Vacuum bag layup process

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Well-Known Member
Log Member
Nov 6, 2012
Marshall, MN
I noticed on the Raptor aircraft videos that their vacuum bagging process is two steps. The 1st step is the outer skin and the core. The 2nd step is the inner skin. On other videos I've seen most people seem to vacuum bag the outer skins, inner skins, and core all in one step. Is there a certain reason for one process over the other?


Super Moderator
Staff member
Log Member
Oct 18, 2003
Saline Michigan
Is there a certain reason for one process over the other?

Usually, you can put the layer against the mold without wrinkling, regardless of the shape. The core can be harder to bend and fit up such that it lays nicely in the mold, but can usually be made to work in combination with the mold side fabric. But if the core is a little off, then the inner skin can be real trouble, and it either does not want to lay in or it wrinkles. Wrinkles are particularly band.

For things like wing skins, you can usually do both skins and the core in one shot. In things like tightly curved and/or compound curved surfaces, you end up doing the part in two, or sometimes in three bag sessions. It is all a meter of being able to get the various layers to all settle down flat. If not, you build in more than one session.

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