The Barn Find Build

[Eric Page]

Today I worked on getting the rudder torque tube assembly put back together properly. I didn't get a photo of them, but the inner torque tubes were in quite a state. It appeared that the first builder adjusted fitment of the outer tubes by scraping the powder coat on the inner tubes. It was anything but smooth, and before I disassembled them they were very difficult to move. The copilot side was so stiff that it could actually hold position against the return springs.

So, I had some work to do. I started by sanding the powder coat on the inner tubes axially until I achieved a smooth surface that allowed the larger outer tubes to slide on easily.

This also required smoothing the inside bore of the large outer tubes. I found a suitable length of aluminum rod in the servo mounting kit, wrapped some 220 grit around it, chucked it in the drill press and went to work removing quite a bit of powder coat overspray from inside the tube.

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I then started work on fitting the bearings. I ordered new bearings from Kitfox because the originals were in very poor condition. The build manual says to cut them so you can get them over the tube, but I didn't really see the point since they slid on from the end with a little bit of twisting. I fine-tuned the powder coat on the inner tubes until the bearings spun smoothly with light fingertip pressure, then tried the whole assembly to check for smooth rotation. It took several iterations of sanding, assembly, testing, disassembly, sanding, etc., but I got a nice buttery action on both sides.

One of the outer tubes had a very slight bend to it. I'm not sure if it was like this from the factory, or if it happened during welding. Fortunately the bend was so slight that I was able to get it to fit nicely by sanding powder coat on opposite sides at each end.

During all of this work I discovered that the new bearings have a thicker flange than the originals from 1995.

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This meant that not only did I not have the required 1/32" of play on the large outer tubes, I couldn't even get the rivet holes to line up. So, I went after the bearing flanges with some 120 grit on a piece of plywood. More sand, assemble, test, disassemble, sand...

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In the end I got a very nice fit-up on both sides, with no resistance to rotation with the assemblies clecoed together. I wish the parts looked better, but overall I'm very happy with the result.

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I'll be in town tomorrow, so I'll grab a tub of grease for the bearings, then I'll be able to pull my first rivet in anger!

[airlina]

The true test at this stage comes when you mount that assembly and hope for that smooth operation that you worked so hard to achieve. can't tell you how many times I had to pull them in and out for more sanding after bolt down in the footwells. This is a common occurrence so keep your fingers crossed. Still remember this from my build 20 years ago as a frustrating part of the process. Bruce N199CL

[alexM]

The true test at this stage comes when you mount that assembly and hope for that smooth operation that you worked so hard to achieve. can't tell you how many times I had to pull them in and out for more sanding after bolt down in the footwells. This is a common occurrence so keep your fingers crossed. Still remember this from my build 20 years ago as a frustrating part of the process. Bruce N199CL

Agreed. It ain't over until they're torqued in place in the plane.

[Eric Page]

The true test at this stage comes when you mount that assembly and hope for that smooth operation that you worked so hard to achieve. can't tell you how many times I had to pull them in and out for more sanding after bolt down in the footwells. This is a common occurrence so keep your fingers crossed. Still remember this from my build 20 years ago as a frustrating part of the process. Bruce N199CL

Agreed. It ain't over until they're torqued in place in the plane.

Where is the additional sanding going to take place? Should I not rivet these assemblies together until I fit them in the plane, or does the additional sanding happen on the mounting channels in the fuselage?

I am planning to use the floating nut plates like you did, Alex, which I presume eases alignment to some degree.

[alexM]

Where is the additional sanding going to take place? Should I not rivet these assemblies together until I fit them in the plane, or does the additional sanding happen on the mounting channels in the fuselage?

I am planning to use the floating nut plates like you did, Alex, which I presume eases alignment to some degree.

Well you're doing it in the right order. Obviously if they don't move freely on your bench they won't cure themselves when installed in the plane. One of the previous builders had sanded on my plastic bearings some, but there isn't much you can sand before they're paper thin.

The problem as I see it is that the two ends of each pair of rudder pedal assemblies are not co-axial (a theoretical line through one bolt should pass exactly through the middle axis of the bolt in the other bearing). In my case it was clearly because the welding of the reinforcement gussets caused the tubes to curve. You'll recall my fixture to show them some love and straighten them out.

Other aggravating conditions are the plywood floor included in the stack up and of course variations in the welded fuselage and the builder's ability to drill perfect holes. Those will become obvious when you install the assemblies in the plane. They may pivot fine but bind up as you torque the fasteners.

I'm not going to say it's a bad design because clearly every builder gets through it (even this knuckle dragger), but at one point I did some bar napkin sketches that would use a spherical bearing on one end. It would be tolerant of variation and eliminate the need for several install/check/remove/fiddle, rinse/repeat cycles.

The floating nutplates I installed don't really reduce the variation from the above conditions. They can make up for a (very) little error in drilling the holes in the fuselage, and assure that you don't cross thread a fastener when installing them. I chose them primarily eliminate the need to mess with the cowl, firewall with the flap that extends back under the rudder pedals, etc if the pedals have to come out for any reason.

EDIT: I actually need to clarify something. Those thin bearings that you noted are supposed to be split can be worked out on the bench and allow you to rivet the inner torque tubes in place. It is the ends of the entire assembly which will bind when you install in the plane. Once I sanded the powder coating from inside the ends of the tubes, the only place left to get freedom of motion is to sand the end bearings (the fat plugs with a bolt through them).

Use the trick where you chuck them up in your fancy drill press and sand the OD until they slip inside the tubes. Pro tip, those things expand like a chinese finger puzzle when torqued. So torque them to spec with the bolt going through them, and chuck that assembly up in your drill press to sand them down. Once those spin freely in the pedal assemblies, then you're ready to fit them in the plane.

