The fuel system is designed to provide an uninterrupted flow of clean fuel from the fuel tanks to the engine. The fuel must be available to the engine under all conditions of engine power, altitude, attitude, and during all approved flight maneuvers . Fuel systems differ greatly from aircraft to aircraft due to the relative size and complexity of the aircraft in which they are installed.

1. AIRCRAFT FUEL SYSTEM

2. CONTENT
 Description of Fuel System
 Different types of Fuel System
 Fuel System Components
 Types of fuel used

3. DESCRIPTION OF FUEL SYSTEM
The fuel system is designed to provide an
uninterrupted flow of clean fuel from the fuel tanks
to the engine. The fuel must be available to the
engine under all conditions of engine power,
altitude, attitude, and during all approved flight
maneuvers . Fuel systems differ greatly from
aircraft to aircraft due to the relative size and
complexity of the aircraft in which they are
installed. In the most basic form. a fuel system will
consist of a single, gravity feed fuel tank with the
associated fuel line connecting it to the aircraft
engine.

4. DIFFERENT TYPES OF FUEL SYSTEM
 Small Single-Engine Aircraft Fuel Systems
 Gravity-Feed System - The gravity-feed system
utilizes the force of gravity to transfer the fuel from
the tanks to the engine. For example, on high-wing
airplanes, the fuel tanks are installed in the wings.
This places the fuel tanks above the carburettor,
and the fuel is gravity fed through the system and
into the carburettor. If the design of the aircraft is
such that gravity cannot be used to transfer fuel,
fuel pumps are installed. For example, on low-wing
airplanes, the fuel tanks in the wings are located
below the carburettor.

5.  Fuel-Pump System - Aircraft with fuel-pump
systems have two fuel pumps. The main pump
system is engine driven with an electrically
driven auxiliary pump provided for use in
engine starting and in the event the engine
pump fails. The auxiliary pump, also known as a
boost pump, provides added reliability to the
fuel system. The electrically-driven auxiliary
pump is controlled by a switch in the flight
deck.

6.  Large Reciprocating-Engine Aircraft Fuel Systems
Large, multiengine transport aircraft powered by reciprocating radial engines are no longer
However, many are still in operation. A selector valve for each engine allows an engine-driven
to pull fuel from the main tank or an auxiliary tank. The fuel passes through a strainer before
the pump where it is delivered to the engine. The outlet of the pump can feed either engine
the use of a crossfeed line with valves controlled in the cockpit. A hand-operated wobble pump
located upstream of the strainer is used to prime the system for starting. Fuel vapor lines run from
pressure carburetor to the vent space in the main and auxiliary tanks. Fuel pressure gauges are
off of the carburetor for power indication.
The hand-operated wobble pumps were replaced by electric pumps on later model aircraft. A fuel
pressure warning light tapped in downstream of the engine-driven fuel pump alerts the crew
fuel pressure decline.

8.  Small Multiengine (Reciprocating) Aircraft Fuel Systems
 Low-Wing Twin
The fuel system on a small, multiengine aircraft is more
complicated than a single-engine aircraft but contains many of
same elements. An example system used on a lowing aircraft is
illustrated . It features the main fuel tanks in the wing tips and
auxiliary tanks in the wing structure. A boost pump is located at
outlet of each main tank. This pressurizes the entire fuel system
from the tank to the injectors eliminating the possibility of vapor
lock. An engine can operate with just its boost pump running in
event the engine-driven injection pump fails. Typically, the boost
pumps are used to prime and start the engine.

10.  High-Wing Twin
A simplified system on a high-wing, twin-
engine aircraft that combines gravity feed
with an electric fuel pump is illustrated .
Directly downstream of the selector valves
are the fuel strainers and then an electric
fuel pump for each engine. This pump
draws fuel from the selected tank and
sends it under pressure to the inlet side of
the fuel injection metering unit. The
metering unit for each engine provides the
proper flow of fuel to the distribution
manifold which feeds the injectors.

