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Wingtip Fitting

1 September 2010: Fitting the wingtip. This was one of those "grab a quick hour to work on the Kitfox" days. Because of that I did not take any photos. I trimmed the edges according to the instructions in the builders manual. On the day I ordered the kit I remember sitting in the office at Kitfox Aircraft talking to John McBean. When I mentioned that I intended to read the builder's manual before I receive the kit he made it clear to me that there will be things that I will not understand until I have the parts in my hand. Today brought all that home to me. I couldn't envision what the instructions wanted me to do until I grabbed the part and stuck in on the end of the wing. The instructions became immediately clear to me.


4 September 2010: My workstation. During past projects I've discovered the hard way that if you're going to do a good job from an awkward position you have to make yourself as comfortable as possible. I'm drilling upward into the end rib. This is as comfortable as I can get and I'm hoping for the best.






Drilling and clecoing the aluminum mounting strips





Positioning the wingtip with zip ties





The mounting holes are carefully spotted and then drilled and clecoed. You will notice that the aft end of the wingtip extends beyond the trailing edge. This has to be trimmed.







I've allowed enough overlap at the forward part of the wingtip to accommodate the layers of fabric that will eventually be over the spar. A guess on my part.





Trimming the tail. I dug out my old dovetail saw and cut the tail flush with the trailing edge. After that I filled it with epoxy.






5 September 2010: Enlarging the mounting holes. I drilled out the holes to the exact size of the mounting screws. The black clecos only approximate the correct size so, where I could, I used the screws backed with hardware store nuts to keep the wingtip in exact position as I drilled.





Drilling the rivet holes for the nutplates.





I used a rivet squeezer to dimple and set the solid flush rivets.







A "Well Duh!" moment. It should have been obvious that the last nutplate on the top would conflict with the one on the bottom. But I installed them anyway. One has to go. As you can see I removed the one the bottom and I'm mulling over what I want to do.





6 September 2010: The mounting strips are complete.







Shaping the trailing edge: I'm fully aware that if I cut a "V" on the outside edge I could have the wingtip terminate in a sharp edge but I feel that my arrangement is more robust and won't hurt so much when I run into the wingtip with my head.





The builder's manual says, "Carefully countersink the capstrips on the wood ribs for the flush head pop rivets." Past experience tells me that using a power drill is dangerous with thin plywood. I choose to do this by hand. The riveting will wait until the fabric is in place and before the final taping.





11 September 2010: Fabricating the Fabric Reinforcement Plates. First, it's confession time. I cut the first piece the wrong size and, as Murphy would have it, I cut it too small. So, before I make the parts for the left wing, I'll have to give John and Debra a call for an extra piece of aluminum. These plates are to reinforce the fabric around the lift strut brackets.


Another on of my makeshift jigs. This one allows me to make the inside cut.






The finished parts.





12 September 2010: Flaperon Assembly


I've decided to work on both flaperons. I started by installing solid, round-headed rivets along the trailing edge. The assembly manual suggests flush rivets but, since the airflow at the trailing edge is typically turbulent, I see no advantage to flush rivets. I stabilize the flaperon with shot bag scuba weights and use my rivet squeezer.





15 September 2010: Riveting is finished. I've turned off the flash to allow the rivets to stand out in the shine of the aluminum skin.







19 September 2010: Drain holes. The slots on the upper skin that accommodate the hinges will allow water to enter. For this reason drain holes are drilled into the bottom skin. They are located at a very thin part of the airfoil. For that reason I've placed a drill stop very "high and tight" on the bit.




Installing the Inboard End Ribs.





25 September 2010: Flaperon tips. The kit provides a block of foam but the builder's manual offers the option of using balsa. I chose the balsa.


  I  held a block of balsa against the end and drew around the outline of the flaperon. With Sketchup I generated a curve and transferred it to the balsa.




I started the shaping process by carving "facets" with a wood rasp. I then rounded them to the final shape with sandpaper. Finally I glued them in place. There is still a bit of work to do to achieve  a final finish.




