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Date:         Wed, 15 Dec 1999 10:48:43 -0500
Reply-To:     Bulley <gmbulley@BULLEY-HEWLETT.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Bulley <gmbulley@BULLEY-HEWLETT.COM>
Subject:      Re: Air intake "scoops"
Comments: To: Paul Schiemer <schiemer@MAGICNET.NET>

So, if I read you correctly, our VW-designed ducts are better than any home-grown scoopy-de-doo shapes? Make senses when you reference the pressure wave forming and cite the shape of current race-car ducting. Cool! Literally.

G. Matthew Bulley Bulley-Hewlett Corporate Communications Counselors www.bulley-hewlett.com Cary, NC USA 888.468.4880 tollfree

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-----Original Message----- From: Paul Schiemer [SMTP:schiemer@MAGICNET.NET] Sent: Wednesday, December 15, 1999 7:33 AM To: vanagon@GERRY.VANAGON.COM Subject: Re: Air intake "scoops"

> Are these really functional as air scoops or are they merely > cosmetic? Scoops DO function to channel air.

> I've always questioned whether any horsepower gained by air scoop ram > effect could overcome the extra aerodynamic drag created by the > scoop. No advantage for this specific type of scoop. It merely cools by moving air into the cavity. They are too far away to add any benefit to the compression cycle of the engine. The drag of these scoops is negligible.

NASA has a compendium of data available (reams & reams of books) on ducting. At certain speeds protruding scoops (as these are) become a detriment and not a benefit. Has to do with the way the leading edge (lip) closes the effective size of the opening by its' resistance (a wave forms in front).

If you'll notice current race cars (F1, GT, etc.) you'll see the popular NACA ducts, which are cut outs in the surface of the vehicle. These are the most efficient type of cooling openings. The laminar flow along the skin is channeled through the duct at the full range of velocity, without adding drag.

Looking at your brick in the car park the air scoops recede into the body, in the NACA style. There's quite a bit of area open to take in air at a wider range of speed, whereas a scoops' effective area is reduced (smaller opening). There IS some speed range where the scoops are more effective than the standard opening, but it's probably very narrow (by comparison).


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