MoTeC Global Forum

Is there a provision in i2 for computing the aerodynamic coefficient of drag (cdA) and wheel drag?
If I know the speed and mass of the vehicle and do a coast down it is mathematically possible to do this.
(Just hopping it is i2 possible)

There is no pre-defined function to do this. If you have the understanding, you should be able to creat the calculation in either maths, or using a custom function.

Some calculations I use are:
Rolling resistance horsepower = 0,013xVehicle weight (lbs)xspeed (MPH)/375

Air resistance horsepower = frontal area (sq ft) x Cd x 0.00256 x (speed (MPH) cubed)/375

Not exactly what you are looking for but if you know frontal area and power you could reverse the calculation to give Cd.

RossB wrote:Some calculations I use are:
Rolling resistance horsepower = 0,013xVehicle weight (lbs)xspeed (MPH)/375

Air resistance horsepower = frontal area (sq ft) x Cd x 0.0256 x (speed (MPH) cubed)/375

Not exactly what you are looking for but if you know frontal area and power you could reverse the calculation to give Cd.

Thanks Ross,

Where do I get documentation on how to use the external maths with i2?
I think that is probably where I should start.

I'm getting some odd results with that calculation

I put it into excel like this

20*0.32*0.0256*150^3/375

150 corresponds to speed in MPH
0.32 Cd
20sq/ft frontal area
=1474 HP?

What am I doing wrong there?

Oops! I made a typo in my calculation, it should read:

Air resistance horsepower = frontal area (sq ft) x Cd x 0.00256 x (speed (MPH) cubed)/375 so the result wouild be out by a decimal point! The 0.0256 should be 0.00256. I will edit the original post with the correct number.

Thanks Ross...
I am doing it the other way around - so I'll measure the speed and roll the vehicle down and get the cdA (coefficient * area) as well as the wheel drag, with both of those based off of empirical measurement.

So (time permitting) I should have a a follow up in a few weeks...