Fuel Distribution - Fuel Systems - Airframes & Aircraft Systems #66
Summary
TLDRThis lesson delves into aircraft fuel systems, highlighting their critical role in storing and delivering fuel to engines. It discusses the systems' ability to prevent engine starvation, especially during high-demand phases like takeoff. The video covers various components, including tanks, pumps, filters, and valves, and their functions in both single and multi-engine aircraft. It also touches on advanced features like vent systems, cross-feed capabilities, and fuel dump systems, essential for maintaining aircraft performance and safety.
Takeaways
- 🛩 The aircraft fuel system's primary function is to store and deliver fuel to the engine, ensuring it never runs out, even during critical flight phases.
- ✈️ Large aircraft like the Boeing 747 can consume up to 10,000 kg of fuel per engine per hour during takeoff.
- 💧 Fuel tanks in light aircraft are typically rigid and located in the wings, filled through a filler cap and refueling pipe.
- 🔧 Mechanical or electrical pumps draw fuel from the tanks, while a hand-operated selector allows the pilot to choose the fuel source or cut off the supply.
- 🚫 A strainer in the system filters out debris before fuel reaches the engine to prevent damage.
- 🔋 Piston engines may require priming with fuel before starting, which is done through a hand-operated priming pump.
- 📊 Multi-engine aircraft have more complex fuel systems with features like integral wing tanks, center tanks, and sometimes tanks in the fin or stabilizer.
- 💨 A vent system in fuel tanks equalizes air pressure above the fuel with ambient pressure, preventing issues during altitude changes.
- 🔁 Boost pumps in each tank are crucial for high-altitude operations, preventing cavitation and low-pressure boiling that could lead to vapor locks.
- 🔄 Cross-feed valves and pipes allow fuel to be fed from any tank to any engine, enhancing flexibility and safety in fuel management.
- ♻️ Some aircraft are equipped with fuel dump systems for emergency weight reduction, ensuring the plane can land safely within structural limits.
Q & A
What is the primary function of an aircraft's fuel system?
-The primary function of an aircraft's fuel system is to store and deliver fuel to the engine, ensuring it can deliver more fuel than the engine can use during its most critical phase of flight.
How much fuel can a Boeing 747 burn during take-off?
-A Boeing 747 can burn as much as 10,000 kilograms per engine per hour during the take-off phase.
What are the different types of fuel tanks used in aircraft?
-Aircraft use rigid tanks in wings, integral tanks, center tanks, and sometimes tanks in the fin or stabilizer. These tanks can be used to increase fuel capacity and adjust the aircraft's center of gravity.
What is the purpose of the vent system in aircraft fuel tanks?
-The vent system allows air pressure above the fuel in the tank to equalize with ambient pressure, preventing excessive vaporization at altitude and ensuring the fuel system operates correctly.
Why are fuel booster pumps necessary in high-altitude aircraft?
-Fuel booster pumps are necessary to prevent bubbles forming due to cavitation or low-pressure boiling at the inlet of the engine-driven fuel pump, which could lead to vapor locks.
How do cross-feed valves work in a multi-engine aircraft's fuel system?
-Cross-feed valves allow fuel to be fed from any tank to any engine, ensuring that in case of a pump failure in one tank, fuel can still be supplied to all engines.
What is the purpose of the fuel dump or jettison system in aircraft?
-The fuel dump or jettison system is used to reduce the mass of the airplane to its required landing mass when necessary, such as in emergencies or to meet regulatory requirements.
How does the fuel system prevent fuel starvation during flight?
-The fuel system prevents fuel starvation by using booster pumps, cross-feed valves, and ensuring the tanks are vented properly to maintain pressure and prevent cavitation.
What is the role of the high-level float switch in the fuel system?
-The high-level float switch shuts off fuel to the tank during refueling when the tank is full, preventing overfilling and ensuring the vent system can operate correctly.
How does the aircraft manage fuel imbalance between tanks during flight?
-Aircraft manage fuel imbalance by using the cross-feed valve to supply both engines from the tank with more fuel, then adjusting the booster pumps to restore the correct balance.
What is the purpose of the collector tank or surge box in the fuel system?
-The collector tank or surge box ensures that the booster pumps are continually submerged in fuel, preventing them from being starved of fuel and keeping them cool.
