> Here’s one for you aerospace guys.

> Can someone explain to me the vacuum bagging process. I know that the home
> built airplane guys use it a lot to get maximum strength/weight ratios out
> of a given thickness of cloth.

> As I understand it you apply the glass and epoxy in a normal way cover it
> in a “peel/ply” and/or “breather” layer, put the whole thing in a vacuum
> bag and then by evacuating the air, you get uniform pressure over the
> surface. My assumption is that less epoxy can be used and still get
> complete wet out and bonding to the surface.

> My questions are:

> 1. how do you peel off the layers after the epoxy cures? I remember trying
> to get my hatch covers off after building the lip for flush hatches. Even
> after liberal doses of past wax the epoxy was holding on pretty good.

the peel ply doesn't stick to the epoxy, but any plastic that won't stick will work.

> 2. I have this vision of the vacuum pressure squeezing out the excess
> epoxy from your layup but where does it go. At best it would come to the
> surface to be sanded down but I don’t think that is right. If it squeezed
> into the peel/ply then I assume you would never be able to “peel” it off

it's absorbed mastly by the 'breather' that you use.

> I have never heard of anyone on this board using it so I assume that it is
> either very expensive or provides only marginal strength / weight
> improvements.

I've done kevlar / carbon fiber / kevlar layups on the solarcar I worked on.

The stuff we did without a vacuum bag turned out _real_ bad, full of voids. We would up rippping it all out. What the vacuum bagging did for us was take out all the voids. You do have to watch how you bag it. run a vacuum line to _both_ sides of the yak to equalize the pressure. If you bag just the outside you could easily crush it. If you don't believe me vacuum bag an empty container and see what happens. Actually do it anyways, its kinda neat to see what happens!

Industrial built boat are made on large forms. We built one to make the 'bubble' canopy. It weight in at 300lbs! Which is nothing compared to what the industry does. Try several tons!

> Jack