Date: Fri, 26 Sep 2008 23:31:49 -0700
Reply-To: Roger Whittaker <rogerwhitt1@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Roger Whittaker <rogerwhitt1@GMAIL.COM>
Subject: Re: Aerodynamics and the Westie luggage rack, etc..
In-Reply-To: <f700b5ac0809262218k39f0ff23hc42f811e2f6b7df2@mail.gmail.com>
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dear fronts piece wanters
you guys all laugh at my millage #'s and say they are untrue ...
oh well what ever --
i know the 1.6 TD achieved 35-38 miles to the gallon and
i have yet to take a significantly long journey with the new 1.9 TD that
replaced that tired little motor
and i know you also laugh at my speed claims ...
yet i just re-listened to the voice diary and in one point of the trip i
had forgotten to shut off the digital recorder
it captured a conversation between wife and i regarding keeping speed at or
around 75 MPH
so i would not get a ticket --
several times on very long stretches of # 10 East bound
i had to tune it down a little as i creeping into the 90MPH zone
doubt-laugh- scorn - no worries
it was simply my experiance ...
with that nifty fronts piece in place on our
1989 5 Speed California Turbo Diesel
yours
On Fri, Sep 26, 2008 at 10:18 PM, Andrew Grebneff <goose1047@gmail.com>wrote:
> On Fri, Sep 26, 2008 at 10:31 PM, Don Hanson <dhanson@gorge.net> wrote:
> > I did some low budget research about aerodynamics, read up on all the
> > sources I could find, etc. So I know a little, but I certainly can't
> spout
> > data or numbers, just general principals.
>
>
> Aerodynamics really only come into play at above 110kmh (~70mph).The
> vehicle may not feel as though it's run into a wall above that speed,
> but your fuel bill will suggest otherwise, almost no matter what
> vehicle (figure that phrase out if you can).
>
> That's probably why the top speed of a 25hp (the so-called "36hp"
> engine) Split will top out at 110kmh, empty ot with a tonne of cargo.
>
> Modern vans still have external gutters, but that's because they have
> a large roof area and concealed gutters couldn't cope with decent
> rain... and of course it would be expensive (anda rust trap) to put
> concealed full-length gutters into one.
>
> The rear of a vehicle is important in drag calculations. A vehicle
> with a sloping back roof and tail (eg a real Beetle) will have a poor
> drag coefficient, because there is no separation of airflow over the
> vehicle from the air behind it, causing a relarive low-pressure area
> behind the entire rear surface of the vehicle, from roof high-point to
> bumper. That's why the more aerodynamic cars have a sharp lip on the
> back of the trunk edge, and probably why T3s have a very good CD (and
> a T2 has a better CD than an E-Type Jaguar)...
>
> Of course, for a given shape, the larger the frontal area, the more
> overall drag there will be, as you are trying to push a larger surface
> through the air (which is a fluid). Take a T3 and double its size in
> all dmensions and you'd be increasing the drag 4 times. So take this
> into account if you're widening your bus by 20cm and want to retain
> what we laughingly call its fuel-economy.
>
> ... the rear lip causes separation of the airflow over the car from
> the turbulent air trail behind, reducing overall drag. It probably
> also creates a little downforce at the rear, but it wouldn't be
> significant.
>
> Putting an airdam on the front, IF the dam is windtunnel-tested... and
> believe me, most are NOT), can decrease drag by reducing the amount of
> air going under the car (which also, by being compressed as it paasses
> under the car, which is acting as one side of a venturi, produces
> lift, which is most noticable at the front). However the airdam itself
> adds frontal area, which increases drag... so a properly-designed
> airdam is a compromise.
>
> Rear spoilers are supposed to work by forcing air upward as it passes
> over the tail, which results in downpressure on the car's tail. That
> is the ideal... again, as with airdams, most "spoilers" are just
> eyecandy and have only one effect... increased drag.
>
> Sideskirts are only functional on cars utilizing radical
> "ground-effect" for downforce eg the banned Formula 1 cars.
> On a road car there is nothing to suck air out from under the car, so
> skirts have nothing but esthetic function... and are one more thing to
> have to repair (as well as being rust-traps, as are most plastic
> addons eg spoilers).
>
> Just as well that parentheses don't cause rust, or this mess
>
> age
>
> would be fall in g t o
>
> pi
>
>
> e
>
>
> c
>
>
>
>
> e
>
>
>
>
> s
>
>
>
> .
>
>
> .
>
>
> .
>
>
> --
> Andrew Grebneff
> Dunedin, New Zealand
> Fossil preparator
> Mollusc, Toyota & VW van nut
> Temporarily in Calgary, AB, Canada
> <goose1047@gmail.com>
>
--
roger w
There are two kinds of jobs in the world:
Picking up garbage and telling people things.
Successful people do both, with the same good attitude. (riw)
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