Fuel Systems - Carburettor Flashcards
What are the three different types of carburettors found in piston engine aircraft?
Updraft, downdraft and sidedraft
In relation to the intake manifold, what position would an updraft carby be?
Below the intake manifold
In its most basic form, what are the main components that make up a carburettor?
A venturi, a throttle valve, float chamber + needle assembly and jets and discharge nozzles
What is the role of the throttle valve in a carby?
It controls the volume of air flowing through the carby into the intake manifold
How is the throttle valve position controlled in an aircraft?
It is controlled by a mechanical linkage that is connected to the throttle lever in the cockpit
What is the role of the float chamber?
To maintain a constant level of fuel in the discharge tube
From where does fuel enter the fuel chamber?
Via the needle valve
When the throttle position is wide open and the engine is at maximum RPM, the fuel feed rate increases at a disproportionate rate to the air flow. How is the problem resolved?
A metering jet in the discharge tube helps to control the fuel flow
What is the main jet used for?
It controls the maximum fuel flow rate at maximum engine speed
At idling speeds, the airflow though the venturi of the carburettor is too low to draw sufficient fuel from the discharge nozzle, so the carburettor cannot deliver enough fuel to keep the engine running. In this case, what is the solution to ensure that fuel delivered sufficiently to keep the engine running?
An idling system with an outlet at the throttle valve is added (idle jet)
When the main discharge nozzle is in operation (throttle open) what does the idle jet operate as?
An auxiliary air bleed to the main system
In most cases, the float maintains a fuel level that is approximately 1/8 inch below the opening in the discharge nozzle. What is this distance referred to as?
The fuel metering head
What is the purpose of the fuel metering head?
It helps prevent fuel leaking out of the fuel nozzle when the engine is shut down
Why are air bleed systems important to a fuel metering system?
Due to the fact that when fuel enters a discharge nozzle, its surface tension can cause it to ‘stick’ to the walls of the nozzle. This can cause the fuel to intermittently discharge from the nozzle.
What would happen if an air bleed passage were to become blocked?
The mixture would become rich at higher power settings
