Aircraft Fuel Systems
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In a commercial aircraft fuel system, what is the primary purpose of the surge tank in the wing?

  • To provide a reserve of fuel in case of main tank failure.
  • To store extra fuel for extended range.
  • To house the fuel pumps and control valves.
  • To accommodate fuel expansion and prevent spillage. (correct)

    • Why are flexible fuel tanks advantageous in aircraft design?

  • They can be easily shaped and fitted into irregular spaces within the aircraft structure. (correct)
  • They are more resistant to impact damage than rigid tanks.
  • They offer better thermal insulation for the fuel compared to integral tanks.
  • Their rigid structure provides enhanced structural support to the aircraft.

    • What is the significance of ensuring that the compartment for a flexible fuel tank is as smooth as possible?

  • To maximize the fuel capacity of the tank.
  • To prevent chafing and wear on the flexible tank material. (correct)
  • To facilitate easier installation and removal of the tank.
  • To improve the thermal insulation of the tank.

    • Which of the following best describes the construction of rigid fuel tanks used in aircraft?

    <p>Metal or plastic material shaped to fit available spaces. (C)</p> Signup and view all the answers

    What is the primary purpose of a sequence valve in an aircraft fuel system?

    <p>To prioritize fuel consumption from inner tanks before outer tanks for structural considerations. (C)</p> Signup and view all the answers

    What is the approximate output flow rate of a typical fuel pump (booster pump) installed in an aircraft fuel tank?

    <p>250-300 liters/min (B)</p> Signup and view all the answers

    Why is it important to have water draining valves at the lowest points of each fuel tank?

    <p>To remove accumulated water, which is heavier than fuel, and prevent icing or corrosion. (A)</p> Signup and view all the answers

    What is a key characteristic of integral fuel tanks?

    <p>They are formed by sealing off parts of the aircraft structure. (D)</p> Signup and view all the answers

    In the event of a fire, which component is activated to isolate the fuel system?

    <p>Low Pressure Shutoff Valve (A)</p> Signup and view all the answers

    Which of these components allows an aircraft to rapidly decrease its weight in emergency situations?

    <p>Fuel Jettison System (C)</p> Signup and view all the answers

    What design consideration allows for fuel expansion without spillage in commercial aircraft fuel tanks?

    <p>Additional space of approximately 2% within the tank. (B)</p> Signup and view all the answers

    What is the function of the air vent fitted to the top of each fuel tank?

    <p>To allow free flow of air in and out of the tank (B)</p> Signup and view all the answers

    What is the main difference between a gravity feed fuel system and a pump feed fuel system?

    <p>Gravity feed systems rely on gravity to deliver fuel to the engine, whereas pump feed systems use pumps to move the fuel. (A)</p> Signup and view all the answers

    What is the maximum fuel pressure at zero flow for a typical fuel pump?

    <p>38 psi (A)</p> Signup and view all the answers

    Where is the Low Pressure (LP) shutoff valve typically located?

    <p>At the top of the pylon on the outside of the front wing spar (C)</p> Signup and view all the answers

    What is the main purpose of a fuel cross-feed system in an aircraft?

    <p>To allow fuel to be transferred from one tank to another. (D)</p> Signup and view all the answers

    What is the primary purpose of 'inwards and outwards venting' in aircraft fuel tanks?

    <p>To prevent over-pressurization due to fuel expansion and contraction. (D)</p> Signup and view all the answers

    Why are open-vented fuel systems less common in modern high-altitude aircraft?

    <p>They are prone to fuel venting during maneuvers and limit maximum ceiling due to fuel boil at low ambient pressure. (A)</p> Signup and view all the answers

    What is the function of a vent float valve in an aircraft fuel tank?

    <p>To control the venting line opening, typically located at the highest point of the tank. (C)</p> Signup and view all the answers

    In a modern aircraft, what type of sensor is typically used for fuel level sensing?

    <p>Thermistors that send signals through amplifiers. (A)</p> Signup and view all the answers

    What is the purpose of high-level sensing in an aircraft fuel tank?

    <p>To prevent overfilling of the fuel tanks during refueling. (A)</p> Signup and view all the answers

    What happens when the high-level shut-off system fails during refueling, and fuel enters the vent tank?

    <p>An amber FULL light illuminates on the refuel panel, indicating overflow. (A)</p> Signup and view all the answers

    What is the significance of having separate low-level sensing for outer and inner/center fuel tanks?

