The wing spars were now ready for nutplate attachment. I began by clecoing the fuel tank attachment nutplates to the spars, and riveted those in place using the pneumatic squeezer.
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| Fuel tank attachment nutplates clecoed into the spar flange |
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| To squeeze the rivets on the MS21053-L08 nutplates I had to hold it in place with two rivets. Using a cleco got in the way of the squeezer |
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| Fuel tank attachment nutplates riveted in place |
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| Fuel tank attachment nutplates riveted at inboard end of spar |
I then skipped ahead a step and also riveted the access panel attachment nutplates in the same way.
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| Access panel attachment nutplates held in place with clecoes |
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| Access panel attachment nutplates all riveted |
With the nutplate riveted, I was ready to start countersinking the screw holes to accept #8 (fuel tank attachment screws) and #6 (access panel attachment screws) skin dimples. To ensure that I countersunk to the correct depth, I took a scrap piece of 0.032" aluminum, drilled it with a #19 and a #27 hole, and dimpled the holes with #8 and #6 dimple dies respectively.
I dimpled each hole in opposite directions to give me maximum flexibility in using this tool to check countersink depth.
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| Test piece dimpled for a #8 screw |
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| Same test piece also dimpled for a #6 screw. Note the dimple direction is opposite to the dimple for the #8 screw |
Next, I took my #30 countersink cutter/cage, and followed the plans to carefully countersink each fuel tank attachment screw hole to accept a #8 skin dimple. With several careful adjustments to increase the countersink depth, I managed to find the right setting to create a countersink that met the specs given in the plans. While making adjustments, I did find it easier to measure the outer diameter of the countersunk hole to ensure it stayed within the 3/8" maximum defined in the plans.
Once I had the correct depth setting, I was able to countersink the rest of the holes with minimal difficulty. The #30 countersink pilot did a good job of keeping the bit centered, and the countersinks turned out nicely. I did however find that because the spar gets razor thin at the inner diameter of the countersunk holes, I had to use a fine needle file to clean up the inner edge a little on some of the holes.
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| Drilling these large countersinks creates a lot of shavings and chips. Keeping a running vacuum close by helps |
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| Fuel tank screw holes all countersunk to the required depth |
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| Majority of the countersunk holes came out perfectly... |
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| ... a few holes had a slightly uneven inner radius due to the thin flange after countersinking. These are easily cleaned up using a fine needle file |
Countersinking the access plate attach screw holes turned out to be harder than countersinking the fuel tank attach screw holes, even though the former were smaller countersinks. The issue I had was there was a fair amount of chatter early in the countersink (with the #40 pilot), but as the countersink got to the required depth the chatter would disappear and the hole would be smoothed out. This turned out to be the case for all 24 of the access plate screw holes along both spars, but I'm happy with how the holes finished up.
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| Chatter causing a countersunk hole that that starts off not perfectly round... |
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| ...same hole after completing the countersink, chatter dimishes and hole is rounded to the required specs |
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| Countersinking of screw holes complete on both spars |
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| Close up of one section of access panel nutplates and countersunk screw holes |
Build Hints
- When squeezing nutplate attach rivets, be careful to keep the shop side squeezer set edge away from the nutplate screw mount. I accidentally nicked a couple of edges while squeezing and decided to replace those 2 nutplates.
- Keep a running vacuum (I used a portable car vac) to clean up shavings while countersinking screw holes.
- Be careful when countersinking the access plate attach screw holes, especially those near the skin attach holes. It is very easy to accidentally insert the #40 countersink pilot into the wrong hole if not paying attention. This is not an issue for the fuel tank attach screw holes being countersunk with a #30 pilot.
- While countersinking the screw holes, if you hear significant high pitched noise coming from the countersink bit, it probably mean the pilot is touching an edge while spinning. Stop, clean up shavings, and try to reposition the pilot slightly in the hole to better center it. Ideally, countersinking should produce no high pitched or low pitched noises.
Dates: July 28 - August 3 2023
Wing Main Spar Total Time: 31.0 hours
RV-10 Build Total Time: 442.2 hours
Priming Total Time: 44.3 hours (not included in build time totals)
