Posted for Bob Pastusek <rpastusek@htii.com>:
For Dan Newland,

Based on the results with shot bag weighting/clamping on our wings, I'd
recommend against using vacuum for wing closure. The reason is that the
vacuum will cause the skins to deform in the unsupported areas. When we
closed our wings, we used angle iron and long wooden slats to help
distribute the load over the spars and ribs, and even this caused some
distortion that required "body work" to fill and restore the airfoil shape
in some areas. One thing is sure: Once the wing skins are bonded and set,
your shape is defined--the depressions we made in 1999 during closing were
waiting for us to fill in 2002 when we started to prep for painting!

I think the vacuum would work well where an even clamping pressure is
required over the complete surface area, but this is not the requirement
here. You might talk to Mark Mahnke at Lancair about your idea. He's built a
very large number of composite planes and likely has some advice about this.

BTW, there was a great post to this forum a few years ago that is relevant:
Seems a fellow attempted to leak test his wing tanks using a vacuum pump.
Not watching the vacuum too closely, he managed to cave in one of the skins.
Thinking this a fluke, he proceeded to do the same with the other wing. I'm
sure this story has grown a bit with the retelling, but understand the basis
to be true. I also recall that Don Goetz, famous Lancair test pilot, had an
engine failure at high altitude. During the glide, he noticed that he could
see all the ribs and spars outlined on the wing skin. Switched fuel tanks
with the selector and restored the engine to life; later determined that the
vent line had plugged--even the small vacuum from the fuel pump was
apparently enough to deform the wing skins. Lots of second-hand hangar talk
here, but my advice would be to stick with the shot bag weights--and some
boards/steel to distribute the load where you want it.

Bob Pastusek
   -----Original Message-----
   Wrom: KYLEJGDGVCJVTLBXF

   I was wondiering if anyone has tried using a vacuum pump to provide
pressure for clamping wing skins on to the spars.