Outer Wings (Part 6)

Continued from Outer Wings (Part 5)
Today I finished sanding the wing to shape. My micro trailing edge is nice and solid, and I sanded the overlapping fiberglass on the leading edge down nice and smooth for the next couple of layers. I hand planed the spars down to slightly below the airfoil contour, which was much easier after I took five minutes and sharpened the blade. I didn't take many pictures, but I did document how I'm prepping the sump drain as well as the WAF cut-outs in the foam. The cut-outs each get some one-on-one time with a Dremel, so that the foam is slightly recessed. Next I take a piece of pre-layed-up fiberglass and cut it to fit the cut-out.

Once I've got all four cut to fit, I mix up some micro and apply it to the foam, then set the fiberglass in the cut-outs. I'm not too picky about how it lays, but generally I try to make it as close to the airfoil contour as possible, erring below rather than above.

For the sump drain, I start by attaching a circular piece of duct tape over the hole. Then I use a really thick micro to build up from the aluminum block to the airfoil contour. While the micro is in the "green" stage, I use a Forstner bit to generate a nice circular hole down to the aluminum block where the duct tape is, which gets removed (because it's now all gummy and may not keep the resin out during the big layup.)

I'll replace the duct tape before I do my layup. I'm prepping for that by cutting templates out of plastic 2 mil drop cloth, then cutting the fiberglass from that. If everything goes well, by this time tomorrow the wing will be finished and off the plane.

Outer Wings (Part 5)

Continued from Outer Wings (Part 4)

I started by sanding down the foam I glued on yesterday to fix the low spot. Once that was sanded to contour, I went ahead and sanded the trailing edge to contour as well. I was a little pressed for time, otherwise I would have finished sanding and gotten ready to glass. I did have time to mix up some more micro, though, so I poured/squeegeed/scraped it into place to finish filling in the low spot. After sanding:

And after adding micro, it's nice and smooth and follows the airfoil perfectly.

I also had time to use a wire wheel in a power drill to scrape away the foam within about 3/4" of the trailing edge, and filled that with micro for strength. I did this on the other wing as well, and it's crazy stiff and crazy strong now.

I have to hand plane the spars down a little so they don't stick out, then sand the leading edge and prep it for two more overlapping layers of fiberglass. I also need to cut and attach some prepreg FG strips over the WAFs so I don't lose a ton of vinylester down those cut-outs. After that, I'll be ready to glass the bottom of the wing, then move on to the wing tips.
Continued in Outer Wings (Part 6)

Outer Wings (Part 4)

Continued from Outer Wings (Part 3)
With the plane upside down and wing reattached, I began by cutting the rest of my foam pieces to shape. It was during this process I realized that, during my fuel tank construction, I glued the bottom center section of foam incorrectly. By incorrectly, I mean that the foam was actually recessed below the airfoil shape for about half a square foot. I had problems fixing similar trouble spots before, but I've decided to try a different method with this area. I didn't take a before pic, but the after pic gives the general idea. The darker area is the low spot.

I decided to go ahead and sand the center section to the airfoil shape so I would have a solid understanding of where the foam was low. After that was accomplished, I traced and cut out a piece of foam 3/8" thick that was 3" smaller around the edges than the space that was low, and I glued that on. My next step will be to sand that to shape, then use micro to fill the outer band of the low spot, utilizing a straightedge while the micro is still wet to get a nice flat surface. This should work much better than my previous attempts, which were to glue foam over all of the low spot and sand it away. The problem was that the micro didn't sand as readily as the foam, and created high spots. 

With that figured out, I turned my attention back to adding foam over the rest of the bottom of the wing. Pretty straightforward, just make sure there's enough foam sticking up to sand away, and enough foam left after sanding that it won't flex after fiberglassing.

I came up with a simple (sort of) way to help hold long pieces of foam in place when they want to sag. First I cut off a piece of string about twice the length of the foam. Next I poked holes every foot or so in the foam I want to attach. The string gets secured at each end, by whatever means necessary. Finally, the string gets pushed up through each of the holes, then pulled until there's no slack. When you're finished, you've got plenty of string loops to help rearrange or secure your foam. I didn't end up using them to hold the foam in place, but they were very helpful for making small adjustments while the micro cured.

Top side:

Bottom side:

Continued in Outer Wings (Part 5)

Outer Wings (Part 3)

Continued from Outer Wings (Part 2)

On the left wing, I tried to modify the plans method to make it easier on myself. I cut out foam nose ribs that, rather than stick all the way out to the leading edge, only stuck out far enough to support the foam planks. Unfortunately, they weren't quite right, and it caused a lot of headache and frustration trying to rip out and replace foam. So this time, I did it a little closer to the plans method. Glued foam nose ribs in place, but then sanded them to the airfoil contour before adding the rest of the foam. It worked quite well, and was much easier than trying to work out the geometry of the nose supports changing size, length from the spar, and angle changes for washout.

Foam planks being cut and placed:

Once in place, I began the arduous sanding process yet again.

Honestly, it only took a couple hours, including frequent hydration (read: lost motivation) breaks and several "Is there *any* other way that would be *slightly* better?" pauses. One of those gave me the idea to cut slits along the entire length of my aluminum angle sanding block, and use that edge as a saw. It worked fairly well for large chunk removal, as long as you were careful not to cut too close to the final shape.

Eventually, I did manage to finish sanding the top of the wing (although not perfect - thank goodness for micro!) and got ready for another round of glassing. It's been so hot, I've been getting all of my supplies ready and all of the prep work done in the evening so I can get up early and finish glassing before 9 or 10 AM. Any later and the vinylester just sets up too fast. One interesting thing with vinylester that seems different than any other two-part system I've used - if the vinylester is gelling, and I'm not quite ready for it to set, I can actually add a little extra time by adding a little more vinylester (with hardener added, of course.) Not sure how or why, but it's saved me from a lot of repair work a couple of times.

I didn't get any pictures of the process, but it went like this:
Step one: micro from the front spar back to the trailing edge (skipping the spars)
Step two: lay one layer of 5.8 oz cloth and one layer of 1.5 oz cloth on the micro'd area, wet out completely
Step three: micro from the front spar forward and underneath, two inches past the chord line
Step four: wet out two layers of 5.8 oz cloth on a piece of 2 mil plastic, then lay the cloth in place on the leading edge of the wing. Much, much easier to do one layer at a time, otherwise you risk wrinkles in the bottom layer that are pretty impossible to get out once the resin begins to set.

The result is quite good, with very very few bubbles and only one small wrinkle. If the thunderstorms stay away long enough tomorrow,  I'll pull the plane out of the garage and flip it, then begin gluing foam around the bottom leading and trailing edges. Beginning to get excited about my progress, and I think I've figured out how I'll do my wing tips next.
Continued in Outer Wings (Part 4)

Outer Wings (Part 1)

I decided I couldn't wait on my landing gear legs to start my wings, so I bolted them up and started gluing foam in place for the leading and trailing edges.

Once it was all glued in place, I started sanding. I sanded grooves in the top, then used a hand power planer to get close to the final shape. I began sanding with a long piece of aluminum angle and some sandpaper attached to it, but decided I needed coarser stuff. I'll be picking up some more paper, then going back at it.

Continued in Outer Wings (Part 2)