Joshua's RV-9A Project

Nursing some wrist pain today, so not much productive shop time.  Finished building the wing cart by attaching some swivel casters I picked up last night, and padding the leading edge cutout with foam pipe insulation, then set the completed left wing in the cart.  Looks good, and rolls nicely.  I think there is enough room between the two wing slots that the horizontal stabilizer could be stored on the cart, as well.

Drilled the flap and aileron brackets to the left wing, and pulled out the gap fairings to mess with for a bit.  Torqued the aileron bellcrank brackets in the left wing.  Dimpled the wing walk doubler for the right wing.  Cleaned up the shop a bit, and spent some time just sitting in the shop and looking at things, pondering.

(NB. This post being counted in multiple categories — something which may happen more often, as a work session touches on multiple items.  I’ve split the last several sessions into multiple posts, as the time blocks were larger and more well-defined.  In the case of multiple categories on a post, each category will total the entire number of hours from the session, but the “grand total” will count it only once.  I wish there was an easy way to resolve this, but it is what it is–and since the hours tracking isn’t a requirement of any sort, just for my curiosity, not a big deal.)

Set up the right tank for a leak test…as with the left tank, still fighting with the tape over the fuel cap, but after a couple tries, I think I got it to seal tight.  The pressure held fairly consistently until the temperature started to fall as the sun went down, and there were no bubbles observed on the spray-with-soapy-water check (except for the plug in the drain fitting, which I tightened to stop the leak), so I’m optimistic about this one.  Having no obvious leaks makes me feel almost as if something’s gone wrong, since reports of leaks on initial testing seem to be common…I suppose the true test will be in several years, when they see fuel for the first time.  Left the tank set up on the manometer, and will check again tomorrow to see how it fared.

Hopefully the last session with Proseal, at least on the tanks…  Encapsulated the rivet heads on all the skin-baffle rivets, checked over all the external seams and touched up anything that didn’t look 100%, then sealed on the access plate.  Swiped some screws out of the fuselage kit hardware for now…will order replacements on the next order from Van’s or elsewhere — $1.50 worth of screws and $10 (or whatever) of shipping didn’t seem like the best use of funds.  This tank should be ready for leak testing this weekend.

Opened the second can of Proseal, and installed the right tank rear baffle.  Same process as the first, using the ziploc bag of sealant.  Butter the rear of the ribs, drop blobs in the four corners, lines along the rivet holes, butter up the baffle seams, and drop it in place.  Cleco every other hole, rivet on the Z-brackets, squeeze the skin-baffle rivets.  Fillet the rear seam, encapsulate the baffle-rib rivets, and peel off the tape.  Encapsulation of the skin-baffle rivet heads will have to wait for another day, as the Proseal was getting rather stiff by the end of the session.  I mixed about 205 grams of sealant, which was enough to do everything here with some left over.  (Of course, a good portion of that squeezed out and was wiped off…)

All in all, not bad progress.  The confidence boost gained by the successful leak test on the left tank helped, as well.  I need to pick up some replacement screws for the access cover before the next sealing session (which, with some luck, should be the last!)  As before, I left the tank sitting with the baffle down, in hopes that the sealant will flow into the seam and prevent any leaks.  Finally, cleaned all the Proseal off the various tools…still have a bucket of clecos to un-glob, once the stuff sets up.

An afternoon of progress!  Began by taking the left tank out of the leak test setup and stashing those pieces for the right tank test.  I primed the tank’s top & bottom inside rear skins–where it contacts the spar–as well as the outboard end where it overlaps the splice strip.  I don’t know if this is really necessary or not, but since it’s in contact with other pieces, and I was setting up to prime today anyway, I figured it wouldn’t hurt anything.

