Fuel System

Today was prepping the front sump wall area and finally floxing and taping it in position. I started about 3pm and finished at 9 for this simple little job.

I can tell you it is quite parallel and that all the surfaces nearby were well dulled and sanded. The piece was set up several times with a carpenters square, I marked more lines for the 2 ply BID tapes.

I cleaned and then wetted the areas with pure epoxy and then added thick flox everywhere. Once the front piece was in position I rechecked the angles and added plenty of flox to the edges, especially on the inside.

Next up were the 2 ply tapes and finally peel ply. Pic 3 is a day later with the peel ply off, cleaning up the edges and a bit of sanding.

Floxed and taped sump wall

Sump wall again

Cleaned up

This was over several days and all with the heater on now the weather is cooler. I continue to have around 25C for my ‘important part’ fiberglass working temperature.

Pic 1 and I’ve done a pretty wet inside layup, pic 2 are outside layups a day later and pic 3 I’ve trimmed everything a day after that.

I drilled through the hard points as I really wasn’t sure how to treat the inside holes. Now its done I can see that I need to dremel down to nearly the hardpoint on the inside so that the fittings can seat. I’ll be putting a lot of flox around too and should get an excellent seal.

Outside glassed

Insides glassed

Trimmed and ready

A huge amount of time went into deciding where to put these common sump hard points. It is reasonable to know where the pipes are all going before you place the permanent termination points in place?

I’m using 2024-T3 1/4″ thick aluminium. Three points are tapped for the 3/8 or -6 pipes I’ll be using for fuel lines and vents. These will be in 5052-0 AL tube probably 0.035″ ID wall and 3/8 OD (0.375″)

I’ve made provision for the fittings by tapping them out. One of these will be a low fuel sensor and I have a 1/4 NPT tap coming in the mail so that may have to be finished off after the tank sides are in place. I have drilled it up as far as I can go.

I’ve dremmeled out cavities and I’ll flox them in place, glass over and retap later.

Tapping hard points

Routed hard point cavities

Ready to glass one side

Today was getting serious about positioning the front wall of the sump. I’ve re-trimmed it so that the rear stick holder bracket is at the very front of the sump and now there is excellent stick clearance.

I’ve angled the front edge and matched the sides to fit this so that the top will fit on easily. This small blending effort has trimmed nearly 2 liters from the tank’s volume. I’ll still get 14 liters in which I feel will be enough to accept the fuel return from the engine.

Pic 3 and I’ve made some access holes for cables and fuel lines. I may need to make them bigger later so I’ll leave the edges unsealed for now.

Sump front wall refitting

Sump side wall fit

Sump front wall access holes

I suppose this counts as build hours as I made some cardboard bits. Having spent some time working out the control positions on the right side it was time for decisions on how and where the sump feed from the wing tanks was going to happen.

I’m going to have to make my own pipes. I’ve been thinking for a while about how to do this and I might try to make some molds out of clay. I did do a cardboard mock-up as you can see which took a lot longer than you’d think! I want around 4 sq” feeding the tanks so they equalise from one side very quickly. What I have mocked up will work OK around the controls and fuel lines. I did need to see how it all worked so I can plan items like the regulator and where wire runs might go.

Another thing was where to put the outlets from the wing tanks. Plans have them right in the aft inboard corner but I have curved bottom strakes. In pics 1 & 2 I have jacked up the nose to 2 degrees… where it will be in flight and had a really good think about low fuel situations relative to the pickups. That said I will have 14 liters in the common sump as my low point and very little unusable fuel.

The laser lines suggested that this tank low point was just a bit more forward than plans. Then I had to account for the back seat belt position too for where my homemade pipes will go. They will be as pictured. (pic 3)

2 degree nose up fuel line

Checking for the low point

Mock up in place

This was over a couple of days but I don’t count planning things in this log as hours. Otherwise you could say a builder spends years just thinking about the project items.

That said I thought I’d share a bit of the process. I’ve bought a few of the engine/fuel components a bit early so I can position them in the plane before I get to the engine install.

Pic one shows the dual fuel pump, which is distressingly heavy, the post fuel filter, the fuel pressure regulator and an Andair valve switch that I’ll be selling on as it is 3 position and I only need an on/off.

Pic 3 has the sump walls just placed in position around the hydramat which is also a 15 micron filter and will act as my ‘pre fuel pump filter’. I thought about how to position all these things down the sides of the sump tank or in the hell hole. That “hell hole” is pretty hard to access so I ruled it out. If I ever had a fuel leak I want to be able to get to things quickly and easily.

