Fabrication of the wing tiedown plates and spacers

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While working through my wing spar hole questions with Van’s, I moved on to fabrication of the wing tiedown plates and spacers. It was much easier to lay out the spacers on the bar stock, pilot-drill the center of each 1″ hole, then cut the holes with a 15/16″ hole saw.

Raw spacers

Regardless of what’s marked on the hole saw, they all seem to cut a hole that’s about 1/32″ larger than spec, so using a 15/16″ saw for these 1″ holes left slightly undersize hole in each spacer that were easy to finish to final size with a Dremel tool.

Spacers done

John Sannizzaro stopped by today. He had a brand new tap that was just itchin’ to be used on my tiedown plates. We tapped both tiedown plates…came out fine!

Countersinking the spar holes

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I decided to take a novel approach to countersinking the spar holes that accommodate the wing access plate – I followed Van’s directions. That meant countersinking rivet holes, riveting the nutplates to the spar, then countersinking the access plate screw holes. I experienced none of the chattering or other problems reported by other builders. I think the key here is using a low-speed, high-torque drill to drive the countersink – a cordless drill works fine.

While getting ready to countersink those additional wing spar nutplates, I noticed that most of wing spar doubler plate (or “waffle” plate, as Van’s calls it) holes were somewhat oversize. Here’s a number #30 rivet in one of them.

Spacers done

I fired off some pictures and questions to Van’s. More to follow…

First step…getting things set up in the shop

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First step…getting things set up in the shop. Here are the spars, laid out for countersinking.

Oooh…pretty!

Like a lot of other new wing builders, I agonized over how best to make nice, clean countersinks for the tank and access plate screws. Some folks claimed that the Van’s approach – attach the nutplates first, then use a #30 piloted countersink that eventually engages the nutplate hole – seemed to result in chattering and countersinks that weren’t smooth and concentric, because the countersink starts cutting with nothing to center it.

My friend Jim used an alternative technique – a jig with a #30 hole to center the countersink pilot. With this approach, the countersink pilot is supported all the time rather than just when the countersink is deep enough to engage the nutplate hole as in Vans’ technique. I decided to use the jig approach for the tank attach screws. Here’s what it looks like…

Tank attach screw countersink jig

How to make this jig? First drill the #30 hole in your scrap Al, then center it under one of the tank attach screw holes. Once the hole is accurately centered, clamp it in place and match-drill to the #40 rivet holes on either side of the screw hole. You’ll need two sets of holes in the jig – one for nutplates parallel to the spar, and one for the angled nutplates at the spar’s root end.

To use the jig, attach it to the spar with #40 clecos, then clamp the plate in place and remove the clecos. Then, countersink the hole to the appropriate depth. The positioned plate and countersunk hole look something like this…

Clamped countersink jig

The first 2005 issue of the RVator has some improved instructions on how to countersink these screw holes to the proper depth without going too far. I strongly recommend you read up on this procedure before countersinking your spars…you might just save yourself some serious heartache.

The finished product. Looks good!

Finished countersinks

Fun with helicopters

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Completion of the inventory was delayed due to a work trip. Had to go to California for more fun with helicopters…

S-92 at Mammoth Lakes, CA

I finished up the inventory this evening. Nothing was missing, everything was in good shape. What a great job by Van’s! Now it’s time to start building. Bring on the platenuts!

The wing kit arrives

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The wing kit arrived today! Captain John, friend and fellow RV-7 builder, drove up from Plymouth MA to help us unpack and inventory. The boxes were big and bulky…definitely a multiperson job.

The big wing kit box

Ellen and I ripped open the wing spar crate. Just had to gaze at those beautiful gold anodized spars!

Beauty and the beast, redux

Van’s did a first-rate job of packing all those parts, and ABF got the boxes to our house undamaged. Everything looked great during unpacking.

Complete

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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

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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

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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

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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

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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.