Outlines
🛩 Overview of Aircraft Fuel Systems
This paragraph introduces the fundamental purpose of aircraft fuel systems, which is to store and supply fuel to the engines. It emphasizes the necessity for these systems to deliver more fuel than the engine's maximum consumption, especially during critical flight phases. The paragraph provides an example of the Boeing 747's fuel consumption during takeoff. It then describes a simple fuel system in a single-engine light aircraft, explaining the components such as rigid fuel tanks in the wings, refueling mechanisms, fuel pumps, tank selectors, strainers, and priming pumps. The monitoring of the fuel system is also discussed, including level sensors and pressure gauges. The paragraph concludes with a brief mention of more complex fuel systems in multi-engine aircraft, which must handle high-altitude operations and fuel distribution to multiple engines.
🔧 Components and Subsystems of Multi-Engine Aircraft Fuel Systems
This paragraph delves into the intricacies of fuel systems in multi-engine aircraft, highlighting the challenges posed by high-altitude operations and the need for multiple fuel tanks. It describes integral wing tanks, center tanks, and the use of tanks in the fin or stabilizer not only for fuel capacity but also for adjusting the aircraft's center of gravity. The paragraph explains the function of vent systems to equalize air pressure above the fuel with ambient pressure, the role of vent surge tanks, and the importance of maintaining a minimum free volume in the tanks for the vent system to operate correctly. It also discusses the use of ram air to pressurize tanks during flight, the necessity of fuel booster pumps to prevent cavitation and low-pressure boiling, and the function of non-return valves. The design of feeder boxes to keep booster pumps submerged in fuel is also mentioned, along with the use of filters and screens to protect pumps from debris.
📡 Fuel System Controls and Operations in Twin-Engine Aircraft
The focus of this paragraph is on the operational aspects of the fuel system in twin-engine aircraft. It details the control panel and schematic fuel system diagram, including selector switches for booster pumps, warning lights for pump failures, and cross-feed valves. The paragraph explains the function of suction valves, temperature sensors, and engine fuel shutoff valves. It also covers the auxiliary power unit's (APU) fuel system, including its shutoff valve and the use of suction bypass valves. The sequence of fuel usage after takeoff is described, with emphasis on the strategy to reduce wing bending stress by using the center tank first. The paragraph also discusses the cross-feed valve's role in balancing fuel between tanks and the importance of following correct procedures to prevent fuel starvation. Additionally, it introduces the concept of extended-range twin-engine operational performance standards (ETOPS) and the modifications in fuel systems to enhance reliability.
✈️ Advanced Features of Modern Aircraft Fuel Systems
This paragraph discusses advanced features found in modern extended-range aircraft designed for ETOPS operations. It highlights the split center tank, duplicated feed valves for redundancy, and shutoff valves in the fuel lines. The paragraph also mentions the APU's DC electric fuel pump, which can supply fuel to an engine for rapid restart in case of a double engine failure. The discussion includes the necessity of fuel dump or jettison systems in certain aircraft types to meet landing weight restrictions and maintain structural integrity. The paragraph explains the mechanics of the fuel dump system, including dump pumps, master valves, and the automatic stopping of fuel dumping when a predefined reserve quantity is reached. It also outlines the regulations that dictate the minimum fuel quantity post-dump, ensuring the aircraft can still climb and cruise safely.
💡 Key Points to Remember about Aircraft Fuel Systems
The final paragraph summarizes the key points from the lesson. It emphasizes the use of ram air in the fuel vent system to pressurize tanks and prevent fuel vaporization. It also reiterates the importance of booster pumps, which are 115-volt AC motor-driven centrifugal pumps operating at pressures between 20 and 50 psi, to prevent vapor lock at the engine-driven fuel pump's inlet. The paragraph reminds us of the cross-feed valve's function, allowing fuel to be fed from any tank to any engine, and the correct procedure for using it. Lastly, it touches on the high-level float valve's role in shutting off fuel during refueling when the tank is full and the necessity of fuel dump systems in certain aircraft, which must automatically stop when a defined reserve quantity of fuel is reached.
Mindmap
Keywords
💡Fuel System
💡Fuel Tanks
💡Vent System
💡Booster Pumps
💡Cross-Feed Valve
💡Fuel Dump System
💡Float Operated Level Sensors
💡Fuel Pressure Gauge
💡Engine Driven Fuel Pump
💡Ram Air
💡Fuel Imbalance
Highlights
Aircraft fuel systems are designed to store and deliver fuel to the engine, ensuring it never starves during critical flight phases.
Large jets like the Boeing 747 can burn up to 10,000 kilograms of fuel per engine per hour during take-off.
Simple single-engine aircraft use rigid fuel tanks in the wings, filled through a refueling pipe and cap.
Fuel is drawn from tanks by mechanical or electrical pumps, with a hand-operated selector for tank choice.
Strainers in the fuel system filter out foreign objects and debris before fuel reaches the engine carburetor.