26 September 2010: Spotting the location of the flaperon mass balance weights. I located and drilled the rivet holes for the mass balance weights. Since control surfaces with the counterweights installed are awkward to handle I will wait to do the final installation just before painting.



28 September 2010: Making the Flaperon Clamping Fixtures. These are necessary in order to be able to align the control horns. I was able to find 2X2 stock made of tulip poplar.




I countersunk the mounting screws. After that I spotted the shape of the cutout using the template provided with the kit. The finished clamp worked, but the buried screws and nuts gave me problems.




1 October 2010: I redid my previous work. I countersunk the heads of the screws on the bottom of the clamps. After that I let the screws protrude through the top where the nut will not annoy me by rotating in a countersunk hole.




3 October 2010: I began to install the control horns. I first cleaned the threaded fitting with a tap. The first photo shows duct tape wrapped around the shaft of the horn. In order to fit the shim I have to remove some powder coating. The tape shows me exactly how much to remove. The second photo shows the shim in place.



The bearing halves trimmed to fit.





The first clecos. The post-it note is marked with the exact dimension above the base. When that was established I gathered my courage and drilled the first hole. When all the holes were clecoed I turned my attention to the left control horn. For some unexplainable reason the shim presented me with quite a lot of resistance that I didn't experience with the right control horn. After a bit of struggling I decided to stop before I do something rash. I'll resume my attack on this problem on the next session.



6 October 2010: Done! By taking time to think through my problem I was able to come up with a solution. I colored the shim with a black marker and used a fine file to remove just enough to take off the ink. This assured me that I'm removing a measured and uniform amount. Two applications of this and I was able to make the shim fit neither too tight nor too loose. I fit the left control horn into position. Through all of this I forgot to take pictures. Sorry!

The instructions indicate that I should wait to finally rivet the horns in place after painting. This is to avoid fouling the bearings with paint. I may regret it, but, since I had such difficulty getting them in place, I went ahead and drove the rivets. I'll have to do some careful masking when I get to painting the flaperons.



8 October 2010: Installation of Flaperon Reinforcement Brackets. I made a cardboard template to spot the rivet holes. The drilling went quickly and I was soon bonding and riveting the brackets in place.




Continuing, I bolted the Flaperon Brackets on the hinges. Tomorrow I'll attempt to "hang" the flaperon on the wing.





9 October 2010: Hanging the flaperon. I attached the flaperon to the wing with spring clamps on the end brackets. I then spotted, drilled and clecoed all the rivet holes. I will permanently attach the flaperon during final assembly after the wing is covered and painted.







Preparing the Ring Wing for Covering


15 October 2010: Reinforcing the Trailing Edge. To allow the fabric to be heat-shrunk to 350 degrees the trailing edge has to be stiffened by bonding aluminum tubing in the gaps.







22 October 2010: Smoothing the edges. Every Fall the demand for my services as a musician increases. I love being a musician and I love being an airplane builder so I struggle to find time for both. Today I sanded the top of the fuel tank and rounded edges that will come in contact with the fabric.






29 October 2010: Super-Fil, Varnish, and Paint: I continue preparing the wing by filling the gaps with Super-Fil, varnishing the remaining woodwork, and began priming the metal with White Poly-Fiber epoxy. A primary concern with an airplane in Florida is corrosion, which is the reason for the primer. It's not very adaptable for brush application but, since I will not be applying a finish coat over it I do my best and accept the brush marks. It will take several coats.




3 - 5 November 2010: Continued priming and varnishing.



14 - 17 November 2010: More priming. Despite the brush marks I try to produce a "workmanlike" job. My schedule is starting to ease giving me more time for airplane building.




25 - 28 November 2010: Continued priming!


30 November 2010: Priming finished.



1 December 2010: Compliance with Service Bulletin 60. Recently published SB 60 requires a more aggressive procedure when flushing the fuel tank. Today I flushed the tank 3 times with acetone.




5 December 2010: The right wing is ready for covering. I rounded the last of the sharp edges and applied anti-chafe tape where needed. (Such as over these rivets.)




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