The Barn Find Build

[jrevens]

Good thinking Eric... Just my opinion, but I think that slotting those particular holes would be fine. It wouldn't hurt to run that by Kitfox for their opinion also. Heck, they might even say that rivets are OK, but if it was my airplane I'd want the bolts.

[Eric Page]

Is it possible you could use something like these, Eric?

MS16998 (NAS1351-3) & MS21042

See below.

The AN525 pan-head screw is also a structural screw that could be used with the low profile nuts.

You could also use clevis pins with a washer and cotter pins.

I'm not sure that clevis and cotter pins would be any stronger than a steel rivet. Probably less...

Good thinking Eric... Just my opinion, but I think that slotting those particular holes would be fine. It wouldn't hurt to run that by Kitfox for their opinion also. Heck, they might even say that rivets are OK, but if it was my airplane I'd want the bolts.

I can certainly check with the factory. Who should I try to reach? John or Brandon?

I grabbed one of the socket head cap screws from the control column stops and put it through the "L" to show what I'm up against. That's probably the fastener with the smallest head diameter, and even it won't sit down flush.

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Underneath, you can see that the weld radius is right next to the bolt threads (for scale, that's a 10-32 bolt).

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It looks like I have enough edge margin on the fuselage tab to slot the hole a little bit. I could also grind a tiny bit of the weld away; just enough to give it a square edge that could stop a nut from rotating, then I could tighten it from above. What do you guys think?

[109JB]

Make a radiused washer.

On the bottom a short piece of bushing stock.

[Eric Page]

Today I started out by test fitting a bubble to a door frame, to confirm @alexM's idea that mounting tape will cover most of the holes. Indeed, the bubble contacts the door frame all the way around the perimeter, leaving only the holes in the center bar needing to be welded (plus the holes from the original latch bracket).

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With that knowledge in hand, I took the frames over to the welder's shop and dropped them off with marks showing which holes to weld and which to ignore. I don't have an ETA for their return, but I won't need them for quite awhile.

When I got back, I masked off the brake calipers, cleaned them with acetone and gave them a shot of primer. Later, when that was dry, I painted them to match the rest of the airframe. The only reason I did this is because I had to sand them quite aggressively to remove corrosion pitting, so they looked pretty rough, with only small areas of their original finish intact and mostly bare metal showing.

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I put the new elevator push-pull tube next to the old one, and using the fret marks from the mid-fuselage bushing as a guide, I masked an area on the new tube about 2" longer than those marks, then used acetone to remove primer in that area.

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With the bearing area laid bare, I used the brush-on method to Alumiprep/Alodine that ~6" area. I didn't get any photos of that due to the need to work quickly. With that done, I reversed the masking so that the bare area was covered, sprayed primer up to the tape line (and on a few other spots that got scratched during all this futzing around), and set it aside to dry.

Having discovered that primer is pretty delicate stuff and easy to scratch, once the tube was dry I painted it gloss black like everything else. So, I'm left with a tube that matches the fuselage and other control hardware, but with a bare, Alodined section (which will be greased) where it will slide through the mid-fuselage bushing.

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Some reamers have arrived in the last couple of days, so I went back to the plastic "bearings" in the rudder pedal mounting tubes. I managed to get a good fit in fairly short order, except for one of them that seems to have been warped during welding. In the end the bolts all rotate easily and don't wobble.

For the life of me, I can't fathom why that assembly was designed with that ridiculous 4" plastic bearing. If the tube gets warped a bit during welding (as one of mine did), it bends the plastic bearing along its length, making it extremely difficult to ream to a straight bore. It's a silly PITA that could easily be eliminated by putting a short 3/16" ID Oilite bronze bushing at each end of the pedal mounting tube. Sand the OD of the bushing to fit the tube, assemble, done.

Anyway, the rudder pedal section is ready to reinstall, once I get the front floorboard rehabilitated (rough varnish job and some mold spots).

[Eric Page]

Make a radiused washer.

On the bottom a short piece of bushing stock.

Yeah, that could definitely work too. I'll have a good think about it. Either way it means ordering hardware...

[alexM]

Make a radiused washer.

On the bottom a short piece of bushing stock.

This. Eric I'm looking at your image and if you can use a socket head cap screw and grind a radius on one edge of a washer so it lays in the radius you wont be the first guy that did that. But that only solves the top side.

On the bottom side? That's a lot of damn weld bead but I cringe at the idea of grinding a weld down. I tend to agree with the slot suggestion. That way you retain the full strength of the AN3 bolts in most directions, which seems better than hollow rivets.

[rv9ralph]

Ok, I'm going to weigh in on the suggestions to correct the issue to attach the angle support on the right end of the control mechanism.

On the bottom side where the weld makes using a nut difficult. You could make a sleve out of 4130 about a quarter inch long to slip over a longer AN3 bolt to allow enough room to fit a nut/washer.

On the top side, fabricate a new angle for the end bracket, drilling the holes further out on the flange of the angle to allow a nut and washer for the AN4 pivot bolt.

Just my $.02.

Ralph

[jrevens]

I think the sleeve idea is a good possibility too, and it's also been suggested by 109JB. It could probably be shorter than 1/4". Relocating the holes in a new angle piece won't work unless the spacer in the middle of the assembly of 3 pieces can possibly be eliminated or a thinner one used. Spot facing those holes on the existing angle with a small counterbore would work also.

[Eric Page]

Thanks, guys. I really appreciate all the helpful suggestions on this. Based on all the input, here's what I'm thinking:

I have a friend nearby with a shop that's well-equipped with metal working tools. How about I take the assembly over there and put it on his mill. Using an endmill a hair larger than the diameter of an AN3 bolt head, I'll create two flats on top of the "L" angle, centered on the bolt holes, so the bolts can sit flush (this should remove a very small amount of aluminum from the inside bend radius of the angle, only where the bolts are located). When that's done, I can smooth the edges of the cut with a small grinding stone in the Dremel.

On the bottom, under the welded tabs, I'll use short steel spacers made from 3/16" ID 4130 tube to gain enough clearance from the weld radii to install washers and AN364 nuts. If necessary, I can put a small chamfer on the spacers to clear the weld, leaving sufficient end surface that it will sit flat and not tend to tip under nut tension.

Kind of like this, except perhaps only 1/3 of the circumference, but probably a bit past the inside diameter. Essentially an inclined plane bisecting a "corner" of one end at a 45 deg angle.

ChamferedTube.jpg

Thoughts?

[Eric Page]

Low effort day today, but progress was made. More of fixing the first builder's messes, sadly. This time I broke out the random orbit sander again and cleaned up the floor boards in preparation for re-varnishing the wood and subsequent installation of the rudder pedal assembly. The floor boards were quite rough (not sanded before varnishing?), they had significant mold staining, the varnish had runs in it, and there were drops of Poly-Tack in many places. Typical before and after pictures follow.

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Once I have the bottom rib in the tail replaced (it was removed for welding the tail post reinforcement), the new elevator ribs installed and the pitot mount figured out, then the woodworking will be finished and I can varnish everything at once.

Merry Christmas, everyone!