Joshua's RV-9A Project

Concert season is winding its way to a close, lawn is mowed and the garden is ready for planting; finally a chance to get back into the shop for some quality Proseal time.  Finished up the left tank today, with only one major moment of frustration…

Before sealing things up for good, I gave as much of the tank as I could see an look-over with light & inspection mirror, with a special eye toward the skin-baffle joint and the four outside corners that received the “blobs” of sealant.  Everything looks good, but that can mean nothing–the proof is in the leak test.  Ran two beads of sealant from a syringe around the access plate opening, and clecoed it in place without trouble, then replaces clecoes with screws one-by-one in a star pattern, like lug nuts or head bolts, also twirling each screw in Proseal, and dabbing a bit in the hole, so that I ended up with a bed of sealant squeezed out around each screw head.

When the access plate was sealed on, all the screws in place, I began to go back with the torque wrench to check their tightness…that’s when it happened.  The second screw I torqued snapped off.  My smallest extractor was too big, so out came the other 11 screws, and a vise-grip was the tool of choice to run the broken screw fragment out the back of the nutplate (plan B would have been to drill off and replace the nutplate, but that has a greater risk of contaminating the inside of the tank with aluminum shavings).  Cleaned up the sealant with acetone, and did it all over again.  I used the screws that had been set aside for the second tank, as I didn’t know which of the 11 screws was the first one I torqued–I didn’t want to have another screw snap off, if I’d streched the first one.  I’ll pick up some replacement screws for the second tank; maybe even the hex-head cap screws some folks like to use.

I’ve heard of people over-torquing these AN fasteners many times, which is why I bought an in-lb wrench to use…I guess 20-25 in-lb is still too close to the bottom of it’s adjustment range to be accurate.  On the second try, I didn’t use the wrench, electing to use instead the ancient “gudentite” torque system.  (I did use the wrench on a bolt clamped in the vise, to get a feel for the required amount of torque…I’m confident I’m acceptably tight.  If these were structural fasteners, I’d try to find a decent torque screwdriver, but they didn’t have any at the stores I visited when looking for the in-lb wrench.)

With the access plate fun out of the way, I encapsulated the heads of all the rib-baffle and skin-baffle rivets.  After a few days to cure, this tank will be ready for pressure test.

Finished up some details on both tanks: sealed the interior vent line conections, put the screws in the fuel senders and sealed them, sealed over the rivet heads for the anti-rotation bracket.  Gave a final look to the tank interiors, and wiped down the baffles with solvent to remove dust.

Lots of Proseal…installed the rear baffle on the left tank.  I erred on the side of “too much,” since it seems this is one of the more common places for leaks to occur.  Mixed up a plate of sealant, and another batch in a ziploc bag, which had the corner snipped off for use like a cake-decorating bag.  That worked quite well to lay the beads inside the tank, the blobs in the corners, as well as beads on the rear flange of each rib.  I also laid a light bead along the top & bottom surface of the baffle, and spread it thin with a popsicle stick.

Having masked off the spar-mating surface with blue tape, I slid the baffle into the tank and clecoed to the ribs, then every other hole to the skin.  Buttered up the back of each Z-bracket and clecoed in place, then went bank with the blind rivets, first twirling them in yet more sealant.  The ground-down puller worked fine, and none of the stems broke off high.  The end ribs are done with solid rivets, since the tails are on the outside of the tank.

Next, squeezed rivets in each open hole, from the center out to each end, then went back and pulled the clecoes and riveted the rest of the holes.  This requires a regular yoke with a deeper throat (my regular yoke isn’t deep enough, so I used the longeron yoke, along with the no-hole yoke where the Z-brackets interfered with access.

Finally, cleaned up the excess sealant from the outside of the tank, smoothed the fillets on the outside, and pulled the tape.  I set the tank on the floor with its aft side down, in hopes that gravity will help the still gooey sealant find its place in the baffle-skin joint.  I’ll need to go back and dab sealant on the heads of the rivets, then let everything cure for awhile before setting up a leak test with fingers crossed.

