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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Full Authority Digital Engine Control

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Pilot's Handbook of Aeronautical Knowledge

Preface

Acknowledgements

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

Appendix

Glossary

Index

Detonation is an uncontrolled, explosive ignition of the
fuel/air mixture within the cylinder's combustion chamber.
It causes excessive temperatures and pressures which, if not
corrected, can quickly lead to failure of the piston, cylinder,
or valves. In less severe cases, detonation causes engine
overheating, roughness, or loss of power.

Detonation is characterized by high cylinder head temperatures
and is most likely to occur when operating at high power
settings. Common operational causes of detonation are:
• Use of a lower fuel grade than that specified by the
aircraft manufacturer.
• Operation of the engine with extremely high manifold
pressures in conjunction with low rpm.
• Operation of the engine at high power settings with
an excessively lean mixture.
• Maintaining extended ground operations or steep
climbs in which cylinder cooling is reduced.

Detonation may be avoided by following these basic
guidelines during the various phases of ground and flight
operations:
• Make sure the proper grade of fuel is used.
• Keep the cowl flaps (if available) in the full-open
position while on the ground to provide the maximum
airflow through the cowling.
• Use an enriched fuel mixture, as well as a shallower
climb angle to increase cylinder cooling during takeoff
and initial climb.
• Avoid extended, high power, steep climbs.
• Develop the habit of monitoring the engine instruments
to verify proper operation according to procedures
established by the manufacturer.

Preignition occurs when the fuel/air mixture ignites prior
to the engine's normal ignition event. Premature burning
is usually caused by a residual hot spot in the combustion
chamber, often created by a small carbon deposit on a spark
plug, a cracked spark plug insulator, or other damage in the
cylinder that causes a part to heat sufficiently to ignite the
fuel/air charge. Preignition causes the engine to lose power,
and produces high operating temperature. As with detonation,
preignition may also cause severe engine damage, because
the expanding gases exert excessive pressure on the piston
while still on its compression stroke.

Detonation and preignition often occur simultaneously and
one may cause the other. Since either condition causes high
engine temperature accompanied by a decrease in engine
performance, it is often difficult to distinguish between the
two. Using the recommended grade of fuel and operating
the engine within its proper temperature, pressure, and rpm
ranges reduce the chance of detonation or preignition.

Full Authority Digital Engine Control (FADEC)

FADEC is a system consisting of a digital computer and
ancillary components that control an aircraft's engine
and propeller. First used in turbine-powered aircraft, and
referred to as full authority digital electronic control, these
sophisticated control systems are increasingly being used in
piston powered aircraft.

In a spark ignition reciprocating engine the FADEC uses
speed, temperature, and pressure sensors to monitor the
status of each cylinder. A digital computer calculates the
ideal pulse for each injector and adjusts ignition timing as
necessary to achieve optimal performance. In a compression
ignition engine the FADEC operates similarly and performs
all of the same functions, excluding those specifically related
to the spark ignition process.

FADEC systems eliminate the need for magnetos, carburetor
heat, mixture controls, and engine priming. A single throttle
lever is characteristic of an aircraft equipped with a FADEC
system. The pilot simply positions the throttle lever to a
desired detent such as start, idle, cruise power, or max power,
and the FADEC system adjusts the engine and propeller
automatically for the mode selected. There is no need for the
pilot to monitor or control the air/fuel mixture.

During aircraft starting, the FADEC primes the cylinders,
adjusts the mixture, and positions the throttle based on engine
temperature and ambient pressure. During cruise flight, the
FADEC constantly monitors the engine and adjusts fuel .ow,
and ignition timing individually in each cylinder. This precise
control of the combustion process often results in decreased
fuel consumption and increased horsepower.

FADEC systems are considered an essential part of the
engine and propeller control, and may be powered by the
aircraft's main electrical system. In many aircraft FADEC
uses power from a separate generator connected to the engine.
In either case, there must be a backup electrical source
available because failure of a FADEC system could result
in a complete loss of engine thrust. To prevent loss of thrust,
two separate and identical digital channels are incorporated
for redundancy, each channel capable of providing all engine
and propeller functions without limitations.

 

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