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Old Jul 19, 2011, 04:11 PM
Phil Barnes is offline
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Germantown, Maryland
Joined Apr 2004
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Quote:
Originally Posted by GaryO View Post
Phil,

Are you hard rolling directly on the wet kevlar? If so, how do you keep the roller from moving the kevlar?

Gary
Important Note: The following post is talking only about the use of lightweight, open weave fabrics that require a wax paper transfer method for handling and require hard rolling to close up the weave of the fabric. Fiberglass layups and Kevlar layups with 1.7oz Kevlar do not require most of the methods discussed here. The lighter 1.0 oz Kevlar and the R&G 1.0oz disser Kevlar fabrics do require these methods or at least benefit from these methods.


Many different methods can work, but what I'm doing lately is as follows: I roll the fabric out on my bench. The bench should be smooth with no snag points for the fabric's weave to get stuck on. Any fabric that is finicky enough to require a wax paper transfer method is the type that will get distorted out of shape if it snags when being moved over a bench. Sometimes I'll even quickly run a sanding block over the bench to be sure it is smooth and then brush the dust off thoroughly. Then I roll the fabric out and I'll spend some time adjusting the fabric on the bench until the weave is all lined up properly and not running in all different directions. Then brush the fabric very lightly with a drafting brush to smooth it down flat to the bench.

I then reel off a long piece of wax paper and lay that on my layup bench (away from where the fabric is) and I put a very light spray of 3M77 on it. I just spray horizontally a foot or two above the wax paper and let the mist settle on the wax paper, just one quick spray. I pick up that wax paper with one hand on each end and drop it in place over the rolled out fabric. I usually will align the wax paper diagonally on the rolled out fabric, usually there is a bias cut end on the fabric anyway so I just follow that edge, or I lay the wax paper parallel to one of the diagonal lines on my bench. For the Zone wing I just did, I had to lay three strips of wax paper side by side on the fabric to cover enough of the Kevlar. I taped the joints of the wax paper with masking tape after laying the wax paper down. If you do this, be very sure that there are no gaps between the sheets of wax paper. The tape will not release from the fabric without a great deal of grief. It's OK if the wax paper overlaps a bit.

My fabric patterns are just made from poster paper and I trace around these with a fine point sharpie marker which writes very nicely on wax paper. I try to remember to make lefts and rights, but when I forget I just have to put wax paper on the other side of half of the pieces and pull the first piece off.

I have my mylars laying on the layup bench, lightly tacked to the bench with 3M77. I roll epoxy on the mylar and then drop the wax paper backed fabric in place. I'll just lightly press the fabric down until I see that it is all wet out. There is a lot more epoxy on the mylar than what the layup needs at this point so it easily wets out the fabric. I then pull the wax paper off. I roll the fabric with the hard roller as soon as the wax paper is off. At this point the fabric is very wet with epoxy so I have to roll gently to avoid moving the fabric around. If the fabric still moves then I would have to put some paper towels over it and hard roll that gently to remove some epoxy. In general, the wetter the layup, the lighter the pressure you use with the hard roller. I'll generally take every opportunity to hard roll.

Next step is to dry the layup in a vacuum bag. I just move the mylar over to the bagging bench and put a layer of paper towels over the wet out fabric. Then I invert the other mylar, face down on top of the first. So you now have the two mylars face to face with paper towels in between. If I'm doing a full wing with four mylars then I'll make a stack of all four mylars in two pairs with paper towels between the wet faces. That goes into a vacuum bag and sits there while I finish prepping the core. I used to try and time how long it stays in the bag to get just the correct amount of epoxy out. Lately I just let it stay in the bag a long time. It just reaches a point where the paper towels are saturated and they won't take any more epoxy. This is also a point where the layup is too dry, all the remaining epoxy is concentrated near or at the mylar face and there is almost none on the face that will be against the foam core. If you bag the wing with the layup like that you'll get a wing like my original Zone wing that delaminates the skins with every slight impact.

The mylars come out of the bag, the paper towels are removed and the mylars sit face up on my bagging bench. I then roll the skins again with the hard roller. This time I'm pushing real hard with the roller because the skins aren't going to move at all. Then I take my foam roller that is used to spread the epoxy and add a little epoxy to the layup again. For this application, the roller needs to be almost dry, just a little epoxy in it. You want to add just enough epoxy to get a little bit of a sheen. Also when you press your finger into the layup, you should be able to just see a little epoxy ooze out around where your finger was. If you press real hard with your finger tip and still can't see any epoxy and if you don't see that little sheen of epoxy then the skins likely won't stick well enough to the core.

As the last step before putting the cores in place, I'll add epoxy to critical areas of the layup. This always includes the trailing edge area. I'll run a stripe of epoxy about a 1/2" wide along the trailing edge of each mylar. Make it sloppy rich epoxy. This will make the wing trailing edge durable so it doesn't turn to mush every time you touch the wing's trailing edge. I also run a narrow (maybe 1/4" wide) strip of epoxy on the hinge line areas. I have a mylar template that I lay over the layup. This template has a window cut in it where the hinge lines are. This ensures that I get a nice narrow strip of epoxy in just the right place. If the wing has prefaced hinge lines then this extra epoxy over the hinge line is not needed and actually is hurtful because it floods the hinge gap with epoxy and makes the hinging job difficult.

The wing is then ready to bag. I didn't talk about some details such as adding doublers, spar rods, etc. I only mentioned the bits that related to wetting out and hard rolling the main skins.
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