Stephan's Sonex #1627 Builder's Log

I completed the rudder today. This involved deburring the edges and the #30 holes of the ribs as well as skins, and of course, cleaning and priming the parts. The skins were primed where it comes into contact with the ribs.

I riveted the long side of the rudder, so it would still be easy to open up the skins for the pre-cover inspection. This is required for Canadian amateur built aircraft (click here for details). The other half of the rudder will remain cleco-ed until the pre-cover inspection has been completed.

The rivets on the rudder control horn were tricky. There were 4 rivets that had interference from the adjacent rivets in the rib. I checked the plans and it appears that this is by design. It would have been better if the top holes were slightly offset so this wouldn't have been an issue. I used a hand riveter to initially pull the rivet until I could push the head flush with the skin, after that, I pulled the rivet with the pneumatic riveter.

I completed the installation of the rudder hinge and the rudder control horn. The hinge installation was a little bit tedious because the supplied piano hinge was bent for shipment causing a wave pattern along the flat edge of the hinge. I put the flat portion of the hinge between two metal rulers and squeezed it with my vice to make it as flat as possible.

I used a piece of 0.060" sheet metal as a spacer for the hinge because that is all I had available. This is slightly larger than the 0.057" that the plans call for, but I don't think it's going to matter.I used a wooden block behind the skin to put counter pressure for the drill. I first drilled the edges then the centre and then alternated between left and right outer edge until all holes were drilled.

The rudder control horn was equally tedious. I first drilled the holes in the skin as per the plans and then marked up the centre line of the flanges on the control horn and lined it up with the holes in the skin. There was a significant gap near one of the edges, but I managed to eliminate it by receeding the control horn slightly into the skin. This caused some holes to be closer to the inside edge of the control horn, but I determined that there was still enough clearance for the rivet.

I continued work on the rudder today. I made a hinge drilling jig (or guide) to help me drill the 41 holes that are required in the rudder hinge. I also cut the pre-formed rudder control stock to length and made the cut-out for the rudder control horn. I used a Dremmel Saw-Max with an aluminum oxide blade that cut the control stock as it if was butter. The cut-out was done initially with aviation snips and then with the Vixen file to clean it all up. 

The ribs were marked up with a centre line on all the flanges. I then marked up on the control stock and drilled the holes as per the plans. Once the holes were drilled in the stock, I put the rib inside of the control stock and used the holes to line up the rib with the centre line that I had drawn on it. I then drilled pilot holes in the ribs with 3/32" bit and cleco-ed everything together.

The rib at the top of the rudder had to be flush with the edge of the stock. I used a metal ruler to make sure that the rib was completely flush. I then drilled the holes and cleco-ed everything together.

It was getting late, so I did not complete the drilling of the control stock or the control horn. or installing the hinge.

The rudder drive horn assembly required a small part (-06) be made from angle stock. I initally clamped all the pieces together and used a metal ruler to make sure that all the flanges were aligned then drilled 3/32" pilot holes and cleco-ed everything together. I then up drilled everything to #30 and deburred and cleaned.

I wanted to experiment with Alumiprep and Alodine 1201 so I setup 3 baths, one with 25% solution of Alumiprep, another with a 33% solution of Alodine and finally a water bath for washing the parts. I scuffed the parts with some maroon Scotchbrite and then cleaned with alcohol and put it in the Alumiprep bath. I left it there for 3 minutes. There was still a significant amount of gas formation, which probably indicated that I had not done as thorough of a job removing the oxidization layer. 

After the Alumiprep bath, I thoroughly washed the parts and then put them in the Alodine bath. The alodine contains chromates, which are very hazardous to health, so I wore goggles, respirator and thick rubber cloves. I waited about 3 minutes and then turned the parts over for another 3 minutes. After this, the parts were washed thoroughly and blown dry with compressed air. The result was not too impressive. The parts did not appear to be uniformly anodized. There were dark spots and very light spots. It also appeared that I could easily remove the anodization by gently rubbing it with my rubber gloves.

I had already bought 4 cans of Sherwyn-Williams GBP 988 self etching primer, I'm going to use that instead on the next part.