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Date:         Tue, 21 Apr 2009 16:41:17 -0700
Reply-To:     mark drillock <mdrillock@COX.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         mark drillock <mdrillock@COX.NET>
Subject:      Re: Westfakia, Poptop, Access, Design
Comments: To: Mike <mbucchino@charter.net>
In-Reply-To:  <CF06387A0DBF4DC2AD2C99F4F6621CD5@mike2d93581d7f>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

I agree, but no one suggested removing the entire roof skin. Only a section for standing in the main floor area is trimmed out, and not anywhere near all the way to the gutters. Cut 1/3 of the center of the shoebox lid out and not all the way to the edge and see the minimal impact on rigidity.

Mark

Mike wrote: > In a 'unibody' (also referred to as 'monocoque') design structure, any > skin section is a structurally-stressed component of the entire > structure. A Vanagon is considered unibody, even though it does > have frame strengthening members underneath. > Those roof support arches are more for rollover protection than > torsional rigidity of the body. The roof skin, however, is an > engineered, diagonal bracing that contributes greatly to torsional > rigidity of the entire body, in addition to providing added metal > structure to add crash or rollover protection. > Take a shoe box, remove the lid and grab the ends and attempt to twist > it; it will easily deform. > Now, put the lid on and repeat; you'll have a hard time deforming the > box from it's basic shape. > And, now, for the final proof of the body weakness created by a > large, unreinforced sunroof opening; cut a good -sized 'sunroof' into > your shoebox lid and repeat your twist test. What happens? My bet is > that a great amount of overall rigidity is lost due the 'missing' area. > You've cut the center out of your 'diagonal bracing! > VW made up for it by adding 'doublers' inside the factory sunroof, not > just a couple of cross ribs. The probably also added outboard, lower > frame cover plates (I know they did on the earlier buses). Side impact > crash protection, must also be taken into consideration in this > modification. (Smack the side of the shoebox to demonstrate this aspect.) > > Mike B. > > > > > As long as you don't cut the 2 main roof arches, one at the front edge > of the slider door and one at the rear edge, the roof area between is > just roof skin and not of much importance structurally, IMHO.


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