April 14, 2006
I've been helping John Sannizzaro with his fuel tanks, so I'm not too worried about the process. In fact, I'm looking forward to something that doesn't require very much priming. I'm really learning to hate that stuff.
The only question in my mind was whether to follow Vans' instructions for fitting the tank to the Z-brackets, or to use the modified method that Dan Checkoway details in his website. I decided to go with the modified method; I don't like the idea of elongating holes in the tank baffles to make them fit, and if some alignment problem crops up in the modified method before drilling any holes, I can always go back to the plans method.
Per Dan's method, I clecoed the right tank together. All the cautions mentioned about fitting leading edge ribs apply to the tank ribs - even more so, since both the tank skins and ribs are formed from thicker material. That makes the hole alignment process more difficult. As with the leading edge ribs, spending some time smoothing the nose of each tank rib and making sure the flanges are 90 degrees to the rib will help the fitting process.
Here's the right tank clecoed together.
April 27, 2006
The last two weeks have been hectic. We're on the verge of closing on a house, so that means getting the wings to a point where everything, including the tank-to-wing attachments, are aligned and match-drilled in the current jig.
I don't have any pictures of the Z-brackets in fabrication, so you'll just have to imagine the process of drilling the brackets to the wing, then deburring, alodining, priming and riveting nutplates to them. Here's a pic of the final product on one wing - the Z-brackets are bolted to one wing and ready to be drilled in assembly with a tank baffle.
May 28, 2006
After the Z-brackets were in place, I followed the Checkoway MethodTM and fitted the clecoed tank on the wing.
With the tank in place the inboard Z-brackets were drilled, and after the outboard leading edges were removed, the outboard Z-brackets were drilled as well. Read and heed Van's instructions to use a drill stop when doing this work - it's damn easy to drill into the spar web or stiffeners if you're not careful. Here's a pic of the inboard bracket.
After the Z-brackets at each end of the tanks were drilled, the tank skins came off and the other Z-brackets were match-drilled to the baffles. Here's the left tank with skin removed, just before match-drilling.
With drilling complete on both tanks, the wings came out of the jig for our move to the new house.
September 28, 2006
I'm sure everyone who surfs this site (all three of you, including my mom) has been wondering why there are no updates. Our move to the new house took most of the summer, and then we disappeared to South Africa on vacation. It's September now, and the shop is back up and running, so it's time to get back to the tanks.
Here's one tank back in the jig for match-drilling and countersinking of the skin-to-baffle holes. This process is slightly tricky, since the tank skins are exactly the minimum thickness (0.032") for countersinking.
Captain John stopped by for a visit. We think that the wingtip plexi would make a great low-profile canopy.
October 15, 2006
Some more progress made on the tanks, this time fabricating and match-drilling tank stiffeners.
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.
There will be no updates for awhile, probably until mid-November. I'm off to Africa again, this time for work.
November 19, 2006
...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.
Only someone with my juvenile sense of humor would appreciate the unintended wordplay in the shrubs at the Zanzibar airport.
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.
These Mi-8/Mi-17 helos were parked at Wilson. They had been used for UN relief work, but were no longer flying.
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.
November 30, 2006
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.
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 -
Here are the left and right tank end ribs with stiffeners and nutplates installed. Nothing unusual here.
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.
December 10, 2006
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.
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...
December 13, 2006
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.
Looks good with the cap in place, huh?
Sorry, no pictures of the drain flange drilling process.
December 16, 2006
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...
January 1, 2007
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.
January 2, 2007
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.
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...
January 5, 2007
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.
And here's one fuel flange sealed and riveted.
January 7, 2007
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...
John had a good time...or maybe it was just the MEK fumes.
I'm just happy that we didn't 'smiley' a tank skin...
January 15, 2007
While waiting for another rib riveting session with John, I worked on fabricating the fuel pickup anti-rotation bracket for the right tank. My airplane will have a flop tube pickup in the left tank for inverted flight, and a standard pickup in the right. The anti-rotation bracket keeps the fixed pickup from rotating around its bulkhead mount, raising the end of the pickup and making more fuel unusable. When I mount the pickup later, the bracket's function will be clear.