Piston engines may require priming with fuel before starting, using a hand-operated priming pump.
Multi-engine aircraft have more complex fuel systems to handle high altitude operations and multiple engines.
Modern aircraft may feature a center tank and tanks in the fin or stabilizer for increased fuel capacity and center of gravity adjustments.
Vent systems in fuel tanks equalize air pressure above the fuel with ambient pressure, preventing excessive vaporization.
Ram air is introduced into the vent system during flight to pressurize fuel tanks and prevent fuel from boiling at altitude.
Fuel booster pumps in each tank are essential for high altitude aircraft to prevent cavitation and low pressure boiling.
Booster pumps are typically centrifugal, driven by 115 volt AC motors, providing a low pressure with a high flow rate.
Cross-feed valves and pipes allow fuel to be fed from any tank to any engine, enhancing fuel management flexibility.
Fuel tank layout on a typical two-engined aircraft includes split wing tanks with pumps in the intersection to reduce wing bending stress.
Pilot's fuel control panel includes selector switches for each main tank booster pump and associated warning lights.
Fuel dump or jettison systems are required on aircraft where the maximum takeoff weight is significantly higher than the maximum landing weight.
Fuel dump systems must automatically stop when a defined reserve quantity of fuel is reached to ensure safe landing.
The fuel system is monitored using level sensors and fuel pressure gauges for continuous operation and safety.
Transcripts
in this lesson we will look at fuel
distribution systems
the aircraft fuel system is designed to
store and deliver fuel to the engine
fuel system
it must be capable of delivering more
fuel than the engine can possibly use in
its most critical phase of flight so
that the engine is never starved to fill
big jets such as the Boeing 747 can burn
as much as 10,000 kilograms per engine
per hour during the take-off phase
here is a diagram of a simple single
engined light aircraft fuel system
the fuel tanks are rigid tanks fitted in
the wings
they are filled by an open line
refueling pipe through a filler cap on
top of the wing
the fuel is drawn from the tanks by
mechanical or electrical fuel pump
a hand-operated tank selector which
allows the pilot to use the fuel from
either the right
or left tank
or turn off the supply completely
the fuel then passes through a strainer
which filters out any foreign objects
and debris before being delivered to the
engine carburetor
piston engines often need to be primed
with fuel prior to engine start this is
achieved by use of a hand operated
priming pump which takes fuel from the
filter housing and delivers it to the
engine Inlet manifold
the fuel system is monitored for
contents using simple float operated
level sensors
and fuel pump operation is monitored by
a fuel pressure gauge
drain valves allow any water in the fuel
to be removed before flight
Multi engined gas
aircraft have more complex fuel systems
to cope with the extra problems brought
about by high altitude operations the
use of multiple fill tanks and the needs
to feed the fuel to more than one engine
the fuel tanks are usually integral
tanks in the wings
many modern aircraft may also have a
center tank a tank in the center section
torsion box between the wings
some aircraft types also have fuel tanks
in the fin or stabilizer as well as
being used to increase the fuel capacity
this fuel may also be used to change the
position of the aircraft's center of
gravity
there are a number of components and
subsystems common to all multi-engine
aircraft fuel systems we will now look
at these in some detail
the fuel tanks are fitted with a vent
system
the vent system is to allow the air
pressure above the fuel in the tank to
equalize with the ambient pressure
the area's above the fuel in each tank
are connected together by a vent pipe
the ends of the vent pipe terminate in
small vent surge tanks located at each
wingtip
vent surge tanks are vented to the
atmosphere
the vent search tanks
to collect any liquid fuel which might
get into the vent system during unusual
maneuvering or because of over filling
of the fuel tanks
any fuel caught in the vent surge tanks
is returned to the main tanks either by
gravity or by the operation of a pump
some systems have float operated vent
files fitted which closed to prevent
liquid fuel entering the vent system
the ER sir regulations require that when
a fuel tank is full a minimum of two
percent by volume of the tank capacity
is free of fuel to allow the vent system
to operate correctly
if during refueling the fuel reaches
this level then the high level float
switch or volumetric top of unit will
close the refuelling valve
as the aircraft climbs the air pressure
reduces this in turn reduces the
temperature at which the fuel boils
leading to excessive vaporization of the
fuel
to help prevent this excessive
vaporization at altitude and to give a
positive pressure of fuel to the pumps
ram air may be introduced into the vent
system to partially pressurize the tanks
in flight
this is normally done through ducks on
the underside of the wings
fuel booster pumps are normally fitted
in pairs in each tank to pump fuel from
the tank to the engine they are a
necessity in high altitude aircraft to
prevent bubbles forming due to
