Nov 18, 2005     Bottom Skin - (7.5 hours)       Category: C19 Wing+Ail

11/17/2005 (2 hours):

Today I finished prepping the bottom of the left wing for skinning. Hopefully I can get this done tomorrow. I made the channel for the flox corner around the wing attach bolt recess, and vacuumed the surface one more time for good measure, this time with my hand and arm encased in plastic to protect it from the loose fibers. I also installed the peel ply strips on the trailing edge and aileron cut line.

I used a slightly different method for this than called for in the plans. I tried small brads, but they dimpled the peel ply, and the plans specifically state that it must lay flat. I would have used staples, but I only had a few left and didn't want to run to the hardware store just for this. Instead, I put down small dabs of epoxy every 6" or so along the strips, let it soak in, and gave it a good stipple and wipe-down. I ended up with perfectly flat strips of peel ply. The only negative is that you have to wait a day for the epoxy to cure or the peel ply will come right off when you lay out the cloth, but that worked fine for my schedule.

11/18/2005 (5.5 hours):

Today I did some of my best work. Ever.

I started by installing plastic curtain rod covers to line the conduit hole, and a NAV antenna about midway down the wing. I had intended to do these steps yesterday to reduce the layup time, but forgot. I then micro'd the foam. In the future, I'll pre-fill low spots (like the electrical conduit hotwire entry slot) a day ahead of time, and allow to cure. That would make this step a bit faster, since micro takes time to settle into deep slots.

I then laid out all of my glass, both layers at once. Laying out one ply at a time is fine if you like 8- hour layups, but I'd like to fly some day. MGS wets out two layers of glass just as well as one. So, I got all of my cloth laid out perfectly as my first step. I then mixed LOTS of epoxy and wet out the entire surface, squeegeeing lightly to spread it around. I used a brush to touch up spots, especially around the LE and TE, and the 4" section over the shear web.

Once I had the glass fully wet out, I squeegeed lightly to remove the worst of the excess. I then peel plied the entire wing, and laid out my plastic sheeting. Finally, I very carefully squeegeed, using the hair dryer. I first worked along the spar cap, then from the spar cap to the LE and TE. I spent the most time on this step, making sure I was getting very consistent results so I won't have any thick (high) or thin (low) spots.

The hair dryer really makes or breaks the process of squeegeeing through the plastic. Yes, it helps liquify the epoxy again, but it also does something more important - it lets the plastic stretch evenly. This lets the plastic deal with compound curves without bunching up.

For the curious, yes, I DID use my "dump and run" technique. Large, flat surfaces like the wing really benefit from this method. All this means is mixing very large cups of epoxy, and dumping it in a stream across a convenient relatively flat spot (like the spar cap area). You then squeegee lightly to spread it around in a thin layer, and move on to your next cup. The epoxy will wet out the cloth on its own. This produces some waste (I removed about 1.5 cup's worth during the squeegee stage, about 10 squirts) but you can do large layups like the wing VERY quickly. My time broke out as follows:

1 hour - Install conduit and NAV antenna

1 hour - Micro foam (next time pre-fill holes and let cure, would save time)

30 minutes - Lay out cloth, scissor trim.

1 hour - Wet out with epoxy

30 minutes - Lay out peel ply, stipple to mostly wet out, lay out plastic

1 hour - Squeegee

These are estimates. I think I actually spent more like 45 minutes wetting out, and 1.25 hours squeegeeing, but the numbers should be fairly close. In any case, I'm confident that if I come prepared with antennae already installed, and the slot pre-filled with cured dry micro, I can do the right wing's bottom skin in 3 hours using this technique. We'll see.

The best part of this whole process is that I no longer have any fear of large layups. It used to be a race to wet out and stipple before the entire thing started to gel, and it took a lot of stippling. That's hard on my hands and wrists - I have arthritis. Now, I hardly stipple at all. I only use one for touching up dry spots before squeegeeing, and painting vertical surfaces.