    <p>It provides differentiated warnings based on the location of low fuel levels. (A)</p> Signup and view all the answers

    If the outer tank low-level sensor is exposed to air, what indication will the flight crew typically receive?

    <p>An amber LO LVL light comes on, indicating low fuel. (C)</p> Signup and view all the answers

    In what operational mode are the inner/centre tank low-level sensing systems active?

    <p>Automatic Mode (D)</p> Signup and view all the answers

    What is the primary purpose of the calibration sensors installed in the fuel trim tank?

    <p>To test the accuracy of the fuel quantity indication during refuelling. (D)</p> Signup and view all the answers

    What action is triggered when the fuel level in either outer tank drops below a certain threshold?

    <p>The maximum flight speed is reduced. (D)</p> Signup and view all the answers

    Which component is NOT part of the fuel quantity measurement and indication system?

    <p>Air Data Computer (ADC) (C)</p> Signup and view all the answers

    In the context of capacitance gauging, what is the variable factor that affects the amount of charge held in a fuel tank capacitor stack?

    <p>The dielectric between the plates. (D)</p> Signup and view all the answers

    What happens to the dielectric as the fuel level in a tank decreases?

    <p>The dielectric gradually changes to air. (C)</p> Signup and view all the answers

    How many probes are installed in each centre tank of a wide-bodied twin aircraft fitted with a fuel trim system, according to examples given?

    <p>4 (C)</p> Signup and view all the answers

    Which of the following is a crucial safety precaution to observe during aircraft refuelling operations?

    <p>Using the correct grade of fuel. (A)</p> Signup and view all the answers

    During aircraft defueling with a pressure-type system, what combination of equipment is used to transfer fuel from the aircraft to the bowser?

    <p>A combination of both fuel supply booster pumps on the bowser and aircraft. (C)</p> Signup and view all the answers

    What is a crucial safety precaution to observe during aircraft refueling operations with a fuel bowser?

    <p>Ensuring the aircraft's electrical state remains constant while connected to the bowser. (C)</p> Signup and view all the answers

    In large aircraft, how is longitudinal balance during flight primarily maintained as fuel is consumed?

    <p>By using fuel valves controlled by the flight engineer to manage fuel usage from different tanks. (C)</p> Signup and view all the answers

    Why is the position of fuel tanks more critical in small aircraft compared to large aircraft?

    <p>Small aircraft lack sophisticated fuel management systems, making them sensitive to shifts in the center of gravity. (A)</p> Signup and view all the answers

    What is the primary purpose of a fully automatic fuel scheduling system in modern high-performance aircraft?

    <p>To reduce the workload on the flight crew by automatically managing fuel distribution for optimal balance. (D)</p> Signup and view all the answers

    Flashcards

    Fuel Systems

    Systems designed to store and deliver fuel to engines and APU in aircraft.

    Types of Fuel Systems

    Includes Gravity Feed and Pump Feed systems for fuel delivery.

    Gravity Feed Fuel System

    A system where fuel flows to engines due to gravity without a pump.

    Pump Feed Fuel System

    A fuel delivery system that uses a pump to move fuel to engines.

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    Rigid Fuel Tank

    Tanks made from metal or plastic, inflexible and fitted internally.

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    Flexible Fuel Tank

    Thin-walled tanks that can be folded to fit tight spaces within the aircraft.

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    Integral Fuel Tank

    Fuel tanks built into the structure of the aircraft; space-efficient.

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    Water Draining Valves

    Valves positioned at the lowest points of tanks to remove accumulated water.

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    Fuel Pumps (Booster Pumps)

    Centrifugal pumps that provide high fuel flow and pressure, driven by 115 volts motors.

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    Sequence Valves

    Valves that automatically transfer fuel from one tank to another while managing fuel pressure.

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    Transfer Valves

    Valves used to move fuel between different tanks within the system.

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    Low Pressure Shutoff Valve

    Valve that isolates the fuel system during emergencies or maintenance.

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    Fuel Jettison

    The process of dumping fuel in emergencies to reduce aircraft weight.

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    Fuel Collector Tanks

    Tanks that gather fuel from various pumps for efficient distribution.

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    Fuel Strainers

    Filters in the fuel system that remove contaminants from the fuel supply.

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    Vent System

    Air vent fitted at the top of each tank allowing air flow in and out for proper operation.

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    Bowser Positioning

    The correct placement of the fuel bowser relative to the aircraft is essential during refueling.