cavitation or low pressure boiling at
the inlet of the engine driven fuel pump
each pump has a non-return valve
associated with it to prevent fluid
flowing back through the pump to the
tank when the pump is switched off or
has failed
booster pumps are typically centrifugal
pumps driven by 115 volt AC motors
providing a low pressure of between 20
and 50 psi with a high flow rate
there may also be a suction feed pipe to
allow the engine driven fuel pump to
draw fuel from the tank in the event of
a double booster pump failure
in the event of a double booster pump
failure in one main tank the aircraft
emergency and abnormal procedure
checklist will invariably limit the
aircraft to a maximum operating altitude
to prevent fuel starvation due to
cavitation or low pressure boiling
causing vapor locks at the inlet of the
engine driven fuel pump
filters or screens are used to prevent
any debris in the tank being drawn into
the fuel booster pumps
the booster pumps are fitted in a feeder
box in the bottom of the fuel tank this
box is sometimes referred to as a
collector tank or surge box
the feeder box should remain full of
fuel at all fuel levels and aircraft
altitudes
this allows the booster pump to be
continually submerged in fuel thereby
preventing them from being starved of
fuel and keeping them cool
electrically operated engine fuel
shutoff valves or low pressure are
fitted to allow the engine to be
isolated from the fuel supply cross-feed
valves and pipes form a cross feed
manifold which enables fuel to be fed
from any tank to any engine in this
example there are only two fuel tanks so
only one cross feed valve is required
as we have already said many aircraft
have a center fuel tank in this example
the fuel from the center tank is pumped
into the cross feed manifold on both
sides of the cross feed valve
the aircraft may also have a fuel tank
located in the fin or stabilizer
in our typical system shown here the
fuel from this tank is pumped into the
center tank for distribution to the
engines
i level float switches are used to
automatically close the refuel valve
when the tank is full during refueling
while low level float searches are used
to maintain a required a minimum amount
of fuel in the tanks during fuel
jettison or dumping
each fuel tank will have a fill drain at
the lowest point in the tank to allow
water to be drained from it
in the event of the fuel tank being over
pressurized due to a malfunction a
relief valve may be incorporated to
prevent structural damage to the tank
the system is completed with the
addition of a refuel manifold which
allows all the tanks to be pressure
refilled from a single point
shown here is the fuel tank layout on a
typical two engined aircraft
the only difference to what we have seen
so far is that the wing tanks are split
into outer and inner sections
the fuel pumps are in the intersection
the outer section remains full until the
inner has reached a predetermined level
at which point the outer section fuel is
transferred by gravity to the inner
keeping fuel outboard in this manner
helps to reduce wing bending stress
on the screen now is the pilots of fuel
control panel and a schematic fuel
system diagram from a typical
twin-engine passenger jet
the control panel shows selector
switches for each main tank booster pump
accompanied by associated low pressure
warning lights which illuminate if the
pump should fail or be switched off
the center tank pumps also have switches
and warning lights associated with them
suction valves in the main tanks allow
the engine to be fed by gravity or
suctioned by the engine driven pump in
the event of both booster pumps failing
in one tank
there is a control switch and indicator
light for the cross feed valve the light
is illuminated when the cross feed valve
is open
there is a temperature sensor in the
number one tank which will transmit the
fuel tank temperature to an indicator on
the control panel
the engine fuel shutoff valve is closed
by the operation of a fire handle for
that particular engine in some aircraft
it is also opened and closed by the
selection of the fuel switch during the
normal engine start or shutdown
procedure
the fuel valve closed lights illuminate
when the Associated fuel valve is closed
the auxiliary power unit or APU takes
its fuel from the number one tank via a
suction bypass valve
if there are no booster pumps operating
but it can be fed from any tank if a
booster pump in that tank is selected on
the APU shutoff valve is typically
operated by the APU automatic start or
stop sequence
there are indicators which illuminate
when they're associated low-pressure
fuel filter bypass valve opens due to a
filter blockage this filter is
downstream of the fuel heater
feel from a pressure refueling system is
fed in at the refueling station and
dispensed to the fuel tanks as required
defueling is achieved by opening the
manual defueling valve the booster pumps
can then be used to pump fuel into a
tanker
the normal sequence of fuel usage after
takeoff would be to use the center fuel
tank first followed by the wing tank
fuel
this sequence again helps to relieve the
wing bending stress
the operation is achieved
semi-automatically
by switching on all tank booster pumps
since the center tank pumps operate at a
higher pressure than the main tank pumps
fuel is used from the center tank first
when it's booty pumps can no longer pump
