Visit from John Sannizzaro

John Sannizzaro came up today and we riveted the first three ribs into the right tank skin. This was mostly a mess, so it was good that John was there to help. As with the stiffeners, it’s somewhat difficult to tell during riveting when the shop heads are correctly formed because they’re covered in Proseal. John looks at the circular “print” of the shop head in the residual Proseal on the bucking bar to make sure the shop head is the correct diameter, and that seems to work.

Another thing I learned is that the $120 tungsten bucking bar I bought from Bucking Bars by Webster was worth what it cost. It’s very easy to maneuver that small 5/8″x1″x4″ bar into the tank leading edge, and it’s a lot easier to keep a grip on it when your hands are covered in Proseal.

The last thing I learned is that an ordinary mushroom set on a 2X rivet gun can do a great job of riveting once you get the hang of placing the set squarely on the rivet. By rocking the gun and set very slightly, you can actually feel the set “center” on the dimple even with a rivet installed. Use one hand to keep the set in place, and the other to hold the gun and squeeze the trigger, and you can get very nice rivets with no ‘smileys’. This also helps avoid the need to press firmly with the rivet gun, which would cause slight ‘dips’ in thinner skin. Of course, this only works when you have a partner who’s bucking the rivet.

Here’s the first couple of ribs we installed…

First tank ribs riveted and sealed

John had a good time…or maybe it was just the MEK fumes.

Captain John

I’m just happy that we didn’t ‘smiley’ a tank skin…

Captain Dave

Riveted tank flange and cap

After a little success on the stiffeners I sealed and back-riveted the fuel cap flanges, then sealed and riveted drain valve flanges. The only tricky area is making sure the fuel cap flange and skin are pressed down tightly against the back-riveting plate when setting those flage rivets. Here’s the right tank fuel cap flange. No pictures of the left tank cap, but you get the idea.

Riveted tank flange and cap

And here’s one fuel flange sealed and riveted.

Riveted drain flange

And then there was Proseal

And then there was Proseal. Vans’ instructions cover this process pretty well, and I used Dan Checkoway’s narrative as well to help visualize the process.

It’s really helpful to have everything you need in one place before doing any mixing and sealing. I found a relatively cheap digital scale which made it relatively easy to measure out the Proseal. I also spent a fair amount of time cleaning the skin and stiffeners with MEK to get them nice and clean. It’s important to have lots of latex or nitrile gloves – you’ll need ’em. Also have lots of rags and MEK (or naptha) on hand for cleanup. I also put a couple dozen rivets in a glass jar with some MEK to keep them clean.

Proseal supplies

There’s not much I can add to Dan’s process, so I won’t try – except to emphasize the difficulty in checking shop heads on the back-riveted stiffener rivets. There’s one rivet there I’m not proud of on the right tank skin, but it wasn’t worth the trouble to drill out – and it’s covered with Proseal anyway. Here’s my first attempt at tank sealing…

Riveted stiffeners

Scuffed tank skin

Nothing much doing over the holiday week but deburring and dimpling tank parts – skins, ribs and baffles. Not too exciting, except for one issue. After reading some VAF posts about cracking dimples, I examined some of the tank skin dimples with a 10x jewelers loop and saw what looked like some tiny cracks on four or five dimples. Somewhat concerned, I emailed Van’s. Their response was that a lot of things on the airplane woudn’t look very pretty when magnified ten times, and that if there were no cracks visibile to the naked eye – which none were – then everything was probably ok. I decided to go with their recommendation.

Any surface that gets Proseal must be scuffed to improve adhesion, so I did just that. Here’s one of the skins scuffed with a maroon scotchbrite pad.

Scuffed tank skin

Little trapdoor

Today’s mission – fabricate the little trapdoor that keeps fuel in the first “bay” formed by the end rib and first interior rib. This is a part of the inverted fuel system – the door opens inward, but obstructs fuel flow outboard when the airplane is in less-than-coordinated flight. In my airplane, only the left tank is so equipped…

Left tank trapdoor

Flange and cap

The only thing I accomplished yesterday and today was fitting and match-drilling the fuel filler cap and drain valve flanges. The only area which requires more-than-usual care is making sure that the curavture machined into the filler cap flange aligns with the upper tank skin curvature. Holding the flange approximately in place against the skin and rotating it slightly will give you a feel for where the fit is best. Once the rotation is correct and the opening is lined up, clamp and drill.

Fuel cap flange clamped in place

Looks good with the cap in place, huh?

Flange and cap in place

Sorry, no pictures of the drain flange drilling process.

Anti-rotation bracket

The right fuel tank gets a standard fuel pickup – an L-shaped aluminum tube mounted to the access plate that picks up fuel from the aft inboard corner of the tank. A few years back, Van’s found out that these pickups could, if not installed properly, rotate up – rendering unusable any fuel below the pickup. The solution for this problem is an anti-rotation bracket, a piece of aluminum angle that fits over the pickup fitting and is riveted to the access plate. Look at the picture and the function is obvious.

