Hi all, I'm getting up to speed on data collection during the cold months up here in the north country. I was just looking for what a good ball park figure for Drag Coefficient and Frontal Surface Area on our cars would be to plug into math channels for data collection. At this time I'm not exactly sure what to do with it, but it plugs into some of the formulas so I thought I would ask

Bill, I don't have the numbers, but if you really want to have an idea of drag (not sure about frontal area), you can do "coast down" tests at a drag strip or a track that has a long, flat straight. For best accuracy you'd want everything hot, which is hard to do at a drag strip, but I know some of my FM competitors used to do that to get data on wing angles.

Thanks Larry. Want and need are two different things, I don't need it that bad! I just happen to have a couple of formulas to fill in that I don't really know what to do with! I'm trapped inside at 0 degrees and nothing to do:-)

Well, it warmed up to 11 here, so I ventured outside. But, if you just feel like playing around...
I seem to recall that FSAE cars (and F1 cars... coincidence?) had a Cd near 1.0... maybe a range of 0.8 for a really aero design, and 1.2 for big honkin' wings.
Google found: http://www.engineeringtoolbox.com/drag- ... d_627.html. I would bet we're a lot like an open top convertible... better in some ways, although the cockpit is a wall in the airstream (but relatively small compared to the rest of the car). A number around 0.6 is probably in the ballpark.
Frontal area should be pretty easy (make sure you calculate or convert to the units the system is looking for). If your tape measure isn't frozen, just calculate the "main box" which would be the width of the car and the height of the rear bodywork, then the added box which is the width of the cockpit opening and the rollbar height above the decklid. Close enough. Good luck.

Just wondering what value knowing the drag for frontal area will be useful for? My only experience with those calculations are used for dyno simulators to give you an estimated HP, which aren't all that accurate.

Bill Parenteau wrote: but it plugs into some of the formulas so I thought I would ask

.cd of the Audi R18 is .471. Probably, pretty close...just use that.

H.(...or a brick. Probably, closer)B.

Basically coefficent of drag and frontal area are terms used in calculating acceleration and terminal velocity of an object. Remember, that the Space Shuttle is proof that even bricks can fly supersonic with enough velocity.

For what its worth - I get pretty close to 2150 square inches for the frontal area.
Has anybody done a Coast Down check yet? I'm planning one - but need to find a place to run - probably not the Walmart lot

Cheers - Jim