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Pilot's Handbook of Aeronautical Knowledge
Aircraft Systems
Powerplant

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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

Powerplant

An aircraft engine, or powerplant, produces thrust to
propel an aircraft. Reciprocating engines and
turboprop engines work in combination with a
propeller to produce thrust. Turbojet and turbofan
engines produce thrust by increasing the velocity of
air flowing through the engine. All of these
powerplants also drive the various systems that
support the operation of an aircraft.

Reciprocating Engines
Most small aircraft are designed with reciprocating
engines. The name is derived from the back-and-forth, or
reciprocating, movement of the pistons which produces the
mechanical energy necessary to accomplish work.

Driven by a revitalization of the general aviation (GA)
industry and advances in both material and engine design,
reciprocating engine technology has improved dramatically
over the past two decades. The integration of computerized
engine management systems has improved fuel efficiency,
decreased emissions, and reduced pilot workload.

Reciprocating engines operate on the basic principle of
converting chemical energy (fuel) into mechanical energy.
This conversion occurs within the cylinders of the engine
through the process of combustion. The two primary
reciprocating engine designs are the spark ignition and the
compression ignition. The spark ignition reciprocating engine
has served as the powerplant of choice for many years. In
an effort to reduce operating costs, simplify design, and
improve reliability, several engine manufacturers are turning
to compression ignition as a viable alternative. Often referred
to as jet fuel piston engines, compression ignition engines
have the added advantage of utilizing readily available and
lower cost diesel or jet fuel.

The main mechanical components of the spark ignition and
the compression ignition engine are essentially the same.
Both use cylindrical combustion chambers and pistons that
travel the length of the cylinders to convert linear motion
into the rotary motion of the crankshaft. The main difference
between spark ignition and compression ignition is the
process of igniting the fuel. Spark ignition engines use a
spark plug to ignite a pre-mixed fuel/air mixture. (Fuel/air
mixture is the ratio of the "weight" of fuel to the "weight"
of air in the mixture to be burned.) A compression ignition
engine first compresses the air in the cylinder, raising its
temperature to a degree necessary for automatic ignition
when fuel is injected into the cylinder.

These two engine designs can be further classified as:
1. Cylinder arrangement with respect to the crankshaft—
radial, in-line, v-type, or opposed.
2. Operating cycle—two or four.
3. Method of cooling—liquid or air.

Radial engine.
Figure 6-1. Radial engine.

Radial engines were widely used during World War II and
many are still in service today. With these engines, a row or
rows of cylinders are arranged in a circular pattern around
the crankcase. The main advantage of a radial engine is the
favorable power-to-weight ratio. [Figure 6-1]

In-line engines have a comparatively small frontal area, but
their power-to-weight ratios are relatively low. In addition,
the rearmost cylinders of an air-cooled, in-line engine
receive very little cooling air, so these engines are normally
limited to four or six cylinders. V-type engines provide
more horsepower than in-line engines and still retain a small
frontal area.

Continued improvements in engine design led to the
development of the horizontally-opposed engine which
remains the most popular reciprocating engines used on
smaller aircraft. These engines always have an even number
of cylinders, since a cylinder on one side of the crankcase
"opposes" a cylinder on the other side. [Figure 6-2] The
majority of these engines are air cooled and usually are
mounted in a horizontal position when installed on fixed-wing
airplanes. Opposed-type engines have high power-to-weight
ratios because they have a comparatively small, lightweight
crankcase. In addition, the compact cylinder arrangement
reduces the engine's frontal area and allows a streamlined
installation that minimizes aerodynamic drag.

Horizontally opposed engine.
Figure 6-2. Horizontally opposed engine.

 

6-2