Pretty much finished up the right elevator this week. The only thing left at the end of the week was to let the proseal on the trailing edge cure for a couple of days so I could rivet it. Actually did that late Sunday night since it cured more quickly than I thought it would.
Here's a shot of the plans from Van's. We use this and a written description as a guide during building.
Counterbalance ribs and skin going together.
Fitting the elevator horn to the spar and making sure it lines up with the whole elevator assembly.
Here's what it looked like once it was all riveted.
Getting ready to back rivet the stiffeners in place. On the far end you can see lines of orange rivet tape. The big steel plate in the table is a back riveting plate.
Back Riveting - thought I'd include a description since most folks won't know what back riveting is.
Normally when you rivet, you put the rivet gun against what is called the factory head, and a tool called a bucking bar against the unfinished side (called the shop head). When the trigger on the rivet gun is pulled, it basically very rapidly hammers the end of the rivet, striking the bucking bar, flattening out the shaft and making what is called a shop head.
Close up of the shop head side of a rivet after it has been riveted.
Back riveting reverses the process. The back riveting plate takes the place of the bucking bar, and is installed in a recess in a table. The factory head of the rivet is placed down against the back riveting plate, and a special rivet set (are you ready - a "back rivet set") is used in the rivet gun and drives the shop head. It makes for an extremely smooth finish. Honestly pretty much anything than can be back riveted a builder will, because the finish is so smooth. It's used a lot on the thin skins of the elevator and rudder to prevent deforming them.
Back rivet plate:
Rivets taped in place. This view is from the inside of the skin.
Stiffener in place and ready to back rivet.
Back rivet set in action.
Riveting the skin to the spar. The wood is holding it vertical so I can get to both sides.
View from the other side. You have to work your hand down in that lower gap, hold the bucking bar against the rivet (which you can't see) then rivet from the far side. Very tight fit, and everything has to be done by feel.
Back riveting the bottom skin stiffeners. The cleco buckets help prop the skin up so I can get in to rivet.
Pretty much everything has been riveted at this point. All I have to do is the trailing edge.
Working on the trailing edge. There is a thin (3/16" by about 1/2" wide) wedge shaped piece of aluminum called an AEX wedge that goes in the back of the trailing edge to make a nice clean line. The wedge is put in position and both the wedge and bottom skin are match drilled to the pre-punched holes in the top skin.
Match drilling the AEX wedge. There is a 2x2 1/8" thick aluminum angle on the back to hold it dead straight. Drill through the skin, wedge, bottom skin, angle *and* the table and cleco the entire thing (including table) together. Want this dude absolutely straight. Any irregularity will affect the flying quality of the plane.
Countersinking the AEX wedge which is used for the elevator trailing edge. The piece of hinge in front is just being used to keep the wedge level. The AEX wedge is about a 12 degree wedge of aluminum about 1/2" wide.
I realized I haven't described machine countersinking, so since I just showed the result I'll show a picture of how that happens (yet another cool tool).
This is the business end of a microstop countersink tool. Basically a tiny drill press, but this has a countersink tool in it instead of a drill bit. The barrel is finely threaded so this can be adjusted to within a few thousandths of an inch. Very precise. Used to make a countersink in aluminum so the rivet will fit exactly flush with the surface.
Microstop countersink in action. The center piece is spring loaded. To use you chuck this in a drill, get it adjusted, then put it in the hole you want to countersink and press down.
Once the trailing edge is dimpled and the wedge countersunk, it gets scuffed, cleaned with acetone, then glued together using proseal.
Proseal. Has an evil reputation for being unbelievably messy. It's like very thick nutella. Not as bad as I feared, and sticks like mad to anything.
This stuff is also used to seal the fuel tanks (that is actually it's real purpose, but Van's like to use it for other things since it is a good adhesive and not horribly expensive).
And this is the final result of all the work on the trailing edge. Let this cure about 48 hours, take out the clecos, then *very carefully* back rivet the whole thing making sure to keep it dead straight.
By the way, the adhesive has nothing to do with the structure of the airplane. It's just there to hold everything straight so it can be riveted. The rivets do all the work structurally.
Jeff Moreau suggested I use some proseal to fill a tiny gap I had in the trailing edge of the rudder that I didn't like. Since I had some proseal left over, and it will not keep, I did exactly that. Good idea Jeff. Thanks!.
Trailing edge of the rudder with some proseal in it. I'll trim it flush once it's cured.
