November 2013 Archives

I took a new role at work, so I've been pretty swamped over the last few weeks.  I wanted to make some progress this weekend though, so I applied a layer of filler to the top of the rudder on both sides.



I also sanded down the filler that I applied to the right elevator.



I sanded the filler on the horizontal stabilizer...



...as well as the filler on the left elevator.  I still have a bunch more filler to apply and sand down, but I can see the light at the end of the tunnel for the empennage fairings.



Sanded Rudder Top Fairing

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I sanded the filler I applied to the top of the rudder fairing.  I still need to mount this to the vertical stabilizer and fair these together, but this should be pretty close.



I installed one of the hinges to the outboard end of the wings a long time ago (like two years!).  Since I had practically the whole day free to work on the plane, I decided to wrap these up so that I could start fitting the wingtips.  Afterward, I started fitting the left wingtip.  I trimmed the flange so that it will slip into place, but had to stop before drilling it to the hinges.



Drilled Left Wingtip

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In preparation for drilling the wingtip to the hinges, I cut a piece of XPS foam and inserted it between the hinges to keep them from flexing inward when drilling.



I installed the wingtip and taped it in place with some clear packing tape.  I drew a line 7/8" outboard of the row of rivets holding the hinge to the wing and marked lines even with all of those rivets.



Finally, I drilled all of the holes to lock in the wingtip's position.



Drilled Right Wingtip

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I trimmed and drilled the right wingtip tonight.  This went substantially faster than the left side.



I drilled additional holes in the hinges that will rivet to the wingtip so that I can form some epoxy/flox "rivets" between the aluminum rivets.



I countersunk the right wingtip and then riveted the hinges on.  You can see the epoxy/flox "rivets" here.  Afterward, I spent a little time cleaning out all of the epoxy that squeezed out around the hinge eyes so that it wont interferere with installing the hinge on the wing.



I positioned the aileron in the neutral position and then used a straightedge to mark the trailing edge of the wingtip.  For some reason, it's made a little long and needs to be trimmed about 1/4".  I cut off the excess and then filed back to the line.



The trailing edge of the wingtip was now much thicker than the trailing edge of the aileron, so I cut the web that was joining the upper and lower pieces.  Somehow, this caused the trailing edge of the wingtip to no longer be in line with the aileron, so I had to split part way up the side as well to allow it to shift back into position.



I mixed up some epoxy/flox and glued the outboard end of the trailing edge back together with a little preload in the direction the tip needed to move to be inline with the aileron.



Unfortunately the duct tape I was using yesterday came loose before the epoxy had a chance to cure, so I had to split the wingtip again and grind out all of the cured epoxy.  I reglued it and used quite a bit more duct tape and some clamps to ensure it won't release before the epoxy has cured.



The trailing edge glueup turned out perfectly.  The trailing edge is perfectly inline with the aileron.  I still need to glue up the trailing edge, but I wanted to reinforce the wingtips before doing so.

The wingtips need reinforcement since they can easily be depressed.  This is because the wingtips just have a thin layer of fiberglass and no core material like the cowl to stiffen it.  Many builders install foam ribs or dowels, but I wanted to try reinforcing the whole surface.  I picked up some Coremat from Tap Plastics and bonded it to the bottom of the right wingtip and then added a couple of layers of 8.9oz glass.



Afterward, I installed the wingtip so that the fiberglass will cure with the right curvature.  This took way longer than expected, and I still have the upper surface of the right wingtip and both sides of the left wingtip to do.  You can see the pattern I made for the fiberglass hanging over the other wingtip.



Well, my attempt at reinforcing the bottom of the wingtip was a failure.  The Coremat didn't come with instructions, and apparently it needs to be saturated with epoxy in order to work.  I managed to pop the glass off and the Coremat released pretty easily from the inside surface of the wingtip.  I tried saturating the Coremat and reinstalling it, but it took a shocking amount of epoxy.  It would have easily weighed a couple of pounds, and I would need to do the same thing on the top and both surfaces of the other wingtip.  This would be far too much weight to add to the plane just to stiffen up the wingtips.



Before calling it quits for the evening, I decided to apply some filler to the left side of the rudder.  I mixed up the epoxy/microlight a little bit thinner tonight, so it should self-level somewhat which will make it easier to sand.



I decided to reinforce the wingtips by glassing in some foam rod.  I mixed up some epoxy/microlight/flox and bonded the rod to the inside of the wingtip and formed a fillet along both sides.  Afterward, I layed up a couple of layers of glass over each rod and then reinstalled the wingtip to put the right curvature in the skin.



I sanded down the filler on the left side of the rudder and then applied some filler to the right side.  I also removed the foam from the fiberglass tip at the top of the vertical stabilizer.  I need to reshape the tip a bit to fair it in with the rudder.



Here's the cured fiberglass over the foam rod.  This worked great.  It's incredibly light (just a couple of ounces per rod at the most), and added a surprising amount of stiffness to the wingtip.  The Coremat I was going to add would have made it stiffer for sure (probably close to the stiffness of the cowl), but that would have been overkill.  The wingtips simply do not need to be that strong and the weight penalty was excessive.



I've been meaning to reshape the vertical stabilizer fairing for some time.  I originally installed the foam rib based on the shape of the tip right out of the box, and not how it looked relative to the rudder horn.  Unfortunately, it turned out fatter and shorter than the rudder horn, so I needed to reshape it.  I removed the old foam rib and used a clamp to squeeze it (making it both narrower and taller).  I then used a heat gut to soften the epoxy so that it would take the new shape.  I wrapped the rib in some fiberglass which will stiffen everything up a lot.  I'll still need to add a bunch of filler to both the fairing and rudder horn and sand them at the same time to fair them together.



