Aircraft Fuel Systems

Define Volatility

A measure of a liquids tendency to vaporize under given conditions

Define Vapor Lock

A condition where fuel does not vaporize readily enough, which can cause hard starting.

List the 6 Fuel types commonly used and the equipment color that represents each type

1. Avgas 80 — Red

2. Avgas 100 — Green

3. Avgas 100 LL — Blue

4. Jet A — Black

5. Jet A-1 — Black and Silver

6. Jet B — Black and Yellow

Define “crossfeed mode”

A term that indicates that an engine is drawing fuel from the opposite wing

What sorts of things commonly contyaminate aviation fuel?

1. Solids

2. Water

3. Microorganisms

7 Basic fuel system components

1. Tanks

2. Lines

3. Valves

4. Pumps

5. Filters

6. Gauges

7. Warning Systems

List the 3 Types of fuel tanks and their differences

1. Welded or Riveted Tanks

   1. Older type of tank, easy and cheap, just welded or riveted sheet metal placed inside of a big enough section in the structure

2. Integral Fuel Tanks

   1. Fuel tanks that are bade from a sealed off portion of the wing; uses the most amount of space for the fuel and no added weight of an actual tank. Most common on newer, larger aircraft.

3. Bladder Tanks'

   1. Fuel is stored in a neoprene impregnated cloth bladder that is placed in a cavity of the structure; installed through small holes; requires that all sharp surfaces be covered or smoothed inside the structure so the bladder is not penetrated.

What is a lay line? Why is it important?

A line that indicates if a flexible hose is twisted, you do not want any twist in a fuel line.

What is the purpose of a flapper valve?

To prevent fuel from flowing away from the boost pump or tank outlet when the aircraft is turning or manuvering

What fuel tank cap should be used with any particular aircraft?

The fuel tank cap approved for use on that aircraft.

List the 3 Types of Fuel Valves listed in the text

1. Hand Operated Valves

2. Motor Operated Valves

3. Solenoid Operated Valves

What is the difference/advantage between motor and solenoid operated fuel valves?

Solenoid Operated valves are much quicker to open and close, and have a physical lock to keep them rigidly in their position as opposed to motor driven valves.

What is the purpose of an engine driven fuel pump?

“To deliver a properly pressured, continuous supply of fuel during engine operation” —page 15-27

What is a “wobble” pump?

A type of hand pump that pumps fuel as a handle is moved both up and down. AKA a double acting pump

What is the most popular type of fuel pump for use as an auxiliary pump? Why?

A centrifugal boost pump, typically installed inside the fuel tank to provide positive pressure to the inlet side of the engine driven fuel pump.

What is the purppose of a fuel ejector? How does it work?

A system that uses a venturi to supply additional fuel to the collector, which is typically where the boost pump is located.

Give an example of a constant displacement pump AND a variable displacement pump.

• Constant displacement: Vane-Type Pump

• Variable Displacement: Gear or Gerotor Pumps

What are the 2 basic types of fuel quantity indicating systems? How do they work?

1. Electrical Ratiometer Type fuel quantity gauges (AKA Float type)

2. Capacitance-type fuel quantity system

How does a Ratiometer-type fuel quantity indicator work?

A float floats on top of the fuel in the tank, and its position is converted into a resistance by a fuel tank transmitter unit that displays on a gauge the fuel quantity in gallons.

How does a Capacitance-type fuel quantity system work?

As the quantity of fuel in the tank changes, the portion of the probe immersed in fuel or exposed to the air varies. The difference in dielectric values changes the electrical capacitance of the probes, and a capacitance bridge measures this quantity IN POUNDS OF FUEL.

What is the process called where a technician manually checks the fuel level in a tank?

“Dipping the tanks”

What do fuel flowmeters measure?

The number of pounds or kilograms of fuel flowing per hour to each engine.

What methods are used to prevent fuel icing?

1. Fuel Heaters, which commonly use bleed air or engine oil to preheat fuel before it enters the FCU

2. Fuel Additives, such as Prist

What is a “surfactant”?

A soap or detergent like material that occur naturally in fuel, or can be introduced in handling.

Usually appear as a tan to dark brown sudsy liquid

Can inhibit fuel filters