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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems Airframe Systems
Fuel Systems

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Pilot's Handbook of Aeronautical Knowledge



Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making




The points where the aircraft drag curve intersects the net
thrust curves are the maximum aircraft speeds. The vertical
lines from each of the points to the baseline of the graph
indicate that the turbojet aircraft can attain a higher maximum
speed than aircraft equipped with the other types of engines.
Aircraft equipped with the turbofan engine will attain a higher
maximum speed than aircraft equipped with a turboprop or
reciprocating powerplant.

Airframe Systems

Fuel, electrical, hydraulic, and oxygen systems make up the
airframe systems.

Fuel Systems

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. Two common classifications apply to fuel systems
in small aircraft: gravity-feed and fuel-pump 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 carburetor, and the fuel
is gravity fed through the system and into the carburetor. 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 carburetor. [Figure 6-30]

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.

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 vaporize 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 is 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 during flight and
can cause an excessively rich mixture. To avoid over priming,
read the priming instructions for the aircraft.

Gravity-feed and fuel-pump systems.
Figure 6-30. Gravity-feed and fuel-pump systems.

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.