Richard Atherton (Entex) wrote:
> Do you have the actual Drag coefficients for the Series IV, V, and Tiger
> MK1, MK1a, and MK2 ?
>
> There were slight differences in these especially in the grills, and
> mirror placements, and would be drastically different with the different
> top configurations. i.e. no top, Soft top , and Factory Hard top?
—-?
-—
> Rich
Guys,
My thoughts, for the day, on this subject. Concisely - "we do all the
calculation we can, but there is NOTHING like a real test."
I don't know that our cars are can not just as well "guestimated" from similar
designs where the numbers are available, such as the MGB,
TR6, etc. They are all, generally, a little bit better than a piece of plywood
of the same frontal area. Those air dams help hold the car on the
road better, and maybe improve air flow thru the radiator, but they don't
affect the drag much. Thing is, the biggest influence on drag is the
part your not looking at (although the top being up is a big help) and that is
the "under carriage". This mess of lumps, bumps, pockets,
beams, and rotating masses is the biggest contributor to drag of the car. In
the record cars (yes, even the prototype of my Jaguar XK120 )
had FULL belly pans, and full wheel covers (on the rear) and steel wheels (not
wire). Almost every record holder I know of does this, and
nobody can drive them on the street. You think the Austin-Healy was bad?
Now there is one trick thing we can do, that ALL record holders know, and that
is to put a good coat of wax on the paint. This cuts the air
resistance of what you do have down measurably. Besides, it looks faster too.
We do extensive wind tunnel testing of our large space launch vehicles. We use
the very best in wind tunnels, model building, and
instrumentation. Your tax dollar costs are hardly considered. After the first
flight, the on-board accelerometers and the weights we measure
before launch, "reconstruct" the actual trajectory, and back-calculate what the
drag (and therefore drag coefficient, must actually be. I can tell
you now that the wind tunnel data wasn't very close. These factors have to be
known very precisely to successfully put a payload of a given
weight where you want it to be. So the NEXT one is a LOT better in prediction
and results by updating that wind tunnel data with the real
thing.
Same thing applies with the car. Measure the horsepower on a dyno, clock your
top speed, then back calculate what the drag must have
been,
considering your gearing. Now this "drag" includes all sources, including tire
flexing, bearing and gear losses, etc., but the wind resistance
is, by far, the greatest contributor.
--
Steve Laifman < One first kiss, >
B9472289 < one first love, and >
< one first win, is all >
< you get in this life. >
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