The Beginnings of a Rudder
June 20, 2011:
I started the rudder today, but quickly ran into a teeny weeny problem of my own creation. The rudder skins are extremely thin (.016″) and need things called stiffeners to provide some rigidity to the structure since the skin is rather flimsy. There are eight stiffeners on each side of the rudder. Van’s requires you to fabricate the stiffeners from stock that is pre drilled and notched to assist in the fabrication.
Each piece of stock makes two stiffeners. I fabricated the first two stiffeners using metal snips to trim away the excess aluminum, then used a bench sander to finish the edges followed by the Scotchbrite wheel to deburr.
On the 3rd and 4th stiffeners, I noticed that the holes in the stiffener didn’t line up with the forward section of the skin very well.
What was not clear to me was the statement to “Trim varying excess amounts from the FRONT end…” I ended up trimming from the wrong side and the holes are not uniformly spaced, so the shorter the stiffener, the worse the alignment if you cut from the wrong end. Time for another Van’s parts order – $5.70 for the R-915. I also ordered some more stuff such as Pro-Seal, rivets, and aluminum stock.
After figuring out the CORRECT way to do this, I fabricated the stiffeners for the right skin and made sure everything lined up properly using clecos.
Next, I devinyled,
deburred and dimpled then primed the skin and stiffeners.
Total time: 2.4 hours, Hobbs: 65.4
June 24, 2011:
I wanted to rivet the stiffeners on, but needed a back-rivet plate so I drove over to Avery Tools at Hick’s airport to pick one up along with some rivet tape. I got into the shop after lunch and finished priming the parts. Walt came by to look at the progress so far. He inspected the VS and showed me a couple of places where the rivets needed to be redone due to a slight gap between the spar and skin or rib. He helped me drill out and replace the rivets. He also said that the skin on the VS and HS were slightly under dimpled which was the cause of the slight distortion around the rivets. He explained that it’s pretty hard to over dimple the skins with the DRDT-2. It’s great to have such a great resource available. Thanks Walt!
After Walt left, I prepared the skin for riveting. Since the skin is so thin, Van’s recommends a process call “back riveting” which uses a large, flat piece of steel as the bucking bar. The basic process is:
1) Insert the rivets into the skin and use special tape to keep them secure
2) Flip the skin over and place the back rivet plate under the skin
3) Place the stiffener over the rivets
4) Rivet using a special back riveting set which has a spring loaded cage to keep the rivet gun on the rivet. A quick squeeze of the trigger for about 1 second results in a great shop head.
One skin down.
One more to go… (As soon as the part arrives).
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