Stephan's Sonex #1627 Builder's Log

I finally riveted the left side of the veritcal stabilizer. I also attached the fiberglass tip.

I fitted the fiberglass tip to the vertical tail assembly. I wanted to be able to hang the rudder so I could check clearances, but the rudder is only partially riveted (for inspection), so I used a piece of sheet metal on a hinge to confirm the distances.

A lot of measuring and double-checking had to be done in order to ensure a good fit. I used a straight edge to ensure that the tip was centered on the tail and that it wasn't angled incorrectly. I drilled pilot holes and up-drilled to #30 and cleco-ed.

I'm ready to rivet one side of the vertical stabilizer, but I'm waiting on feedback from Kerry at Sonex to find out if it is acceptable to have the skin under tension. There is a significant amount of spring left in the skins and I'm concerned that riveting the skins under tension will cause issues.

I riveted the forward spar and main spar assemblies. I also installed the AN3 bolts. The thread on the bolts did not extend far enough down, requiring a total of 3 washers instead of the 2 the plans call for. I did not get a chance to complete the riveting of the vertical stablizer.

I did more work on the vertical stabilizer today. I spent time fitting the skins and making sure that all the holes lined up on the center of the various ribs. I then pilot drilled all the holes and cleco-ed everything together and then up-drilled to #30.

The SNX-T12-10 clip that I had previously fabricated did not appear to cause the tip rib to be positioned correctly for the holes in the skin. I checked the measurements of the clip and it was all correct. If I used the clip, the holes would be too close to the inside edge of the rib. I contemplated putting the clip inside the rib instead of on top of the rib. This would have moved the rib up and lined up the holes with the center of the rib better. However, this is not standard aircraft construction practice, so I decided to fabricate a new clip that had a longer flange so that I could push the clip up more. 

I attached the rudder hinge and drilled all the pilot holes. I then up-drilled to #30 and cleco-ed everything togeher. Once I had updrilled everything, I took everything apart and deburred, cleaned and primed all the parts. Next time, I'm going to rivet everything together.

I worked on fitting of the vertical stablizer assembly and skins. I laid out the whole stablizer on a flat surface and then clamped everything together. I then drilled all the holes for the various attachment clips. I have not yet drilled the SNX-T10-04 (tip rib), because I want to make sure that the holes in the skin are going to line up with the forward spar assmebly and if I drilled the tip rib and fastened it, it would make lining things up more difficult.

I was surprised how well overall the holes lined up with the center lines I had drawn on the various ribs. I'm going to have to figure out what I'm going to do with the 4 bad holes I drilled in the main spar assembly before I go any further.

I contacted Kerry at Sonex and provided him with a picture of the problem. He indicated "...the only thing we would ask you to do is add one additional rivet between each of the errant hole locations. Even that is most likely unneeded but it is insurance against the unlikely possibility of those holes tearing out.". In other words, a straightforwrd fix and I don't have to redo the part. Excellent!

I worked on the SNX-T09-01 main spar assembly and the SNX-T09-02 forward spar assembly for the vertical stablizer. This required a lot of measuring and checking because I wanted to make sure that the pre-drilled skins were going to fit without too much trouble.

I needed to drill the holes for the AN3 bolts, but could not find any documentation on what the correct drill size is for this. I find it a bit perplexing that there is no universally accepted standard for this. I found a lot of different ways people in various groups suggested on doing this, some say start with #13 and then drill with #12 and then use a #12 reamer. I contacted Kerry at Sonex and he suggested to either use #11 or 3/16" bit. I did not have any #11 drill bits and checked with Aircraft Spruce and they didn't appear to have any either, so I settled on 3/16". I drilled a test hole and the fit was reasonable. However, when drilling the actual main spar, I found that there was way too much slop. I will have to get a #11 and #12 and reamer and see if that provides better results.

The plans indicated the location of the rudder hinge, which I carefully located and then fastened to the main spar, with the eye of the hinge centered on the edge of the spar. After I had it all lined up, I went ahead without thinking and started to drill the holes so I could cleco the hinge. While I was doing this, I realized that the skins were already pre-drilled and unless I had located the holes perfectly, they weren't going to line up! 

I quickly assembled the vertical stablizer and wrapped the skin around only to discover that the 4 holes I had drilled were exactly on the center of the edge of the channel, whereas the skins had the holes located more to the right edge of the channel. I'm not yet sure if I'm going to have to scrap the SNX-T12-03 upper spar channel piece, or if I can salvage it. It looks like the distance between the bad hole and the correct hole is approx. 5.4mm. I believe the minimum edge clearance is supposed to be 6.4mm, so I may have to scrap this piece.

I fabricated the SNX-T12-10 clip from a scrap piece of SNX-Z03-02 channel stock. I was supposed to have a 12" piece of SNX-Z02-03 angle stock in my kit to make that part, but it was missing from my kit. I contacted Sonex to find out if there were any issues making it from 0.032" instead of 0.025" and Kerry Fores indicated it was not an issue.

I worked on fabricating more parts for the vertical stabilizer today. I fabricated SNX-T12-03, 04, 08 and 09. The SNX-T12-09 part had to be fabricated from 0.060" aluminum sheet. The bend on the part is 65° and the bend radius was 3.2mm. I used the extension rod that came with my deburring tool which had a diameter of 6.2mm, close enough to give me the proper bend. I used my bending brake with the rod secured as indicated in the picture below. 

I also wanted to fabricate SNX-T12-10, but it calls for SNX-Z02-03 angle stock, which I don't appear to have. I believe the angle stock is 0.032", so I can probably make it from scrap SNX-Z03-02 channel stock.

I completed the fabrication of SNX-T10-02 today. This completes all the fabrication that is necessary for drawing SNX-T10. It took me two tries to properly fabricate this part. On the first try, I bent one of the flanges at the wrong location and on my second try I scratched up the part too severly to be usable. I'm going to have to purchase some additional SNX-Z03-04 channel stock.

I worked on the vertical Stabilizer today and fabricated the ribs out of channel stock. I also cut the piano hingest to size. For the ribs, I used a form block the width of the channel to do the bending. I messed up on SNX-T10-02, so I just cut it smaller and made SNX-T10-01 out of it. Next time, I'll pay better attention to make sure I'm bending straight.

I thought that I would start the Sonex build with something simple: bending the forward spar fitting. This part came with the tail kit already cut to size, all that needed to be done is bend it to 35°. This proved not as straight forward as I had hoped. I initially inteded to use my Arbor Press, as Sonex suggested with the wood cut out, but I decided to use the dowel and vice method that other builders had successfully used. 

When you're using the dowel method, the dowel is centered between the bend tangency lines. I managed to split my wood dowels so I ended up using 1" diameter steel pipe instead. It is important to make sure that the steel pipe extends above and below the edges of the part, so that you don't get any imprints on the part. The steel pipe tended to move around while I closed the vice, so I drilled two 1" holes about 2.5" apart in a piece of 2-by-4 and split it in half to hold my steel pipe in place.

The steel pipes also tended to deform, so I decided to use a socket wrench with a 1" OD. This ensured that the part had the proper bend radius. I ended up needing to bend almost 10° further just to end up at 35° when the part is removed from the vice.