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Airplane Flying Handbook
Turbo-propeller Powered Airplanes
TURBOPROP ENGINE TYPES

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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

Fixed shaft turboprop engine.
Figure 14-2. Fixed shaft turboprop engine.

TURBOPROP ENGINE TYPES

FIXED SHAFT

One type of turboprop engine is the fixed shaft
constant speed type such as the Garrett TPE331.
[Figure 14-2] In this type engine, ambient air is
directed to the compressor section through the engine
inlet. An acceleration/diffusion process in the two stage
compressor increases air pressure and directs it
rearward to a combustor. The combustor is made up of
a combustion chamber, a transition liner, and a turbine
plenum. Atomized fuel is added to the air in the
combustion chamber. Air also surrounds the
combustion chamber to provide for cooling and
insulation of the combustor.

The gas mixture is initially ignited by high-energy
igniter plugs, and the expanding combustion gases
flow to the turbine. The energy of the hot, high
velocity gases is converted to torque on the main shaft
by the turbine rotors. The reduction gear converts the
high r.p.m.—low torque of the main shaft to low
r.p.m.—high torque to drive the accessories and the
propeller. The spent gases leaving the turbine are
directed to the atmosphere by the exhaust pipe.

Only about 10 percent of the air which passes through
the engine is actually used in the combustion process.
Up to approximately 20 percent of the compressed air
may be bled off for the purpose of heating, cooling,
cabin pressurization, and pneumatic systems. Over
half the engine power is devoted to driving the
compressor, and it is the compressor which can
potentially produce very high drag in the case of a
failed, windmilling engine.

In the fixed shaft constant-speed engine, the engine
r.p.m. may be varied within a narrow range of 96
percent to 100 percent. During ground operation, the
r.p.m. may be reduced to 70 percent. In flight, the
engine operates at a constant speed, which is
maintained by the governing section of the propeller.
Power changes are made by increasing fuel flow and
propeller blade angle rather than engine speed. An
increase in fuel flow causes an increase in temperature
and a corresponding increase in energy available to the
turbine. The turbine absorbs more energy and
transmits it to the propeller in the form of torque. The
increased torque forces the propeller blade angle to be
increased to maintain the constant speed. Turbine
temperature is a very important factor to be considered
in power production. It is directly related to fuel flow
and thus to the power produced. It must be limited
because of strength and durability of the material in the
combustion and turbine section. The control system
schedules fuel flow to produce specific temperatures
and to limit those temperatures so that the temperature
tolerances of the combustion and turbine sections are
not exceeded. The engine is designed to operate for its
entire life at 100 percent. All of its components, such
as compressors and turbines, are most efficient when
operated at or near the r.p.m. design point.

 

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