9-08->10: Elevator Prep continues

Elevator prep continued with the drilling of the tiny little corner gussets which connect the end ribs to the rear spar. These were difficult to get to and for one i ended up removing the front spar and using the mega #30 drill bit. Sometimes you really have to think creatively to get things done!

I also installed and match drilled the tip-rib assemblies. There was some confusion as to whether the counterbalance skins were under or over the elevator main skins. There is a note on page 9-22 "NOTE: The E-913 Counterbalance Skins lie underneath the skins" however, the images on the same page were a little confusing as to which way the skins should go (the left image seemed like the lower counterbalance skins went outside of the lower elevator skin. I decided to check with the mother ship:

"The counterbalance skin should be covered by the elevator main skin, I have however seen it done both way and structurally either is acceptable.

Sterling Langrell

Tech Support, Van’s Aircraft, Inc."

I elected to place them UNDER the skins on the top and the bottom. I think it looks nicer. 

Tip Rib assemblies in place. 

Trailing Edges

Next was fitting, marking and trimming the trailing edges. At the outboard ends, they are a lot thicker than the fiberglass tips, so you have to use the belt sander to sand the trailing edge cross-section so that it matches. I left it sitting a little proud of the glass, as i filed the glass ends a bit to make them flatter and these will eventually need some filler etc - so this way i can fill up to the skins (bondo etc) and get a perfect fit. 

This is the inboard end of the left hand trailing edge - i think i will fill the hole with pro-seal etc eventually. 

Left hand tip in place - these will need something inside to help them into the right shape (foam?)

Left hand trailing edge before sanding..

This is how much has to some off. I took the curve away by sanding the fibreglass tips to a more flatter profile - this will be filled later. 

The left hand trailing edge after profiling. 

Right hand trailing edge after profiling. 

Right hand trailing edge after profiling.

Trim Tab Spar / Left Aft Spar

Next, i countersunk the trim tab spar and the aft left spar where the trim tab goes for the elevator skin. This is countersunk instead of dimpled (the rest of the spar is dimpled) because if you dimple the hinge material it can distort, and you don't get a free swinging trim tab. I had not countersunk such thin material before, so i did a test piece the same thickness (0.032") and used my coupon to check the fit. As usual it was 0.007 deeper than flush as per Van's directions. 

The trim tab spar countersunk for the elevator skins in the location of the hinge. The CSK was done with the hinge in place to help support the CSK pilot.

Trim Tab Access Doubler

There is a doubler on the left elevator skin, where the cover plate will mount that holds the trim tab servo. This cover plate needs nutplates installed (K1100-06). These are dimpled where the -6 (#27) screw goes, but as not dimpled where the nutplate attach rivets go.

As such, the plans call for you to dimple the trim access doubler (so the rivets holding the nutplates on are flush, and will allow the cover plate to sit flush). You mush therefore also dimple the actual holes in the nutplate tabs themselves. Not that there is anything wrong with this procedure, but i decided not to proceed with this dimpling, but to rather countersink the trim access doubler.

This piece is 0.032" thick, which according to section 5 is too thin to be countersunk for the head of AN426AD3 rivet (i.e. the skin would be knife edged, and would not provide any support for the shank of the rivet at all). However, you can use a NAS1097 rivet, in place of the AN426 rivet - this has the same shank diameter as an AD3 rivet, however has the head size of an AD2 rivet. You therefore just countersink lightly, until this tiny rivet is flush. There is no tensile force on this rivet in this instance, as it is just there to hold the nutplates on - all of the force is in shear, when you try and screw in a screw (stops the nutplate rotating)

CSK for the head of a NAS1097 rivet - you can see a single on in place. 

However, here is the small issue i have created for myself; the lower 4 nutplate attachment holes in the below image, are also used to hold on a trim tab brace - i did not think of this before countersinking as above. The question is, are these rivets providing any structural advantage to holding the brace to the trim access doubler? or would the screws provide this function once the cover plate is installed? (i feel that the latter is the answer, and i am ok to proceed, however i have sent an email to check with the mothership! - i will include their response below when it comes).

You can see the relationship of the parts here:

This is what Van's Motership said:
"The doubler is .032. You can countersink .032 for an AN426AD3 rivet. The 1097s are probably OK – the screws will hold it all together anyway"

SO: Moving forward, i think i will have a go at countersinking some 0.032 material for an AD3 rivet and see what it looks like. If it is too hard, or knife edges too easily i will stick with the NAS1097's, but if it goes well, i will look at countersinking the doubler for an AD3 rivet.

As part of this step, i also fabricated the double flush riveted trim pushrod - some parts in this aircraft are TINY!

Left Elevator Trim Tab Close out Tabs

Next, i had to pull out the big bertha drill bit again to match drill the skin close out tabs where the trim tab will go - i taped a foam rib in place and clamped the skin to make sure i kept the correct shape before these were matched drilled.

The flexibility allows you to still drill normal to the surface, but have the drill motor off at an angle. 

Getting my horn on

Next, was to match drill the elevator horns in place. This went without a hitch, despite reading others who had alignment issues with these. The #40 holes were a little off, but within tolerance of the #30 final drill holes.

#40 holes very slightly off. Pretty amazing tolerances on this kit. 

 

Other items:

As well in this step, i went ahead through the plans and checked whether there was any other drilling etc that needed to be done. I ended up putting the parts together for the trim tab servo mount, and drilling this off, as well as countersinking the trim servo cover plate. I also competed the trim tab trailing edge, and drilled the close out tabs of the trim tab. I unclecod each elevator, and as i did so, i finished deburring any edges that i had missed (the lightning holes in the forward spars for instance), as well as any holes i had drilled and not already deburred. I ran out of time to finish deburring the skin edges, but once this is done i can go ahead and begin to prime the various parts. There are a lot of parts in the left elevator (more than the right), so i think i will prime the left elevator minus the trim tab components, then do the right and the trim tab components together, and finally in a 3rd batch, all 4 skins (including the masking for the trailing edge and also foam rib locations).

A fun couple of days of work!