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Re: REFLECTOR: Bulkhead Installation-Layup forming



James F. Agnew wrote:
> 
> A long time ago I posted my method of compressing layups that produces well
> fitting and beautifully formed edges and curves.  Anyone that has seen these
> layups will tell you that they many times look like they are molded.
> 
> First get a large selection of compressible foam blocks four to six inches
> thick.  Don't use soft foam use the type that is generally used to pack delicate
> items that is firm and rebounds slowly.  Wrap these blocks with plastic and duct
> tape the back sides.
> 
> After you do your layup cover it with either peel ply or plastic (Peel ply will
> give you a dull sanded finish, plastic will give you a high gloss glass like
> finish with smooth tapered edges).  Place a foam block larger than the layup
> and a solid backing (piece of plywood works well) and compress the foam to
> between 1/2 & 3/4 its original thickness.  The foam will conform to the shape
> and provide a nice even compression of the layup that will generally prevent
> high pressure areas and dry spots.  If the plastic or peel ply wrinkles it may
> produce a wrinkle like pattern on the surface.  The wrinkle area is still
> compressed and the imperfection is usually just a little epoxy.
> 
> On internal layups you can usually just wedge the foam in place.  For those of
> you that have done the heavy Triax layups on the underside of the spar you will
> quickly understand the beauty of the foam blocks since they can apply pressure
> to the top and sides at the same time.
> 
> Before you do the layups select and fit the foam blocks to make things go
> smoothly.
> 
> WARNING - the foam blocks will not push heavy layups in place, you must do the
> layup properly.  The foam blocks will hold the layup in place and provide that
> last small forming pressure on the surface, curves and edges.
> 
> Jim
> 
> David M Parrish wrote:
> 
> > From:                   "Schweitzer, Bill" <bill.schweitzer@compaq.com>
> >
> > > I learned that doing multiple layer triax layup is a real gravity defying
> > > challenge.  We always wet-out the glass on plastic, so that all the plies
> > > were well connected and equally wet and well squeegeed (sp?).  Then we
> >
> > Doing just about any layup on plastic first is the way to go, and the
> > thicker/more complex the layup, the more useful it is. But, when
> > you have multi-ply triax layups that have to be vertical, I like the
> > idea of letting the layup gel a bit before placing it. (Low flow, but
> > still very tacky.) Leaving the plastic in place after the layup is put in
> > place also slows drainage.
> >
> > In fact, though I never tried it, you could have peel ply as the first
> > layer on the plastic so it faces out when the plastic is removed.
> > Peel ply is great for protecting the glass surfaces from enviromental
> > contamination before more layers are added.
> >
> > > The trick is to CLAMP EVERYTHING in place with good solid, stiff pieces of
> >
> > Be careful about clamping, as you can use too much pressure and
> > squeeze out too much epoxy.
> >
> > ---
> > David Parrish
> 
> --
> //------10--------20--------30--------40--------50--------60--------70--------80
> 
> // James F. Agnew
> // Tampa, FL
> // Velocity 173 FG Elite ( http://www.VelocityAircraft.com/ ) under construction
I'd like to add to Jim's recomendation and method of using foam covered
pads to assist in putting on the heavy triax layups.  I've seen Jim's
work and used the same technique. It can take a fair amount of time to
fabricate these pads, but I found multiple locations where they can be
reused.  Using spring clamps, or in some cases a simple wedge can
achieve great results. As a matter of fact while putting in the front
gear inside keel layups, you could see epoxy seeping through the keel
walls, this would indicate to me that a good mechanical bond was
achieved. And when fully hardened this is not a layup that will peel
off. Even good sanding on a secondary layup and pre-wetting with pure
epoxy is no guarentee that you've achieved the best attachmnet. My plane
has been inspected by the EAA tech reps and  other EAA builders and
everyone as responded positively about the quality of this technique.