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
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