Making Due with What You Have Just Lying Around the Shop

Looks like it has been a week since my last post. This is not because I have not been working on the plane. This past week has been heavy with research, calling Vans to get answers to various questions, searching VAF to see how others have done things concerning the fuel tanks, and then the holidays managed to rear their ugly head once head, severely impeding what would otherwise be pretty good progress on the fuel tanks.

I ended up getting involved in one particular project that I managed to finish up today, that at face value does not seem to have anything to do with airplane building. More about that later.First I need to pick up where I left off, which was with the fabrication and match drilling of the stiffeners for both fuel tanks.

After that I took a deep dive into the plans and diagrams again, and started hitting up VAF pretty hard in search of answers to some very specific questions. It started when I was looking at the steps to fabricate and drills the rivet holes and holes for the fuel fittings and the vent line. I'll start with the vent line:

Q: The plans for the capacitive senders said to run the wires attached to each sender plate through the SB437-4 bushings that simply insert into the holes at the top of each rib that support the 1/4 inch OD hollow aluminum tubing from one end the tank to the other. The plans say to drill a small hole in the inner portion of the outer flange of this bushing to route the 18 ga. wire along side the vent line tubing. When you look at the snap bushing you just laugh, because Vans instructions are ridiculous. The question to them was how to drill this magical hole without exposing the wiring to the sharp edges of the hole in the tank rib where the snap bushing snaps into it. (There ain't a lot of room between the vent line and the snap bushing.

A: I was told by Vans to take a solid piece of 1/4 inch rod an insert it into each of the several snap bushings and then drill a hole on the inner surface of the bushing right next to the rod.

NOTE: I have since found out from my buddy Mike Rettig that the REAL way that most builders have done this is to take a jewelers circular file and file a small depression in the inner wall of the bushing - just enough to allow the wire to be inserted right next to the vent line. This needs to be done for each bushing through about 5 of the tank ribs.

Now, after having spent all this time writing up that little gem. you'll LOVE this:
As soon as I asked the above question to Vans, there was a pause on the other end of the phone for several seconds, and the next thing I heard was this:

"You must have ordered your wing kit with the capacitive sender kit a long time ago." Yes, I said, about 2010 as I recall. "Can I give you some advice?" Sure. "Take that capacitve sender kit that we sent you and throw it all away." Your kidding-right? " Nope. They have had so many problems that we stopped providing it as an option about 4-5 years ago (2012).

So there I was - all but ready to start working on the sender kit, and now I was being told not to use it. The reasons why were numerous. The most important reason was that different fuels with different blends have different capacitance values. If you ever plan to run auto gas and/or 100LL or some other type of approved avgas, the the capacitance is different for each type. Since most avionics and fuel gauges out there require calibration of the fuel system, the capacities and fuel gauges will all be calibrated with whatever fuel you put into the tanks at the time all this is done. If you then go and change fuels, your calibrations will be off, because the senders will be dealing with a different capacitance value due to the the different fuel. SO basically this will render your fuel gauges completely useless, unless you plan on recalibrating them every time you switch fuels.

I would also suspect that deposits from different fuel blends and additives might even contaminate the plates over time. Next, I was told a story about one of the Vans employees that still flies to work every morning in his RV, which also has the capacitive senders. Each day he flies past a group of three very tall radio towers, and every time he does this his fuel gauges drop to NOTHING due to some sort of RF interference playing havoc  with the capacitve senders and electronics involved with the fuel gauges in his avionics system.

SO you might say - well I don't ever plan on switching fuels, so that shouldn't bother me. Well, how do you know what kind of fuel you are getting from place to place as you travel the country side in your new plane? Answer - you NEVER know exactly what kind of fuel you're getting, unless YOU were the one that refined it, tranported it to the airport, put it in the fueling truck, and fueled the airplane your self. Just because a fuel truck says it has 100LL in its tank does not mean that 100LL is what you are getting.

Anyway, the problems begin as soon as you end up with a mix of different fuels in your tanks. Between that issue and the stories of RF interference wreaking havoc on the system, I have decided that I am NOT going to install these stupid things. I'll give you one last consideration about all this, which VFR pilots will just never understand. If you are going to fly in IFR conditions, there will come a time when the weather throws you a curve ball, and you are going to have to make some decisions WHILE YOU ARE IN THE AIR about selecting and navigating to a NEW alternate airport. NOT the one that you filed you flight plan with because at the time when you were planning your flight your original selected alternate airport was within alternate minimums, but the NEW one you are going to have to determine if you ave enough fuel to get to safely, when all the "expected" weather conditions got crap on you while you are airborne.

If you cannot rely on what your fuel system is tellling you, then you have no business flying in IFR conditions in the first place IMHO.SO----now I ahve to purchase VANs fuel senders, which are standard float-type senders with essentially a potentiometer integrated into them. Another slight "hitch" to all this is that since I plan on putting a flop tube in my left tank for some added insurance during aerobatic maneuvering, the flop tube is long enough that it can interfere with the float sender arm, so instead of mounting the float sender in the normal location in the most inboard bay of the fuel tank, you have to mount it in the next bay over from the rear of the baffle plate. Vans plans show where this mod should be done, and the only thing I ponder is access to that unit for repair, removal, or replacement should the need arise - and it WILL arise at some point.

The only way to service the sender from this location, without having to remove the fuel tank from the wing, is from one of the access plate openings under the wing. I need t make sure that I can get to the screws and do whatever is necessary to remove any sealant material for that sender in order to get it out of the tank.

This will take me to the discussion/research about sealants, and some different things that various builders have done to facilitate "ease of maintenance" when the time comes. But it's late, and this post is already long enough with a week's worth of other stuff to report on, so I will end here for tonight. More to come this week. Like I said, lots of research and decisions to make at this stage of the build. Lot's of other experience to evaluate from others that have come before.


Other topics I will cover later:
Fabrication of the T405 and T410 tan k attach and support brackets
Sequence of installing AN833 6D and 4D AN elbow fittings
All about different types of sealant, applications methods, types of sealant to use inside and outside the tank, and more..
Semco Sealant gun and cartridges
Cutting large tank access holes in tank ribs using a fly wheel cutter in a drill press (That was scary and interesting all at the same time).
Using torque or allan head screws for the tank access plate instead of standard Phillips head #8 screws, as well as a different type of sealant for this area than standard proseal
What to do about planning for and putting in a fuel return (purge) line now - if anything?
Bung kit install procedures from SafeAir for extended fuel tank "readiness."
Searching for a piece of hinge material for the infamous "trap door," and what that is all about, and having to get up on my garage shelf for the first time in years to locate the flap hinges to borrow the hinge material I need for this.
Figuring the pivot point/radius   from my tubing bending tool, which I will have to use once I start working on the vent lines.
Decisions to make about my standard Vans Fuel caps, i.e. to keep and use those or get some different ones
Bending and fabricating the standard fuel pickup tube from the 3/8 inch tubing supplied by Vans.
Relearning how to flare the ends of the tubing with the flaring tool.

And I'm just gettin' started.......... I'll get around to explaining what I mean by the title for this post in the next post, just to keep y'all guessing!

Till next time,

KPR.