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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Starting System and Combustion

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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




Starting System

Most small aircraft use a direct-cranking electric starter
system. This system consists of a source of electricity, wiring,
switches, and solenoids to operate the starter and a starter
motor. Most aircraft have starters that automatically engage
and disengage when operated, but some older aircraft have
starters that are mechanically engaged by a lever actuated by
the pilot. The starter engages the aircraft flywheel, rotating
the engine at a speed that allows the engine to start and
maintain operation.

Electrical power for starting is usually supplied by an onboard
battery, but can also be supplied by external power through
an external power receptacle. When the battery switch is
turned on, electricity is supplied to the main power bus bar
through the battery solenoid. Both the starter and the starter
switch draw current from the main bus bar, but the starter
will not operate until the starting solenoid is energized by
the starter switch being turned to the "start" position. When
the starter switch is released from the "start" position, the
solenoid removes power from the starter motor. The starter
motor is protected from being driven by the engine through a
clutch in the starter drive that allows the engine to run faster
than the starter motor. [Figure 6-20]

When starting an engine, the rules of safety and courtesy
should be strictly observed. One of the most important is to
make sure there is no one near the propeller. In addition, the
wheels should be chocked and the brakes set, to avoid hazards
caused by unintentional movement. To avoid damage to the
propeller and property, the aircraft should be in an area where
the propeller will not stir up gravel or dust.


During normal combustion, the fuel/air mixture burns in a
very controlled and predictable manner. In a spark ignition
engine the process occurs in a fraction of a second. The
mixture actually begins to burn at the point where it is ignited
by the spark plugs, then burns away from the plugs until it
is all consumed. This type of combustion causes a smooth
build-up of temperature and pressure and ensures that the
expanding gases deliver the maximum force to the piston at
exactly the right time in the power stroke. [Figure 6-21]

Typical starting circuit.
Figure 6-20. Typical starting circuit.

Normal combustion and explosive combustion.
Figure 6-21. Normal combustion and explosive combustion.