Here's the inside face of the sender plate with the bulkhead mount and bracket Prosealed and riveted.
Here's the outside face of the sender plate; this is where the fuel pickup will attach to the rest of the fuel system.
January 28, 2007
Another rib riveting session, with special guest builder Antony Parchment in attendance. John has been helping both me and Antony do our fuel tanks, and Antony trekked down from Maine to help out. With this session we finished the first two ribs in the left tank.
February 4, 2007
I've been on the road a lot recently, having started a new job. John and I finished riveting all the ribs in both tanks except for the inboard and outboard end ribs. With the interior ribs in place, I plumbed the vent line into the right tank. Here's the inboard vent line fitting; the wire coming from the BNC connector attaches to the inboard capacitive sender plate, and it gets routed with and wrapped around the vent line.
And here's the outboard end affixed to the clip previously riveted to the fuel cap flange.
Unfortunately, I didn't get any pictures while I wired up the capacitive sender plates. The outboard plate is installed with the vent line, and the connecting wire from it is wrapped around the vent line as heads in toward the inboard sender plate. It connects there with the wire from the BNC connector installed on the inboard rib (see the first picture for this entry).
February 17, 2007
Not too many more pictures to show; I've haven't accomplished much on the airplane recently and what little I've done, I don't have too many pictures of. But here's one thing I did - fabricate a fuel pickup for the right tank, connecting to the fixed pickup and anti-rotation bracket I put together on 15 January.
What's missing here are the slots cut with a saw into the aft end of the pickup tube. I think this is a cheezy approach by Van's - anything the size of the saw kerf or smaller will go straight to the gascolator or fuel filter. My tech counselor thought the same thing, so he bought some brass screen from McMaster-Carr and fabricated a pickup like those used in production aircraft. I ordered some of the same material - 16x16 brass screen - and I'm going to try my hand at doing the same thing.
March 3, 2007
The last rib sealing/riveting tasks are installing the end ribs on each tank. Here's the right tank with the outboard rib riveted; there's obviously some cleaning-up to do.
The only detail worth mentioning on the outboard ribs is how to fit the T-410 nose reinforcement plate. With the rib clecoed in place, I laid out and drilled pilot holes in the reinforcement plate, then taped it in place against the inside of the rib with two-sided tape. That kept the plate in place while I removed the rib. It was easy, then, to match drill the plate and rib. The plate was sealed and riveted to the rib before the rib itself was riveted to the tank skin. Clear as mud, right?
March 23, 2007
I'm getting burned out on proseal and the mess and cleanup that accompany it. So I've been pushing pretty hard to get the inboard ribs riveted into both tanks. The only 'gotcha' on these ribs is fitting the T-410 reinforcement plates and the T-405 attach angles to the rib. The plans don't specify an exact location for the angle, it just fits as far as possible into the leading egde of the rib.
Some builders get into trouble by riveting both the angle and the plate in place before the rib is riveted; they then find out that there's no room to squeeze those rib-to-skin rivets that lie between the angle and the rib. Take a look at the picture below and you'll see how everything fits together.
For me, the best way to put this assembly together was to rivet the inboard rib in place with a minimum amount of sealant around the front of the rib. I held the T-405 angle in place and match-drilled through the top and bottom pilot holes into the rib, clecoing as I went. Then I removed the angle, taped the reinforcement plate in place inside the rib and match-drilled it through the holes just drilled in the rib. Finally, I clecoed both the plate and angle to the rib and match-drilled the remaining holes. For the left tank, the center hole also became the pilot for a 3/8" hole which will accomodate the flop tube bulkhead fitting.
March 24, 2007
Had a visit today from Jon Ross, my EAA tech counselor, and Mike Muratore, friend and former flight test colleague. We talked about tank sealing technique and fuel pickups. Looks like I'm still on the right track, and we'll plan another visit before I close out the wings.
