Step 5.7, Riveting the top skins

Well, there it is.  The right wing leading edge section all riveted on!  With the left wing on as well, it's time to move on with riveting the top skins on.  There are four wing skins per wing, two on top and the rest below.  We won't need the bottom skins for a while, but I decided that while we were match drilling, deburing and dimpling the top we might as well do the bottom skins as well.  There are hundreds of rivets in the skins so it doesn't take much imagination to see how boring this process can be.  I'll bet you're experiencing bit of that right now!  Fortunately, Carol came down to help out with a lot of it.

One thing that I found helpful during the tedious parts is to listen to the radio or podcasts online.  I really like a podcast called Big Picture Science.  It's funny and informative.  Give it a try.  

So we finished most of the boring parts and I moved on to the scarf joints.  These are sections of overlap between the skins that would end up too thick if left alone.  So matching tapers are cut into the top of the skin below and the bottom of the skin above.  The idea is to try to maintain the same thickness of a single skin where the two overlap.  In this case, it is only necessary to scarf the corner of the sheet where a third skin abuts (fuel tank skin along the main spar). 

To cut the tapers I used a vixen file, then just a small amount of sanding to smooth.

Meanwhile, Carol continues the deburring...  Ok, so we weren't quite finished with the boring parts.

The edges of the skin are fairly rough as delivered.  The high spots come right off with the vixen file. Then the edges can be dressed with a smooth mill file or Scotch-Brite pad.

There probably won't be many pictures of the top skin riveting process as it takes both of us to accomplish.  I did manage to snap this one while Carol examines the work.  The process goes like this: I shoot and she bucks.  Which means that I place a rivet into a hole and put the rivet gun with a flat set over the rivet.  She sees the rivet coming through from the other side and says ready when her bucking bar is in place over the rivet.  Then I give it a short burst with the 3x rivet gun.  She then evaluates the rivet and says good.  Or she says give it another tap.  Or, my least favorite outcome, she just says oops!  In the latter case the rivet is drilled out and the process repeated.  

Thus far, we have completed the inboard top skins on the left and right wings.  On the first skin, we had 3 rivets that had to be redone.  On the second, none.  Also, the second only took half as long to complete.  So we are improving.  Yeah!

Step 5.65 Leading Edge to spar complete

Here comes Carol and her entourage down to help.  She's going to help me remove the blue plastic from the wing skins.  The dogs will most likely wait patiently until our hands are full or we are otherwise preoccupied and then misbehave somehow.  Roxy will lick you persistently, with much determination and no mercy whatsoever.  Trina, on the other hand, will run out of the shop carrying a tool, a glove, or just a piece of paper.  Looking over her shoulder all the while, she wants someone to chase her.

After the blue plastic is remove along the rivet lines, the edges of the skin are smoothed and the inside rivet lines are primed.

The little block of wood is used to turn down the edge of the skin slightly where it will overlap another skin.  This helps keep the edge down tight after the skin is riveted.  Once the skins are debured they will be dimpled and be ready to be riveted to the wing.

Here I am, up to my armpit in airplane.  I'm still working on getting the leading edge ribs attached to the spar.  In my previous post, I had planed to use pull rivets since it's very difficult to get rivet gun or bucking bar inside.

After having mentioned my difficulties with this section at our local Experimental Aircraft Association meeting, I was offered help in getting these most difficult rivets set.  I didn't want to pass up this opportunity to learn from more experienced builders and so, on the following weekend Keith Pederson came over to help out.  He took the more difficult position of bucking from inside, while I shot from underneath with the offset rivet set. 

Unfortunately, there was no one else present to capture any of the excitement for posterity.  After about 3 hours we had 10 ribs in 2 wings solidly attached.  Yes, there was some bloodshed. And yes, at one point we had hundreds of rivets spilled on the floor.  But we persevered and now I can move forward.  Thanks Keith. 

Step 5.6 Leading edge to spar

Well, I must confess, that attaching the leading edge is more difficult that I expected.  I fact, I hadn't even planned on posting on this subject as it would seem a trivial task.  I thought I would just mention that the leading edge sections were attached at the time of riveting the top skins.  I turns out though, it's not quite that easy.  The ribs in the leading edge section which we assembled in an earlier post, must be riveted to the spar. Preferably the manufactured head should be on the rib side of the assembly since, between the spar and the rib, the rib is the thinner material.

Leading edge section

leading edge section on spar

In order to rivet in that direction, the rivet gun needs to be inside the leading edge which means threading the gun and air hose through the lightening holes in the ribs.  Ok, so far.  Then one must put his arm through the same holes and maneuver the gun about in very tight quarters without denting or scratching the skins or spar.  Did I mention that my x-ray vision isn't too good these days?  That's right , the ribs on the inside bays must be done by braille.




After a lot of struggling on the outside bay, I gave up on the idea of driving the rivets in the proper direction, and decided that a backward rivet didn't sound so bad after all!

Driving the rivets from the back side of the spar is a lot easier from the rivetor's point of view.

However, I found that having a partner to buck was necessary going this direction because I was unable to stick my hand through the hole in the spar to hold the bucking bar.

No-go

 Fortunately, Carol came down to help me.  She could get her hand through the spar, but found it very difficult to hold the bucking bar without being able to see it or the rivet.  And so we switched positions and were able to slowly proceed.

Inside the leading edge section.  The spar is the gold anodized part.

So after an hour of that madness, we had only finished one rib -- 5 rivets.  At this point I was pretty disgusted with the whole situation and decided to pack it in for the night and go consult the oracle of all knowledge.  The internet, of course.

Well, it's amazing what you can find out when you know what to look for.  Based on what I read, it seems that I may be kind of a boob for even attempting to use solid rivets in there.  My mistake for following the manual.  In fairness though, I did read of several individuals who did manage to get the solid rivets in, although it's not clear if their rivets were placed in the preferred orientation.  I suspect that these extraordinary builders may have possessed the very rare, but nevertheless, requisite physical attributes:  X-ray vision, a very long right arm, and a very small left one (Tyrannosaurus Rex style).

So what is the alternative to the Van's method?  Use blind rivets otherwise known as pull-rivets.  On the recommendation of several builders online, I will be using Cherrymax brand available through Aircraft Spruce.  In addition to the pull rivets I will also need to grind down the pull rivet tool along its top edge for clearance to the rib, but I think most of the rivets will be accessible from inside the leading edge section.

The only difficulty with the Cherrymax rivets was, according to one builder, that super human strength is necessary to pop the rivets.  No problem :)