[simpits-tech] Display walk-around.

[Gene Buckle]

On Wed, 8 Jun 2011, Brian Sikkema wrote:

>
>> The current setup requires nearly the full draw of the Fein Turbo III dust
>> collector that I'm using and even with my 60gal air compressor going full
>> tilt, I can't approach that amount of volume.  The Fein will pull a 105"
>> water column which is roughly equivalent to about 8in HG.
> Just spitballing here, but IIRC there's a fair amount of space behind
> the mirror, no? It seems if you could reduce that volume that maybe your
> vacuum requirements would be eased.
>
> Just thinking about our sim and how the mirror is set up, and the
> backing behind it matches the shape of the mirror pretty closely. I'm
> sure there are multiple reasons, but it stands to reason that one of
> them is to minimize the amount of volume you're drawing the vacuum on.
>
It's not so much the volume as it is the vacuum required to stretch the 
Mylar in the desired shape.  Commercial systems have a smaller space 
because they build the Mylar framework as a single monolithic assembly 
that is perfectly air tight.  They can use a much smaller vacuum inlet 
that feeds a much lower CFM, but much higher draw vacuum pump.  Because 
our system is very (comparatively) "leaky", it takes a pretty stout CFM 
rating to keep the mirror formed properly, but not that much actual draw 
(if that makes any sense).  The max the Fein can pull is about 7.7PSI, 
which in the world of vacuum pumps is pretty weak.  The tiny vacuum pump I 
bought to test with can pull 25 inHG (Fein can do about 8 inHG) or roughly 
12psi.  Unfortunately the small vacuum pump has such a low CFM rating that 
it can't overcome the system losses AND hold the mirror shape.

We're going to be adding reinforcing ribs to the frame on Saturday to 
avoid deforming the back and we'll do some caulking & adjusting at that 
point to drop the losses as best we can.

If I could afford it, I'd just build one out of fiberglass.  That would be 
a pretty expensive undertaking though - especially when working with a 
plug mold that size. :)

g.


-- 
Proud owner of F-15C 80-0007
http://www.f15sim.com - The only one of its kind.
http://www.simpits.org/geneb - The Me-109F/X Project

ScarletDME - The red hot Data Management Environment
A Multi-Value database for the masses, not the classes.
http://www.scarletdme.org - Get it _today_!

Political correctness is a doctrine, fostered by a delusional, illogical
minority, and rabidly promoted by an unscrupulous mainstream media, which
holds forth the proposition that it is entirely possible to pick up a turd
by the clean end.