[Eric Page]

Well you're doing it in the right order. Obviously if they don't move freely on your bench they won't cure themselves when installed in the plane. One of the previous builders had sanded on my plastic bearings some, but there isn't much you can sand before they're paper thin.

Indeed. Two of the originals had been sanded to the point that they had holes in them. Meanwhile, there was still ample rough powder coat on the metal parts. I didn't actually have to remove any​ material from the OD of the new bearings.

Other aggravating conditions are the plywood floor included in the stack up and of course variations in the welded fuselage and the builder's ability to drill perfect holes. Those will become obvious when you install the assemblies in the plane. They may pivot fine but bind up as you torque the fasteners.

Got it. If the mounting tabs aren't at exactly the same height, or there's variation in the thickness of the plywood or varnish, or the holes in the mounting brackets aren't at exactly the same height, then the bolts won't be axially aligned, and hey presto: binding.

...at one point I did some bar napkin sketches that would use a spherical bearing on one end.

Hell, I'd buy one of those, and I'm a real cheapskate!

The floating nutplates I installed don't really reduce the variation from the above conditions.

Yeah, I see that now. They just reduce criticality of hole location a bit and ease maintenance in the future.

Use the trick where you chuck them up in your fancy drill press and sand the OD until they slip inside the tubes. Pro tip, those things expand like a chinese finger puzzle when torqued. So torque them to spec with the bolt going through them, and chuck that assembly up in your drill press to sand them down. Once those spin freely in the pedal assemblies, then you're ready to fit them in the plane.

Now that's a useful piece of consumer advice. It wouldn't have occurred to me to torque them to spec before sanding, but it's obvious if you think about it. I'll definitely keep that in mind. Thanks, Alex.

[109JB]

I'll start by saying that I'm not exactly sure how it is done on newer model Kitfoxes, so what I did may be totally not applicable. That said, working on my Kitfox 4 project I too was unhappy with the freedom with which the rudder pedals moved. The method used on the K4 is like the top sketch in the attached picture. It sounds like the newer model Kifoxes are at least similar. I dorked around with the stock setup for a while and couldn't get it working to my satisfaction so I did the modification in the lower sketch. Basically I took a piece of 5/16" x 0.035 wall 4130 tube (green in sketch) and cut it to length to make an axle for the pedals. I reamed the ends slightly to 1/4" ID, and took a couple bolts and cut the heads off (blue) and rosette welded them at the white dot into the reamed 5/16" tube. I then bored out the stock plastic bearings (Orange) for a good bearing fit on the 5/16" tube and voila. Now I just bolt it in, tighten everything as tight as I want and the pedals still move very freely, falling under their own weight but with no slop to speak of.

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[Eric Page]

Wow, that's a really clever idea, John. I'll give mine a try as-is just to see if I'm lucky that day, but if I start having problems I'll come back to your method for sure. Thank you!

[Eric Page]

Today I started by getting the control column mounting block out of the paint stripper and cleaning it up. I soon discovered that it wasn't going to come clean without complete disassembly, so I drilled out four rivets and knocked it apart. The two smaller aluminum parts went back in the stripper bath, and I set about making the large part look presentable. I did some hand work with 220-grit sandpaper, then used the Scotch-Brite wheel to smooth it out as much as I could. It still has some scratches that I can't remove without deep sanding, so they'll just have to stay. Since it's not a structural part, I'm not going to lose any sleep over it.

The doors for my plane had already been assembled and installed by the first builder, but I wasn't happy with their appearance. A few of the rivets didn't line up with the others or weren't spaced evenly, the window plastic was scratched and yellowed, and I wasn't happy with having half the door covered in fiberglass (particularly since the knucklehead riveted Lexan over the edge of it before it was painted!).

Don't be fooled by my reflection in the Lexan; the windows don't bear close scrutiny.

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So, I ordered bubble doors from Kitfox. They arrived (along with a new windshield; that's a mess too) a couple of days ago, minus the frames. I contacted Kitfox and was somewhat disappointed to learn that the bubble doors I thought were a complete kit are in fact only the plastic bubbles.

With that knowledge in hand, and a quote of $490 delivered for two new frames, I contacted the guy who did the welding on my fuselage and rudder tubes. He said he wouldn't charge more than $100 to plug weld all the rivet holes in my door frames, so today's next project was drilling 89 rivets out of the first door. That removed the Lexan and fiberglass panels, as well as the small aluminum hinge mounting plates on the top rail.

Since the door latch bracket was also held on with Scotch-Weld, I first attacked it with a cutting disc on my angle grinder to get rid of the protruding parts, then switched to a grinding disc. My plan was to carefully grind it off the frame, but I got lucky: the heat of grinding made the powder coat under the Scotch-Weld boil, so it pulled off easily!

I was about to celebrate when I realized that I now had a door frame full of rivet stems. Fortunately, I just had to open up two rivet holes to 1/4", shake the frame vigorously for a couple of minutes, and they all fell out. This left me with a bare door frame that looks pretty second hand.

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I'll need a fine grit flap disc to clean up the remaining Scotch-Weld and remove powder coat in preparation for welding. Finally, I cleaned up the edges of the hinge mounting plates, put them and the control column block through the Alumiprep/Alodine treatment and called it a night.

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Tomorrow should see the other parts for the control column block cleaned, Alodined and reassembled, and the other door frame stripped. I forgot to buy grease yesterday, so I couldn't rivet the rudder torque tubes back together yet. I'll get that done early next week.

[bbs428]

Some serious elbow grease being applied there Eric.

Those used parts are looking great!