Daniel,
It seems to me that it might be possible to measure the aerodynamic drag of
a car without a wind tunnel if you knew of some hilly roads with a known
gradient where you could do some experimenting with a stopwatch.
You would measure the acceleration of the car (coasting, of course) and
deduce the overall drag from the equations of motion, as a function of
speed. Then you would have to remove the drag portion that is rolling
resistance, possibly by towing the car on a flat road with a spring-scale
in the tow mechanism. You'd do this with the same tire pressures, and at
low enough speeds to ignore aerodynamic drag, but at a range of speeds that
would allow you to extrapolate to obtain the rolling resistance at the
higher speeds you reached when coasting down the hills. So theoretically
you might get the aerodynamic drag this way, and with a real "rolling
road".
This would be quite interesting to do. With enough data points to get a
good basis for drawing curves, I doubt that it would be much less accurate
than a wind tunnel measurement. And. as you noted, wind tunnels of car
size don't come easily. If anyone tries this and is aiming for low drag, I
would suggest to use a tonneau or a hood, in both cases with the windows
up, and the least number and size of wing mirrors and luggage racks. Let
us know what the drag coefficient is, and how many cops gave you a ticket.
Daryl
----------
> From: Daniel1312@aol.com
> To: Spridgets@autox.team.net
> Subject: Wind tunnel access
> Date: Wednesday, December 09, 1998 2:02 PM
>
> Hi Listers,
>
> Read all that great stuff about thermodynamics and radiators and just
loved
> it. Made me think that with such a great pool of knowledge and people
working
> with it someone might have access to a wind tunnel. Doesn't have to be
full
> size moving floor job, scale size and flat floor would do.
>
> Reason I ask is that I am very interested in the aerodynamics of the
Sprite &
> Midget - all types and want some data. I could hire a wind tunnel in the
UK
> for half a day at I think a cost of £1000 but couldn't find 9 owners who
would
> stump a £100 for the privilege.
>
> Thanks
>
>
> Daniel1312
>
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