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    Defueling Procedure

    Defueling is nearly the reverse of refueling and uses a de-fuel bowser connected to the fuel system.

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    Longitudinal Balance

    The aircraft's balance changes during fuel usage, affecting stability and control in flight.

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    Automatic Fuel Scheduling

    High-performance aircraft utilize systems to automatically manage fuel distribution, ensuring balance easily.

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    Inner/Centre Tank Low Level Sensing

    Sensors that detect fuel level in the inner/centre tank during AUTO MODE for calibration.

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    Calibration Sensing

    Process to ensure accurate fuel quantity indication during refueling using sensors in the trim tank.

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    Full Level Sensing

    Reduces maximum flight speed when fuel in outer tanks drops too low to protect wing structure.

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    Fuel Quantity Measurement Tasks

    Measuring and indicating fuel quantity across various systems like indicators and ECAM.

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    Capacitance Gauging Principles

    Measuring fuel levels based on capacitance changes due to dielectric variations between fuel and air.

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    Fuel Quantity Indicating System

    System with probes ensuring at least one is immersed in fuel to accurately indicate levels.

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    Safety Precautions for Refueling

    Safety measures including using correct fuel type, no smoking nearby and appropriate footwear during refueling.

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    Fuel Probes Arrangement

    A group of probes installed in tanks ensuring one is always immersed, differing by aircraft type.

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    Inwards and Outwards Venting

    A system that prevents over-pressurisation of fuel tanks by allowing air and fuel to escape and enter as needed.

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    Unpressurised System Venting

    A simple venting method where tank orifices connect directly to a vent pipe gallery, allowing fuel to vent via free atmosphere.

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    Reid Vapour Pressure (RVP)

    The rate at which fuel releases vapour, affecting how aircraft fuel systems are designed.

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    Float Valves

    Vent openings in wing tanks controlled by float valves, which activate at the highest point of the tank.

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    High Level Sensing

    Detects overfilling of fuel tanks, causing the refuel valve to close and indicating with a blue FULL light.

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    Overflow Sensing

    Senses if fuel overflows into the adjacent vent tank, indicated by an amber FULL light.

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    Low Level Sensing

    Detects low fuel levels in tanks, alerting with an amber light when tanks are low.

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    Study Notes

    Fuel Systems Overview

    • Fuel systems are designed to store and deliver fuel to aircraft engines and auxiliary power units (APUs).
    • Aircraft must carry enough fuel for extended operation.
    • Fuel is stored and supplied to engines safely and at a controlled rate.
    • Systems include tanks, lines, connections, and fittings compatible with all fuel types.
    • Sub-systems include storage, refueling, distribution, transfer, venting, and indication.

    Types of Fuel Systems

    • Gravity Feed: Fuel flows by gravity from higher-level tanks to the carburetor, avoiding pumps
    • Pump Feed: Employs pumps to deliver fuel under pressure to the engine.

    Fuel Tank Categories

    • Rigid: Constructed from metal or plastic, installed where space allows
    • Flexible: Thin, flexible walls (bag-style tanks), or thicker, can be folded.
    • Integral: Integrated into the aircraft structure

    Fuel Feed Components

    • Fuel Pumps (Booster Pumps): Two centrifugal pumps per tank, driven by 115-volt, three-phase motors. Output is approximately 250-300 liters/min, and maximum pressure at zero flow is around 38 psi. Each pump has a non-return and bypass valve.
    • Jet Pumps: Used to deliver fuel to different parts of the system.
    • Sequence Valves: Automatically transfer fuel between tanks, limiting outer tank pump pressure to 17.5 psi (priority for inner tanks).
    • Transfer Valves: Transfer fuel between tanks.
    • Low Pressure Shutoff Valve: Isolates the fuel system for maintenance or fire.
    • Cross Feed Valve: Transfers fuel between different sections of the system.

    Fuel Tank Construction

    • Rigid tank structure, interior attachments, vent connections, and attachment rings for fittings.

    Water Draining

    • Drain valves situated at the lowest point of each tank, for water and sediment removal. Valves are typically opened with standard tools. Outer seal is replaceable without emptying the tanks.

    Fuel Tank Drain Points

    • Design allows for easy opening and closing of the valves

    Fuel Collector Tanks

    • Used in systems for coordinated fuel collection from various tanks.

    Fuel Lines and Fittings

    • MIL-spec lines and fittings (MIL-18794) define fuel line safety and durability.

