Fuel Tank

Curtis Drain Valve Hose

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To drain the fuel from the airplane I installed some Curtis quick drain valves CCA-4850 and purchased the Curtis drain hose assembly CCB-39600-5. They claim that “Waste liquid flows through 5 feet of high grade vinyl tubing, preventing messy spills and making a cleaner, safer environment.” A better description would have been “95% of the fluid flows through the hose, the rest makes a messy spill”

At first I thought maybe the particular valve I got was the problem but looking on their site I see that my valve is listed with the hose I have. Upon further inspection of the valve I see the problem. There is no seal between the valve and the valve body when the valve is opened. So some of the fuel leaks between the valve and it’s body while the majority of it runs through the valve into the hose.

Curtis drain valve not sealed between valve and body
Curtis drain valve not sealed between valve and body

I removed the brass piece from the drain hose assembly and decided to make a simple modification. The brass is shaped like a little cup and can catch the fuel that leaks between valve and valve body. So all I needed to do was drill a small hole to allow the captured fuel to drain into the hose instead of overflowing and making a mess. I used a 0.09″ drill bit inside the nipple at a slight angle.

Side view demonstrating the angle of the hole
Side view demonstrating the angle of the hole

Drill bit angled to drill the hole
Drill bit angled to drill the hole
Modified Curtis drain hose, small hole in the
Modified Curtis drain hose, small hole in the “cup”
Modified Curtis drain hose, small hole in the
Modified Curtis drain hose, small hole in the “cup”

After trying out my modified drain hose I discovered that it does work much better but not perfect so I added a second drain hole on the opposite side. At this point I’m satisfied. Some fuel vapors will come out around the connection and sometimes a little will condense on the valve tabs. But fuel was not pouring down the outside of the hose and making a puddle on the floor like it did before the modification.

If it’s not obvious, it has one drawback, if the drain hose is obstructed in any way the fluid will follow out the holes, overflow the cup and make a big mess. Maybe a valve and a nipple to drain the fuel would have been a better choice.

CCB-39600-5 Curtis Drain Hose locked into drain valve
CCB-39600-5 Curtis Drain Hose locked into drain valve
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Wing Tanks Installed

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To cushion the bottom of the tank I got some 1/8″ thick neoprene. The best deal I found was sold as “tool box drawer liner.” I cut it so it is wider than the bottom so it wrapped up the sides a little then notched out the inboard rear edge to match the plywood.

The tank needed two holes, one for the drain and one for the fuel level sensor. I first drilled a small pilot hole then used a 1/2″ forsner bit. Never use a regular twist drill bit for this step, you will end up with a triangular shaped hole instead of perfectly round and the bushing won’t seal. 

Small pilot hole in tank
Small pilot hole in tank
1/2 inch hole in tank drilled with forsner bit
1/2 inch hole in tank drilled with forsner bit

Then installed the rubber bushing.

Fuel tank bushing
Fuel tank bushing

At this point I realized this particular tank is too deformed to install the fuel level sensor because the top and bottom are curved inward so there is not enough clearance for the sensor.

Knowing these tanks do expand the first time they are filled with gasoline I had to stop the installation and fill this tank with gas and hope that resolves the problem. After a few days the tank was still deformed, so I sealed the tank and put a few psi of air pressure in it. The following day I removed the air pressure and let it sit with gasoline in it. After a few more days the tank is back to its normal shape and has held that shape for over a week. 

Now I can install the fuel level sensor. I made sure that the sensor was about 1/4″ above the bottom of the tank and pressed it into the bushing.

Tank with fuel level sensor installed
Tank with fuel level sensor installed

I was concerned that the polycarbonate cover might bump the calibration switch on the sender so I cut a ring of plywood to protect the switch. I used some silicone to hold the ring in place.

Small plywood ring to protect calibration button
Small plywood ring to protect calibration button

The drain hole in the bottom of the tank was drilled and fittings installed.

