The tail end

Over the last month and a half I’ve been slowly working on getting the horizontal and vertical stabilators attached. There’s nothing terribly complex here, but there are some places where access for drilling holes and installing fasteners is tough.

Starting with the horizontal stabilizer, I aligned it with the fuselage per plans and drilled the inboard holes that attach the forward spar. Access isn’t so good here for a regular drill so I used the angle drill and my technique wasn’t great…despite using an undersize drill bit, the holes wound up oversize.

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The outboard holes were easier to drill, but required some extra care to ensure that edge distance was maximized on the stabilizer, fuselage longerons and bulkhead. I drilled these holes initially to #30 to check alignment, then final-drilled them to #12.

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I talked with Vans about how to handle the oversized inboard holes. Their recommendation was to upsize the holes to 0.25″ and use AN4 fasteners. Before I did that, though, I wanted to try a first-oversize close tolerance NAS6604 fastener that’s approximately 1/64″ larger than a norman AN3 fastener. That would preserve 2D edge distance on the hole. I reamed the oversize holes to accommodate the NAS6604 bolt, and the bolts were a perfect fit – problem solved.

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With the forward horizontal stab spar drilled to the fuse, I clamped the rear spar to the fuselage attach bars. If you look carefully, you’ll see the business end of a 3/16″ punch between the rear spar and fuselage aft deck. That 3/16″ gap establishes proper incidence for the horizontal stab relative to the fuselage.

With that gap set, I clamped the fuse bars and rear spar together, and using my Brown Tool drill block, drilled the four #12 holes that hold the assembly together.  I use the drill block whenever I can…it works great for getting nice, clean, straight holes.

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Here’s everything bolted in place. Look carefully and you’ll see the dimpled heads of the NAS6604 bolts on the front spar.

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Here’s the HS stab in place. It’s been sitting in storage for ten years…and now it’s part of the airplane. Cool.

The next step was to attach the vertical stabilizer.  There are several steps in this process, and a couple of them were somewhat tricky. Just getting the vertical stab aligned correctly was a challenge – it was tough to get everything clamped in place firmly enough that the vertical stab didn’t shift while measuring its alignment relative to the horizontal stab.

I had already fabricated the upper stab attach bracket and match-drilled it to the fuselage – with the stab aligned I used my trusty drill block and match-drilled the attach bracket to the stab. All those vise-grip clamps I’ve been collecting sure came in handy.

Drilling upper VS attach

Upper VS attach bracketAfter the upper attach bracket was match-drilled, I fitted the angled attach plate that connects the vertical and horizontal stabilizer forward spars.

Drilling VS front spar 1 Here I’ve already match-drilled the plate to the horizontal spar – those holes will be opened to #12 – and I’ve started drilling the plate to the vertical spar as well. I had to insert a 0.020″ shim between the plate and spar to improve the fit.  The plans tell you to anticipate this, and have dimensions for fabricating a shim if one is required.

Drilling VS front spar 2

I used the angle drill sparingly on these holes. Some of them didn’t get final-drilled until I removed the vertical stab for priming.

Rear VS attach

Here’s the vertical stab’s rear spar primed and bolted into place.

Tailwheel fitting bolted and torqued

I neglected to take many pictures of the measurement and drilling process for the lower three bolts – they secure the vertical stab lower spar and tailwheel aft attach bracket to the fuselage.

The measurement process was a little tricky – edge distance has to be maintained on the tailwheel bracket and the vertical stab spar, but they’re on opposite sides of the aft most fuselage bulkhead so it’s impossible to directly measure edge distance. The only way I could get this done correctly was to establish a series of reference points for the tailwheel bracket measured from the fuselage sides and aft deck. Those reference points allowed me to project the location of the tailwheel bracket onto the rear side of the aft fuselage bulkhead.

With the vertical stab clamped into place, I was then able to pick hole locations that met all of Vans edge distance criteria. After that, drilling the holes was a piece of cake.

Tail in place

Here’s the vertical stab bolted and torqued into place…very cool.

Tail attached from the rear

Another pic? Sure, why not…

Nice tail!

And I couldn’t resist temporarily installing the rudder…it’s been waiting a long time to be on the airplane!

Drilling away at the horizontal stab service bulletin

For the last few months I’ve been chipping away at Van’s horizontal stabilizer service bulletin. This service bulletin addresses cracks found in some the front spar center section web on some RV horizontal stabs.

My stab obviously hasn’t flown yet, but I decided to go ahead with the SB mod anyway. If I screwed up the mod, I’d still have the option of building a new horizontal stab. But once the stab is drilled to the fuselage, I’d be committed to modifying it as it would be very difficult to fit a new stab to mounting holes already drilled in the fuselage.

