Category Archives: Section 11, Empennage Attach

Upon return from AirVenture 2018, I began assembling parts for the trim mount bracket.  These parts were alodined in an earlier batch, but needed to be primed before riveting.

The pushrod ends and small parts for the trim mount bracket were primed using PPG DP40LF with an old airbrush I had acquired almost 40 years ago.  The amount of paint applied is very easy to control and the very low volume in the paint bottle was perfect for this small batch. The idea is prime just those parts touching one another with the airbrush, rivet, then prime the larger external surfaces of the whole assembly with the regular spray gun.

The trim mount parts were clecoed together prior to rivet assembly.  A pneumatic squeezer with a longeron yoke was needed due to geometry requirements to reach the Trim Cable Anchor Brackets.

Here are the riveted Trim Mount Bracket Assembly and the Trim Servo Links. The next actions were to continue work on the secondary battery mounting platform, battery contactor mount brackets, and the ELT device mount.

The plans call for numerous parts requiring custom lengths or special fabrication.  I decided to process all the remaining control and push rods together.  This should reduce the alodine batches required, plus get some minor shop efficiency by not changing tools for every single piece.

Here are some follow-up pictures from the last post about how the larger diameter (>1″) aluminum tubes are measured and drilled.

The smaller flap actuator rods (1/2″ diameter) made of steel are much more difficult to handle, as the tolerance and angles are tighter.  Here a dremel tool with small grinder wheel is used to open up the end large enough to accept the screwed fitting.

Next comes the measure and alignment of the holes.  For these rods, two through holes perpendicular to one another and offset back 1/2 and 3/4 from the edge are required.  Unfortunately, the drilling on one rod end was not correct the first time. This resulted in a hole not aligned properly through the center of the rod.  It was bad enough I will have to make these over again.  Stay tuned for an update.

Fabrication of elevator trim components and push rods was the order for this week. The trim motor housing was completed to the point of final riveting.  At this point the alodine/prime sequence will be used to treat the parts before assembly.

The distance between the attach brackets for the trim bellcrank must be measured carefully to ensure parallelism for the faces, properly aligning the pivot bolt with the trim motor.  Here an analog caliper is used to check the distance from the front edge to the back edge.  After a number of adjustments, I was able to get the faces within .005″ of parallel.

The elevator pushrod is made from a 73″ piece of AT6-035 x 1.5″ aluminum tubing and an appropriately sized threaded insert.  Here the circumference of the tube is measured for accurately drilling six evenly spaced #30 holes. After alodine/prime these parts will be connected with long shanked pop rivets.

A spring-loaded center punch is used to mark the six rivet holes 1/4″ from the edge of the tube.  After processing on the drill press, the clecoed parts are checked for correct alignment.

Also during the week I finished the end cap for the rudder bottom.  Looks nice.

Use of paint booth and fabricate custom parts for empennage attach.

Over the last few months, Tal and I have been constructing a paint booth in his workshop.  This was our first run of priming parts in the just finished facility. Here he prepares to apply PPG DP40LF primer to the internal side of his canopy/overhead console, plus my horizontal and vertical stabilizer fiberglass tips.

My tips had to be sanded heavily to get the properly rounded outside profiles to match the elevator tips.  My experience is the fiberglass parts from Van’s are just rough approximations – to get this right requires plenty  of work.  Witness the sanding completely through the gel coat on the left part, this required additional fiberglass/resin layers on the inside to prevent holes.

Next up is prepare and fabricate additional parts on the empennage attach sequence.  The left photo shows a supplimental cover on the rudder bottom.  Not necessary, but it should help deflect some water from entering.  The right photos shows HS attach shims being made.

Attach points for the elevator trim motor and cables are being prepared on the left.  A 3/8″ spotting drill in a clamped vice ensures the attach rivet and bolt holes for the AN6 pivot bolts are correctly aligned to hold the trim bellcrank.

While the horizontal stabilizer is in the jig for work on the fairings, there are also elements of control surface configuration which can be performed.  Checks on elevator up +30 degrees and down -25 degrees confirmed proper range of motion.  Then both sides are set to the “trail” position for drilling the elevator center bearing and elevator push rod bolt holes. To accomplish these tasks two drill guides were fabricated.

The first drill guide protects the center bearing while the pivot points in the elevator horns are configured.  The outer diameter of the guide needs to be reduced just small enough for a snug fit in the inner bearing.  The Delta drill press and Pferd files did the trick.  Once again I am amazed and happy at the incredibly small runout on the drill press!

The left photo shows the drill guide inserted into the center bearing for drilling the right elevator horn.  Next comes the actual drilling operation.  The right elevator is then removed and the same process used on the left elevator. The guide aligned everything perfectly and an AN4 bolt fits cleanly between both elevator horns.

To facilitate proper alignment of the push rod holes, a drill guide is made from a piece of oak sanded to the exact thickness spanning between the elevator horns. Caliper readings were used for initial hand sanding.  Then the piece is aligned and drilled perpendicular to the surfaces with the drill press.

Here the oak drill guide is clamped into place prior to drilling the second hole.  A piece of 3/16″ stainless rod is inserted to align the first hole for the right elevator with the undrilled face of the left elevator.  After drilling is completed, an AN3 bolt passes cleaning through both horns with perfect alignment.

This week was also some final sanding and fitting of the HS tips. The desired 1/8″ gap between the tips and the elevator fairings look good.