Sonex 1404

Posts Tagged ‘counterweights


Posted on: July 6, 2013

The last set of control surfaces I had to build were the ailerons. These are slightly more complex than the other surfaces because of the lead counterweight assembly. First step was to assemble the control horns.


Next step was to cut the lead block into shape. I had read that this was a fairly difficult thing to do because of the tendency of the lead to bind to the cutting tool. The trick apparently was to use something with large teeth. I had the perfect tool for that – my wood saw that I used when building the workbenches. It worked beautifully. The cut isn’t very clean, but I’ll beat the rough surface into shape after I have balanced the assembly.


I then built the counterweight assembly which holds the lead weight. This is basically two ribs attached by a bridge which goes into the aileron, while the extended aluminum plates on the other side hold the lead between them.


I drilled all holes in the lead before riveting the assembly together. The easiest way to drill lead is to use the slowest speed with plenty of lubricating oil. You have to give a chance for the drill bit to cut into the lead.


I then riveted the assembly and bolted the counterweight. Little did I know that I had to remove the counterweight at a later point.


I then proceeded to cut the skins to size and make all the notches necessary. The cutting on the outboard edge is a bit tricky because the three points of the triangle are at differing lengths from the inboard edge – no perpendicular cuts there.

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The next few steps were easy – locating the ribs, pilot drilling the holes, and clecoing everything together.

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The outboard tip ribs were part of the kit and one of the edges had to be bent for it to fit into the end. The bending brake proved useful, but I still had to use my hands to get it to bend all the way.


After this, there was a bit of a wrestling match to get the tip rib in properly. I had to fabricate a little tool to help me pull back and hold the rib’s end while I drilled the pilot holes and clecoed them together. You can see the tool sticking out in the middle picture. It came off when I removed everything to clean and deburr.

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I repeated this on both ailerons and then updrilled, deburred and clecoed them altogether again. This is when I found out that I had to remove the counterweights to get access to two holes at the bottom which would have been otherwise impossible to get to.

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I riveted everything together, but still couldn’t get my riveter to pull a rivet from those two holes at the bottom.

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I decided to put the counterweights back on and put this on the list of things to ask my tech counselor. Some people have drilled one hole in the middle and put a rivet in there, but I don’t want to do that before talking to someone knowledgeable. Kerry and Sonex said it should be possible to put rivets into those holes, but I can’t quite figure out how. All my “riveting in hard to reach places” techniques seem to not work here.


I put away the ailerons up in the rafters. I took a trip to India after this. Next step – attach the ribs to the spars!