Wing Tip Lights

While waiting for the fuselage kit to ship from the Van's factory in Oregon I still had a few things left to do on the wings, namely adding on the fiberglass wing tip light extensions, match drilling rivet holes, making the wire connections, and installing the wing tip nav-strobe lights.  This actually took me a while, although the actual hurdles were mostly mental ones having to transition from working with metal to working with fiberglass and epoxy resin.  To start with, the fiberglass wing tip light extensions were over-sized from the factory molds and had to be trimmed and sanded down to a barely-there scribe line on the fiberglass.  Rivet holes were then drilled at various locations around the outside edges of the fiberglass extension, and then those holes were used to guide rivet holes into the wing tip close-out skin.  After that, any gaps along the edge of the wing tip edge rib where the extensions wrap around is filled with an epoxy-flocking fiber mixture called flox.  Flock + epoxy = Flox.  Cute huh?  On the right wing the gap was mostly at the front end of the extension, and on the left wing it mostly at the aft end.  I'm not sure if the gaps are due to irregularities in the factory fiberglass molds or what.  I wouldn't rule out first-time builder error, but I did try to sand it so that it matched the edge rib as close as I could, which required some trial and error fit-sanding.  Here's what the gap on the right wing tip extension looked like (wing is upside-down, btw):

Flocking fibers, or "flock" are cotton fibers ground up into a flour and not available locally.  Only a few tablespoons of the stuff were needed to fluff up the two-part epoxy I picked up at Home Depot to the desired consistency for use on the extensions but the smallest amount you can get from Aircraft Spruce is one pound, which is probably more than I'll need for the whole plane.  Fortunately it's not very expensive.  As usual shipping from AS cost more than the product.

Here's everything needed for the flox work - car wax, popsicle sticks, table spoon, modeling clay... the usual high-tech airplane builder stuff.
 
So what's the car wax for?  It's a release agent.  It keeps the flox from sticking to the aluminum wing skins and wing-tip rib while hardening and works pretty well.  The picture below shows the stuff smeared all over the wing tip rib.


According to the plans, a small dollop of modeling clay is used to create a recess in the flox for a nut used to fasten the bracket for the wing tip light.  My daughter had some left over from one of her school projects last year, so I didn't have to buy any, but it was a little dry.  So I mixed in some water and waited a couple days and it was ready to use.  Here's where the dollop is placed on the fiberglass extension:

Did I get it in right shape and place?  Not exactly, but it was close enough to be able to get a nut on the back of the nav-light attach bracket with the designated screw, and that's what counts.  I probably shouldn't have made it quite so high ("proud") off the fiberglass 'cause I think it got nudged and smooshed out-of-position a little when I cleco'd the fiberglass extension in place.

Here's how it turned out after adding the flox, letting it harden, and digging out the clay with a small screw driver:

Not as nice as the plans photo, but I guess it'll work.  The two-part epoxy I used had a five-minute set time after mixing the hardener so I didn't have time to make it purty before attaching the extension onto the wing skin with clecos.  Since there is so little time once you mix the two-part epoxy to start the chemical reaction, I couldn't take any pictures.  But all there is to it really is to use a popcicle stick to mix and spread the flox along the edge like peanut butter, cleco the extension on, wipe away any drips, and wait 24 hours.

After the flox hardens, the bottom* rivet holes are drilled, a hole is drilled and filed to pass-thru the connector for the electrical wires, and holes are drilled** for the bracket screws.


*They're actually the top holes - the wing is upside down.

** Be careful!  The holes you want for the bracket screws may not be exactly where the dimple marks in the fiberglass ext. say they should be.

Male and female wiring connectors are attached to the wires coming out of the nav light and wing tip.  More micro-fit pins (male and female).  Had to use a magnifying glass for those.  My eyes just keep getting worse and worse.  I am getting better at crimping micro-fit pins though.  All pin connections were tested with a really good pull on the wire.

With the wiring connected the $400-plus (each!) nav-light is attached to its mounting bracket with a set screw.  Hope I never break this thing - the CFO would kill me.

And here is the right wing, the side that also has the landing light.  The position of the light on the extension turned out slightly better than the left wing, so I hope that's the side that gets scrutinized by other RV builders.


Here's another couple pictures of the right wing extension.  A little blurry, but see how the body of the nav-light makes a smooth transition with the fiberglass extension, which itself transitions smoothly onto the wing skin?

And the ugly gap I showed you at the top of this post?  It's filled in quite nicely.

There's one more task before riveting the light and light extension onto the skin and that's to mask and then caulk a small bead around the edges of the fiberglass extension with a product called ProSeal.  I'm holding off on that step because 1) I don't have any, 2) it's relatively expensive, 3) it doesn't keep very long, and 4) I only need a tiny bit to finish the wing tip lights.  It's kinda disappointing that I can't finish this final task before hanging the wings back up on their ceiling straps, cleaning up, and starting the fuselage kit next week, but that's how it goes sometimes.  If any Sacramento-area (or Davis) RV builders could help a poor airplane builder out with an ounce or two of ProSeal, please let me know.