1.2 Hours -
After installing all those platenuts on the spars, I was happy to move on to something different today. The wing tie-down assemblies are incredibly simple. They consist of a piece of extruded aluminum and two spacers which are attached to the spar.
The first step is to tap the extruded aluminum pieces so that the tie-down eye bolts can be screwed into them. I’ve never tapped anything before, so I chose to do this first just in case I ruined the pieces. After all, one ruined piece is easier to replace than three!
The tap is used to make threads for the tie-down ring to screw into...this should be interesting.
A couple minutes into tapping the first tie-down, I realized that using a tap wasn’t rocket science. Since the extruded aluminum already has a hole in it, there was no problem starting the 3/8-16 tap and keeping it straight. One turn to the right, followed by a quarter turn to the left, back to the right, repeat for about 5 minutes, and done.
Getting the tap started was much easier than expected. The hole in the aluminum made it easy to get started and keep the tap straight.
At about the halfway point, I decided I better check the fit. Another 1/2" to go.
Next, one of the top holes is drilled into the tie-down. This is the only hole that is drilled by measurement, the rest are drilled using the spar as a guide. I drilled this hole in both tie-downs and then sat the left tie-down aside since my right spar was already on the bench.
The first hole is drilled off the spar at a set location dictated by the plans. The rest of the holes are drilled using the spar as a guide.
Before drilling the remaining 7 holes in the right tie-down, the tie-down and spacers have to be clamped into place. Like other builders, I used tape to hold the spacers in place, then used a square to make sure the tie-down was straight before holding it in place with a c-clamp. Once everything was in place, I drilled the rest of the holes with a 3/16” bit.
The only way to keep the spacers in place is to tape them. The tie-down is clamped on over these.
Appropriately, I used a square to square the tie-down.
The rest of the holes were drilled from behind using the pre-drilled holes in the spar as a guide.
Fortunately, the spacers stayed in place throughout the process.
Once all the holes were drilled, I removed the clamp and tape and then carefully marked the orientation of each part so that I can put everything back together correctly.
Tomorrow, I’ll drill the platenuts in the right tie-down and try to finish up the left as well. Then, all the pieces can be primed before finally be attached to the spars.
