Aircraft Fuel System

Aircraft Fuel System

1. Basic Fuel System Requirements

   • Fuel System Lightning Protection
     • prevent the ignition of the fuel within the system
       • direct lightning
       • corona
         • a luminous discharge that occurs as a result of an electrical potential difference between the aircraft and the surrounding area
       • Streamering
         • a branch-like ionized path that occurs in the presence of a direct stroke or under conditions when lightning strikes are imminent
   • Fuel System Independence
     • independence between multiple fuel storage and supply systems
   • Title 14 of the Code of Federal Regulations (14 CFR)
     • 14 Part 23—Normal, Utility, Acrobatic, and Commuter Category Airplanes
     • 14 Part 25—Transport Category Airplanes
     • 14 Part 27—Normal Category Rotorcraft
     • 14 Part 29—Transport Category Rotorcraft
     • 14 Part 31—Manned Free Balloons
     • 14 Part 34- outlines requirements that fall under the jurisdiction of the Environmental Protection Agency (EPA)
       • A turbine engine fuel system must be capable of sustained operation throughout its flow and pressure range even though the fuel has some water in it
         • with water at 80 °F
           • having 0.75 cubic centimeters (cm) of free water per gallon added to it
             • then cooled to the most critical condition for icing likely to be encountered in operation.
     • Fuel
       • Pumps
       • Filters
       • Fuel Lines
       • Valves
       • Methods
       • Metering devices
       • Storage Tanks
       • monitoring devices
   • Fuel Flow
     • powerplant functions properly in all likely operating conditions
     • auxiliary power unit functions properly in all likely operating conditions

2. Fuel

   • Fuel Storage System
     • Each tank must be isolated from personnel personnel compartments and protected from hazards due to unintended temperature influences
     • must provide fuel for at least one-half hour of operation at maximum continuous power or thrus
     • fuel tanks must be designed to prevent significant loss of stored fuel from any vent system
   • Fuel Storage Refilling or Recharging System
     • must be designed to prevent:
       • contamination of the fuel stored during likely operating conditions
       • improper refilling or recharging
       • the occurrence of any hazard to the airplane or to persons during refilling or recharging
   • Types of Aviation Fuel
     • kerosene
       • fuel with a much higher flash point, so it is less flammable
       • should never be mixed with aviation gasoline
       • higher viscosity with much lower volatility and higher boiling points than gasoline
       • operate in cold environments
       • must start readily and be able to restart while in fligh
         • Fuel with high volatility makes this easier.
       • Fuel Types
         • Jet A
           • the most common turbine engine fuel available in the continental United States
             • low volatility and low vapor pressure
         • Jet A-1
           • is the most popular globally
             • low volatility and low vapor pressure
         • Jet B
           • is primarily available in Alaska and Canada
             • High volatility and low freezing point
       • Fuel Issues
         • areas where water can settle, and microbes can flourish
     • AVGAS
       • Combustion releases energy in the fuel, which is converted into the mechanical motion of the engine
       • is very volatile and extremely flammable, with a low flash point
       • has been available in different formulas
       • is a blend of numerous hydrocarbon compounds, each with different boiling points and volatility
       • Vapor Lock
         • AVGAS vaporizes in the fuel line or other components between the fuel tank and the carburetor
           • boost pumps located in the fuel tank can prevent that
       • vapor pressure be between 5.5 pounds per square inch (psi)
         • 7.0 psi at 100 °F.
       • Aromatic Fuels
         • In years past, considerable quantities of aromatic hydrocarbons were sometimes added
           • increase the rich mixture performance of AVGAS
       • Octane and Performance Number Rating
         • a single 100 octane low-lead fuel (100LL)
       • Fuel Identification
         • 100LL AVGAS
           • is dyed blue
         • 100 AVGAS
           • is dyed green
         • 80/87 AVGAS
           • no longer available
             • is dyed red
         • 82UL (unleaded)
           • is dyed purple
         • 115/145 AVGAS

3. Small Single-Engine Aircraft Fuel Systems

   • Gravity Feed Systems
     • High-wing aircraft
       • gravity is used to deliver the fuel.
         • shutoff valve has two positions:
           • fuel ON
           • fuel OFF
         • selector valve provides four options:
           • fuel shutoff to the engine
           • fuel feed from the right-wing tank only
           • fuel feed from the left fuel tank only
           • fuel feed to the engine from both tanks simultaneously
     • is the simplest aircraft fuel system.
   • Pump Feed Systems
     • Low- and mid-wing single reciprocating engine aircraft
       • one or more pumps are used to move the fue
         • fuel cannot be drawn from both tanks simultaneously
   • High-Wing Aircraft with Fuel Injection System
     • equipped with a fuel system that features fuel injection rather than a carburetor
       • It is first delivered from the fuel tanks by gravity to two smaller accumulator or reservoir tanks.
         • These tanks, one for each wing tank, consolidate the liquid fuel and have a relatively small airspace.
           • They deliver fuel through a threeway selector valve
             • LEFT
             • OFF
             • RIGHT
             • The selector valve also acts simultaneously as a diverter of air that has been separated out of the fuel in the engine-driven fuel pump and returned to the valve
               • It routes the air to the vent space above the fuel in the selected reservoir tank
   • Small Multiengine (Reciprocating) Aircraft Fuel Systems
     • Low-Wing Twin
       • t is more complicated than a single-engine aircraft
         • Two selector valves are required
     • High-Wing Twin
       • combines gravity feed with an electric fuel pump
         • The metering unit for each engine provides the proper flow of fuel to the distribution manifold which feeds the injectors
   • Large Reciprocating-Engine Aircraft Fuel Systems
     • are no longer produced
       • They are mostly carbureted and share many features with the light aircraft systems
   • Jet Transport Aircraft Fuel Systems