Rear wing spars

With all of the main and nose ribs deburred and straightened, it was time to start construction of the rear wing spars.  The primary component of the rear spar is an aluminum Z channel, to which several doubler plates are attached in critical areas for reinforcement.  The inboard doublers (W-707D and W-707G) require trimming at a specific angle prior to being attached, and an opening in the middle doubler (W-707E) must be drilled to allow movement of the aileron pushrod.  For surprisingly simple structures, it seemed like it took quite a bit of time to get both of the rear spars ready for rivets.  It was rewarding to have them finished though.

Started match drilling doubler plates to spar channels

Trim lines marked on W-707D.  This will be used as a template for W-707G

Aileron pushrod opening started with unibit.  Remaining material removed with dremel.

Opening enlarged to final size and deburred.

Outboard portion of rear spar ready for rivets

Center doubler only requires 5 rivets at this time

Inboard doubler plates attached and ready for rivets

Rear spars finished

Trim tab motor test

A small amount of work needed to be done to finish up the trim tab.  I needed to increase the size of the opening in the skin where the threaded rod exits to allow full up/down travel.  This was accomplished with a rat tail file and some emery cloth.  Once that was finished, I connected the motor leads to my cordless drill battery, and tested the motor in both directions. It was cool to see the motor moving the trim tab for the first time.

Increased size of opening in skin for trim tab threaded rod

Used cordless drill battery to test movement of trim tab

Completed rudder and elevator leading edges

I've been working on finishing the last items on the empennage over the last few days.  My wing kit arrived a few days ago, and I'm anxious to start working on the forward spar.  The leading edges on the elevators and rudder needed to be closed up, and I have a small amount of work on the left elevator where the trim tab motor sits, and that's it for the tail section!  

Getting the leading edges of the elevators and the rudder to come together nicely takes a bit of work.  It's easy to roll the leading edges, but it's challenging to get the outer skin to sit flush without any gaps after the blind rivets have been set.  To resolve this, I ended up slightly over bending the outer skin, which allows the two skins to sit flush next to one another.   Bending one section at a time, outboard to inboard, makes the process easier.

Several builders have written that they used a pipe wrench to grip the dowel (3/4 inch) that is used to roll the leading edge.  I found that a steel handle, such as that used for a bending brake, worked much better when inserted into a hole drilled through the dowel.  The wrench was hitting the forward spar of the elevator, limiting the amount the leading edge could be rolled.  Using the steel handle at the inboard end of the elevator by the control horn eliminated this issue.  

After I had the skins rolled, I taped them in place with strips of duct tape and match drilled the holes.  I didn't find it necessary to use the ultra sticky duct tape that some builders use - the standard duct tape worked great, and didn't take the primer or blue vinyl off where I didn't want it removed.  The tape was then removed, the holes deburred (with a scotchbrite pad on the interior surface), and the blind rivets were set.  I wasn't happy with one of the elevators after it was finished, so I drilled out the rivets, slightly adjusted the leading edges by bending the skin a bit more, and re-riveted.  I was very pleased with the results.

Two sections rolled on right elevator

Right elevator leading edge finished

Left elevator leading edge clecoed - ready to be match drilled

Two sections on rudder complete - one to go

Rudder leading edge finished

The completed airplane parts are getting larger!

Vertical stabilizer finished

With the elevators and rudder complete except for the leading edges, I went ahead and finished the vertical stabilizer.  Jim and I set the internal rivets with rivet gun and bucking bar, and I finished the perimeter rivets with the hand squeezer.  No surprises here - everything was fairly straight forward.  There are a couple of rivets along the rear spar that are difficult to squeeze since they are located right next to the hinge brackets, but the no hole yoke worked pretty well in those areas.  Once everything was finished, I removed the blue vinyl and hung the completed stabilizer from the ceiling.

Hand squeezing perimeter rivets

Vertical stabilizer finished - ready to hang next to the horizontal stab

Ready for storage

More rudder work

This weekend I made good progress on the rudder.  I notched the counterweight to fit between the rivets in the counterbalance rib, and torqued the #10 screws after the weight was in place.  All of the perimeter rivets were then set, with the exception of the trailing edge (and a few in the top and bottom ribs for trailing edge access).  I've been doing some reading about the best method to tackle the trailing edge, and decided to use Proseal to keep the skins attached to the AEX wedge and keep everything straight during riveting. I allowed the Proseal to cure for nearly a full week, as it has been pretty cool in the hangar, which likely increased the cure time.  

