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Attaching the Empennage

When it came time to attach the empennage to the fuselage, I discovered some minor issues at almost every step.  Here's how I resolved them. Hopefully this information will save you some time and effort.

Horizontal Stab

Leveling the horizontal stabilizerYou start by leveling the horizontal stab.  Take your time here and ensure all the measurements are accurate.  Any errors you leave here will result in lost speed.  You may not be able to see it, but your plane will be slipping through the air with the control surfaces not fully in the trail position.  This causes drag, slowing you down.

I found an easy way to check that the horizontal stab was level front to back was to insert a drill bit into each tooling hole.  Make sure you use bits that just barely fit, so they stick straight out on their own.  Then I placed the level on them.

Alternate method to align elevatorsIn my empennage attachment process, I only had trouble at one spot on the horizontal stab.  My best guess is that the clamps slipped, because somehow one of the outboard holes I drilled to attach the HS-814 didn’t line back up when I went to insert the bolts again.  The hole was nicely centered on the stab, but it wasn’t centered in the F-887.  When I lined up the other three front holes, this last one didn’t match.  How did that happen?  But more importantly, what do I do about it?

I countersunk from the top and bottom of the F-877, and bucked an AN426–5 rivet until the shop head filled the lower countersink.  If you have to do this, don’t worry if you use too large a rivet.  Once the countersink is filled, stop bucking, and get the grinder out.  Grind and sand the leftover rivet until it is smooth.  This leaves both the top and bottom of the F-877 smooth and the erroneous hole filled in.

Then I clamped the horizontal stab back on, and inserted temporary bolts in all the other holes.  This time when I drilled, the hole was true.  I still don’t know how it happened.

Vertical Stab

The next step in attaching the empennage is the fitting of the vertical stabilizer.  Locating the new match drilled vertical stab is a lot easier than the older one.  I had to figure out the actual height of the vertical stab that is now determined by the predrilled hole that goes into the F-812B angle.  I started at the bottom of the vertical stab by setting the VS-803 main spar to a height that would allow the bottom two bolts in the VS-410 to go through the WD-409 with enough edge distance.  If you have the match drilled tail, make sure the marks you make to drill the three holes in “View A-A”, DWG 73 will have the required edge distance when drilled through the WD-409.

Front of vertical stabilizerThen I adjusted the front of the vertical stab and F-681 (now the F-884) attachment plate until they were in the proper position.  I dropped a plumb line through the hinge brackets to ensure the vertical stab was true and the hinges were in line.  The front of my vertical stab was too close to the turtle deck skin, so I had to trim the bottom of the vertical stab skin and flange to get the required clearance.  You may not have installed your turtle deck skin yet, just be ready for this when you finally do.  You wouldn’t want to put a big scratch or dent in the skin because you didn’t check to ensure there was clearance.

Attaching the Elevators

To continue with the empennage, it's time to attach the elevators.  Once you determine the required washers or spacers for the elevator horns, make a little drawing.  Set the washers and the drawing aside together.  It may be a while before you finally install the elevators, and you don’t want to have to spend the time to figure the required spacers again.

When you are drilling the F-841 pushrod hole in the elevator horns, make sure you use some sort of guide block.  I used a hardwood block just like the directions, but I have seen others use a metal guide.  The material you use isn’t that important, but the fact that you use something is.  There is too much play between the horns if you don’t.  If the holes in both horns don’t match, your elevators will not be even, and the plane won’t fly straight.

Two parts left to the empennage:  the elevator and rudder.

Elevator Control System

The plans have you make and fit all the control pushrods for the elevators at this time.  Don’t final install them however.  Just fit them and then remove them.  You will want access to the inside of the tail while installing wiring and other components, and when riveting the top skin.  Then you can go back and final install the control system.

I used washers to "jig" the elevator bellcrank.I wanted to ensure I had the F-635 bellcrank in the neutral position to adjust the lengths of the pushrods.  So I measured 3 1/16 from the F-808 bulkhead per the plans by clamping a piece of angle across the back of the bulkhead, then measuring from it to the center of the top hole in the F-635.  I also made a little “jig” using some washers that filled the access hole in the F-818 ribs and left a small center hole that I could align with the lower hole in the F-635.

Elevator Control Stops

Aft elevator stop

The front stop was easy to adjust.  I had not yet riveted it in place, so I removed it, filed some metal off, reinstalled and checked it.  I tried to file the rear stops with the elevators still installed, but there just wasn’t room.  That meant I had to file a little off the stop, then reinstall the elevator and check.

Forward elevator stop

Balancing the Elevators

If you have already installed the fiberglass tips, now is a good time to balance the elevators.  Disconnect the pushrod from the elevator horns so each elevator floats free.  Spray some WD-40 or LPS on the hinges, so they move easily.  Now you have a perfect horizontal platform for balancing the elevators.  I plan on test flying my RV-8 before painting, so I left them a little front heavy until after I finish painting.  Then they will have to be balanced again.

Rudder Stops

Finish the empennage attachment and fitting by adding the rudder stops.  Take it slow and remove a little metal at a time.  Remember that you can always take more off, but you can’t put it back.

Rudder stop
Rudder elevator clearance

A few more Vertical Stabilizer attachment photos

Forward vertical stabilizer bolts
Forward vertical stabilizer bolts
Lower aft vertical stabilizer bolts
Lower aft vertical stabilizer bolts

Vertical stablizer rear attachment
Vertical stabilizer rear attachment

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