Tank drain
Tank drain

Now the tank was installed into the wing. To hold it in place I purchased some tie down straps. They were way too long so I cut them shorter and heat welded the end so it does not fray. I routed then under the plywood and diagonal supports then over the top of the tanks. 

Two straps hold tank in place
Two straps hold tank in place
Tank strap buckle
Tank strap buckle

The fuel line was routed from the elbow to a tee. Then to the drain and quick disconnect. This was not an easy task to accomplish without kinking the lines. It would have been easier if the quick disconnect was moved an inch or two forward but that would have made the quick disconnect higher which is undesired and more likely to get bumped by my elbows when sitting in the cockpit. Maybe cutting one barb off of the tee would help too.

Fuel line routing in wing
Fuel line routing in wing
Fuel line routing in wing
Fuel line routing in wing

After installing the cover panel I’m amazed at how well it looks. 

Tank cover panel installed
Tank cover panel installed

Not much remains on the wings now. Grease aileron bearings, safety wire aileron bracket bolts, install wing tips and I need to get the rest of the wing polished so it shines like the tank cover and ailerons.

Fuel Sender Wires

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Time to route the fuel level sensor wires. The first thing I did was mount the wings and locate a location to drill a hole for the wires. After drilling the hole I added a grommet.

After locating the hole I determined how much wire needs to protrude from the fuselage so they can be easily disconnected after removing the wing.

The sensor outputs need routed to the fuel selector switch so I decided to make some splices near the sender switch to accommodate this. I routed the left fuel sensor wire down the left fuselage side, across the floor and up the right side and through the grommet. On the right side near the fuel selector switch I spliced in the fuel selector and right side sender wires.

The red and black (power and ground) are spliced to the right side sender so both senders get power. The white wires from each sender are spliced to the wire going to the selector switch, right to red and left to black. The white wire from the dash and to the selector were spliced.

Terminal ends were added, the resulting harness looks pretty good.

Behind the dash the black is connected to ground, red to power and white to the green EIS Aux input.

Fuel System – Firewall Forward

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Two fuel lines pass through the firewall.  One is from the electric fuel pump,  the other is gravity feed. In the picture below the right line comes from the electric fuel pump. The inline check valve ensures fuel can only flow towards the engine. 

Fuel lines at firewall
Fuel lines at firewall

After the check valve is a tee, shown below. Left side connects to the electric fuel pump check valve,  right to mechanical pump check valve and the top goes to the carburetor.  Behind the tee is the inlet for the mechanical pump.  It’s fuel line is connected to the left line in the picture above. Rest assured, the top hose now has a clamp, it was not installed when I took this picture.

Tee connecting both pumps
Tee connecting both pumps

Below you can see the mechanical fuel pump on the right.  The outlet connects to a check valve that’s connected to the tee. I wrapped some silicone tape around the check valve so won’t chafe nearby components. 

Mechanical fuel pump connections
Mechanical fuel pump connections

The outlet of the tee connects to the fuel inlet banjo on the Dellorto PHBE34BD3 carburetor. 

Carburetor fuel line connection
Carburetor fuel line connection

This is one complaint I have about the Hirth F-33, it came with the fuel pump and carburetor.  The outlet on the fuel pump is made for 1/4″ (6.3mm) ID hose but the inlet on the carburetor is only 6mm. To resolve this I ordered a new fuel inlet banjo, Dellorto part number 6273 that has a larger diameter barb.

Dellorto banjo 6475 (top) 6273 (bottom)
Dellorto banjo 6475 (top) 6273 (bottom)

Now all I need to do is fasten the fuel tanks in the wings and install the air filter and she is ready to run!

Fuel System

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I’ve spent many hours researching and thinking about the best way to design the fuel system. Originally I planned to use the five gallon fuselage tank that came with my kit. But after deciding to register my airplane instead of going Part 103 I decided to add wing tanks. It would have been nice to use the fusealge tank as a header tank but the fact it interferes with my toes when working the rudder pedals I decided it would be best to remove it. Maybe I can build a custom header tank that does not hit my toes but for now I decided to move forward without it.

