I've been on the road much of the last three weeks - trips to Wichita and Vancouver. The few days I have been home I've made progress on a few small items.

I was waiting for the Proseal to cure after doing the fuel tank service bulletin. I've finished a leak check on one tank, and the other one is almost done. The first tank had no leaks, and I'm 99% sure the second one is OK (the water level in the manometer is down a tiny bit after a week, but that is likely due to atmospheric pressure variations).

There have been at least three engine failures caused by fuel pickup tubes that came loose inside fuel tanks. One aircraft was destroyed in a forced landing (the pilot survived, fortunately) and at least two other aircraft did successful forced landings. In February, Van's released a Service Bulletin (SB) on the subject. The SB calls for the tank access covers to be removed, the fuel pickup tube fittings to be drilled for safety wire, tightened, and safety wired.

It seems that two of the three incidents were on aircraft that had been built from quick build kits. The builder does not build the fuel tanks on these kits - he just has to inspect them, then install the access cover. The fuel pickup tube is in place, but not tightened. It seems that many builders miss the step in the instructions where they are told to tighten the fuel pickup tube.

I was reasonably sure that my fuel pickups were tight, but decided to open the tanks up just to be safe. It took several hours work to get the access covers off and clean the old Proseal off. I drilled the fitting the for the fuel pickup on the right tank and secured it with safety wire.

The left tank has a flop tube (fuel pickup on the end of a flexible hose) to provide fuel during inverted flight. The SB calls for the flop tube to be safety wired to its attachment elbow fitting. I wasn't crazy about this, as it means you have to pull the attachment elbow out of the tank so you can so the safety wiring. Then you have to Proseal it back in place and hope it doesn't leak. And, you have to do this all over again whenever you replace the flop tube (they gradually stiffen up as the hose ages).

Having a flop tube come loose doesn't really add a new risk, as flop tubes can get hung up inside the tank so that they aren't resting on the bottom. The result is the same in either case - a bunch of fuel in that tank becomes unusable. So, if you have a flop tube, you need to always operate the aircraft as if fuel in that tank may not all be available. In other words, you plan to use the fuel in that tank first, so that if it all doesn't feed you can switch to the other tank and land.

Given that having a flop tube come loose is no worse than having it hang up, which is a risk that I have already accepted, I decided to not put safety wire on the flop tube. I simply made sure it was very tight, and then put some Proseal between the fitting and the threads. The Proseal will be almost as good as safety wire, but it won't make it too much harder to replace the flop tube when that time comes.

For some reason, I thought I should check the resistance of the fuel senders while I was working on the tanks. This turned out to be a good idea, as the one on the right tank gave screwy results. It turned out that the fuel sender was not grounded to the tank - the Proseal acted as an insulator. I'm glad I discovered this now, as I would have needed to mix up some more Proseal whenever I found the problem. I fixed it by removing one of the fuel sender attachment screws, and put a ring terminal on it, with internal tooth lock washers above and below the ring terminal. The teeth on the lock washers made a good connection between the fuel sender and the attachment bolt, and now it seems that the attachment bolt has a good connection to the tank. Now the fuel sender resistance is correct, even without hooking up that ground wire.

I had some left over Proseal, so I used it to seal the bottom corners of the firewall. I wish I had done that a long time ago, as I spilled some oil when I pulled one of the oil hoses off to pressure test it. The spilled oil ran down the firewall, and some of it seeped inside the lower fuselage. The oil later seeped out near the right landing gear leg area. The spilled oil is inside the lower fuselage, where I can't get at it. It will probably cause untold grief when it comes time to paint the aircraft.

It's been two steps forward, and three steps back with the fuel tank leak fixing. Last weekend I put some Proseal inside a corner of the left fuel tank to hopefully fix a leak. It's a week later, the Proseal is cured, so I started a leak check yesterday. It is hard to say for sure, as the level in the manometer goes up and down with the temperature and atmospheric pressure, but there certainly isn't a large leak. I'm hopeful.

