Got the wing skins and inspection hole covers prepped and primed today, that’s the last major work on the skins before they get riveted on the wing boxes.
Category Archives: Wings
Or at least I thought they were done.
Or at least I thought they were done.
I thought I had torqued the left tank’s bulkhead fitting down sufficiently when I installed the flop tube. But while preparing the tanks for leak checks, I torqued a sealing cap onto the bulkhead fitting and the fitting shifted despite being torqued and prosealed in place. So…I pulled off the access plate, cleaned off the cured proseal, torqued down the bulkhead fitting a bit more, and replaced the access plate. What fun. Really. Can’t you tell by the expression on my face?
To get my hand inside the tank far enough to get a wrench on the bulkhead fitting, I had to cut the anti-hangup guide away and rivet a new piece of aluminum after the bracket was finished.
Finished installing the Duckworks landing light kits in both wings
No, I haven’t been doing nothing for the last month. Go look at the Tanks page to figure out what I’ve been up to.
Over the last four days I finished installing the Duckworks landing light kits in both wings. This is one of the last things I needed to do on the leading edges before they go onto the wings for good. Most of the ticklish and potentially expensive stuff got done back in April, like cutting openings in the LEs. What’s left is trimming and fitting the plexiglass lenses, and installing reflectors and halogen bulbs in the light brackets.
If you’re reading this you either (a) are building – or want to build – an RV, (b) don’t have anything better to do, or (c) are my mom. So for the benefit of you folks in group A, I’m gonna give you the gory details of finishing these lights as I learned to do it.
The first step is taking the plexiglass lenses as provided and trimming them to a size slightly larger than the leading edge opening – the instructions give apprpriate dimensions. You gotta provide enough space on the top and bottom for mounting strips, but not so much extra that you can’t get the lens in and out through the LE opening – which you’ll have to do when changing bulbs. To make this a little easier I stuck a drop light in the leading edge and used the illuminated opening to measure and lay out cut lines on each edge of the lens, as well as to marks the opening itself on the lens..
Before working with the lens, I covered it with removable masking tape to make marking easier and protect against scratches.
Marking the LL plexi lens
Once the cut lines were marked on both lenses, I trimmed them with a cutoff wheel in my Dremel.
Trimming the LL plexi lens
Following the instructions, I then fabricated “handles” from fiberglass-reinforced packing tape and coaxed the lenses into the leading egde. Pulling the lens tight against the leading edge, I match-drilled the mounting screw holes through the skins into the lenses. It’s important to keep that lens snug – it directly affects the final fit of the lens – but not to push on the lens from the back. That, apparently, can make the lens too snug and make it difficult to install. It’s also important to use a dull drill bit to make those initial holes in the plexi; sharp drill bits dig into the plastic and can cause it to crack. Here’s the lens with all but one hole match-drilled and clecoed.
Match-drilling the LL plexi lens
The next step was edge-finishing the lenses and drilling the mounting screw holes to their final sizes. Edge-finishing was easy with some sandpaper. I opened up the holes to final size using a special plexi drill bit from Avery, then countersunk the screw holes with a #30 piloted countersink. Countersinking is another opportunity to crack the lens if you go too fast – slow and steady gets the job done nicely.
Lens trimmed and drilled
A few other steps need to be accomplished before the installation is done. First, the reflectors and bulbs must be installed in the light brackets. Duckworks provides automotive driving lights that must be disassembled to provide those parts; the only gotcha here is to make sure you wear gloves when handling the reflector and bulb – skin oil on either can cause them to get too hot. Otherwise, it’s straightforward.
Lamps and reflectors installed
Second, the retaining brackets that hold the lenses in place had to be final drilled and have nutplates installed to accomodate the lens mounting screws. The brackets are match-drilled to the leading edges just as the lenses are. The only real work here is installing the nutplates, and attaching the brackets to the lenses with two-sided tape. One last thing – the skins must be dimpled to accomodate the mounting screws…#6s, I believe. Do yourself and use a real #6 dimple die set. The instructions imply that you can use #30s, but that just wouldn’t look right.
Lens installed
Finally, the light brackets were installed and the lenses attached. Overall, I was pretty happy with the results. The right wing lens fits a little better than the left, but both will get the job done.
One side finished!
It’s time to dimple the skins
It’s time to dimple the skins. Dimpling a relatively stiff part like a leading edge is easy to do with minimal help, but the wing skins are large and floppy. Even with Ellen’s help, some additional support was needed. So I dusted off the support table plans that came with the DRDT-2 and made a runto Home Depot for some particle board and carpet remnants. Throw in some wood glue, wood screws and a little elbow grease, and voila – a dimpling stand.
