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Airplane Flying Handbook
Turbo-propeller Powered Airplanes
TURBOPROP AIRPLANE ELECTRICAL SYSTEMS

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Airplane Flying Handbook

Preface

Table of Contents

Chapter 1,Introduction to Flight Training
Chapter 2,Ground Operations
Chapter 3,Basic Flight Maneuvers
Chapter 4, Slow Flight, Stalls, and Spins
Chapter 5, Takeoff and Departure Climbs
Chapter 6, Ground Reference Maneuvers
Chapter 7, Airport Traffic Patterns
Chapter 8, Approaches and Landings
Chapter 9, Performance Maneuvers
Chapter 10, Night Operations
Chapter 11,Transition to Complex Airplanes
Chapter 12, Transition to Multiengine Airplanes
Chapter 13,Transition to Tailwheel Airplanes
Chapter 14, Transition to Turbo-propeller Powered Airplanes
Chapter 15,Transition to Jet Powered Airplanes
Chapter 16,Emergency Procedures

Glossary

Index

Beginning at power lever positions just aft of flight
idle, propeller blade pitch angles become progressively
flatter with aft movement of the power lever until they
go beyond maximum flat pitch and into negative pitch,
resulting in reverse thrust. While in a fixed shaft/
constant-speed engine, the engine speed remains
largely unchanged as the propeller blade angles
achieve their negative values. On the split shaft PT-6
engine, as the negative 5° position is reached, further
aft movement of the power lever will also result in a
progressive increase in engine (N1) r.p.m. until a
maximum value of about negative 11° of blade angle
and 85 percent N1 are achieved.

Operating in the beta range and/or with reverse thrust
requires specific techniques and procedures depending
on the particular airplane make and model. There are
also specific engine parameters and limitations for
operations within this area that must be adhered to. It
is essential that a pilot transitioning to turboprop
airplanes become knowledgeable and proficient in
these areas, which are unique to turbine-engine powered
airplanes.

TURBOPROP AIRPLANE ELECTRICAL SYSTEMS

The typical turboprop airplane electrical system is a
28-volt direct current (DC) system, which receives
power from one or more batteries and a starter/
generator for each engine. The batteries may either be
of the lead-acid type commonly used on piston powered
airplanes, or they may be of the
nickel-cadmium (NiCad) type. The NiCad battery
differs from the lead-acid type in that its output
remains at relatively high power levels for longer
periods of time. When the NiCad battery is depleted,
however, its voltage drops off very suddenly. When
this occurs, its ability to turn the compressor for engine
start is greatly diminished and the possibility of engine
damage due to a hot start increases. Therefore, it is
essential to check the battery's condition before every
engine start. Compared to lead-acid batteries, high performance
NiCad batteries can be recharged very
quickly. But the faster the battery is recharged, the
more heat it produces. Therefore, NiCad battery
equipped airplanes are fitted with battery overheat
annunciator lights signifying maximum safe and
critical temperature thresholds.

The DC generators used in turboprop airplanes double
as starter motors and are called "starter/generators."
The starter/generator uses electrical power to produce
mechanical torque to start the engine and then uses the
engine's mechanical torque to produce electrical power
after the engine is running. Some of the DC power
produced is changed to 28 volt 400 cycle alternating
current (AC) power for certain avionic, lighting,
and indicator synchronization functions. This is
accomplished by an electrical component called an
inverter.

The distribution of DC and AC power throughout the
system is accomplished through the use of power distribution
buses. These "buses" as they are called are
actually common terminals from which individual
electrical circuits get their power. [Figure 14-9]

Buses are usually named for what they power (avionics
bus, for example), or for where they get their power
(right generator bus, battery bus). The distribution of
DC and AC power is often divided into functional
groups (buses) that give priority to certain equipment
during normal and emergency operations. Main buses
serve most of the airplane's electrical equipment.
Essential buses feed power to equipment having top
priority. [Figure 14-10]

Typical individual power distribution bus.
Figure 14-9.Typical individual power distribution bus.

 

14-8