b-9fuel200313-w21
TRANSCRIPT
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FUEL SYSTEMS
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Aircraft Fuel
Reciprocating engine fuels
Turbine engine fuels
Jet A which is Kerosene Jet B a blend of kerosene and gasoline
Jet A-1 used for operation at extremely low
temperatures
Jet A and Jet B are the most common
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Fuel System Contamination The higher the viscosity of the fuel, the greater its ability to hold
contaminants in suspension
This is why jet fuels, which have a higher viscosity than av-gas,are also more susceptible to contamination than av-gas
The main contaminants that reduce the quality of fuel are: Other petroleum products
Water
Rust
Scale Dirt
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Water Contamination Water contamination in fuel can be in two forms:
Dissolved in the fuel
Entrained or suspended in the fuel
Water in fuel can cause icing in the aircraft fuel system,usually in: Boost pump screens
Low pressure filters
Large amounts of water can cause engine stoppage
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Microbial Growth Microbial Growth is produced by various forms of micro-
organisms that live and multiply in water which is in jetfuel
These micro-organisms form slime that can be red,brown, green, or black
The organisms feed on hydrocarbons in the fuel butrequire water to multiply
This buildup can: Interfere with fuel flow and quantity indications
Start electrolytic corrosive action
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Contamination Detection
Coarse fuel contamination can be detected
visually
Uncontaminated fuel should be: Clean
Bright
Contain no perceptible free water
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Contamination Detection (cont.)
Clean means the absence of any readily visible
sediment or entrained water
Bright refers to the shiny appearance of clean, dry fuel
Free water is indicated by a cloud, haze, or water slug
Water saturated in fuel is not always visible
Perfectly clear water can contain as much as three times the
acceptable limit
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Contamination Detection (cont.)
There is no accurate method of detecting fuel entrainedwater when it is frozen
For this reason, it is important that fuel is checked when
the water is in a liquid state This should not be done following a flight at altitude when the
fuel would be below 32 degrees F
It is more effective to drain the fuel after the fuel has setundisturbed for a period of time, allowing the water toprecipitate and settle to the drain point
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Fuel Systems The purpose of an aircraft fuel system is to store and
deliver the proper amount of clean fuel at the correctpressure to the engine
Fuel systems should provide positive and reliable fuelflow through all phases of flight including: Changes in altitude
Violent maneuvers
Sudden acceleration and deceleration
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Fuel Systems (cont.)
Fuel systems should also continuously monitor
system operation such as:
Fuel pressure
Fuel flow
Warning signals
Tank quantity
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Types of Fuel Systems
Fuel systems can be classified in two broad
categories:
Gravity-Feed Systems
Pressure-Feed Systems
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Gravity-Feed Systems Gravity-Feed Systems use only the force of
gravity to push fuel to the engine fuel-controlmechanism
The bottom of the fuel tank must be high enoughto provide adequate pressure to the fuel-controlcomponent
This type of system is often used in high-wing lightaircraft
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Pressure-Feed Systems Pressure-Feed Systems require the use of a fuel pump to
provide fuel-pressure to the engines fuel-control component
There are two main reasons these systems are necessary: The fuel tanks are too low to provide enough pressure from gravity
The fuel tanks are a great distance from the engine
Also, most large aircraft with higher powered engines require apressure system regardless of the fuel tank location because ofthe large volume of fuel used by the engines
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Fuel System Components Pumps
Tanks
Lines
Valves
Fuel Flow-meters
Filters and Strainers
Quantity Indicators
Warning Components
Fuel Drains
Heaters
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Fuel Pumps Fuel pumps are used to move fuel through the system
then gravity feed is insufficient
There are three main functions of fuel pumps, they are
to move fuel from: The tanks to the engines
One tank to another
The engine back to the tanks
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Fuel-Pump Requirements
Engine fuel systems require main pumps and in
some systems emergency pumps
These requirements depend on the type ofengines installed on the aircraft
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Reciprocating-Engine Fuel-Pump
Requirements
Reciprocating-engines which are not gravity-fed
require:
At least one main pump for each engine
These pumps must be engine-driven
The pump capacity must capable of providing
enough fuel flow for all operations
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Turbine-Engine Fuel-Pump
Requirements
Turbine-Engines require:
At least one main pump for each engine
Main pump power supply must be independent of all
other main pump power supplies
Each positive-displacement main pump must be able
to be bypassed
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Turbine-Engine Fuel-Pump
Requirements (cont.) Turbine-engines also require emergency pumps
The emergency pump must be immediately available tosupply fuel to the engine in the event of a main pump failure
Emergency pump power supplies must be independent ofthat of the corresponding main pump
If both the emergency and main pumps operate continuously,there must be some means of alerting the flight crew of afailure of either pump
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Fuel Pump Classification
One way to classify fuel pumps is according to
the pumps function
These classifications are: Boost Pump
Scavenge Pump
Cross-feed Pumps
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Fuel Pump Classification
Another way to classify fuel pumps is by their
method of operation
These pumps are: Vane-type
Variable-volume
Centrifugal
Ejector
