Date: Thu, 22 Aug 2002 19:50:32 -0400
Reply-To: 80 Westy Pokey <pokey@VANAGON.ORG>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: 80 Westy Pokey <pokey@VANAGON.ORG>
Subject: Re: Custom Scoop Update - Should you care! FISH Y
Content-Type: text/plain; charset=iso-8859-1
OK, so how do I create low pressure in the engine
compartment so that more air flows in? Someone must know
what the intended engineering airflow was supposed to be in
our vans.
Thanks,
Chris
---- Original message ----
>Date: Fri, 23 Aug 2002 00:23:56 +0100
>From: Clive Smith <clive.harman-smith@NTLWORLD.COM>
>Subject: Re: Custom Scoop Update - Should you care! FISH Y
>To: vanagon@GERRY.VANAGON.COM
>
>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
>>
