FUEL SYSTEMS

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FUEL SYSTEMS

• CARRYING AND DISTRIBUTING THE GO JUICE!

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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. Usually
  in 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, or one at a time.
• On large aircraft the order in which tanks are
  filled and burned off has an effect on weight and
  balance.
• Some complex fuel systems have fuel burn
  schedules which involve systematic burn off and
  transfer between tanks to ensure limits are not
  exceeded.
• In the case of wet wing aircraft outboard tanks
  are usually filled first and emptied last, to
  ensure wing structural integrity. The fuel in the
  wings counteracts the forces of weight.

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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 which absorbs any interruptions in feed due
  to sloshing.

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Collector tank prevents engine fuel starvation
due to sloshing.
COLLECTOR TANK
INTEGRAL WING TANK
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FUEL PUMPS

• High wing carbureted aircraft are usually gravity
  fed and dont need fuel pumps. (C-172)
• Fuel injected and low wing aircraft require a
  fuel pump to supply positive pressure to the fuel
  metering system.
• Fuel pumps are also used to transfer fuel between
  tanks and provide crossfeed.
• Fuel pumps are usually lubricated by the fuel
  itself and can overheat 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 of the pump can cause cavitation.
• Fuel pumps are incapable of pumping a gas.
• This can cause pump damage, and possibly an
  interruption 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 engine failure due to pump failure at
  a critical point.
• Boost pumps are also used to provide positive
  feed pressure to engine 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 and
  congealing.
• Fuel heaters are incorporated to ensure the fuel
  is warmed to optimum operating temperatures
  before it reaches the engine.
• This is usually accomplished by some form of heat
  transfer. Ex. Running the fuel lines through a
  heat exchanger plumbed with warm oil lines.

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FUEL VENTS

• As fuel is removed from a tank it must be
  replaced with air or a vacuum will be created and
  fuel 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, or
  recessed 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 fuel quantity 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 of
  accomplishing this.

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CROSSFEED

• Crossfeed capabilities of a multi-engine fuel
  system are essential to ensure fuel on the failed
  engine side is available for use.
• Crossfeed also enables the pilot to correct fuel
  imbalance situations.
• It is important to understand how the system
  works for your specific aircraft.
• In some systems certain tanks may be unavailable
  during crossfeed.
• Specific procedures may apply. (B-95 failed
  engine selector must not be off)
• The decision to crossfeed fuel after an engine
  failure should not be taken lightly. If the
  engine failure was the result of contaminated
  fuel it could mean trouble for the operative
  engine.

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C-172
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C-210
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B-95
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B-95
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C-402
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