aero dynamic drag calculations

[wideopen231]

Im working on some aero dynamic side pods for lack of better wording. I know probably not goint to make car any faster and may do just oppisite. Wondering if anyone knows how to figure air drag based on speed,area shape and any other helpful tips. I am mainly doing this because i think it looks cool as he11. Plus its bracket car so max speed is not as important as would be on headsup car.

[Greenlight]

Aero drag force is calculated by using the following equation:

F = 1/2 ro Cd A V^2

where,

ro is the density of the fluid (air). A typical value is 1.21 kg/m^3 or 0.765 lb/ft^3

Cd is the drag coefficient. This value is dependent on the shape of the object. For a sports car the value is typically about 0.28 to 0.35.

A is the cross section area of the object, when viewed from the direction of the fluid interacting on the object. For a sports car the value is typically about 20 ft^2.

V is the relative velocity of the fluid to the object.

Make sure you use the correct units in your calculations (i.e. don't use MPH, use ft/sec).

Here is a link to a website that gives more details.
http://en.wikipedia.org/wiki/Drag_(physics)

[jacksoni]

And remember that HP=DxV/375 so HP required goes up by cube of speed. D in this formula is F in the one quoted above. You do not want to increase the frontal area with your pods if possible or you need to have the improvement in Cd be proportional to the increase in A so the product ( CdA) stays the same or better. Short of wind tunnel testing ( which is affordable, more or less, to the hobby racer at A2 wind tunnel in North Carolina) coast down testing is probably the best other way to judge these effects. Not so easy with a race car since you need a good long flat spot (highway maybe) to do it. David Redzus who frequents the Engine sections here has some formulas/software for this which he has shared no cost. You might look at "Race Car Aerodynamics, designing for speed" by Joseph Katz (available from Amazon etc) or other aero books similar also from Amazone etc. There are plenty of sites on line where people have done screwy things to their street cars in name of economy as well as racing. Google is your friend.

[MadBill]

Aero drag force is calculated by using the following equation:

F = 1/2 ro Cd A V^2

where,

ro is the density of the fluid (air). A typical value is 1.21 kg/m^3 or 0.765 lb/ft^3

Cd is the drag coefficient. This value is dependent on the shape of the object. For a sports car the value is typically about 0.28 to 0.35.

A is the cross section area of the object, when viewed from the direction of the fluid interacting on the object. For a sports car the value is typically about 20 ft^2.

V is the relative velocity of the fluid to the object.

Make sure you use the correct units in your calculations (i.e. don't use MPH, use ft/sec).



Here is a link to a website that gives more details.
http://en.wikipedia.org/wiki/Drag_(physics)

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