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.
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
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