March 25, 2007
With the end ribs in place, I worked on some of the cleanup items that needed doing before the tanks are sealed. One of those items is a Van's service bulletin that calls for safety-wiring fuel pickup attachments. Fortunately, the pre-made flop tube I bought from Van's already had a safety wire hole drilled in the flare nut, so all I had to do was attach the flop tube to the bulkhead fitting - using the proper torque, of course - then safety-wire the assembly.
Looks like this...
I was definitely out of practice with the safety wire pilers - took me a couple of tries to get a nice, tight twist on the wire.
March 26, 2007
A couple of weeks ago I received the brass screen I ordered from McMaster-Carr. I needed to finish up the right tank's fuel pickup, so I broke out the wire cutters, soldering iron and solder to fabricate a pickup screen.
This turned out to be a lot easier than I anticipated; the only trick was keeping the screen from unraveling while cutting and forming it. Running a bead of solder along one edge of the screen 'locks' the individual brass wires in place, making it easy to roll into a cylinder using a piece of 3/8" aluminum tube as a mandrel. Solder the long side of the cylinder together with more solder, trim the excess screen away then close the end - and voila, a pickup screen.
Before somebody emails me, yes, I do know now that Van's sells a pre-made fuel pickup with screen. But I already had the screen on order when I found out, so I decided to experiment - and it was easy to make an acceptable screen. I'll probably continue to experiment with this over then next couple of days.
April 2, 2007
The practice screen came out so well that I went straight to fabricating the flight article. The only change I made was to add some screen to the aft end of the pickup, rather than smash the end together and solder it closed.
Here's the screen in place on the pickup. It will be safety-wired and prosealed in place on the pickup tube.
April 15, 2007
Over the last three days I finished a lot of prep work on the left tank in preparation for attaching the baffle. Got the outboard rib sealed and riveted, attached and wired the sender plates, and permanently installed the flop tube into the inboard leading edge.
I also had to find a way to secure the hinge pin that holds the trap door in place on the second inboard rib. The second rib and trapdoor form a sort of header tank that retains fuel when doing aerobatics. I can foresee a need to remove the hinge and door at some point, so I wanted to make a clip that I could reach just by removing the access plate. The little clip has a small hole for safety-wiring the hinge pin, there's a little proseal on there as well.
May 28, 2007
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.
June 9, 2007
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.
July 21, 2007
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...
August 18, 2007
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.
September 7, 2007
This time, the tanks are really done and it's time for the dreaded leak check. Van's lists a couple of different options for pressurizing the tanks just enough to spot leaks with soapy water, while not rupturing the tanks in the process. I chose to build manometers for each tank and pressurize them together; if the water level in the manometers tracks together as temperature and air pressure changed, I'm assuming that the tanks probably aren't leaking. That, plus the usual spraying of soapy water should be sufficient. Here's the setup...
So how did it work? Pretty well, actually, once I sealed up all the expected leaks around filler caps, sump valves and vent lines. The temperature in our garage goes up and down quite a bit when the furnace/hot water heater comes on, and the manometer levels for both tanks matched over a full day's worth of monitoring. So I cleaned off the soap scum and declared success....again.
February 2, 2008
Ok, so the tanks aren't completely done - in particular, the left one. I was never really happy with the flop tube installation and the ability to properly torque the AN924 bulkhead nut that holds the flop tube in place. So to address this, I pulled the access plate off and drilled out the rivets holding the anti-hangup guide in place.
Using some spare 1/8" angle I fabricated an anti-rotation bracket similar to that installed in the right tank, eyeballed a location that would allow the flop tube to position correctly in the tank, drilled it to the inboard rib, and riveted it into place.
After that, I reinstalled and safety-wired the flop tube with a new AN elbow fitting and then re-riveted the anti-rotation bracket. A little proseal, a fresh cork gasket and some screws...and the job was complete.
