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Old 03-10-2008, 07:44 PM   #8 (permalink)
aerohead
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optiwatch' aero calc

Quote:
Originally Posted by optiwatch View Post
Understanding that HP to overcome aero/drag is helpful. I want to include vehicle weight in my calculations to fully understand the impact of weight.

I came across this, but didn't get to an understandable value. I may just be overlooking some error in my calculations.
Pmotive=1/2*Cd*A*rho*v^3+Crr1*m*g*v
from http://www.geocities.com/greglocock/

My attempt at this calculation is attached on the second tab. Please let me know if anyone can fix it or provide the conversion from Pmotive to HP (or if you have a better spreadsheet). The first tab has the calculation from this discussion (The results look correct to me).

With significant investment, I think I can lower my weight by 200 lbs. Hopefully I can get some idea of the pay back. Spending most of my time at a stead speed (70 mph), I expect less pay back than the average vehicle. Taming my driving habits has already given me a 10% improvement (from average of 27 mpg to a max of 31.5).

I also want to find [easy] ways of reducing my RPMs at highway speeds from current 2750 to about 2200, but that's a different topic...

Thanks.
optiwatch,sorry! I'm way late to the party.I ran your numbers for 70 mph and got 19.1 horsepower aero load at that velocity.I used 0.00238 slugs/ft cubed for density,102.67 feet per second velocity,Cd 0.32,and 25.5 ft-square for frontal area.Sorry,as yet,don't have my estimation stuff for rolling resistance with me.I don't know if your formula also simultaneously figures rolling resistance horsepower.I stuck with what I'm familiar with.Also ,apologize to members for the US Standard notation.I'll put some conversion stuff together and try and post metric units in future.Its tough living in the stone age!
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