Toes caught on fuselage tank support
Toes caught on fuselage tank support

Starting at the wing we have the valved quick disconnect. I used a 90° male end to keep the hose along the fuselage side.
Directly after that are the fuel filters. This location is easy to access for service and inspection.

Fuel filter and wing quick disconnect
Fuel filter and wing quick disconnect

I still wanted some sort of header tank to ensure the fuel pumps won’t suck air when I’m banking and the tank is not full. The simplest solution to this was to add an inexpensive one quart tank for each wing tank. 

1 quart tank
1 quart tank

These were originally designed for radiator overflow and came with a small vent hole that I sealed with some heat.

The bottom of the tanks are routed to the right and left input of the selector valve. This valve is from a jet ski, easy to find so it can be replaced periodically before it fails. It only provides left, right and off positions. For midwing airplanes, like mine having a both position could result in the pump sucking air from an empty tank instead of fuel from the full tank.

Silicone tape to protect fuel lines from chafing
Silicone tape to protect fuel lines from chafing
Fuel lines connected to selector valve
Fuel lines connected to selector valve

After the valve is a tee, each outlet is connected to a different fuel pump. An electric pump and a mechanical pulse pump on the engine. I mounted the electric pump in the fusealge right after the valve. 

Some day I’ll need to drain all the fuel so I can replace fuel lines, valves and to service the fuel filters. The outlet of the electric pump connects to a tee, one outlet towards the firewall, the other to the Curtis drain valve I installed on the bottom of the fuselage.

Tee to fuel system drain valve
Tee to fuel system drain valve

Mounting the valve was simple after making a retaining bracket out of some plywood and a piece of RS-7. The bottom plywood is made from 1/8″, this is needed to lift the brass piece off the floor to leave room for the hose clamp.

Retaining bracket for fuel drain
Retaining bracket for fuel drain
Retaining bracket for fuel drain
Retaining bracket for fuel drain

The RS-7 was cut so it fits around the brass piece and then some 1/16″ ply was added as a top.

Retaining bracket for fuel drain
Retaining bracket for fuel drain

The round part on the brass is 0.550″, I used a 1/2″ forsner bit and a file to make the hole. I placed the brass piece in the hole and slid the retainer over the brass to through drill the two mounting holes.

Next I used a small file and made a notch from the body hole to one of the mounting holes.

This will allow the Curtis valve to fit through the hole.

The retainer is slid over the valve and mounted in place.

Some of these pictures were taken before I tightened down the drain valve into the brass. Before I did that I coated the threads with Permatex Aviation Form-A-Gasket to help ensure I have no leaks.

Added some washers and lock nuts and the drain is ready for use.

Fuel drain valve
Fuel drain valve

The nice feature of these valves is that they have a mating drain hose that locks onto and seals against the valve so you can drain without spilling or dripping fuel.

Fuel drain valve with locking drain hose attached
Fuel drain valve with locking drain hose attached

To speed up draining just turn the Facet pump on, using the selector valve you can select what tank to drain.
I used some copper pipes to make the penetration at the firewall. The reason I did this is for safety. If there is ever a fire in the engine compartment the blue fuel line will melt from the heat and I’d have fuel leaking by my toes near a fire. The long copper lines will take some time to transmit heat from an engine fire all the way back to the blue lines. 

Fuel lines to firewall
Fuel lines to firewall

Tank selector valve and pump plumbing
Tank selector valve and pump plumbing

I’ll cover firewall forward in a future post.

Fuel Gauge

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Started working on the electrical wiring and discovered that the EIS 2000 I have only supports a single fuel level input. They sell the EIS 2000 as a two or four stroke model when in reality it does not matter if you have a two or four stroke the difference between the two models is features not engine type. When I build the next airplane I think I will build my own EIS or use the flybox.

