Monthly Archives: April 2014

It’s almost a rudder

Rivet count: 349 + 254 = 603!

I got a little time to pull a few rivets last Sunday, but it was hardly worth a blog post, so I saved the pictures for this week’s posting.

I tied together the bottom rib pieces with some pop rivets.  I think I did this step out of order which made riveting the skins at the trailing ends of the rib a bit harder though… I should not rush!

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So I started in fresh and early this Saturday with the goal of finally riveting the trailing edge.  I see a lot of people who do it right after they glue (or tape) up the trailing edge, but the instructions have you do it next to last.  In the end, this makes sense because you want some play to get those tight rivets at the aft end of the rudder.

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These last couple rivets are really hard to get to.  I managed to get my 4″ thin nose yoke in there.  As the instructions intimated, I had to uncleco and spread the trailing edge a bit.  I didn’t like having to crack the epoxy, but so it goes.  I used a little RTV to glue it back together after I finished the rivets.

Next you rivet most (but not all) of the left attach strip.  You leave the front rivets open so that you can more easily get the rudder horn brace attached.  It took a lot of finagling to get it to finally snap into place.  I started with the four holes on the horn and got a couple clecos in.  Then I worked it around the attach strips and finally pressed it up into the trailing edge.  Here it is in all its cleco’d glory with one rivet test fit!

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A lot of people seemed to have had trouble getting these rivets set (well, not the pull rivets into the bottom rib, but the ones in the horn).  I decided to try my longeron yoke.  Sure enough, there was just enough room to fit it over the side edge and swing it into position for all twelve of the interior rivets.

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There was still a lot of work to do before getting to the dreaded trailing edge… First I riveted the skin to the countersink rib.  I thought I might have to drive these, but after doing a couple with the rivet gun I realized that my 4″ yoke would reach, so I squeezed the rest. I then had to bolt the counterweight in… This wasn’t too hard (despite my long search for the bolts themselves a few weeks earlier).  The bolts snugged right up and fit neatly into the countersinks.  I added some Loc-tite to make sure that the lock nuts really stay in place.2014-04-19 12.40.40

 

 

With that done, I needed to rivet the skin to the spar.   There are 50 holes on each side.  Again, the 4″ yoke would reach, but I really didn’t want to hand squeeze that many rivets, so I finally pulled out the pneumatic squeezer.  I didn’t have very good luck with it when I did the toolbox project and we did all hand squeezing in the EAA workshop, so I was a little worried.  It was fine though… I knocked out the rivets cleanly and accurately.  It went so well, I used it again to do the top rib.  Well, most of the top rib.

The aft most rivet is a total pain to get to.  The rudder tapers to a very narrow point and there is absolutely no room for even my thin nosed yoke.  A bucking bar is out of the question.  I puzzled for a while and then decided to try bucking the rivets with a piece of 3/16″ steel I had thought to use for a back rivet plate (I got a thicker one that I actually use for that purpose).  I was able to slip the steel bar into the rivet space.  Using a piece of scrap wood as a fulcrum, I was about to lean on the bar with an elbow, hold the skin up with the fingers of my left hand, and drive the rivet with my right.  It sounds more complicated than it turned out to be in practice.

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I had to turn the air pressure up a lot to get the rivet to drive because there wasn’t a lot to buck against.  I was running close to 90 pounds (I normally drive at 40 to 44 pounds to help with control).  Here’s the final result.

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It’s smooth and flush and has a good shop head to boot.

No more stalling, it was time to rivet the trailing edge.  I was filled with dread as the boards are rife with stories about curving and warping and oil canning and bad looking rivets.  I pulled out all the clecos and rivet taped in all the rivets.  I have a 5 foot long back riveting plate, so the whole thing fit easily. I shimmed the rudder to try to get the edge to lie flat.  It looked like there was a pretty big curve in the edge, so I was worried.

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It was a total non-event.  I hit every tenth rivet lightly with the back rivet set and then started sub-dividing the rest until I had the rivets mostly set.  Then I finished with the swivel mushroom head to drive the shop heads fully flush with the skin.  The whole think seemed to tighten up and straighten out as I went. I don’t think it took 5 minutes total to do the whole edge.  The instructions call for a .1″ tolerance across the edge.  I measured at the point of largest divergence.  It was about .04″.  I’m calling this one straight enough.

