Sonex 1404

Posts Tagged ‘drilling

I finished up a few things on the main spars the last few weeks. The first thing I did was to clamp the left and right spars and align them by the holes through the attach blocks. Everything looked good except that a washer on one of the bolts was coming in the way of one of the spars being perfectly aligned. In the process of diagnosing the problem, I found out that I had used AN3-10A bolts instead of AN3-7As, which had prompted me to use extra washers. I checked the rest of the bolts and found the same problem. I replaced all the hardware with the right sized ones.

I also checked the bolts on the other spar, and found that the washers were riding the inside of the attach angle – not good. I removed the bolts, ground down some of the washer (I had used AN4s on this spar because of an error I had made while drilling), and put in new hardware.

Here’s the ground down washer, followed by the washer on the bolt.




The next step was to rivet the vertical stiffners and tie-down brackets to the main spar. The stiffners are solid riveted to the spar, and the tie-down brackets are bolted to the bottom of the spar.

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For some strange reason, Sonex doesn’t do this solid riveting work on their pre-assembled spar which is what I bought. I was apprehensive of doing this riveting, especially the “bang on a bolt” Sonex method. I fretted quite a bit, and then thought I would practice this method a little. I wasn’t too happy with the result, so I got in touch with Barry Weber, a three time Lindy award winner in my EAA chapter to borrow his rivet gun. I practiced with the gun and the results were OK, so I went ahead and set the first couple of rivets, with not so good results! I set the rest of them using the Sonex method!

There were two rivets where the rivet gun (a 5X gun) set hit against the stiffner itself. I’ll have to ask the Tech Counselor if that’s OK. But otherwise, the rest of the rivets turned out well. All that trouble for 10 rivets!

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The next step was to put in the AN3 bolts at the bottom of each spar. There are 8 of them on each spar.

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After this, I finally got to mating the spars and updrilling the holes to 1/4″. I decided I didn’t want to hand drill the holes, so I got my drill press on to the floor and drilled up from 3/16″ to 1/4″ in steps. I used a reamer for the last step. I bought some 1/4″ bolts from Home Depot to hold the spars in alignment. These holes will be updrilled to their final size of 3/8″ when the wings are installed to the fuselage. There’s also the obligatory photo of me with the mated spars!

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Despite the precautions taken, one of the holes became oblong! But I think this can be fixed during final sizing.


The last step in completing the spar was to attach the wing tip attach angles.



This was straightforward enough. These go together with CCP-42s like most of the rest of the airplane.


Not so fast. On the other one, I put a little too much pressure with my riveter resulting in a bent angle.


A fluting plier did the trick.


I’m finally done with the spars! I stored them away under my workbench. I’ll get started on the aileron bell crank assemblies next.