drag coefficient
#31
02-07-2003, 04:27 PM
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Re: drag coefficient
I joined this discussion a little late, but I saw some discussion over the equation for drag force on a car. I looked it up in my fluid mechanics notebook and found it.
Drag Force = 0.5*(air density)*(Drag Coeff)*(Frontal Area)*(Velocity)^2
The frontal area is the "projected area" of the car. If you put a light behind the trunk of your car and cast a shadow on your garage door, the shadow area is the frontal area of the car.
From this equation, you can see how important speed is when considering drag. Doubling the speed will incread the drag force on the car by a factor of 4. That's 4 times the force trying to slow the car down. That's the reason that small gains in speed at the upper level (200+ mph) is so difficult.
Drag Force = 0.5*(air density)*(Drag Coeff)*(Frontal Area)*(Velocity)^2
The frontal area is the "projected area" of the car. If you put a light behind the trunk of your car and cast a shadow on your garage door, the shadow area is the frontal area of the car.
From this equation, you can see how important speed is when considering drag. Doubling the speed will incread the drag force on the car by a factor of 4. That's 4 times the force trying to slow the car down. That's the reason that small gains in speed at the upper level (200+ mph) is so difficult.
#32
02-07-2003, 06:15 PM
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#33
02-07-2003, 06:22 PM
Re: drag coefficient
And since Cd is a fraction already, reducing it has a bigger effect than increasing power to compensate. Although, that's something the engineers have to deal with, there's not much of an aftermarket for streamlining cars. Drop the roof 2 inches without changing your springs!
That frontal area is where Ferrari does well. They incorporate the air channels into the body, keeping the frontal area the same, instead of adding a spoiler which would increase the frontal area. Thanks for bringing up that equation.. that's the one I couldn't remember.
2003.5 G35 Sedan Desert Platinum/Graphite Premium/Sport/Aero/Nav/Winter
That frontal area is where Ferrari does well. They incorporate the air channels into the body, keeping the frontal area the same, instead of adding a spoiler which would increase the frontal area. Thanks for bringing up that equation.. that's the one I couldn't remember.
2003.5 G35 Sedan Desert Platinum/Graphite Premium/Sport/Aero/Nav/Winter
#34
02-07-2003, 07:50 PM
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#35
02-07-2003, 08:13 PM
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Re: drag coefficient
By utilizing the underbody, you have generally a larger area to work with aerodynamically compared to a wing, the close proximity of the ground also adds to the benefit of speeding the air up under the bottom of the car to get a nice low pressure zone under it so that airpressure may act on the car above it....And since you are still working with the same basic car, you are not adding to the frontal area of a car like the wind does, as well as not disturbing the airflow around the upper body which adds to the drag.
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