Right bottom skin fitting and an successful experiment
TLDR
- Prepped the right bottom skin
- Test fit it onto the spar
- Reversed a few rivet direction on the rear channel
Back ordered parts arrived
Earlier this week I requested a few parts as they were back ordered, and also requested left rib 304 as it was damaged during shipping. They arrived today! This must be one of the fastest shipping I have seen during this build! Kudos to TAF team.
Skin prep details
The usual stuff
Spent like forever to peel off the plastic protective film from the bottom skin. After this was done my fingers are properly raw. It’s my least favorite part of the build process.
And I deburred, wiped with alchohol, and scuffed the outer skin with scotch pad.
Then I proceeded to dimpling. It took me a moment to orient the parts so the correct side is dimpled. I marked out the side on each part to avoid mistakes.
The dimpling process was very time consuming but straightforward once all the marks were marked. I noticed all dimples done on my DRDT did not require match drilling. The dimpled hole was large enough to fit the rivets. OTOH the dimpled holes from my hand squeezer required match drilling. Not a big deal, but it’s interesting there is such a difference between the 2 methods.
Inspection hatch
While the skin was still off the main spar, I installed the 2 inspection hatches. I did this on the elevator before, so it’s a familiar process this time. All holes were already dimpled. I had to enlarge-drill the holes for rivets to go through though. After than, just clecoed the inspection hatch grip on plate (WG-PLT-014-X-F ) to the skin, and shot the rivets. The 2 hatches came out nicely.
Test fit
After dimpling and enlarge drilling the 3.2 holes done on the hand squeezer, I started to test fit the skin. I started with clecoing the skin to main spar, then clecoing to the rear spar, lastly ribs.
Throughout the process, I kept testing the flap torque tube rotation. It became easier and easier to turn. That was a relief and gave me more confidence to keep going.
Misdrilled hole?
During the test fit, I noticed one hole on the overlapping root skin and long skin were factory pre-drilled differently. On the instruction it’s supposed to be a 4.0 counterskin hole. And it’s predrilled as 4.0 on the long skin. But it’s pre-drilled as 4.8 on the root skin, also 4.8 on the spar. So when I fit the 3 pieces together, essentially two 4.8mm holes sandwiched a 4.0mm countersink hole. Obviously that’s not going to work. Since the spar is already drilled as 4.8, I flattened the 4.0 countersink hole and enlarged it to 4.8, and decided to go with a 4.8 mm x 15mm rivet for maximum strength.
Fitting rivets
I spent some time to fit rivets into each hole, and my goal is to matchdrill ZERO holes if possible.
About half of the holes on both spars were very easy to fit the rivets. Others were much harder to insert the rivets. I used a trick I learned from other builder to help with this situation - use an icepick. When a hole does not fit, push an icepick through the neighboring hole, and wiggle it around to micro-adjust the alignment between the different metal layers. 99% of the time the rivet was able to go in. In a few holes I needed to apply a little bit force to push them through. But still, I was able to push all rivets through both spars with ZERO match drill.
Countersink reinforcement plate
WG-PLT-012-X-F - I almost forgot to insert these two strips when fitting the rivets. I picked them out of my pile of parts and set them next to the wing. I will install them when I set rivets next.
(Experimental) Reversing rear spar channel rivets
The rear channel (2 long pieces) is connected together using a doubler and 8 rivets. Today I realized that I riveted them in the wrong direction. This will most definitely be a problem when I install alerons/flaps because of their tight clearance. So I decided to drill them out and reverse the direction.
The 6 rivets further out from the rear spar were easy. I had space for my drill to reach and drill out the rivets. But it’s not possible to drill the 2 remaining rivets closer to the spar. I do not want to force it as it will either damage the spar, or elongate the hole. Both were not acceptable to me.
So I tried to remove the 2 rivets from the back side.
I was a little worried but it was actually fairly straightforward. TLDR: ** bruteforce with a very good flush cutter. ** I just too a flush cutter and started to cutting the backside of the rivet. It was surprisingly soft and easy to cut. It didn’t take much effort to cut off the back side, then I used a centerpunch to push out the front piece. No drilling were involved. To be honest I felt like this was safer than drilling from the front side..