Earlier in the day, also managed to get the bottom spar dimples primed.  More primer on order, as I don’t have enough in the can to do the wing skins.

My Rolo-Flare tool arrived in today’s mail, so spent some time fiddling with it on a piece of scrap tube, then did the flares on the fuel tank vent lines and attached them to the bulkhead fittings.  Also drove the two rivets in each tank that were a pain before, where the inboard attach bracket is too tall for the straight rivet set (much easier to set now that the sealant is cured, and not lubricating the set; was able to use the single and double-offset sets to finish them up).  All that remains on the tanks is to encapsulate those inboard end rivets, Proseal the vent line fittings, and attach the baffles & Z-brackets.

Finished attaching the right LE assembly to the spar by squeezing the top & bottom rivets in place.  Done.  Pulled out the left top wing skins and deburred, edge-finished, and dimpled them; ready for primer, but too windy to prime today.  Made it through spot-priming of half the rear spar dimple/countersinks before dinner.

Jacked up the right wing, measured and tweaked the fixture, then clecoed the leading edge assembly in place.  More measureing and checking, then riveted the rib-spar rivets, as on the left wing.  All came out fine, only had to drill two.  Allison did a great job driving the rivets on the two-man rib (third inboard).

Finished dimpling the wing skeletons, and enlarged the rear spar dimples with the deburring bit as described in the manual.  Checked the left wing in its fixture, re-stringing the line along the spar rivet row, and hanging the plumb lines at inboard & outboard ends.  Leveled, measured and adjusted until the twist was zero, then dropped the LE assembly on top and clecoed in place.

Riveted the assembly to the spar, and managed to use all solid rivets.  Going in, I was convinced that I would end up using blind rivets on many of the ribs (as many 7 builders do, with Vans’ approval), but the 9 wing design must allow more space, as I didn’t have any trouble.  I did need all three of my universal-head rivet sets (straight, offset, and double-offset) in various places, and the third rib from the inboard end is a two-person job due to the reach.  (Thanks to father-in-law Bob for help driving those rivets!)  None needed to be drilled out, and the rows of skin-to-spar rivets went quickly with the squeezer.  Left leading edge is installed!

Next will be the right LE to spar, then deburr/dimple/prime the wing skins.  Still need to get a flaring tool so I can flare the ends of the tank vent lines in order to seal up the tanks.

Finished the riveting of the leading edges; worked the right assembly in the cradle, then stood both L & R on end to reach in and drive the last 3 rivets at the nose of each rib.  Both came out nicely.

Primed the skin countersinks on the spar flanges, as well as dressed out & primed several bucking dings on the webs.  Started dimpling the wing skeletons…lots of holes!  Got a little more than halfway through.

About 3/5 of the way through riveting the leading edge assemblies.  Completed the bottoms of both left and right, and the top of the right excepting the forward-most three rivets on each rib.  Those are at an angle where the tabletop interferes with the rivet gun, so I’m going to finish both sides through that point; then either stand the assemblies on end to rivet those final three (the same way I did the fuel tanks), or tilt the cradle blocks so they’re accessible.

Also drilled out the tie-down ring holes in alignment with the tie-down bars bolted to the spar.  Test-fit the left LE to check fit again; no problems noted.

Clecoed the primed LE components together and test fit on the wing skeletons (again, to be sure they went back together correctly, remembering the trouble I had fitting the left LE the first time).  No problems with the fit, so they’re ready to be riveted.  Need to touch up some bucking dings on the spar before they can be riveted on for good.

Also riveted the LE light brackets together and fit the reflectors in place.  These won’t go into place until the LE assemblies are riveted onto the spar, to save them from vibration.  I’ll fit the lenses once the LE’s are riveted together, but probably off the spar for easier access.

Skeleton deburring complete, and nice weather outside, I prepped & primed the leading edge skins, ribs, splice strips, and landing light components.  Ready to rivet!