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The next step (also dreaded) is rolling the leading edges.  I decided to do it with some 1″ PVC pipe (I also have some 3/4″).  I screwed some pipe clamps into the table to guide the pipe.  I added some cardboard and tape to make sure I didn’t drag the skin over the sharp edge of the clamp.

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I added some gorilla tape to the leading edge and tried to make the bend.  The first thing that became clear was that I really needed to do the three sections one at a time.  I tried bending by hand, but ended up using some channel locks to help spin the pipe.  I didn’t have time to complete the bends, but that will be the first order of business next weekend.

Next up… finish and hang the rudder.  And then start gathering parts for the horizontal stabilizer (it’s huge!).

 

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The dreaded rudder trailing edge

Rivet count: 349

Just got to work half a day today… my wife and I went to the art auction (the interest for loans at the bank of marital bliss is expensive!) to buy some art and get a nice Persian rug.  That went pretty well (I liked what we bought), but it took up the whole afternoon.  Still, I had enough time in the morning to be productive.

I started the day by heading off to the Home Depot Aviation Supply store.  I needed to find a replacement chuck key for the one I misplaced at the shop.  I still don’t have a clue where it might be, but I didn’t want to lose the better part of a short day looking for it.  I found a nice (cheap) Ryobi one.  I added a big triangle of orange safety tape so it should be easy to spot.  I also needed some RTV sealant for the rudder stiffeners and some epoxy putty for a home project, so it was worth the early morning trip.

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I picked up where I left off… countersinking the trailing edge wedge.  Lots of holes to do.  Both sides!  I created an awful lot of aluminum “pixie dust”  The conventional wisdom is to be careful not to countersink these too deep or you will ruin the trailing edge (and get a bend).   I’m not sure what “too deep” is, but a 3/32″ rivet fit in pretty much flush. You can see the new chuck key in the photo above as well.

The instructions call for using double sided tape to hold everything together while you rivet.  People online had mixed reports, but it was more negative than positive, so I opted to use the older “glue and clamp” method. I prepped the edge and wedge by scuffing with some sandpaper and then cleaning with acetone.  I wanted the glue to really stick.

The conventional wisdom also calls for clecoing the edge to a piece of angle to keep it straight whilst waiting for the epoxy to cure.  I wanted to make sure I had some angle that would not flex, so I got some 1/4″ x 1.5 inch stock from OnlineMetals. It is very stiff, but it was a horror to drill.  I didn’t want to dull my aviation jobber bit, so I started with a bit from my cheapo Home Depot bit set.  It lasted 10 holes and then broke off.  I finished the rest with my #40 bit.  This was pretty time consuming and it used a lot of compressor air.  Definitely called for hearing protection!  Then I ran a belt sander across the holes to make sure the whole thing was flat and finished with a piece of painters tape on top.  I didn’t want to bond the rudder to the angle permanently!

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Finally, with everything prepped, it was time to dive in. I went to mix up a batch of epoxy to glue the wedge.  But the epoxy had hardened in the tube.  I could get catalyst out, but not the epoxy base.  Luckily, there is a little hardware store at the bottom of the hill.  I shot down there and bought old fashioned epoxy with the help of the wizened old guy behind the counter.  I like mixing the epoxy.  I reminds me of working with my Dad building his boat.

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The next step looks like it requires six hands… and in fact the instructions suggest you get a helper.  A lot of people said that they did it solo, so I dove in.  Here, I use a piece of painter’s tape to curl back the left rudder skin while I pop-rivet the stiffeners and sheer clips in place.

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This was a bit awkward and at times messy since I was also advancing a thin line of epoxy cement on top of the wedge as I went.  I didn’t want to get any pillowing between rivets, so I tried to used the epoxy sparingly.  My hands were busy (and often goopy), so not too many pictures. Not show is the blob of RTV at the trailing edge of each rib.  It is supposed to help keep the edges from vibrating and cracking. Here’s a picture of the whole shebang clecoed up and hardening.  The one missing cleco is the hole where I broke off the drill bit.  The edge is nice and tight and uniform.  We’ll see how the riveting goes next!

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Next up… riveting the trailing edge (double flush technique) and assembling the counterbalance.

 

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.

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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.