Date: Fri, 23 Aug 2002 00:23:56 +0100
Reply-To: Clive Smith <clive.harman-smith@NTLWORLD.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Clive Smith <clive.harman-smith@NTLWORLD.COM>
Subject: Re: Custom Scoop Update - Should you care! FISH Y
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Scoops do not pull in air
Aerodynamics, especially guessaerodynamics is not a black and white subject
(my normal rant).
F1 aerodynamicists are at the top of the tree for this reason - with 3D
objects moving close to a ground plane it gets even more complex.
So for someone to think they know exactly whats going on without a lot of
empirical back-up (exhaustive real size testing and instrumentation) is just
wishful thinking - even today, its not an exact science - though its getting
pretty good with computational fluid dynamics (that were one of the driving
forces behind the development of supercomputers - if that gives you an idea
of whatyou're asking!
Anyway, I'm having to pick and choose exactly what you're asking, as that is
so vague...
.. you want of know if air gfoes into an input hole (flush or scoop) and if
so, wahat sort of flow rate.
If you really have read all the back mails on this subject then you'll know
something already - as I and others have waxed technical more than once,
although I must say, and admit, that most has been to DISPEL incorrect ideas
ans statements, rather than to state SPECIFICS - for the reasons outlined
above.
.. but if you have read ALL previous you'll know this - UNLESS THE EXIT VENT
IS AT A LOWER PRESSURE THAN THE INLET THEN THE FLOW RATE WILL BE COMPROMISED
OR NEGATED.
Also, I wouldn't go directing fresh air over just cylinder #3 - a bad idea
for simple reasons.
The boundary layer on a Spitfire wings at 400mph is about an inch thick
(meaning that the velocity 1" away from the surface is still only 99% of
that of the full stream velocity). It is unlikely to be more than about 1/4"
thick at the back of your van at 60mph so even a splitter plate 1" away
SHOULD allow plenty of full stream air to flow in - PROVIDED their isn't a
big separation bubble sitting just in front of the intake, PROVIDED the
total cross sectional area of the duct entrance is matched to the duct
itself, PROVIDED the sink at the other end of the duct can handle the flow
volume and PROVIDED the sink (exhaust) pressure at that flow rate is
significantly lower than atmospheric (but I'm not prepared to say how much!)
and no doubt provided a few OTHER things as well.
Experimentation with a grasp of fundamental principles, an open mind and
devise instrumentation to prove the case - e.g. smoke flow, tufting etc. are
cheap.
Technicians know what they know
Engineers know what they don't know
If you have studied your subject to such an extent that you know areas of
knowledge exist, but maybe you don't know their specifics, that is quite a
powerful situation to be in - much better than when you don't know whats
round that big blind knowledge corner - or even that the blind corner
exists!
Put simpler - a little knowledge can be a dangerous thing.
Hope this helps a bit more (but something makes me think I'm going to regret
responding - again)
Clive
'88 Syncro Transporter
----- Original Message -----
From: "Robert Steven Fish" <fish@SALZBURG.CO.AT>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, August 22, 2002 11:50 PM
Subject: Re: Custom Scoop Update - Should you care!
> A List Member asked whether these air vents actually do suck in air, or
vent
> out air. I am still not certain that anyone has answered this clearly.
>
> I have followed this thread with interest, as I live in Austria now, and
was
> forced to remove my rear side running lights. As these are now gone,
there
> is a nice large space, especially on the driver's side, where a cutout
could
> be made and a scoop could be constructed to pull air in while driving...
it
> could even be directed pretty much directly onto cylinder #3 if the design
> was good.
>
> Before I consider this for the left or right or both sides... it would be
> good to know what really happens to the air as one drives. If you create
> airflow using scoops (and if it even works at all, is another question)
> where does the resulting flow end up going... and does it result in bad
> things, like creating backflow or vacuum areas anywhere.
>
> How far out must one actually go, to obtain a successful "scoop" effect?
> Would an inch end up pulling any air in??
>
> Aerodynamics experts on the list... PLEASE set us all straight on this
> mess... and deliver the final word, so we all can get on with our lives.
>
> RSF
>
> IMPORTANT!!! In order to reply to me, you must have the word "FISH"
> somewhere in the subject line of the email. Otherwise it goes directly in
> the trash.
>
> <º)))>{ <º)))>{ <º)))>{ <º)))>{ <º)))>{ <º)))>{
>
> <º)))>{ <º)))>{ <º)))>{ <º)))>{ <º)))>{ <º)))>{
>
> Robert S. Fish
> Salzburg, Austria
> 1987 Wolfsburg Vanagon 2.1 GL Weekender
> 1987 Golf Cabriolet
> 1991 Golf
>