I’m going to put the pumps and filter ahead of the sump and make a sloping cover for it. There needs to be a gentle angle from the sump anyway for the ferry tank bladder to sit without sharp corners so this is a two in one solution. The regulator will go in the left side cavity and the stop valve that side controlled from the front seat for emergencies. I’m not sure if I’ll pay the big bucks for another Andair Valve or gerry rig something much cheaper.

Fuel system components

Test layout 1

Test layout 1a

The sump floor took me about a day and a half to carve. Its just the floor in the back seat. I’m imagining the plane on its nose gear with the gear slightly down. Its morning and I need to check for water in the sump. So this is the position that I carved the sump floor out for. Back a little from the sump wall which will be the lowest point. Any water should flow to here and then into a large drain hole area you can see in pic one. If there is any water I hope it will pool below the fuel pickup too as a bonus should I miss any in the morning checks that were somehow hidden in the wing tanks.

Meanwhile I have acquired a 1/8 NPT tap and have an aluminium slug with the hole taped for my fuel drain fitting. After some thought I decided to do a ply on the floor first so I could later flox in my metal fitting with a glass bond rather than foam. I also have a bit of glass to glass on the floor of this sump area which I always like for a bit of extra strength.

The fuel tap will be under the line of the fuselage bottom but by the time I do the NACA scoop it should end up just about flush.

Meanwhile, Pic2 shows that I have cloth with the bias at 45 although the pic doesn’t show it! and I wet it out and then trimmed it to size. Pic 3 is after peel ply on a pretty wet layup. Which is not pretty. I am planning on no leaks. The peel ply I have quite wet too which makes for terrible photos!

I went for 3 separate and complete layups in the end. So thats three ply in the bare areas and 5 ply where the floor was not breached. Quite enough.

Floor carved

Cloth in place

Ugly peel ply

Ahhh common fuel sump time. This has been an adventure to plan. Now I’m going to build it. After some test setups I confirmed the front postion of the rear passenger thigh rest AKA ‘the sump’.

Pic 1 shows it is finally placed in a position and height that will work. I expect it will be 14-18 liters which is what I need for the engine return line and the special fuel filter I’m going to use. Years of planning have gone into this. Yeah… I have a lot of notes and files! I’m going to capture the rear control stick in this so it all blends together. You’ll see.

Pic 2 is the outside of the front sump piece. I’ve done it it the regular araldyte 360 system epoxy I use. Pic 3 shows the first ply of the inside (fuel side) of the sump. This is the EZ-Epoxy that was super expensive and I have limited quantities of. That said, its a very wet layup. I peel plied it and after cure and a lite sand I’ve put another ply of BID on it. Also wet and peel plied. This is going to be my fuel proof sump!

Test fit front of the sump

Sump front outside

Sump front inside

Following on from the last log entry you can see I have released the top ‘dome’ and then made another one.

Pic 2 has a trial fitting of the fittings! AN912-4D inserts which hopefully will accept 269-N06X06 3/8″ Nylaseal fittings when I order some.

Pic 3 is after a couple of cure cycles. The fittings are floxed in place and I spent a few happy hours then trimming much of the excess fox away. All that remains is to flox the end pieces on.

Maybe I should have trimmed the fittings a bit too for weight reduction. I was just not sure how the nyloseal fittings work and chose to leave the inserts long. I’ll get over it.

Tops done

Trial fitting

Floxed in and cleaned up

Finally at Chapter 21 the Strakes! Well really this is a side job… a part of the fuel system is to vent the two main tanks and the common sump. So the pressures are equal, I am going to plumb the two lines from each wing tank AND one line from the common sump to a ‘manifold’. This will sit under the turtleback and then have two lines going to underneath the plane in case they over flow.

I’m going with 3/8″ lines or dash six. Both to minimise the chance of blockages and to be able to move large volumes of displaced air when refueling and still keep the ‘head pressure’ even.

Others have done this before me in EZ type planes. They all use a regular aluminium can as a mold. So I had to go for a slim can of Beyond Coconut water. Ha! Might take up less space but work just as well. Pic 1 has the can removed and my tube fiberglass body nicely cured.

Now a note on all this. For everything to do with fuel I’m using a different epoxy. EZ-10 Epoxy resin and EZ 87 Hardener. It has a dangerous goods ‘tag’ so the import costs are over $500 extra for two cans. Arrrgghh!!! BUT this is the best known fuel resistant epoxy that has been proven in our planes for over 30 years.

Pic 2 has a foam plug in the cylinder than I shaped and then glassed as you see in pic 3. I’m just doing two plie for this manifold part.

Tube out of the ‘mold’

Top shaping

Glassed top