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.
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.
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 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.
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.
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.
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.
The plans are kinda sketchy on how to check elevator fitment on the HS. After some web surfing and questioning other builders, I came to the conclusion that the elevators seem to be fitting ok. The elevator counterweight arms are parallel to the HS skins, and there doesn’t appear to be any binding – yet. With the counterweight arms clamped to the HS, the elevators also appear to be aligned in trail. The control horns don’t quite line up with each other, but from what I can determine from VAFWWW and the Matronics list, they don’t have to.
After the HS skins were trimmed sufficiently to allow the elevators to swing freely, I used a digital level to check elevator range of motion. Looks like the elevators have a few degrees’ margin of up-travel before they contact the HS skins, and according to Van’s there is no minimum spacing requirement between the elevator skins and HS. So as long as they swing freely, I think I’m good to go. If you’re reading this and know something different, please don’t hesitate to email me!
The next step is to trim some HS flange material away to allow the elevator control arms to reach maximum down-travel. I debated doing this before riveting the HS spar together, and now wish that I had. Some substantial care will now be required to avoid damaging the spar stiffeners.
Ellen and I dusted off the horizontal stab and temporarily mounted the elevators. The rod end bearings in both elevators required some tweaking to get their centers 13/16″ from the elevator spar webs, but that turned out to be no problem. As noted in the plans, some HS skin trimming is required to get the elevator counterweight arms to swing freely.
And after inserting the rod-end bearings, the left elevator is complete.
Ahh…my favorite part of control surface building – rolling the leading edges. I used the same procedure described earlier on this page, plus some liberal application of hand-tweaking to make the overlap as smooth as possible. This one came out better than the other side, I think.
My disease seems to have abated somewhat, so I spent some time downstairs and riveted the trim tab hinge to both the tab itself and the left elevator. The pneumatic squeezer is the weapon of choice for setting these rivets, but I had some problems getting the flush set to fit between the spar web and some of the hinge eyes. If the flush set is too far forward it can push on and bend hinge eyes, not a good thing. And surfing through the Van’s Air Force forum, I found others had the same problem. My solution was to take a spare flush set and grind it down a bit to reduce its radius. Worked great!
Here’s the trim tab, essentially complete.
The riblets came out fine, I think.
Over the weekend, Ellen and I got the trim tab fitted to the elevator and the hinge drilled. After some primer touchup, everything was ready for final riveting. At least that was the plan. I came down with some bizarre stomach bug and didn’t accomplish much. I did manage to get the elevator trim cutout riblet blind-riveted…