Anti-rotation bracket

The only catch to fabricating this bracket is accurately locating the 9/16″ hole that accomodates the fitting. If the hole isn’t quite right – too far out or in – the fitting won’t fit squarely on the access plate. Maybe I’m the only builder to have problems with this…

Back to airplane building stuff

Back to airplane building stuff. I spent a day or so refamiliarizing myself with the the plans, then started preparing tank end ribs and capacitive fuel quantity sender plates.

Preparing the inboard ribs is a straightforward task with the right tools. I used a flycutter to cut the sender access plate holes, and a unibit to cut smaller holes for the vent lines and capacitive sender BNC connectors. If you use the flycutter, make sure to clamp the rib firmly to the drill press and keep your hands or other appendages clear while the cutter is working. It will make a mess of the rib – or your hands – if you don’t.

After the hole is cut, the instructions call for locating and match-drilling the cover plate screw holes by clamping the cover plate to the rib. That requires some extra work to make sure that the cover plate is actually centered on the hole. It seemed to me that it would be easier to center the stiffener ring on the rib and match-drill the holes that way – so I did. The only catch is that ring must be rotated so that the holes will allow the access cover’s flat forward edge to line up with stiffening ridge pressed into the rib. Clear as mud, right? Here’s a pic of one prepped rib, with the stiffener ring platenut holes drilled and dimpled.

Tank access, vent, and BNC holes

The left tank will be fitted with an inverted ‘flop tube’ fuel pickup. That requires fabricating a couple of ‘anti-hangup’ guides that keep the flop tube from becoming lodged in or around the access plate or between the tank stiffeners and ribs. Here’s the access plate guide, it’s just a strip of 0.025″ aluminum bent, drilled, dimpled and riveted to the stiffener ring. Looks like this –

Anti-hangup guides

Here are the left and right tank end ribs with stiffeners and nutplates installed. Nothing unusual here.

End ribs prepped

I’m fitting my tanks with capacitive senders. The sender kit comes with two aluminum plates for each tank that must be drilled to ribs, then outfitted with nutplates and connectors. The plates are attached to those ribs with plastic spacers and insulators; more on that later. Here are a couple of plates ready to have the connectors covered with Proseal. The square cutouts on the bottom of each plate fit around the fuel tank stiffeners.

Capacitive plates

First stop – Zanzibar…

…and I’m back from Africa. It was a long trip – we traveled to Dar es Salaam and Zanzibar, Tanzania, then to Nairobi, Kenya, and finally to Kampala and Soroti, Uganda. The work was tiring and stressful, but I’m glad I went. I’m not gonna do a travelogue, but I’ll throw out some some pics for all you aviation types.

First stop – Zanzibar. For those of you in the States who slept through geography in high school, Zanzibar is an island in the Indian Ocean off the cost of Tanzania. It’s a prime tourist destination, and there are lots of GA airplanes flying tourists from Dar to Zanzibar. We hopped a short (~20 minute) flight to the island in a Cessna Caravan – a neat airplane, and very popular in that part of Africa. Here’s our flight on the ramp at the Zanzibar International Airport.

Zanzibar Caravans

Only someone with my juvenile sense of humor would appreciate the unintended wordplay in the shrubs at the Zanzibar airport.

Zanzibar shrubs

The next stop was Nairobi. We visited both the main international airport (Jomo Kenyatta) and the largest GA airport (Nairobi Wilson). There are a lot of ex-Soviet aiframes flying around east Africa. Here’s an Antonov An-12 transport parked at JKIA. Some of these airplanes are barely airworthy and are used for running guns and other illegal stuff around the hotter spots in Africa. This one actually looks pretty reputable.

An-12 at JKIA

These Mi-8/Mi-17 helos were parked at Wilson. They had been used for UN relief work, but were no longer flying.

Mi-8 at Wilson

Last stop – Entebbe/Kampala, Uganda. This picture is of the old Entebbe terminal and the UN relief aircraft flying personnel and supplies to the Sudan and DR Congo. Those of you who were paying attention to the news in July 1976 will remember that this terminal was the scene of the famous “Raid on Entebbe” by Israeli special forces who freed passengers from a hijacked French airliner.

Entebbe terminal

More progress made on the tanks

Some more progress made on the tanks, this time fabricating and match-drilling tank stiffeners.

Tank stiffeners match-drilled

After that, fabricating the T-405 tank attach brackets was next. This was a lot of work, and the plans aren’t much help. A full-scale layout would have made this job a lot easier. There’s also a bit of guesswork to make sure the brackets fit into the tank leading edge with some room to spare for rivets. But they’re done, and I think they look good.

T-405 backets

There will be no updates for awhile, probably until mid-November. I’m off to Africa again, this time for work.