09fuel 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 whichindicates 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 reducesweight.

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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http://www.airliners.net/open.file?id=1188132&size=L&width=1024&height=683&sok=JURER%20%20%28nvepensg_trarevp%20%3D%20%27Ybpxurrq%20WrgFgne%27%29%20%20beqre%20ol%20cubgb_vq%20QRFP&photo_nr=24


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http://www.airliners.net/open.file?id=1185201&size=L&width=1200&height=812&sok=JURER%20%20%28nvepensg_trarevp%20%3D%20%27Ybpxurrq%20WrgFgne%27%29%20%20beqre%20ol%20cubgb_vq%20QRFP&photo_nr=28


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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 and

burned 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 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 whichabsorbs any interruptions in feed due to sloshing.


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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 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 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.

An electrically or engine driven pump providesflow 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) orelectrically 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 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 be

replaced 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 thermalexpansion.

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 thebottom. To drain tanks for maintenance.

Strainers collect contaminants in the fuel toensure they are not ingested by the engine.


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MEASURING QUANTITY

Most light aircraft utilize floats to measure fuel quantity.

More sophisticated aircraft use capacitance typequantity 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 available

for use. Crossfeed also enables the pilot to correct fuel imbalance

situations.

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 operativeengine.


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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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Date post:	14-Apr-2018
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09fuel Systems

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