While that's curing, I added some foam rod and glass to the upper side of the right wingtip and then reinstalled it on the plane to set the curvature.



You can clearly see the profile of the vertical stabilizer tip and rudder tip together don't form a single continuous curve.



You can also see that the gap between them isn't uniform.  I'll fill this later to create a uniform 3/16" gap which is the same as the lower horizontal gap.



I mixed up some filler and applied it to both fairings.  You can see that I built up the rudder tip quite a bit.  I also widened the rudder horn about 1/16".  I'll sand all this down with the rudder clamped in trail so that they're perfectly faired together.



With the internal stiffeners glassed in, I could glue the trailing edge back together.  I mixed up some epoxy/flox and put a bead down the back.  I used a bunch of small spring clamps to hold the trailing edge closed while the epoxy cures.  The clamp in the back is holding a couple of scrap pieces of aluminum angles and span the gap between the aileron and wingtip ensuring that the wingtip perfectly follows the edges of the aileron.



You can also see some epoxy/flox on the outer edge of the wingtip.  I needed to add a little bit so that the outer edge of the wingtip could be filed to a straight line.



I laid out and drilled the holes for the right wingtip rib.  Getting this in the correct position was pretty easy by using the other wingtip rib with the flanges on the outside of the wingtip.  I then just slid this inside the wingtip until it was tight.  I confirmed on the wing before drilling to lock in the position.



I then added the reinforcement to the bottom side of the left wingtip.



I finished up the last of the wingtip reinforcement.  I'm super happy with how this has turned out.  It's very light and the tips are substantially stiffer.



I needed to start fairing the rudder and vertical stabilizer, but I wanted to do it on the plane since it will be at a more comfortable working height.  With the rudder bottom fairing in place though, the rudder couldn't be mounted since the fairing hits the tailwheel spring.  I measured and chopped off a chunk of the fairing.



This fits a little too tight at the front, so I'll cut off more later.  I can't just parallel the tailwheel spring though since the spring can flex quite a bit.  I need more room at the back to account for this.



I started fairing in the rudder and vertical stabilizer.  You can see that there is now a continuous curve along the top and the sides match nicely.  I need to add a little more filler in a few low spots, but this is turning out very nice.



Since the wingtip is held on with hinges, I needed a method to secure the hinge pins so that they can't come out.  I fabricated these retaining blocks out of a chunk of Delrin that I machined down to fit inside the trailing edge of the wingtip rib.  It's held on by an AN509-8 screw.



The screw screws into a nutplate mounted on the back of the rib and through the tooling hole that was already present in the rib.



In the sides of the blocks, I drilled a #43 hole and machined grooves aligned with the holes to capture the hinge pins.  I bent the aft ends of the hinge pins 90ยบ so that they will go into the holes.



Here's how they look when installed.  The hinge pins can't back out of the block because they're trapped by the flange of the rib.  The block also provides a convenient handle to extract the pins.



With those done, I primed the backside of the ribs and installed them with epoxy/flox and soft rivets.



I also sanded down the additional filler I applied yesterday.  I still need to apply some filler inside the gap, but the outside shape looks great.



I drilled the bottom of the wing for the outside air temperature probe.  I installed it in the wing, adjacent to one of the inspection plates (just to the upper left in this picture).



I also cut a small hole in the conduit here so that the OAT probe wires could exit.  You can see the 2 conductor molex connector I used here as well.  I'm honestly not sure the connector is worth the trouble since it would have to be cut off to remove the probe anyway.  It's probably better to just use a couple of butt splices to crimp the probe wires together with a service loop for future maintenance.  With this done, I think I'm done with the wings until they go to the airport.



I needed a little more filler on the front of the rudder.



...as well as the aft side of the vertical stabilizer.



After that cured, I filed and sanded it down to create a uniform 0.150" gap (the same as the lower gap under the rudder horn).



I also trimmed a little more off the bottom rudder fairing and then removed all of the gel coat around the hole in preparation for bonding a patch.  For a non-structural patch like this, removing the gel coat isn't necessary.  I did it more so that the patch would be flush with the gel coat and I wouldn't have to use as much filler to fair it in.



Finally, I added a patch made of three layers of 8.9oz/yd cloth.



To keep it tight against the fairing, I laid a piece of plastic over the patch and taped it tight.  I then taped a piece of scrap aluminum over the patch to ensure it cures totally flat.



The rudder bottom fairing patch has cured.  After filing down the high spots and giving it a quick sanding, I applied some epoxy/microlight filler.  The leading edge of the fairing also needs to be built up a bit to match the rolled leading edge of the rudder.



I also added some filer to fair in the horizontal stabilizer and elevators.  Here's the right side.



...and here's the left.



I removed the rear window because the masking tape I applied a few years ago was all dried out and stuck tight.  I used some mineral spirits to soften the adhesive and removed all of the tape.  This took much longer than expected, but I wanted to use a mild solvent to avoid damaging the plexiglass.  After reinstalling the window, I laid a line of tape to mark where the Sikaflex primer will go.



I'm going to paint the inside of the rear window where it passes over the roll bar support channel.  I've noticed on other planes that it's often fairly dusty on top of the channel, and it's pretty tight against the window, especially toward the back.



After the horizontal stabilizer and elevator filler cured, I filed and sanded it down so that they're faired together nicely.



I needed just a little bit more along the leading edges of the elevators.



I also sanded down the filler I applied to the bottom of the rudder.  There were a couple of low spots, so I added a little bit more.



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