After the primer had set, dropped the tank onto the spar and bolted in place, which went easily enough.  Followed up by installing the tank-to-spar screws, and only messed up the heads on 8 or so…sigh.  I think I need to find some better screwdriver bits.  They’re not too bad, but they’re a bit screwed up in the forward direction.  Throughout the process of attaching the tank, I was measuring and re-measuring the plumb lines to check for wing twist, but it stayed right on the whole time.

Some folks have trouble with the fit between the leading edge and the fuel tank, but mine is close enough that I don’t think it’s worth fretting over; it’s out by a half-skin-thickness in a couple places, but not bothersome.  I think this may be caused in part by the flat nutplates riveted to the curved splice strip, pushing it out of the necessary curve profile.

Later, I went back and did a final torque of the tank-spar bolts, and marked each one with torque-seal.

I’ve spent several days of on-and-off fiddling with the leak test of the left fuel tank, but am finally ready to declare victory.  It’s been holding pressure for almost 24 hours now, and passed the soapy-water test without any bubbles.  The fuel cap was the fly in this ointment–I had a bear of a time getting a leak-free seal.  The key, I think, is to use only as much tape as is required.  I was over-zealous with the tape for the first few go-rounds, which just created more joints where the air could leak out.  I tried the rubber glove trick…nope.  Tried chapstick (not having any Fuel Lube/EZ Turn) on the o-ring…nope.  (I have the “deluxe locking caps.”)  Finally, two very carefully-placed strips of packing tape seem to have done the job.

Pressure test was conducted using a homemade U-tube manometer built of small tubing, duct taped to one of the workbench legs.  The tubing is fit onto a stub of aluminum tubing and attached to the vent line fitting.  The tank drain was capped with the schrader valve from Van’s leak-test kit, however, I didn’t use that as the inflater, since I don’t have a bicycle hand pump (didn’t want to blow the tank by trying to use the compressor, either).  A piece of flared 3/8″ tubing was attached to the fuel suction fitting, and a short length of larger vinyl tube fit to the end.  Blow into the tube until the desired pressure is observed, fold the tube over, and clamp with a small vise-grips.  Perfect.  (The vinyl tubing didn’t leak–it’s ID was small enough that I had to heat it in order to slip it on the aluminum tubes.  Had there been leaks, I have some hose clamps that would have fit both junctions.)

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.

With a syringe of fresh sealant in hand, I went through the left tank and encapsulated all the rivet heads, touching up any other spots that looked even slightly questionable.

Installed the snap bushings and ran vent line in both tanks, as well as installing the vent line fittings on the inboard end ribs.  Easy enough.  I did have to adjust the vent line clips at the fuel cap flange, making them slightly larger in diameter to accept the vent tube without binding.

Also attacked the tank access plates – deburred, attached nutplates for the fuel sender, installed the fuel line fitting, fuel pickup, anti-rotation bracket, and fuel sender, and prosealed over everything (as well as the vent line fittings in the tanks).  The fitting of the fuel line fitting and pickup was an iterative process, as I put the plate on the tanks repeatedly to ensure that the end of the pickup was positioned as near the bottom of the tank as possible, yet reliably not rubbing on the tank skin.  The plans designate drilling the rivet holes for the anti-rotation brackets to #30, which allowed me to fix the misalignment of the holes I would otherwise have had, as the fuel fitting didn’t end up directly centered between those two rivet holes, in order to put the pickup where I wanted it.

I also used AD1097AD4-5 rivets (flush “oops” rivets) on the anti-rotation bracket, rather than the specified AD470AD4-5′s (universal head), as there was simply no way any of my rivet sets would get in there with the fuel pickup installed (the nut gets in the way), and you can’t install the bracket before you install the nut, as its whole point is to keep the nut in place.  So I used the oops rivets (this isn’t a structural point), and back-riveted them.  Even then, the angle wasn’t perfect, so a couple of the rivets aren’t perfect, but I don’t see it being a big deal.

Nearly ready to put the baffles on these tanks…need to find a flaring tool to make the vent line flares, and have a second pair of eyes take a look inside first.