So the Grand Rapids folks suggested using a switch so I can select what tank level I want to monitor. After thinking about this for some time I decided this is the best option but that it needs to be implemented carefully. Imagine monitoring the full tank but running the engine from the empty tank. That could result in a bad day. 

In designing this I decided the goals should be as follows: 

  1. The position of the tank selector valve dictates what fuel tank is monitored by the EIS
  2. If the fuel selector valve is in the off position then the EIS should see an empty tank triggering the warning 

The typical inexpensive fuel selector valve is not suitable for triggering some electrical switches. I ended up purchasing a WSM 006-600 jet ski fuel valve on Amazon.com and a couple of 2750017 micro switches from the local RadioShack. 

Fuel valve and micro switches
Fuel valve and micro switches

Using a file I put a flat spot on the knob that was parallel to the flat side of the D hole in the knob. The location of the flat spot is important so if you have a different valve you might need to change the location.

Fuel valve knob modified with notch
Fuel valve knob modified with notch

When the knob is installed on the valve the flat spot should line up with a micro switch roller only when the valve is turned to the left or right tank. This will require the switches to be mounted 180° from one another. I used OnShape.com to make a drawing that I printed out in reverse on toner transfer paper. This will provide accurate centers for the holes and the labels for the valve. 

Putting the switches to their marked locations on the toner transfer paper you can get an idea of how this will work. 

Arrangement of micro switches
Arrangement of micro switches

I varnished a piece of plywood, sanded it smooth and applied the toner transfer. Then the parts were cut out and drilled. A smaller valve support plate needs to be 5/8″ away from the panel so the notch in the knob is just below the plywood. 

Micro switch actuated by notch
Micro switch actuated by notch

On the outside, for asthetics I used 1/4″ X 3/4″ pine. A 1/8″ notch was cut into the outside piece and the valve support set into the notch. The inboard side used a small piece of 1/4″ X 5/8″ pine. Alignment is important so I glued this together with the valve and knob installed to keep everything indexed.

Fuel valve support
Fuel valve support

Once the epoxy cured the switches were mounted using #3 screws and the valve installed. 

Fuel valve, switches and wiring
Fuel valve, switches and wiring
Fuel selector knob and labeled panel
Fuel selector knob and labeled panel

The electrical wiring did take a little bit of planning. I wanted to make sure that should there ever be a malfunction that only a single fuel level sensor would be connected to the EIS. Here is the wiring diagram that does this: 
http://schematics.com/embed/fuel-sender-selector-46440/full

Before takeoff simply turning the valve to all three positions will confirm if the system is functioning properly.

I think this turned out well, looks pretty good mounted on the fuselage side. 

Fuel tank selector valve
Fuel tank selector valve

Wing Tank Part Four

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The lexan is trimmed to fit into the opening, since it is 1/16″ just like the plywood trim around the opening the top surface is flush giving it a great look.

Lexan tank cover

Holes are drilled every 2″ around the perimeter of the lexan then screwed into place.

To prevent the holes in the wood from stripping over time some thin CA is soaked into the holes and allowed to dry before reinstalling the lexan cover.

The lexan is marked and drilled to create an opening for the filler neck. To locate the filler neck position I installed the tank and used a square to locate the center front of the neck. Note that this picture was taken after making the hole and is intended to help show how this step was performed but this step was performed without the lexan in place.

Large square used to locate filler neck location

Then the lexan was installed and the center of the filler neck was marked then drilled using a 2 1/2″ hole saw.

Square used to mark location of filler neck on lexan

The final result looks great.

Tank cover installed

Because I will need to remove the wings I wanted quick disconnects for the fuel line and some way to drain the fuel.

For the drain I got a 90° 1/8″ NPT to 1/2″ barb brass and a quarter turn drain valve.

