3J Airplane Systems - Fuel System Flashcards
- When is the auxiliary fuel boost pump used?
Proper usage of the fuel boost pump varies with different aircraft. In general, the fuel boost pump should be used during takeoffs and landings, when switching fuel tanks, and anytime fuel pressure falls below a selected value. The fuel boost pump in a Cessna 172-RG should be used anytime the fuel pressure falls below 0.5 PSI.
- What type fuel system does this aircraft have?
The fuel system consists of the following: a. Two vented integral fuel tanks b. A four-position fuel selector valve c. A fuel strainer d. A manual primer e. An engine-driven fuel pump f. An electric auxiliary fuel pump g. A carburetor The airplane uses a gravity-feed type fuel system. Fuel is delivered to the engine-driven fuel pump, unassisted, except by gravity. Fuel flows from the wing tanks to the fuel selector valve which is marked with BOTH, RIGHT, LEFT and OFF positions. From the fuel valve, fuel flows through a fuel strainer and then to the engine-driven fuel pump. The fuel pump then delivers fuel to the carburetor. After the carburetor, the fuel/air mixture is delivered to the cylinders via intake manifold tubes.
- Why is it necessary to include a left and right position on the fuel selector valve?
During cruise flight, with the fuel selector valve on “Both,” unequal fuel flow may occur if the wings are not consistently kept level during the flight. This will result in one wing being heavier than the other. A fuel selector valve with the left/right option allows a pilot to control the situation by selecting the tank on the heavier wing and remaining on that tank until both tanks contain approximately the same amount of fuel.
- Where are the fuel vents located for each tank?
The left fuel tank is vented overboard through a vent line with a check valve. The right fuel tank is vented through the filler cap. Both fuel tanks are vented together by an interconnecting line.
- What purpose do fuel tank vents have? (FAA-H-8083-25)
As the fuel level in an aircraft fuel tank decreases, without vents a vacuum would be created within the tank which would eventually result in a decreasing fuel flow and finally engine stoppage. Fuel system venting provides a way of replacing fuel with outside air, preventing formation of a vacuum. Tanks may be vented through the filler cap or through a tube extending through the surface of the wing.
- What type fuel does this aircraft require (minimum octane rating and color)?
The approved fuel grade used is 100LL, and the color is blue.
- Can other types of fuel be used if the specified grade is not available? (FAA-H-8083-25)
Airplane engines are designed to operate using a specific grade of fuel as recommended by the manufacturer. If the proper grade of fuel is not available, it is possible, but not desirable, to use the next higher grade as a substitute. If using a higher grade fuel than that specified as a minimum grade for your engine, the engine manufacturer’s instructions must be observed. This is because the higher octane fuels normally used in higher-compression engines must ignite at higher temperatures—but not prematurely.
- What are some examples of different fuel grades (octane ratings) available? (FAA-H-8083-25)
Grade - Color 80 - Red 100 - Green 100LL - Blue Jet A - Colorless or Straw
- What is the function of the manual primer, and how does it operate?
The manual primer’s function is to provide assistance in starting the engine. The primer draws fuel from the fuel strainer and injects it directly into the cylinder intake ports. This usually results in a quicker, more efficient engine start.
- Where are the drain valves located?
A drain valve is located on the bottom of each main wing and also directly under the fuel selector valve. A fuel strainer drain is located under an access panel on the right side of the engine cowling.
- How is fuel quantity measured?
One float-type fuel quantity transmitter and one electric fuel quantity indicator measure fuel quantity for each tank.
- Are the fuel quantity indicators accurate? (FAA-H-8083-25)
Aircraft certification rules only require accuracy in fuel gauges when they read “empty.” Any reading other than “empty” should be verified. Do not depend solely on the accuracy of the fuel quantity gauges. Always visually check the fuel level in each tank during the preflight inspection, and then compare it with the corresponding fuel quantity indication.
