the units as "Ft.2"...

 

I know Jim, I was simply pointing out that the number he gave wasn't entirely wrong, he just fudged up the units.

BTW, thanks for the extra negative rep. points, I really deserved 'em in this thread.

 

The equation you're looking at is really simple:

P = 1/2 * rho * Cd * A * V^3

Where P is power, rho is air density (1.3 kg/m^3 roughly), A is frontal area, Cd is drag coefficient and V is velocity.

What's much more interesting is when you build a more powerful calculator that also includes a model for the rolling resistance of your tires, a model of engine power output vs. rpm (and, of course, tire size and gearbox ratios) and then you can calculate the actual top speed, approximate acceleration times (not including launch times or turbo lag, of course, but gear shifts are easy), etc. I have a spreadsheet like this I built awhile ago... I was able to predict the correct top speed of the FD :-).

Also, as a sidenote, you can also calculate the lift forces:

F = 1/2 * rho * A * Cl * V^2

Where A is still frontal area (yes, not a typo... this point is often confused and people think it's the area of the bottom of the car, but it isn't), F is your lift force, and Cl is the coefficient of lift.

Take care,
Shad