    Fuel Filler Caps

    • Designs for filling aircraft fuel tanks are safety critical and must not permit fuel leakage.

    Hand Operated Valves (Cone Type)

    • Components including handle, detent plate, spring, brass cone, valve housing are involved in manually controlling fuel flow.

    Hand Operated Valves (Poppet Type)

    • Components such as spring, poppet valve, and cam, control fuel flow in the valve mechanism.

    Motor Operated Valves

    • Components such as a gate, and a motor direct fuel flow to the engine.

    Solenoid Operated Valves

    • Components such as spring, Solenoid are used to electronically control fuel flow.

    Hand Gasoline Pump

    • Components such as handle, outlet valve, housing, vane shaft, and inlet valve in the manual fueling pump.

    Boost Pumps

    • Motor-driven pumps for fuel delivery that are used in aircraft systems to increase pressure.

    Fuel EJectors, Strainers

    • Components used in fuel system to filter and manage flow.

    Fuel Cross-feed System

    • Coordinated transfer and distribution of fuel to various aircraft engines, and systems.

    Vent System

    • System elements such as vent float valve, breather assembly, and overpressure protector, direct air flow into and out of the fuel tank.

    Drip Sticks

    • Devices for measuring fuel levels in specific locations.

    Flow Indicators

    • Electronic gauge for measuring and displaying various fuel flow and remaining data.

    Fuel Dumping (Jettison)

    • Method to jettison fuel in emergencies for weight reduction. System components include jettison valves, drive motors, and piping.

    Fuel Jettison Control

    • System elements used for controlling fuel jettisoning systems, including separate valve controls and electrical connectors.

    The Vent Sub Systems

    • System components that direct airflow into and out of fuel tanks to safeguard against pressure build-up or excessive pressure (inwards and outwards venting).

    Venting Due to Heat

    • Fuel systems must dynamically adjust to variations in temperature-driven expansion and contraction. Vents adapt to varying atmospheric pressures.

    Unpressurized System Venting

    • Venting of fuel tanks directly to the atmosphere.

    Reid Vapour Pressure (RVP)

    • Rate at which fuel vaporizes.

    Float Valves

    • Float valves adjust vents to regulate air flow in and our of tank at different flight levels.

    Fuel Level Sensing

    • Modern systems use sensors (thermistors) for precise fuel level readings. Older aircraft utilize float switches.

    High Level Sensing

    • Trigger mechanisms that close refuelling valves, and light-up 'FULL' warning on instrument panel in the case of over-fueling.

    Overflow Sensing

    • In case of over-fueling, the associated 'FULL' error warning will signal to the aircraft operator.

    Low Level Sensing

    • System that detects low fuel levels in outer tanks.

    Calibration Sensing (Fuel Trim Only)

    • System used to accurately measure the fuel levels in different tanks for quality assurance purposes.

    Under Full Level Sensing

    • System that detects low fuel levels.

    Fuel Quantity Measurement and Indication

    • System components and their related functions designed to quantify and display current fuel levels.

    System Components

    • Components employed in the system that quantify and display fuel levels.

    Principle of Capacitance Gauging

    • Principles describing how fuel level is measured based on capacitance variations.

    Capacitance Gauging

    • System components that facilitate sensing of fuel levels based on variations in electrical capacitance.

    Fuel Quantity Indicating System

    • System for measuring and displaying fuel quantity in aircraft tanks.

    Basic Fuel System

    • Overview of the core components making up a fuel system.

    Refueling and Defueling

    • Procedures for fueling and emptying aircraft fuel tanks.

    Safety Precautions When Refueling

    • Safety measures to prevent accidents during fueling, such as no smoking, appropriate gear, and proper positioning of equipment.

    Defueling

    • Techniques to empty aircraft fuel tanks, such as using a fuel tanker and aircraft booster pumps.

    Longitudinal Balance Fuel System

    • Aircraft configuration that dynamically adjusts to changing fuel levels to maintain stability and balance while flying.

    Longitudinal Fuel Transfer

    • System elements involved in adjusting fuel distribution for better aircraft trim during different phases of flight(e.g., take-off, landing, cruising)

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    Aircraft Fuel Systems PDF

    Description

    Explore aircraft fuel systems, including surge tanks, flexible tanks, and fuel pumps. Learn about fuel tank construction, sequence valves, and emergency fuel dump systems. Understand the importance of water drainage and fire isolation.

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