Date: Thu, 22 Aug 2002 23:16:09 +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!
Content-Type: text/plain; charset="iso-8859-1"
Mathew,
Whilst some of your reasoning makes a little sense, what doesn't is the term
'laminar flow ducts'. Theres nothing specific about the boundary layer at
the
back of a vanagon that would entice an aerodynamicist to use that term.
What these 'flush' vents might be called are just that - flush vents or
maybe -
at a push - NACA flush intakes, although they're not exactly designed as a
true NACA slotted intakes.
I think what you're trying to point out is this: if the flow rate drawn off
by the
sink (the induction system) can't handle the flow rate into the Mark's scoop
then there will be spillage, which in itself will increase drag.
However,
> Maybe I've missed out by being off list.
which was a few messages a month or so ago, where Mark was advocating these
for enhacing the flow through either an oil cooler or an turbo intercooler
positioned
down where the duct shaft exhausts. Provided the other side of the cooling
matrix
is in a relatively low pressure region, they could indeed provide a good
flow rate, as
a cooler could pass more air than an engine intake (unless we're talking a
RR Merlin
at full chat).
If other sources refer to flush inlets as laminar flow ducts, I'd be pleased
to know
the source, as the relevance of what at the back (and even less so the
front) of a
15 ft object travelling at 60mph is a thin boundary is pretty irrelevant.
Boundary layer
state and overall flow attachment/separation, although interrelated, are
quite different
things - a turbulent boundary layer for instance does not imply separated
flow, and can
actually prevent it (e.g. the well-known golf ball dimpling example).
Additionally, flow rate into and through a duct as large as the vanagons at
the speeds its
likely to be going, would if anything be greater for a trubulent b.l.,
following on from the
golf-ball reasoning - it wouldn't separate as easily around the bends (which
create adverse
pressure gradients on their inside radius).
Hope this helps, not that I am a fan of scoops; maybe Mark should make it
clear again that
they were designed for an oil/intercooler installation and that any dynamic
pressure head gain
for an inlet system, however well designed, is negligible until about 120
mph (about 1%).
Clive
'88 Syncro Transporter
----- Original Message -----
From: "G. Matthew Bulley" <gmbulley@BULLEY-HEWLETT.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Thursday, August 22, 2002 3:27 AM
Subject: Re: Custom Scoop Update - Should you care!
> Scoops? For what?
> Maybe I've missed out by being off list.
>
> I pray these are not some sort of DIY 'improvement' the laminar flow
> induction duct at the rear of our vans. Boston Bob and I have gone a
> round or two on p-mail in the past over his "ears" 'improvements' the
> well-designed VW ducts.
>
> Long and short, if these 'scoops have to do with airflow into the rear
> ducts, think again. Then look at *all* modern sports cars and realize
> that "scoops" have gone the way of the Holley 4-barrel. Scoops create a
> pressure wave right in front of the induction hole, making their intake
> negligible. Measure your before and after head temp to confirm.
>
> Laminar flow ducts, (like on the Vanagon, Porsche Boxster, MR2, Saleen
> SR & S7, Honda S2000, and a host of other cars) are multifold more
> efficient, and are only ruined by 'scoops' and 'ears'.
>
> So what are these "scoops" all about?
>
> Developing business and guiding change since 1996,
>
> G. Matthew Bulley
> Bulley-Hewlett
> Marketing & Communications
> Business: www.bulley-hewlett.com
> AIM = IExplain4u
> Phone: +1.919.658.1278
>
>
> -----Original Message-----
> From: Vanagon Mailing List [mailto:vanagon@GERRY.VANAGON.COM] On Behalf
> Of Mark Thoma
> Sent: Thursday, August 22, 2002 12:06 AM
> To: vanagon@GERRY.VANAGON.COM
> Subject: Custom Scoop Update - Should you care!
>
> The scoop on the scoops,
> After patching up my screw ups on one of the scoop molds, I took them
> both (right and left) to a boat repair guy here in the Cleveland area
> who does a lot of fiberglass gelcoat kinda stuff and he said "well they
> look pretty darn nice, but... (like peewee herman said, "Everybody's got
> a big but") you need to polish and buff the molds now, then spray in
> release agent, then a layer of gelcoat then 4 layers of fiberglass cloth
> and the fiberglass cloth needs to go on top of the gelcoat while the
> gelcoat is still tacky."
> Me, feeling an assault on my wallet coming on, said "How much?"
> He said "$100 bucks for the pair of finished scoops." To which I said,
> "Go for it."
> Then he said, "But you can sell these things to all of your Vanagon
> buddies and make all your time and effort pay off." And I said "Well
> why wouldn't I just make all the subsequent scoops myself, after all I
> have the molds?"
> To which he replied, "You could but the molds have to be polished and
> buffed between each use, and that takes a lot of work, and then you have
> to shoot the gelcoat, lay the 4 layers of fiberglass cloth, etc."
> So I said "Well how much for each set of scoops?"
> And he said "$100 per pair no matter how many pairs we make."
> And I said, "But how much could I sell them for?"
> And he said, "Something this nice, $175 for the pair."
> And I said, "Those cheap bast----I mean those economically minded
> fellows on the Vanagon list will never pay that much."
> And he said, "Okay tell them $150 for the pair and you'll pay the
> shipping. And if you don't sell one pair what do you care, you still
> have the scoops you wanted in the first place?"
> And I said, "MAKES SENSE TO ME!"
> So that's the long and short of it. I should have the first pair back
> in a week. I'll take some pictures of them mounted on the van and
> you'll know how to reach me should you want a set.
> Mark
>
> Mark Thoma
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