But the bad news is that on Thursday Van' Aircraft released Mandatory Service Bulletin (SB) 06-2-23, which "requires" RV owners to open up the fuel tanks to add safety wire to the fuel pickups. It was triggered by a fuel pickup that became undone inside a fuel tank, resulting in fuel starvation and an off-field landing. After Van released the Service Bulletin, another builder reported that the same thing had happened to him, but he was able to glide to an airfield. So, with two known incidents, I agree that it is wise to secure the fuel pickups so they cannot unscrew. I'll have to open both fuel tanks up to do this, so that'll mean yet another round of leak checks. The leak check I'm doing now is still useful, as I need to know whether the repair I did last week is working.

SB 06-2-23 "requires" the owner to remove the fuel pickups, drill a small hole in each securing nut, and to use safety wire to secure the nut after tightening it. This is easy enough to do with the normal fuel pickup, but it is a much bigger job if you have an inverted fuel pickup (as I do in the left wing). The normal fuel pickup is mounted on the access cover on the inboard end of the fuel tank, so you it comes out of the tank with the access cover. But the inverted fuel pickup screws onto to an elbow way up in the very front of the fuel tank. It would be pretty much impossible to get safety wire on it, working through the access cover near the back of the tank. So, Van recommends that the elbow be removed so the safety wiring can be done on the bench. But, this means that you need to somehow scrape off the Proseal that keeps it from leaking around the elbow, then put some new Proseal in place after reinstalling the elbow. That looks like a leak waiting to happen.

I'm planning an alternate means of compliance with the SB. I'm going to spread some Proseal on the nut that secures the inverted fuel pickup to the elbow, after making sure the nut is properly tightened. There is no way that nut will come loose if I put a good layer of Proseal on it and the elbow. The inverted fuel hose I've got now is made from a type of hose that is supposed to be replaced every few years. I'll order a length of Teflon lined flexible hose, as it has a supposedly infinite service life. - I've learned that the Teflon hoses are quite a bit stiffer than conventional hoses, and it is quite possible that they are too stiff to work properly as an inverted fuel pickup. I will not order a Teflon hose for this application.

Update - 28 Feb 06 - Another builder has stepped forward to say that he totaled his RV several years ago after the fuel pickup came undone, so we are up to three known events.

I spent the week in Seattle, in a Synthetic Vision workshop sponsored by the FAA. Synthetic Vision is a new technology that is just starting to show up in avionics for type-certificated aircraft, and the workshop was an attempt to start getting all the manufacturers and certification authorities on the same page about certification requirements.

Thursday evening I managed to meet up with RV-8A builder Terry Watson. Terry is building a very nice RV-8A, but like me his completion percentage vs time curve looks to be asymptotic. After visiting Terry's project, we went to Paine Field to meet up with Mike Robbins - Mike has a very nice RV-8. And we visited the project of RV-8A builder Marc Drake.

Marc also works on another very interesting aircraft, the R-4360 powered Sea Fury Furias. They are in the midst of adding a second seat, and plan to have the aircraft back together in time for the Reno air races. The Sea Fury looks absolutely huge compared to the RVs, but it has had 28 cylinders and 4,000 hp, so it gets out of its own way without too much trouble.

Yesterday I did some more wiring bundle clean up. A package of misc hardware arrived from Van's while I was in Seattle. So today I attacked some of the little odds and ends that were waiting for parts. The biggest item completed was I put some Proseal inside the fuel tank to hopefully seat the leak I had. Then I Prosealed the access cover back on. I'll give it a week or two to cure, then try a leak check again.

I got up early this morning and hit Home Depot when they opened at 8 AM. I searched the plumbing section high and low, and finally found a 2" plumbers test plug. It is a cylindrical piece of rubber, with a thick steel disk on each end of the cylinder. There is a large bolt through the two disks with huge wing nut. You insert the plug in the item to be sealed, then turn the wing nut to compress the rubber, causing its diameter to increase. I stuck one in the fuel filler hole and snugged it in place. No more leak there.

