Sunday, September 13, 2015

Wing Spars

I decided to take advantage of the warm weather and get as much fiberglass work done as possible. Since I can't build the cowl until I have the engine mounted, and I can't build the turtledeck until I at least decide what I want to do for a canopy, the wings were next. The wings consist of two wooden spars that span the length of the wing, foam glued to the spars and shaped to the airfoil, and fiberglass covering everything. The spars attach to the fuselage by way of steel fittings and bolts. I built a handful of stands to adjust and hold the spars where I needed them. Bolts and internal nuts allowed me to raise and lower the stands to achieve the desired result. Because of space constraints, I have to build one wing at a time. First order of business was the front spar. For this particular wing design, I needed to raise the bottom tip of the spar 5" above the bottom root of the spar. Once the spar was in the correct location, I attached the outboard wing attach fittings (WAFs) to the inboard WAFs, positioned the outboard WAFs where I wanted them on the spar, and clamped them on tight.

After checking my height and dihedral again, I began using a jig to drill straight through the spar for the WAF bolts. After the holes were drilled, bolts, washers and nuts were inserted and torqued.

Next, the rear spar. This wing is designed with 3˚ of washout, from 3.5˚ at the root to 0.5˚ at the tip. In order to achieve this, a plywood template was nailed onto the forward spar, then onto the rear spar, in the proper locations. The rear spar was then adjusted until the template showed 0.5˚ along the chord line. I then turned my attention to the root end of the rear spar, lining it up with the fuselage. I had to adjust the root and tip a few times to get it perfect. The next step was bending the rear WAFs to compensate for the angle of the rear spar. Once these lined up well with the spar and the inboard WAF, they were attached the same way the forward WAFs were.

The plywood template that's not attached will be attached at the root prior to gluing the foam in, and I'll shape the foam to those templates.

The final adjustment was reaming the WAF to WAF holes to the correct size. Each wing is held on by 4 bolts, and any amount of slop at the WAFs means play at the wing tip. I selected bolts that were the same size according to my calipers, then ordered reamers that were .001 smaller. This gave me a little wiggle room, since I'd be reaming with a cordless drill. Using a jig, I was able to (CAREFULLY!) drill and then ream the holes to exactly the size I wanted. The bolts were then inserted and secured. I'm using socket head cap screws and captive nuts, so I only need small holes drilled in my wings for the bolts to be inserted. Once the rest of my hardware shows up I'll be making a plate to rivet the nuts to. After that, it's on to foam and fiberglass.

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