Spar-to-skin countersinks
With an hour’s help from my awesome, wonderful wife, the skins were dimpled. Following that, I whipped out the squeezer and dimpled the wing inspection plates and corresponding screw holes in the wing skins.
Countersinking
I’ve been avoiding countersinking the skin attach holes on the spars, but I couldn’t put it off any longer – I hate drilling/cutting those things. I reviewed Vans’ instructions on countersinking and found out – once again – that their instructions were right. They specify that countersinks which accept dimpled skins should be deep enough so that a test AN426 rivet should sit flush to 0.005″ below the countersunk surface. So, I tweaked up my countersink and did some checking with the depth measurement pin on my calipers just to make sure that everying was set correctly – then fired away. Here’s the beautiful finished product…
Spar-to-skin countersinks
…and here they are primed. I really don’t like to prime in the shop, but in this case I had no choice. I cranked down the air pressure and flow volume on my HVLP detail gun and had no problems.
Spar-to-skin countersinks primed
A lot of deburring
Got the wing skin edges and holes deburred this weekend. Four skins per wing times two wings = a lot of deburring. The edges were easy; the holes took a lot of time. I used Ellen’s cordless screwdriver and threaded deburring bit adapter that I fabricated last year.
The right tank is complete!
Oshkosh is looming on the horizon, we’re headed out in a few days with Mr. and Mrs. Captain John. I wanted to get the right tank closed out, so John and I took a Saturday to seal and rivet the baffle and Z-brackets. This one went smoothly as well, but took us a couple of hours longer because we didn’t have the services of master prosealer Antony Parchment. As before, we used a 60cc syringe with the tip cut to provide the 5/16″ diameter sealant bead recommended by Van’s.
Happy to be almost done, I’m applying proseal with the syringe.
Almost as happy to be almost done – or maybe it’s because he know’s we’re headed for margaritas – John inspects my work with the obligatory magnifying glass.
The only real problem we encountered was setting the solid rivets that attach the inboard and outboard Z-brackets. We were on the verge of using blind rivets after a couple of the solids took a couple of tries to get right. It worked out in the end, but I definitely need to work on my bucking/shooting technique for #30 solids.
The next day, I buttered up the access plate (this one with a fixed pickup) and sealed/screwed it in place. With that, the tanks are done – except for leak checks. I’m keeping my fingers crossed…
Busy working on the tanks
Not much going on with the wing structure in the last three weeks – my time has been spent working on the tanks. All I accomplished was re-checking the jigs to make sure there’s no twist orsag as I get ready to put the skins on for good. I also started deburring wing skins. Boy, that’s a lot of fun.
Yet again, more stuff that I won’t waste your bandwidth with boring pictures.
Nutplates on the stiffener ring was either stripped, or too big
I had great plans last weekend to close out the left tank by attaching the access plate. I mixed up a batch of proseal, butttered up the cork gasket and plate, and had everything almost completely done when I found out that one of the nutplates on the stiffener ring was either stripped, or too big. What a freakin’ mess – two hours wasted on putting the plate in place, then removing it and cleaning off the proseal.
Today, I drilled out the offending nutplate. Looks like I accidentally installed one that was too large. – d’oh! I installed the correct one this time – and checked all the nutplates in the yet-to-be completed right tank to make sure I didn’t make the same mistake there.
Did a bit more cleaning up to make sure no rivet residue was left in the tank, then mixed up a batch of sealant and attached the access plate. Had to do some on-the-fly research to find the right torque for those screws, looks like it’s 15-20 in/lbs. And with that, the left tank is complete.
Critical mass of builders
Got a critical mass of builders together today to seal and rivet the left tank baffle and z-brackets. Captain John came up from Plymouth, and Antony Parchment came down from Maine to help out. Attaching the baffle is more complex than it appears, it was certainly handy to have two extra brains and two extra pairs of hands and eyes.
Antony is a whiz at proseal. I copied his process and have wasted a lot less material. Here he’s mixing up the first batch and loading up the large 60cc syringe we used to apply sealant to the skin and rib flanges. We followed Vans’ instructions here and everything seemed to work fine.
Here’s the tank with sealant applied, just before the baffle was dropped in place. We followed Vans’ instructions, I really don’t have anything to add to the process except the syringe worked out really well. The local medical supply store probably wonders why I’m always there buying latex gloves and syringes…
One word of caution, when you’re attaching the Z-brackets, check to make sure that they’re oriented correctly – it would be very painful to find out that one Z-bracket was on backwards after the tank was complete! Just to be sure, all three of us checked the brackets with the plans before we pop-riveted them in place.