It took a lot of trial and error with soapy water, but I finally found a slow leak at the fitting where the fuel line attaches to the fuel tank. There is a bulkhead fitting that comes through a hole in the tank. A large aluminum nut on the outside secures it in place. I had put Pro-seal around the edges of the nut, but I didn't seal the interface between the nut threads and fitting. I've got a small leak at the threads. It is pain to have a leak to fix, but the good news is that I don't have to open the tank up to fix it. I have to put some sealant around that threaded joint.

This is the fuel outlet fitting on the other tank. You can see that I did cover the threads with Pro-seal on this tank. I don't know why I didn't do that on the other one.

The fittings on the two tanks are in different places because the left tank has a flop tube for fuel pick up. The flexible tube has a weight on the fuel pickup end, so it goes to the top of the tank in inverted flight. The other end of the tube is connected at the very front of the inboard tank rib, so that is where the fuel line attaches. The right tank has the normal fuel pickup, which only works in normal flight. The fuel line attaches to its fitting in the middle of the inboard tank rib.

This afternoon I hooked up the right tank for its leak test. I had a slow leak, but finally found that I needed to tighten the connection at the fuel line fitting. It was only finger tight. I fixed that, but the water level in the manometer was still coming down a bit. I spent a long while with the soapy water, but couldn't find a leak. I went back down a few minutes ago, and the water level has increased since the last check. I guess the air from the air compressor was warmer than the basement, so the pressure decreased while it was cooling down. Now it has reached equilibrium, so the water level should go up and down as the temperature varies. I'll leave it for a day or so to see whether it is holding pressure.

So, I have to seal up that leak on the left tank, but the initial indications are the right tank doesn't leak. And I have to eventually get the fuel caps to stop leaking. Not as bad as I feared, but not as good as I hoped either.

Update - 1 Dec 05

I left the right tank pressurized for two and a half days. The water manometer level fluctuated up and down a couple of inches, as the temperature in the basement went up and down, and the atmospheric pressure changed. But, the average manometer level didn't decrease, so I'm satisfied that there is no leak.

Here is a shot of the 2" plumbers test plug that I used to seal the filler cap opening.

I took Wednesday off, as it looked like the only day this week where it wouldn't rain or snow. It was cloudy, but cold, which allowed me to sand the fibreglas filler on the wheel pants outside. I almost froze to death, but at least I didn't make a mess in the garage.

Today I put several coats of thinned resin on the sanded filler to seal it. Then I decided the Pro-seal on fuel tanks was cured well enough to chance a leak check. I cobbled together a hook up to a water manometer, and put about two feet of water pressure (about one psi) in the tank. The fuel cap was leaking. I put some duct tape over the fuel cap and tried again. The duct tape seemed to be stopping that leak, so I watched the water manometer level. It was slowly coming down, so I had a leak somewhere. Drat :(

I mixed up some soapy water, and started putting it on all the rivets, joints between sheet metal, etc. I spent about a half hour looking, but couldn't find the leak anywhere. I finally put some of the soapy water on the edges of the duct tape over the fuel cap, and found that it was still leaking. I tried all manner of ways to seal the fuel cap, but it would always leak. I checked the RV-List archives, and found that this is a very common problem. Some people keep plugging away until the cap stops leaking; others put the cap aside and use some other means to seal the tank filler hole for the leak test. The main purpose of the leak check is to confirm that there are no leaks in the rivet joints, etc, so there is some argument to put the fuel cap aside for now. In flight, there is normally no fuel against the fuel cap, so a small leak may not be critical.

Tomorrow I'll try putting some grease on the fuel cap O-rings. If I can't get it to seal, I'll head to Home Depot to see what I can buy to seal the fuel filler hole.

This week I was out of town a bit, and spent some time doing more "get the yard ready for winter" stuff.

There is a fairing that covers the gap between the inboard end of the wing and the fuselage. This week I drilled the holes and riveted most of the nut plates on the inboard ends of the fuel tanks and wing where that fairing. I ran out of nut plates before the end, as I guess I didn't order enough to replace all the ones I used to make the cockpit floors removable.

