Rivets and rudder skins

 

Rivet count: +232 bringing us to 560

Last week’s work was dramatically truncated by a trip out to Bucknell University.  I was going to fly, but the weather was awful, so I choose to drive to my sister’s instead and carpool from there. After the trip, I stopped off to see my daughter at nearby Ursinus College for dinner.  After a nice meal, I dropped her off and phone my wife to say I was headed off for the two hour drive home.  She said, “Don’t.”  She was right, the weather was awful.  It took me 50 minutes of driving in pouring rain just to drive the 20 miles back to my sister’s house.   So I drove back Sunday…. and then went tile shopping for the remodel. So, the long and the short of it is that I managed only a couple hours at the shop…. But I did at least get the rest of the rudder parts deburred and smoothed.  And…. I got the one missing rivet pulled on the rudder spar (I needed some double sided tape to finish it).  I also got the ribs clecoed onto the spar for a test fit.

 

 

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Oh, and I got all the rudder stiffeners primed and ready for the next steps.

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This week was better.  I spent nearly the whole day at the shop.  It was a little chilly (the air compressor is balky when it’s cold), but not too cold to work.  The first job was to replace the timing belt on the band saw.  The old one broke when an aluminum shard fell through the blade hole and sliced through the belt.  It took a bit of maneuvering, but I finally got the drive wheel off and the belt replaced.

The next thing to do was to trim the trailing edge piece to fit the skins.  You cleco it on one skin to mark it for cutting.  You also draw a line to show where to scuff the skin for bonding.  I did that before I primed the skins, so I was a little ahead of the game.  A quick snip job with my straight ahead yellow handled tin snips did the job (the band saw was overkill).  I polished the edge with my ScotchBrite wheel.  Remember to get the bottom edge too… mine overhung by about 1/32″ and needed some rounding to fit inside the skins.

Finally, you assemble the skins onto the frame and trailing edge piece.2014-04-05 10.33.15

Most things lined up pretty nicely.  The rudder horn was a little tight.  I had to massage the skin a little bit and slide the counterbalance rib into place to get it to go.  Oh, and one of the holes has to be match drilled.  Be careful to get the correct (left) skin on top so that it all works out.

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The rudder has a lot of weird gotchas.  One which apparently gets a lot of people is that the rivet holes are drilled perpendicular to the chord of the wedge, not perpendicular to the skin.  The practice kit has a similar restriction, but it doesn’t have the predrilled holes to worry about.  I saw several builder blogs that recommended using a drill guide, so I whipped one up with my chop saw.

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Notice that the bottom edge isn’t square,  rather it’s sitting at about 84 degrees.  The triangle on the top edge was just a scrap edge, but it was helpful to remember which side was up.  The guide was very helpful.  My drill went straight through each time and I didn’t widen any of the predrilled holes.  Notice how the hex key sits normal to the table top and not normal to the skin.  It’s pretty much parallel to the drill guide.  Perfect holes every time!

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The rest of the match drilling goes pretty quickly.  Then we take everything apart once again.  At this point we have to dimple the skins.  They are a little bit awkward in the DRDT2, but I managed to get things dimpled up.  My wife stopped by for lunch and she helped with one of the skins.  Much easier with four hands.

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After all this prep work, the actual back riveting was anticlimactic.  You just line up the stiffeners and bang them out.

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Take care with the left/right skin and stiffener orientation! I used my overkill back riveting plate.  It was a 5 foot by 3 inch by 3/8 inch piece of cold rolled steel from onlinemetals.com  I wanted a long piece because of all the horror stories I read online about people getting into a groove and back riveting past their dinky one foot plates.  I got a five foot length because it matched the length of my table and was longer than any back rivet run I could possibly make.  Three feet probably would have been enough (or whatever the elevator trailing edge is).  The skins were very bendy and a bit awkward, but the riveting went pretty fast.  I got the right skin finished on Saturday.  100 rivets in that skin (+1 for the last one on the spar).  101 rivets for the day!

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I had time for a couple of hours in the shop on Sunday (I made another small deposit in the bank of marital bliss by fixing a light switch and going tile shopping — the price we must pay!).  This was plenty of time to do the left skin stiffeners and bottom rib section (117 rivets).  I also got the sheer clips pop-riveted in.

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There was even time to rip a guide for countersinking the trailing edge wedge.  I want to do this carefully as it will dramatically impact the quality of my trailing edge if I over- or under-countersink it or if I don’t get the countersinks straight.  I cut the wedge so that I could cleco the wedge to the guide and countersink with the drill bit normal to the skin edge.

2014-04-05 17.20.28

 

I tried doing it with my drill press on a scrap piece of wedge, but I found that I was much too likely to over countersink.  I was going to switch to my air drill, but could not for the life of me find my drill chuck.  This despite the fact that I had not walked more than  8 feet.  And the chuck is wrapped with a piece of safety orange tape.

In situations like this, my father always blames my grandfather’s ghost for “borrowing” his tools.  I figure Grampa needed the chuck key more than I did, and it was dinner time anyway.

Lots done this weekend.

Next up… countersinking the wedge, gluing the wedge to the skins, and skin assembly.

 

 

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