> > > Then I turned on the A ircon, and it showed a drop of 5MPG.  I
> > > repeated the experiment a few times, and it was pretty consistent.
> >
> > I think the usual argument goes that in hot weather you either run
> > the air conditioner (increasing engine load, as you say), or you
> > open the windows (which interferes with the aerodynamics, increases
> > drag, and thereby increases engine load.)  At highway speeds, the
> > drag issues is supposed to be bigger (drag goes up with V^2, air
> > conditioner extra load is a constant...)
> >
> > That COULD all just be urban legend.
>
> Well they did some experiments on that Mythbusters show. Unfortunately
> those guys aren't always the most scientific with the way they do
> things.
>
> In my case it doesn't matter, whether the windows were open, closed, or
> the AC was on our Olds and Buick always seemed to get the same highway
> mileage. Now, they were pretty much bricks through air, so opening the
> windows probably HELPED the aerodynamics...
>
> Was it 50's cars that turned out to be MORE aerodynamic when going in
> reverse rather then forward? :)
>
It's not urban legend, it's just difficult to measure more of it. There
have been a lot of testing in exactly those types of things. For a excellent
reference Look at Hoerner's Fluid Dynamic Drag and chapter 7 pages 12-5 and
12-6 shows measurements for exactly what has been discussed.

Dave

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