A local RV-3 builder had told me that he had quite a bit of difficulty getting the wires on his fuel gauge sender floats bent so the fuel gauge read empty when the float was at the bottom of the tank, and full when the float was at the top of the tank. I hadn't checked mine out, so today I installed the fuel gauges, and fished out the wires that go to the fuel gauge senders. I hooked everything up with jumper clips, and moved the tanks around to make the floats go to either the top or bottom. I must have gotten lucky, as the only problem was a bunch of wasted time sorting out which fuse I needed to insert to power up the fuel gauges. Once I got the gauges working, they read zero when the float is on the bottom, and full when the float is on the top.

This afternoon I mixed up some Proseal and sealed the fuel gauge senders and fuel tank access covers in place. I'll let the stuff cure for a couple of weeks then do the leak test.

I'm going to be out of town on a course all week, so no more progress until the weekend :(

Not a productive week :(. I did two rounds of prime, fill and sand on the windscreen fairing. Yesterday I had to do a bunch of "get ready for winter" stuff, so no progress. Today, I planned to Proseal the access covers onto the fuel tank so I could do the leak tests. But first, I thought I should take the tanks up to the garage to hook the fuel level senders to the wires to the fuel gauges to make sure everything worked OK. Another local builder had reported that he had to tweak the bends in the wires that hold the floats on the fuel senders to get the gauges to read zero when the float hit the bottom of the tank.

I figured it would only take a little while this morning to test the fuel senders, then I could mix up the Proseal this afternoon. Piece of cake, right? Wrong! I had overlooked the fact that the tanks were currently attached to the wings. I had put them on the wings to check the fit, and had never taken them off. And the wings were in a stand, leading edge down. I pulled the screws off that held the aft end of the left tank skin to the spar - a real PITA for the surface that faced the other wing, as I had to squeeze into the space between the wings on the wing stand. I removed the bolts that hold the aft face of the tank to the spar, put the end of the main spar on a support to take the weight off the leading edge, and tried to remove the left tank. Nothing. No movement. I looked for screws or bolts that I had forgotten to remove, found one, removed it, and tried again. Still no movement. I pulled harder. Nothing. More looking, more pulling. Still nothing.

I eventually gave up in frustration, as I couldn't get the tank to move, and I was afraid to pull too hard and bend something. I'll pull out the mirror and light tomorrow night to have a closer look for fasteners that I missed. And Terry got back tonight from a weekend away, so she can help me pull the wing out of the stand so I can get better grip on things.

I was on the road for two days this week, but I managed to find time to bond in aluminum strips to support the nut plates that will attach the wing tips to the wing. And today I did the physical installation of the wing tip antennae. The electrical installation will happen after the wings are permanently attached and I run the coax from the fuselage.

Tomorrow I think I will put some filler at the wingtip leading edge, as they don't perfectly match the wing leading edge. I won't install the nut plates until the fibreglas work is done, as they nut plate screw holes are two small to take a cleco. That means that once I install the nut plates I will have to use the screws to attach the wing tips every time I put them on to check the fit. It is much quicker to use clecoes, so I'll delay the nut plate installation until I have a perfect fit.

Saturday afternoon I finished the aileron trim installation, except I didn't hook up the springs to the controls. I'm going to leave it disconnected until after first flight, as it will be easier to sort out the lateral rigging if the trim isn't masking any rolling tendency.

We are having a bit of a cold snap, and it took a long time for the garage to get warmed up yesterday. So today I decided to work in the basement, where the wings are stored. I attacked the left wing tip - it took quite a bit of trimming to get it to fit, and a lot of measuring to get the holes evenly spaced. It fits fairly well, except that the trailing edge of the wing tip sits about 3/16" higher than the aileron, and the wing tip extends aft a bit further than the aileron. I'm not going to mess with it now, as I want to wait until the wings are mounted and I have confirmed the aileron rigging is perfect. Then I'll split the wing tip trailing edge open and make it fit properly. I've got to fit all the platenuts to allow the wing tip to be removable, and I have to install the wing tip antennae.