Working on the HS SB

Drilling out rivets isn’t fun, and drilling out AD4 rivets in a confined space is even less fun. Getting the inboard ribs out wasn’t hard, but drilling out the AN470-AD4 rivets in the front spar was a bitch.

Rivet heads removedHowever, with some patience and persistence, and more importantly some help from Bob DiMeo, I was able to get the heads drilled off of all the hard-to-reach front spar rivets. All that’s left is to punch them out, and start fitting the mod kit.

Rivets punched out

It was tough to punch out the rivets on each end of the angles, but a little patience and persistence won the day.

Front spar

Seems like years since I riveted this structure together…oh, wait – it was years ago, ten years to be precise.

Spar angle

One angle removed…

Trimming front spar flanges

Another tedious task…trimming the upper and lower flange on each side of the front spar. The black line marks the cut line, and Van’s thoughtfully includes a small piece of stainless steel to slide beneath the spar flange to protect the skin while cutting. Following the instructions, I used a small cutoff wheel on my Dremel tool to do the trimming. Gotta be careful using a motorized cutter in this area…

Front spar flanges trimmed

The end result, with some additional polishing to remove some scrapes left from rivet removal. I’ve also enlarged the U-shaped relief notches per the instructions.

Spar doublers drilled 1

After all that work, fitting the doublers was relatively easy. I deburred them, adjusted the bend angle slightly to match the front spar, then drilled them in place. Some care is required to make sure the holes are drilled perpendicularly to the spars, angles and doublers.

Here’s another picture of match-drilling in progress…

Front spar doublers drilled 2

And the end result – doublers ready for priming…

Front spar doubler deburred

I had to do some additional cleanup and prep of the doublers and angles before priming.

Priming front spar partsPriming wasn’t a big deal, just had to keep the hangar warm enough to let the primer cure.

I had to upsize a couple of holes to #20 because

Enlarged holesI encountered one other problem…a line of rivets added for the mod interfered with one of the nose rib flanges. After a quick call to Vans, I decided to cut off and replace the offending flange. You can see in the next picture where the rivets lie relative to the nose rib web after I cut the flange off.

Nose rib flange mod 1Here’s the new one…

New nose web flange

And here’s the final result after priming and riveting the new flange, then riveting the ribs to the skins –

HS mod complete

Rudder cables and ELT mounts

Over the course of this week I’ve been at the hangar a few times to take care of random stuff prior to mounting the wings.

Before we moved the fuse to the hangar, I installed and secured the rudder/tailwheel steering cables to the tailcone. It would have been good to check the plans and see which end of the cables attach to the rudder control horn (the two ends of the cable aren’t the same), but I neglected to do that.  Compounding that mistake, I had already fished the cables through several holes in the tailcone and aft fuse and installed snap-in plastic grommets in those holes that make it impossible to remove the rudder cable once they’re installed. As an extra bonus, the grommets can be installed with access to one side of a hole, but access to both sides of the hole is required to remove them – which is a problem in several places in the tailcone and baggage area where panels are already riveted in place that limit access. D’oh!

Other builders have made this mistake and wound up drilling out rivets and removing panels to get at the grommets, but I was determined not to do that. So…I went on a trek to Home Depot (there’s one about five minutes from the hangar – bonus!) and bought a small propane torch and an X-Acto knife.  A red-hot knife slices through plastic pretty easily, and working from one side of the hole, it’s not too hard to slice out the clips that hold the grommets in place. After an hour of heating and cutting, the grommets and the rudder cables were out.  30 minutes later, the rudder cables were installed the right way.

I also started working on the Emergency Locator Transmitter (ELT) mount.  Over the last several months I’ve been working out where to install the ELT and have never been very happy with a lot of the options I’ve seen, including Van’s own ELT/strobe mounting plate which seems far too flexible to ensure that the ELT will work when it’s supposed to.  Many RV builders regard the ELT as a bureaucratic nuisance and don’t care how it’s installed.  They’re certainly free to do as they see fit, but if the device has to be in the airplane, I want it to work as it’s designed to.

My friend Andy mounted his ELT on the horizontal bellcrank rib, which seems like a good place for both longitudinal strength and access for installation, testing and battery changes.  The only downside is that the rib doesn’t have a lot of lateral stiffness, and theoretically the ELT mounting surface should withstand a 100-pound pull in any direction without deflecting more than 0.1 inch.  I came up withe the idea of fabricating an L-shaped reinforcement plate to provides extra stiffness, and had my fellow FAA DER Tom – who’s a structures engineer – run the numbers to make sure my design would be strong enough while not impacting the existing structure.