Fuel drain valve

Some blocks were glued in place to hold the drain and a piece of plywood is screwed on top to keep it from moving.

Fuel drain and disconnect mounts
Fuel drain and disconnect mounts

A piece of 1/8″ plywood was glued to the root rib to hold the panel mount quick disconnect.

Quick disconnect assembly

With the disconnect removed the wing was mounted if the fuselage so the hole could be marked and drilled into the fuselage. Once drilled the quick disconnect was reinstalled to test the fit.

Fuselage hole for fuel disconnect

The hole is just large enough so I can get my finger into the release tab. The 90° make disconnect will make routing the fuel line’s much easier.

90° fuel disconnect in fuselage

Wing Tank Part Three

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The RS-5891 plywood bottom is cut to shape and glued to the RS-9 supports and drag brace. Unlike the plans I decided to extend the rear of the floor to the rear spar by gluing an extension to the plywood.

Plywood tank floor

Two RS-4 are glued to the ply in front of and behind the tank to keep it from sliding forward and aft.

A RS-3  is glued between rib #2 and #3 to reinforce rib #2.

Support keeps rib in place when shrinking fabric

Wing Tank Part Two

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With the drag brace supports in place it’s time to frame in the opening at the top of the wing. I cut a piece of RS-17 to length and notched the side of it where the gussets are located on rib #2 then glued to the side of the rib.

RS-17 glued to rib #2
Notch for gusset so it fits against the RS-1
PVC pipe clamps very helpful

Next I located the rear of the opening and cut the plywood connecting the root and #1 rib. Then removed the front portion of the plywood.

Cut plywood at rear of opening

Another RS-17 was cut to fit between the root and #1 rib. At the rear of the opening the RS-17 is notched to make room for a horizontal RS-17.

After checking the fit it was glued into place.

The clamped RS-1 keep the RS-17 level while for dries

Once the glue was dry rib #1 was cut at the rear of the opening where the notch was made in the RS-17.

Another RS-17 is cut and glued into the notch forming the rear of the opening.

RS-17 at rear opening

A 1/16″ ply gusset is added to the bottom at ribs #1 and #2 to strengthen the rear opening.


A 1/16″ piece of ply is added to the rear of the opening and over the root rib.

Plywood creates recessed opening for tank cover

Lastly a piece of RS-3 is glued to the front spar to provide a surface for attaching the lexan cover.

Rubber bands make great clamps

Now it’s time to install the tank floor.

Wing Tank

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Since I decided to register I can carry more than 5gal of fuel so I decided to install wing tanks. I never did like the fuselage tank so I am going to remove it.

Following the plans for the wing tanks I added two more RS-9 ‘drag’ braces to create a support for the tank. These need to be notched on the front with just 1/4″ sitting on top of the bottom front spar cap.

Notched RS-9 for tank support
Notched RS-9 on front spar

On the inboard side of these braces I put a piece of RS-5 between the ribs where the brace will be located.

RS-5 spacer for RS-9 tank support
RS -9 tank support at root rib

I glued those in place and let the glue set over night.

The next task is the only difficult part of adding wing tanks. The existing RS-9 drag brace needs removed and a new one installed lower. Had I known this I would have installed the inboard drag brace in a tank ready manner from the beginning. TEAM should update the plans so they all show the inboard drag brace in a tank ready manner.

After getting the drag brace removed I made a new one. The new one glues to the side of the spar cap instead of on top of the spar cap. At the rear spar the drag brace top is flush with the spar cap top.

RS-13 gusset at rear spar

At the front spar a 3″ piece of RS-5 is glued to the top of the spar cap.

RS-5 spacer for plywood gusset

The brace top should be flush with the top of the newly added RS-5.

Once the brace glue is dry corner gusset blocks made from RS-13 are glued in place.

Glueing rear gusset
Glueing front gusset

After the corner blocks dry plywood gussets made from RS-553 are glued in place.

Glue plywood gusset