Aviation Float Fuel Sender - Historical Perspective

Dawn of Aircraft Instrumentation

The initial non-electrical float system was used on various aircraft, the most famous being the Piper J-3 "Cub." which used a cork with a wire imbedded in it that extended into the view of the pilot. Lots of wire showing, lots of gas; no wire showing, no gas.  Equally glass sight gauges are used in high wing aircraft and high wing fuel can to flow to the engine by means of gravity.

Electrical Aircraft Instrumentation Comes of Age

With the addition of electrical systems in aircraft the float was connected to the arm of a variable resistor whose electrical leads are brought through the wall of the tank and connected to the fuel quantity gauge and to the ship's electrical bus. 

Thus, the change in resistance as the float follows the level of the fuel.  This electrical value causes the needle on the fuel quantity gauge to deflect indicating the quantity of fuel in the tank.  Simple and direct.

For odd shaped tanks, particularly a flat tank in a wing with dihedral, multiple resistance floats are connected in series to correctly categorize this onger sloped tank.

This is the fuel gauging system on most, if not all, automobiles, the majority of piston engine aircraft, and some turbine aircraft. This system has been given very poor reviews over the years, some of which is deserved, but a large portion of the criticism is not.

If the resistance float is poorly designed and constructed, if the gauge is poorly designed and constructed, if the gauge is poorly marked, if the damping of the complete system is not suitable for aircraft or it's particular use,  or if the system is poorly installed and calibrated,  criticism for poor operation is rightly deserved. 

Digital Display and Interface  

In the instance of fuel level - Nothing really 

Well in the case of Commercial Aircraft the capacitance value was converted to ARINC 429 protocol and transmitted to the cockpit.

Until Now 

The First Digital Output General Aviation Fuel Level Sender 

  

Fuel Level Senders - Automotive

Fuel level sending has been the providence of electrical resistance since somewhere in the 1930's when electrification of the automobile hit full stride.  The Ford Model A used a very clever sight gauge so that you actually saw a liquid representation of fuel level - neat design but expensive.

http://www.facebook.com/Fuellevel

Resistance Level worked very well and was easy to understand  -  X Ohms Full - Y Ohms Empty

Simple

And then suddenly somebody decided to add alcohol -  to fuel -

Methanol and ethanol contain soluble and insoluble contaminants.[5] Halide ions, which are soluble contaminants, such as chloride ions, have a large effect on the corrosively of alcohol fuels. Halide ions increase corrosion in two ways: they chemically attack passivating oxide films on several metals causing pitting corrosion, and they increase the conductivity of the fuel. Increased electrical conductivity promotes electrical, galvanic and ordinary corrosion in the fuel system. Soluble contaminants such as aluminum hydroxide, itself a product of corrosion by halide ions, clogs the fuel system over time. To prevent corrosion the fuel system must be made of suitable materials, electrical wires must be properly insulated and the fuel level sensor must be of pulse and hold type (or similar). In addition, high quality alcohol should have a low concentration of contaminants and have a suitable corrosion inhibitor added.

So if you turn to any car chat blog (ANY CAR CHAT BLOG)  -

Failed fuel level sensors are driving OBD II cars to the shoulder.

So we need to find a replacement  Smiths (Stewart Warner, VDO, Veglia, Et al) in a Pulse and Hold fuel senders - Not compatible 

We are producing  a patented new non-contact fuel level sensor.

We are applying the sensor presently  to aviation (aircraft, rotorcraft) - In aviation we don't have alcohol,  but we can't put wires in the tank - something about electricity and fuel

Aviation  requires - what cars - all cars using Alcohol mixed fuel need - A non contact fuel level sensor

It is also helpful in this environment 

Fuel Level Sensor Under Test

We use a new concept in our sender called Magnetoresistance - certain materials change resistance in the presence of a rotating magnetic field and they can do this from as far as 3/8" away actually from the dry side of the tank.

Most of us see this everyday in the compass on our smartphone

There is no pivot or contact resistance,  so the float can be smaller and the range can be larger (fuller fulls and emptier empties)

Neat thing is that the  output of this sensor  can mimic a resistive sensor

Hey if you find this interesting let us know

scott.philiben@ciescorp.com