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Vane-Type Pumps
Vane-type fuel pumps are the most common
They use a rotor which turns vanes in a cylinder,
the vanes act to push the fuel through thesystem
Vane-type pumps can have from two to six
vanes and they may be variable volume also
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Centrifugal Pumps
Centrifugal pumps are used to move fuel from
one tank to another or from the fuel tank to the
engine
They are electrically driven and some may
operate at different speeds
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Ejector Pumps
An ejector pump is normally used to scavenge
fuel from remote areas
These pumps have no moving parts they rely onreturn fuel from the engine to pump the fuel
Ejector pumps work on the venturi principle
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Fuel Tanks
Fuel systems on different aircraft may use
several types of fuel tanks
The three basic types of fuel tanks used onaircraft are:
Integral
Rigid Removable
Bladder
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Integral Fuel Tanks Integral Fuel Tanks are commonly located in the aircrafts wings
or fuselage
These tanks are ones that are built into the structure of theaircraft and generally can not be removed
Integral Fuel Tanks are formed by the actual structure of theaircraft
The seams are sealed, usually with synthetic rubber, to producean area inside the aircraft structure which will contain the fuel
This type of tank is used in some light high-performance aircraftand turbine-powered transports
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Rigid Removable Fuel Tanks Rigid removable fuel tanks are often made of aluminum
components that are welded together
These tanks are installed in compartments specifically
made for the tank The tanks may be held in place with padded straps
This type of tank is often found on more expensive lightaircraft and reciprocating-engine-powered transports
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Bladder Type Fuel Tanks Bladder type fuel tanks are basically a reinforced
rubberized bag
These tanks are installed in compartments which
support the weight of the fuel The tank is held in place with buttons or snaps on the
bottom and sides of the tank
This type of tank is usually found on light aircraft and
some turboprop and turbine-powered aircraft
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Fuel Lines Fuel lines on aircraft are either made of rigid metal
tubing or flexible hose
Most of the fuel lines are the rigid type which are usually
made of aluminum alloys The flexible hose fuel lines are either made of synthetic
rubber or Teflon
The diameter of tubing used is decided by the engines
fuel requirements
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Valves
Fuel selector valves are used in aircraft fuel
systems to:
Shut off fuel flow
Cross-feed
Transfer fuel
Selector valves may be operated manually or
electrically depending on the installation
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Filters and Strainers Fuel is usually strained at three points in the system
Through a finger or bootstrap strainer in the bottom ofthe fuel tank
Through a master strainer which is usually located atthe lowest point in the system
Through a third strainer near the fuel control unit
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Quantity Indicators
Mechanical
Inverted float gauge
Rotating dial gauge
Upright float gauge
Sight-glass gauge
Resistance
Capacitance
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Fuel Subsystems
Some aircraft fuel subsystems allow for fuel:
Jettison
Heating Cross-Feeding
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Fuel Jettison
The fuel jettison system comprises a
combination of fuel lines, valves, and pumps
provided to dump fuel overboard during an in-
flight emergency
This will reduce the weight of the aircraft so an
emergency landing is possible
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Fuel Heating Fuel heating is necessary for turbine engines to
thaw ice particles in the fuel that would otherwiseclog the filters
Fuel is routed through a heat exchanger thatuses either engine oil or compressor bleed air tobring the fuel up to an acceptable temperature
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Cross Feeding Cross feed systems allow the flow of fuel from
any of the tanks to any of the engines
Some reasons that this system might be used
are: Engine failure
Problem with one or more fuel tanks
Redistribute fuel for weight and balance purposes
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FUEL TANKS
Aircraft fuel tanks come in a variety of types and
sizes.
Can be located almost anywhere in the aircraft
(wings, fuselage, tail).
Managing fuel distribution between tanks on
large aircraft can be very involved.
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BLADDER TANKS
Rubber bladders are used to store fuel. Usuallyin the wings.
Will deteriorate over time, but are easier to
replace than metal tanks. Black flecks may appear in strained fuel which
indicates deterioration.
Tend to deform over time which causes water,fuel, and sediment entrapment.
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BLADDER TANK DEFORMATION
Over time the bladder begins to deform and rise up between attach points.
This causes fuel, water, and sediment to collect in the valleys.
Which results in increased unusable fuel, inaccurate quantity readings,
possible contamination during aggressive attitudes.
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RIGID REMOVABLE TANKS
Welded aluminum tanks inserted into the aircraft.
Usually fuselage tanks.
A disadvantage of this type of tank is added weight.
An advantage is the ability to remove and repair.
The Selair C-172 fleet is equipped with this type of tank
with the exception of two airplanes:
OSQ- 50G integral tanks SPY-60G integral tanks
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INTEGRAL TANKS (WET WING)
Integral tanks are made by sealing off
compartments inside the wings.
They have the advantage of utilizing existing
aircraft structure to contain fuel, which reduces
weight.
Commonly found in large aircraft.
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EXTERNAL WING TANKS (TIP TANKS)
These fuel tanks are mounted externally.
Tip tanks at the end of the wingtips. (C-310)
Underwing tanks: no those arent bombs.(Lockheed Jetstar)
Tip tanks can have an aerodynamic advantage
as they act like winglets.