11. FUEL SYSTEM COMPONENTS
 Fuel Tanks
The fuel tanks, normally located inside the wings of an
airplane, have a filler opening on top of the wing through
which they can be filled. A filler cap covers this opening. The
tanks are vented to the outside to maintain atmospheric
pressure inside the tank. They may be vented through the
filler cap or through a tube extending through the surface of
the wing. Fuel tanks also include an overflow drain that may
stand alone or be collocated with the fuel tank vent. This
allows fuel to expand with increases in temperature without
damage to the tank itself. If the tanks have been filled on a
hot day, it is not unusual to see fuel coming from the
overflow drain

12.  Fuel Gauges
The fuel quantity gauges indicate the amount of
fuel measured by a sensing unit in each fuel tank
and is displayed in gallons or pounds. Aircraft
certification rules require accuracy in fuel gauges
only when they read “empty.” Any reading other
than “empty” should be verified. Do not depend
solely on the accuracy of the fuel quantity
Always visually check the fuel level in each tank
during the pre-flight inspection, and then
it with the corresponding fuel quantity indication.
If a fuel pump is installed in the fuel system, a
pressure gauge is also included. This gauge
indicates the pressure in the fuel lines. The
operating pressure can be found in the
or on the gauge by colour coding

13.  Fuel Primer
Both gravity-feed and fuel-pump systems may
incorporate a fuel primer into the system. The fuel
primer is used to draw fuel from the tanks to
fuel directly into the cylinders prior to starting the
engine. During cold weather, when engines are
difficult to start, the fuel primer helps because there
not enough heat available to vaporize the fuel in the
carburetor. It is important to lock the primer in place
when it is not in use. If the knob is free to move, it
may vibrate out of position during flight which may
cause an excessively rich fuel-air mixture. To avoid
over priming, read the priming instructions for the
aircraft.

14.  Fuel Selectors
The fuel selector valve allows selection of fuel from
various tanks. A common type of selector valve
contains four positions: LEFT, RIGHT, BOTH, and OFF.
Selecting the LEFT or RIGHT position allows fuel to
feed only from the respective tank, while selecting
BOTH position feeds fuel from both tanks. The LEFT
or RIGHT position may be used to balance the
amount of fuel remaining in each wing tank.

15.  Fuel Valves
There are many fuel valve uses in aircraft fuel
systems. They are used to shut off fuel flow or to
route the fuel to a desired location. Other than
sump drain valves, light aircraft fuel systems may
include only one valve, the selector valve. It
incorporates the shutoff and selection features into
a single valve. Large aircraft fuel systems have
numerous valves. Most simply open and close and
are know by different names related to their
location and function in the fuel system (e.g.,
shutoff valve, transfer valve, crossfeed valve). Fuel
valves can be manually operated, solenoid
operated, or operated by electric motor.

16.  Fuel Pumps
Fuel pumps are part of most aircraft fuel systems.
Standards exist for main pumps and emergency
pumps. Operation of any fuel pump may not affect
engine operation by creating a hazard, regardless of
the engine power or thrust setting or the functional
status of any other fuel pump. On reciprocating
engines, one main fuel pump must be engine-driven
and there must be at least one for each engine.
Turbine engines also require dedicated fuel pumps for
each engine. Any pump required for operation is
considered a main fuel pump. The power supply for
the main pump for each engine must be independent
of the power supply for each main pump for any
engine. There must also be a bypass feature for each
positive displacement pump.

17.  Fuel Strainers.
All aircraft fuel systems have filters and strainers
to ensure that the fuel delivered to the
is free from contaminants. The first of these is
encountered at the outlet of the fuel tank. A
sump is used to encourage the collection of
debris in the lowest part of the tank, which can
then be drained off before flight. The actual
outlet for the fuel is positioned above this
Some type of screen is used to trap
contaminants attempting to flow out of the
into the fuel system. Finger screens are
on light aircraft

18. TYPES OF FUEL USED
 Conventional aviation fuels:
1.Jet fuel:is a clear to straw-colored fuel, based on either an unleaded kerosene (Jet A-1), or a
naphtha-kerosene blend (Jet B). Similar to diesel fuel, it can be used in either compression ignition
engines or turbine engines.
2.Avgas (aviation gasoline:is used by small aircraft, light helicopters and vintage piston-engined aircraft.
Its formulation is distinct from the conventional gasoline (petrol U.K.) used in motor vehicles which is
commonly called mogas or autogas in aviation context.
 Emerging aviation fuels:
1. Biofuels :Alternatives to conventional fossil-based aviation fuels, new fuels made via the biomass
to liquid method (like sustainable aviation fuel) and certain straight vegetable oils can also be
used.
2. Compressed natural gas (CNG) :are fuel feedstocks that aircraft may use in the future.

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