Proposed ELT mountIt turns out from Tom’s analysis that a piece of 0.040″ 7075-T6 aluminum sheet, bent into the required L-shape, will do the job nicely.  It will be held in place on the vertical flange with ELT mounting bolts and the rivets which also attach the bellcrank stiffener angle, and on the horizontal flange with some AN426-3 rivets.  Easy peasy!  The only downside is that my candy-ass little Harbor Freight bending brake won’t handle 0.040″ 7075 sheet, so I’m gonna have to find someone with the appropriate tools to make the bend.  Stay tuned…

Complete

Vertical surfaces complete!

Since I’ve decided not to tackle the fiberglass tips right now, the only remaining empennage task was to adjust the rudder rod ends and fit it to the VS. After the elevators, this task was a no-brainer…only took 45 minutes or so to complete.

With that, I’m officially declaring the empennage to be complete. Looking back at my build log, I’m definitely one of the slowest builders I know…but it’s not a race, is it?

It’s time for a victory beer…

The last remaining task

The last remaining task on the HS and elevators was installing washers between each elevator horn and the center bearing, then torquing down the whole assembly. As with the elevator brackets, the objective here is to avoid binding in elevator travel by eliminating any sideload on the center bearing. That means eliminating the horn-to-bearing hap with washers.

Center bearing spacers

The plans call for using AN960 (thick) and/or 960L (thin) washers on each side, but on the left side I couldn’t find a combination of washers that would fill the gap. Some other folks have fabricated spacers from aluminum tube in lieu of using washers, so I tried that using some spare 6061-T6 tubing. Came out pretty nice but after the nut was torqued down, elevator movement wasn’t quite as free as before.

Horizontal surfaces complete!

After doing some additional research, I think the elevator movement is fine. The bearings will wear in a bit, and if not there are some tricks that will reduce center bearing friction if required. So with that, the horizontal portion of the empennage is complete!

Welcome back

Center bearing and elevator brackets drilled

Welcome back to the empennage page. There are just a few wrap-up items to take care of before the wing kit arrives in August.

The first wrap-up item was verifying the correct spacing on each elevator rod end, then match-drilling the elevator control horns to the HS center bearing. Setting rod-end distance was easy…the control horn holes proved to be a little tricky.

The plans call for using a 1/4″ OD, 3/32″ ID drill bushing to drill a #40 pilot hole in each control horn. Taking a cue from Dan Checkoway’s website, and wanting to be more precise when drilling these holes, I ordered a drill bushing from McMaster-Carr. This is a press-fit bushing and had to be turned down slightly to fit in the bearing, but once in place it worked well. The #40 pilot holes were enlarged to just under 1/4″ with a drill, then reamed exactly to size.

One detail to look for on those elevator control horn weldments is the minimum spacing between the bolt hole and torque tube. If the hole is drilled too close to the torque tube, it will be impossible to get a washer and nut on the bolt. The plans don’t say anything about this minimum spacing, so beware…other builders had this problem and were forced to weld up the original hole and start over.

Wanting to avoid this pitfall, I checked the spacing by sticking the non-fluted end of a 1/4″ drill bit through the center bearing with one elevator mounted, then the other. I was able to use that drill bit to visualize where the bolt hole would be located. After checking, I found that the rod ends on both elevators hat to be backed out to the maximum distance in order to get these holes in the right place.

Elevator horn weld detail

Also note that Van’s has left a little gap in the torque tube weld fillet to accommodate the washer and nut – above and just to the right of the bolt hole.

With the elevator horns drilled, I tweaked the HS elevator brackets to make sure the rod end bearings fit precisely between them with no space on either side. That prevents any side-load on the bearing when hinge fasteners are torqued down, thus preventing a source of friction and binding in elevator movement.

Officially declaring the horizontal stab to be complete

Lots of things going on at work and at home, so not much progress to write about. I did manage to prep and prime the spar cutout mentioned above, but there are no pictures. Just look at the pic above and imagine that bare aluminum covered with beautiful yellow primer. After that, the center bearing bracket was torqued back into place.

And with this entry, I’m officially declaring the horizontal stab to be complete – at least for now. I’m postponing any fiberglass work for awhile.

HS spar lower flange

HS flanges trimmed

Here’s the cutout on the HS spar lower flange. The plans don’t call out any specific dimensions, so I cut the flange to accomodate the elevator control horns with a 1/8″ clearance on both outboard sides. The flanges were trimmed forward until they were just about flush with the spar stiffeners.

With this cutout, elevator down-travel more than meets Vans’ requirements. Next step…drilling elevator control horns to the HS center bearing.