Fuel Systems Flashcards
What is a wet wing?
Wet wings are wings that are sealed so they can hold fuel inside. They have largely replaced rubber bladder tanks found in many older aircraft.
Bladder tanks would often deteriorate over time. That caused the tanks to distort, which trapped water and fuel.
What does unporting mean?
Unporting is fuel interruption caused by fuel in a tank sloshing away from the intake that draws it into the engine.
What is a collector bay?
A collector bay is a solution to the problem of unporting where fuel flow to the engine is interrupted because of fuel sloshing away from the intake that draws it into the engine.
A collector bay is a separate segment of a larger fuel tank located near the engine. If there is a momentary fuel supply interruption from the regular tank, the collector bay picks up the slack and provides the engine with a continuous flow of fuel.
A header tank is a small, separate tank that serves the same function as a collector bay.
What is a flapper valve?
A flapper valve is a spring-loaded, one-way door that is sometimes installed between the collector bay and the rest of the fuel tank in order to prevent reverse flow back to the main tanks.
What is a surge tank?
A surge tank is a fuel tank that is normally empty. They are located near the wing tips of large aircraft to help manage fuel movement, overflow, and venting.
What kind of fuel pumps are used to move fuel from tanks to the engines and from tank to tank on turbine aircraft?
The most common types of fuel pumps are…
- High-pressure pumps
- Low-pressure pumps
- Auxiliary pumps
- Jet pumps
What does the high-pressure fuel pump do?
The high-pressure fuel pump is driven by the engine and supplies fuel to each engine at pressures of about 900–1,000 psi.
Use of high pressure for this purpose is important because the amount of fuel required on takeoff may be two or three times greater than that needed at normal cruise. Therefore, both pressure and flow capacity must be available to rapidly provide large increases in fuel delivery.
What does the low-pressure fuel pump do?
The low-pressure fuel pump draws fuel from the tanks and sends it to the high-pressure pump, often through a fuel filter and heater.
The low-pressure pump is usually also engine driven.
What do auxiliary fuel pumps do on a turbine aircraft?
Most turbine fuel systems are equipped with electric auxiliary fuel pumps. These are otherwise known as aux pumps, standby pumps, fuel transfer pumps, or boost pumps.
Aux pumps have various purposes depending on specific aircraft fuel system design.
They are often used to…
- Move fuel from one tank to another
- Provide emergency backup for the engine-driven low-pressure pump
- Cross feed fuel if the engine fails
In large aircraft, boost pumps operate continuously in tanks that are being used, since low-pressure engine pumps don’t have enough suction at high altitudes to draw enough fuel.
What is the potential danger in having a boost pump turned on in an empty fuel tank?
Most fuel pumps cool and lubricate themselves with the fuel they pump. So be careful. You could burn up a fuel pump by having it turned on from an empty tank!
What is a jet pump?
A jet pump is also often called a motive flow pump. It refers to the use of small venturi-type ports, which draw fuel into collection lines.
Turbine aircraft collect fuel from several places in each tank in order to prevent unporting and to back up
any clogged pickups.
Instead of installing lots of mechanically driven pumps all over the tank, these venturi devices, or jet pumps, draw fuel into the lines by creating low-pressure areas in the passing fuel moving through the lines.
Therefore, jet pumps can’t pump fuel by themselves. Rather, they act as localized secondary pumps - sometimes called scavenge pumps.
They are powered by the main pump on the line, which is usually the low-pressure, engine-driven pump or an electric auxiliary pump.
What is a fuel control unit / FCU?
A fuel control unit / FCU is a precise hydromechanical or computerized electronic device that delivers fuel to the engine.
The FCU notes the thrust lever position, air pressure, and engine temperatures.
It then meters the proper amount of fuel from the high-pressure fuel pump to the engine’s combustion chamber.
Different types of electronic fuel control units are sometimes known as FADECs / full-authority digital engine controls or as ECUs / electronic control units.
For redundancy, some aircraft have mechanical FCUs backing up ECUs in the same fuel system.
What is a bladder fuel tank?
A bladder fuel tank is a tank made from reinforced flexible material such as rubber.
A bladder tank contains most of the features and components of a rigid tank but does not require as large an opening in the aircraft skin to install.
The tank, or fuel cell as it is sometimes called, can be rolled up and put into a specially prepared structural bay or cavity through a small opening. Once inside, it can be unfurled to its full size.
Bladder tanks must be attached to the structure with clips or other fastening devices. They should lie smooth and unwrinkled in the bay. It is especially important that no wrinkles exist on the bottom surface so that fuel contaminants are not blocked from settling into the tank sump.
In an turbine aircraft fuel system, what does a check valve do?
A check valve only allows fuel to travel in one direction.
In an turbine aircraft fuel system, what does a fuel-selector valve do?
Fuel selector valves allow the pilots to select which tanks supply fuel to the engines.
What is a fuel quantity measuring stick?
A fuel quantity measuring stick measures fuel quantity from beneath the wings. It is located in one or more hollow tubes that run vertically through each fuel tank.
The measuring sticks are usually locked in place in each fuel tank. To manually measure fuel quantity, each stick is unlocked and lowered until its top is level with the fuel surface.
