Tank tested for leaks

Got myself some NPT taps. Had to be as sure as possible that I could get these stupid NPT threads tight without applying so much force that I would destroy the molds. Drilled a hole in one nut and inserted a nipple, so I could get some pressurized air into the tank.

Then inserted the all the blocking nuts and the oops fittings. Used Loctite on all the NPT fittings. The local shops had closed for Easter vacation, so I made some soap and water and used as a leak finder. That worked - I think. No bobbles could be detected at least. So the tank is tight. Sonex has stopped making this tank. The new tanks use oops fittings only. The oops fittings are very nicely made, and have proven themselves. The original tank with the molded fittings for NTP threads is just a sad story. I just hope that without any mechanical forces acting on the remaining molded fittings, they will stay tight. There is no pressure in there to speak of, so I think they will keep.

More tank and oops fittings

Started making a new handle for the fuel shutoff valve. Had some scrap from the canopy that will work fine as a torque tube, and made mounted it to the valve with an angle so that the torque tube is in the center of the valve rotation. I'm not exactly sure how long it needs to be, and I need som descent looking knob, ut the function is OK.

Looking closer at the 1 inch oops fitting with the O-ring removed, I found that it was maybe 1/2-1 mm too close to the sight tube outlet and touched the protruding plastic on the inside. There is enough space on the inside to cut the hole at least 2-3 mm farter aft, but that is impossible to know up front. Using the sight tube outlet is probably a better choice? who knows. Filing off the oops fitting a little solved the problem.

Oops fittings

Decided to install the oops fitting, rather now than later. It's not 100% clear how these oops fittings are to be installed on the old Onex tank, but I hope I got it right. According to revision B on ONX-G01 from 12/03/2015, is says:

Added Oops fittings for fuel ports. Use of Oops fittings requires moving fuel supply port to bottom of tank sump. Removed optional fuel sight gauge. Added warning to NOT slosh fuel tank.

So I made a big new hole in the tank, with a tool that looks brutal enough for a picture. In hindsight I could also have up-drilled the hole for the sight gauge to 1 inch, but there is no way to look inside the tank and see how things are before drilling a hole, so it's a catch 22. Can't see that the exact placement will harm, it's pretty sturdy in that little box at the bottom.

These oops fittings are not straight forward to install. They require considerable trimming on the inside, and it's almost hopeless to get there. David Amsler has made some super smooth tools for this job. The tools are sent around the community (very nice gesture), but me living in Norway, the shipping will cost a lot. He gave me some ideas though, and explained a lot of the job, regardless of actual tool used.

To fix the 1/8 inch NPT hole I updrilled to 10mm. This was my largest drill. I then reamed it up using adjustable reamers to the correct size, 9/16. But then comes the really hard part, that is to fix the inside so the oops fitting have a nice flange to seat the O-ring. That is where the tools from Amsler comes in, and makes this a piece of cake. I wondered how to do it without the tool, but then I found this adjustable wood drill. The edges of it is very sharp, also on the back side (the side towards the drill), and the diameter is about 13.5 mm, fitting nicely inside the 9/16 hole.

This worked just fine. The edges became a bit rough, but nothing that a small Dremel disk mounted through the hole couldn't handle. The result was a perfectly smooth flange on the inside.

The 1 inch hole works just fine with no trimming because there is no insert to drill out. Mounted everything, just to see how it fits, and it all looks just fine to me.

All in all, looks OK. I need to clean the tank, and then test for leakage, and hopefully it should be OK. I made this push-pull fuel valve knob with support. This will be redundant now. I need to make a turn handle instead, out of tube or something. 

The power supply actually works

Got the Mascot 8660 today, and had to hook up the stuff ASAP on the kitchen table. Simulated the setup with my shop battery (7.2 Ah, 12 V), a car battery charger (4 A), my backup battery (6 Ah, 12V), the Mascot 2A DC-DC charger and all the lights and the EFIS. It just works. I can hook up the battery to the charger, or to the secondary system. No noises or heating or anything. I also tried handheld airband radio receiver to see if I could pick up some noise - nothing. So far so good.

I run down the backup battery until the lights stopped working. I then tried to hook the backup up to the charger and directly to the 8660. Everything just worked then as well, no heating or noise. Even an empty backup battery is no match for the Mascot 8660. The whole clue is due to the drooped voltage-load relation of the 8660 in my opinion. I will keep the charger though, it will off load the 8660 and charge the battery correctly, at very little added weight. With a 3 way switch I have full control. I had to open it up. It also has a TVS diode on the input, so no need to add another one.

It's a bit heavy, 1000 grams, but I guess I can easily offset that by eating a few cookies less the next months. I'm very happy about how things turned out in the end :-)

Final iteration of the power supply?

I hope so, but I will find out soon enough. More about the Aviogard and DC-DC converters in general can be found here. These are the premises for the power supply to the secondary system. The primary system is standard, as set by the engine documents.

• Only sensitive instruments, delicate electronics with little or no protection on their own
• I need a backup battery, or I will lose every bit of info in case of a main battery failure
• The backup battery must not be too large.
• The backup battery needs to be charged by a real charger. A DC-DC converter is not a charger according to Mascot.
• A DC-DC converter with a galvanic barrier will isolate the secondary system from the primary.
• The DC-DC converter must be able to have a battery as the load without entering into hiccup mode for some reason or the other.
• The charger draws 2 amps max. It us put on the primary side to off load the DC-DC converter.
• The charger allows visual inspection of the state of the backup battery
• Make it as simple as possible (feels like this is a joke at the moment, but it's actually not much more complicated than the first iteration with the Aviogard, which doesn't work).
• If it dosen't work, remove the DC-DC converter and replace it with a secondary master switch.

The system looks like this:

Mascot charger

Got the Mascot charger. Works like a charm, no noises of any kind, or heating.

But, the solution with a charger has a weak point. It is way too easy to forget the switch to the backup battery in "ON", and this will overload the Aviogard. A diode would do the trick - I guess. Then again, the main problem is that the Aviogard is not dimensioned with enough amp to be able to charge a battery without entering into break-down mode. There is another alternative. That is to charge the backup battery from the primary system, with or without the Mascot charger.

So, the old fashioned way will need at least three switches. A secondary master switch, a secondary backup switch in addition to the master switch and a diode to prevent the backup battery feeding the primary system. With the Mascot charger, I only need the primary and the secondary backup switch, and the charger will report the state of charge.