fuel from the center tank any remaining
fuel can be moved to the number one tank
by operation of the center tank scavenge
jet pump
the main tanks will now feed their
respective engines
the cross feed valve allows both engines
to be fed from one wing fuel tank
or one engine to be fed from both wing
tanks
fuel imbalance in flight between the
number1 and number2 tank can be
corrected
by opening the cross-feed valve
and then switching off the pumps in the
tank with less fuel until the correct
balance is achieved by supplying both
engines from the tank with more fuel
it is important that this secrets is
followed exactly as there is a danger of
starving an engine of fuel
if their fuel pumps are switched off
before the cross feed valve is opened
when the correct balance is achieved
their previously switched off booster
pumps are switched on again first
and then the cross feed valve is closed
again it is important that this sequence
is followed this will restore what is
known as tank to engine configuration
that is number one tank feeding number
one engine and number two tank feeding
number two engine
you
this diagram shows the fuel system from
a modern extended range 24 ment
standards or etops aircraft
it is very similar to our previous
system apart from a few additions to
improve its reliability
the center tank is split into two parts
but it operates at all times as a single
tank
feed valve is duplicated to provide
redundancy normally both valves move
together as one
shutoff valves in the fuel line to the
engine
our valve shuts off the fuel as it
leaves the tank system
engine fuel shutoff valve shuts off the
fuel at the engine firewall
the APU has a DC electric fuel pump
which will switch on automatically if
the APU is operated with no booster
pumps operating
this pump will also automatically start
and the APU isolation valve will open to
allow the DC pump to supply fuel to the
left engine for rapid restarting in the
event of a double engine failure
some aircraft types have a fuel dump or
jettison system fitted
this system is required if the maximum
landing mass of the aircraft is
significantly less than the maximum
takeoff mass and landing at the higher
mass would compromise the structural
integrity of the aircraft or if the
aircraft cannot satisfy the discontinued
approach climb gradients required by the
AR sir regulations at its maximum
takeoff mass
in an emergency fuel can be dumped to
reduce the mass of the airplane to its
required landing mask
the fuel dump system consists of fuel
dump pumps in each of the tanks from
which the fuel is to be dumped
connected by pipes to fuel dump master
valves and dump outlets
typically there will be a dump master
valve on each wing at the outboard
trailing edge to enable the fuel to be
dumped safely with no danger of it
entering the aircraft or any of its
systems
on older aircraft fuel dumping is
controlled from the pilots or flight
engineers fuel control panel
on modern aircraft the pilot has a
selector knob which allows him to select
the amount of fuel to be dumped or the
amount of fuel to remain
the fuel dumping process will be
automatically stopped when this level
has been reached
if operation of the flaps or slats will
cause the fuel being dumped to impinge
on the airframe a placard must be
displayed warning the pilot not to
operate the flaps or slats during fuel
dumping operations
would be clearly undesirable to dump all
of the fuel in the aircraft and
safeguards must be in place to allow a
minimum amount of fuel to remain
er sir regulations stipulate that the
minimum amount of fuel remaining after
dumping must be sufficient to enable the
aircraft to climb to 10,000 feet
and thereafter allow 45 minutes cruise
at a speed for maximum range
this minimum fuel quantity is calculated
at the design stage and the low-level
float switches in the main tanks are
calibrated to stop the fuel dump if this
level is reached
that is the end of the lesson here are
the main points you should remember
the fuel vent system uses ram air to
pressurize the fuel tanks to help
prevent vaporization of the fuel
to feel booster pumps our 115 volt AC
motor driven centrifugal pumps
and they operate our pressures of
between 20 and 50 psi
their purpose is to supply a head of
pressure to the engine driven fuel pumps
in order prevent cavitation or low
pressure boiling causing a vapor lock
at the inlet to the engine driven fuel
pump
the booster pumps are fitted in a
collector tank or feeder box or surge
box in the bottom of the fuel tank this
allows the booster pumps to be
continually submerged and fuel thereby
preventing them from being starved of
fuel and keeping them cool
the cross feed valve or valves allow the
fuel to be fed from any tank to any
engine
remember that when commencing cross
feeding the cross feed valve is opened
before the booster pumps in the low tank
are turned off
when cross feeding is complete the pumps
are turned back on before the cross feed
valve is closed
the purpose of the high-level float
valve is to shut off fuel to the tank
during refueling when the tank is full
fuel dump or jettison systems are
required on aircraft types where the
maximum takeoff weight is significantly
higher than the maximum landing weight
the fuel dump system must automatically
stop dumping fuel when a defined reserve
quantity of fuel is reached
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