Engine - Textron Cessna Grand Caravan Ex 208B Pilot's Operating Handbook And Faa Approved Airplane Flight Manual

SECTION 7 CESSNA
AIRPLANE AND SYSTEMS DESCRIPTION MODEL 208B 867 SHP
GARMIN G1000

ENGINE

The Pratt & Whitney Canada Inc. PT6A-140 powerplant is a free
turbine engine. It utilizes two independent turbines; one driving a
compressor in the gas generator section, and the second driving a
reduction gearing for the propeller.
Inlet air enters the engine through an annular plenum chamber formed
by the compressor inlet case where it is directed to the compressor.
The compressor consists of three axial stages combined with a single
centrifugal stage, assembled as an integral unit.
A row of stator vanes located between each stage of compressor rotor
blades diffuses the air, raises its static pressure and directs it to the
next stage of compressor rotor blades. The compressed air passes
through diffuser ducts which turn it 90° in direction. It is then routed
through straightening vanes into the combustion chamber.
The combustion chamber liner located in the gas generator case
consists of an annular reverse-flow weldment provided with varying
sized perforations which allow entry of compressed air. The flow of air
changes direction to enter the combustion chamber liner where it
reverses direction and mixes with fuel. The location of the combustion
chamber liner eliminates the need for a long shaft between the
compressor and the compressor turbine, thus reducing the overall
length and weight of the engine.
Fuel is injected into the combustion chamber liner by 14 simplex
nozzles supplied by a dual manifold. the mixture is initially ignited by
two spark igniters which protrude into the combustion chamber liner.
The resultant gases expand from the combustion chamber liner,
reverse direction and pass through the compressor turbine guide vane
to the compressor turbine. The turbine guide vanes ensure that the
expanding gases impinge on the turbine blades at the proper angle,
with a minimum loss of energy. The still expanding gases pass forward
through a second set of stationary guide vanes to drive the power
turbine.
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7-46 208BPHCUS-00
U.S.