I used one of the rudder skins prior to final assembly to match drill the trailing edge holes in a piece of angle aluminum.  That piece of angle was then clamped to a second piece, onto which the holes were transferred.  That allowed me to clamp the trailing edge together after the Proseal was applied to the AEX wedge until the curing finished, keeping everything straight.  I have to say I was more concerned about messing up the trailing edge than I was bending the ends of the trim tab, which gives many people trouble.  I looked at several examples and spoke with several accomplished builders, and decided to squeeze all of the rivets rather than use the back rivet technique.  I felt that backriveting left too much room for error, and that I could control how much the rivets were driven more effectively with a hand squeezer.  This was the method I used:

• Numbered the trailing edge holes 1-6, then repeated the pattern down the entire trailing edge.  I used these numbers to set the rivets in a systematic pattern to prevent warping.
• Starting in the middle and working to one side, I set all of the number 6 rivets half way, then repeated the process in the opposite direction.
• Repeated this process for all number 5 rivets, and so on, until all of the rivets were set half way.
• I then took a flat set I had ground down on my Scotchbrite wheel to match the angle of the trailing edge, and set the rivets the rest of the way, using the same pattern as before.  I constantly checked to make sure no warping was taking place. 

This process resulted in a nice straight trailing edge with no dings in the skin.  I'm very pleased with the results, and happy this portion of the rudder is complete.

Counterweight notched and countersunk, ready for installation

Torquing counterweight screws

Front spar attached to left and right skins

AEX wedge clecoed to table for countersinking.  Holes were match drilled in table to center the countersink pilot

Aluminum angles match drilled and clecoed to trailing edge

Removed primer from inside portion of skins where Proseal will be applied

Thin layer of Proseal applied to both sides of AEX wedge and placed in trailing edge

Trailing edge clecoed between aluminum angles to cure

Rivets taped in place (all in the same direction) ready for squeezing

All rivets set half way with flush set in squeezer

Rivets completely driven with angled set.  Shop heads showing.

Finished trailing edge.  Nice to have this done.

Rudder revisited

The last few days I've been working on the rudder components.  I was waiting to rivet the stiffeners until I had more experience riveting the elevator stiffeners, since the skins on the elevator are slightly thicker (.020").  This turned out to be a non issue.  I back riveted some scrap stiffener aluminum to some .016" sheet for practice, and to get the rivet pressure dialed in.  After that, I riveted all of the stiffeners to the left and right rudder skins.  Last weekend I cleaned, primed and riveted all of the skeleton components, so the rudder is now ready for final assembly.  I haven't decided exactly how I'm going to address the trailing edge wedge, but I'll figure that out over the next couple of days.

Parts deburred and ready for priming

Skeleton parts primed...

... and ready for riveting

Installing reinforcement plates on front spar (used hand squeezer and a longeron yoke for this)

Skeleton completely riveted and installed in left and right skin

Back riveting stiffeners to left and right skins

All stiffeners riveted in place - only leading and trailing edge work remains

Trim Tab

Many people make the trim tab several times until they are satisfied with it, so as on the trim tab opening on the left elevator, I practiced making my bends on some scrap aluminum before I made the those on the trim tab itself.  This procedure worked well for me, and I'm happy with how the trim tab turned out.

Prior to making the first bend, I sandwiched the skin between some angled pieces of oak and clamped them to my workbench.  I used double sided tape on the skin to prevent the oak wedge from slipping while the bending was taking place.  I made the initial bend with another piece of wood, which I used to push the skin down toward the forming blocks.  After that was finished, I used my rivet gun with low pressure (approx. 10 psi) with a flush set to complete the bend.  Prior to bending, I made a radius on the oak wedge upper edge, which allows the skin to from a nice radius rather than a sharp angle.  My initial practice pieces had very sharp angles that would eventually crack.  With the bottom side finished, the assembly was turned over, re-clamped to the table, and the process repeated.  The same procedure was then used for the inboard edge.

With all the bends complete, the hinge was drilled and attached to the trim tab and later to the elevator.  The trim tab motor and cover plate were assembled, and the control horn was riveted to the trim tab.   A few of the rivets for the control horn near the trailing edge are a bit difficult to reach, so I riveted the control horn prior to setting the rivets in the trim tab edges.  This allows the trim tab to be opened, which makes it easier to access the more challenging rivets for the control horn.  With that step complete, the remaining rivets were set.

First bend is made around angled oak blocks

Inboard edge bends completed

Control horn riveted to trim tab skin

Hinge riveted to leading edge of trim tab and fit to elevator

Rivets set attaching hinge to elevator

Trim tab motor assembly work

Motor assembly completed