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FUEL TANK LAYOUT
Fuel tanks can be arranged in multiple tank designs.
Fuel can be used simultaneously from different tanks, orone at a time.
On large aircraft the order in which tanks are filled andburned off has an effect on weight and balance.
Some complex fuel systems have fuel burn schedules whichinvolve systematic burn off and transfer between tanks toensure limits are not exceeded.
In the case of wet wing aircraft outboard tanks are usuallyfilled first and emptied last, to ensure wing structuralintegrity. The fuel in the wings counteracts the forces ofweight.
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F l b i t i i ft
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Fuel burn in swept wing aircraft can
have a significant effect on C of G.
Involved fuel burn schedules
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COLLECTOR TANKS
Aircraft with long wings are subject to fuel starvation
due to sloshing.
This is guarded against by incorporating collector tanks
into the system. All fuel goes to the collector tank prior to reaching the
engine.
This smaller collector tank is always full of fuel whichabsorbs any interruptions in feed due to sloshing.
Collector tank prevents engine fuel
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Collector tank prevents engine fuel
starvation due to sloshing.
INTEGRAL WING TANK
COLLECTOR TANK
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FUEL PUMPS
High wing carbureted aircraft are usually gravity fed and dontneed fuel pumps. (C-172)
Fuel injected and low wing aircraft require a fuel pump to supplypositive pressure to the fuel metering system.
Fuel pumps are also used to transfer fuel between tanks andprovide crossfeed.
Fuel pumps are usually lubricated by the fuel itself and canoverheat if run dry.
These pumps are usually engine driven. Fuel is fed to the engine at a rate faster than it can be used, this
means return lines are necessary.
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CAVITATION
The formation of an air pocket (cavity) in the fuel.
If the fuels pressure becomes too low it will vaporize.
The pump creates a low pressure area as the fuel is
accelerated. Air pockets forming on the suction side ofthe pump can cause cavitation.
Fuel pumps are incapable of pumping a gas.
This can cause pump damage, and possibly aninterruption in flow.
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BOOST PUMPS (STANDBY PUMPS)
Boost pumps are used:
As a backup for the engine driven pump.
Crossfeed operation.
Priming.
Start operation.
Fuel transfer.
Provide positive pressure to the engine driven pump.
Usually on for take off and landing to guard against an enginefailure due to pump failure at a critical point.
Boost pumps are also used to provide positive feed pressure toengine driven pumps which helps prevent cavitation.
These pumps are usually electrically powered.
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MOTIVE FLOW PUMPS (JET PUMP)
These pumps are usually used for inter-tank
transfer.
They rely on venturi effect to create suction.
A electrically or engine driven pump provides
flow in the line, then a venturi creates suction.
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FUEL VALVES
Used to guide the flow of fuel within the system.
Fuel valves can be manual (C-172, B-95) or
electrically powered.
Check valves restrict flow to one direction.
Tank selector valves control which tank is to be
used.
Firewall shut-off valves prevent fuel from reaching
the engine. Used to secure engine in emergency
situations.
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FUEL HEATERS
Jet fuel is prone to ice crystal formation andcongealing.
Fuel heaters are incorporated to ensure the fuel
is warmed to optimum operating temperaturesbefore it reaches the engine.
This is usually accomplished by some form of
heat transfer. Ex. Running the fuel lines througha heat exchanger plumbed with warm oil lines.
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FUEL VENTS
As fuel is removed from a tank it must bereplaced with air or a vacuum will be created andfuel flow will stop.
The vacuum could possibly create tank collapse. Provides an escape for air in the case of thermal
expansion.
Vents must be heated or flush mounted, orrecessed to protect against icing conditions.
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DRAINS AND STRAINERS
Drains at the low points of a fuel system are
important to drain water which collects at the
bottom. To drain tanks for maintenance.
Strainers collect contaminants in the fuel to
ensure they are not ingested by the engine.
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MEASURING QUANTITY
Most light aircraft utilize floats to measure fuel quantity.
More sophisticate aircraft use capacitance type quantity
indicators.
Jet fuel volume changes significantly with temperature.
Mass will remain constant and can be measured by
electric probes or light sensing prisms.
The gauges of this sort of system usually indicate fuelquantity in pounds.
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DIPSTICKS
Dipping fuel tanks is common practice with light
aircraft.
The gauges tend to be inaccurate and dipping the
tanks often results in more accurate readings.
Most large aircraft have a manual method of
determining fuel load in the event of gauge failure
Magnetic measuring sticks are one method ofaccomplishing this.
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CROSSFEED
Crossfeed capabilities of a multi-engine fuel system areessential to ensure fuel on the failed engine side is availablefor use.
Crossfeed also enables the pilot to correct fuel imbalancesituations.
It is important to understand how the system works for yourspecific aircraft.
In some systems certain tanks may be unavailable duringcrossfeed.
Specific procedures may apply. (B-95 failed engine selectormust not be off)
The decision to crossfeed fuel after an engine failure shouldnot be taken lightly. If the engine failure was the result ofcontaminated fuel it could mean trouble for the operative
engine.
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C-172
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C-210