Cessna 208B - Engine

CESSNA SECTION 7
MODEL
2088 (675 SHP) AIRPLANE AND SYSTEMS DESCRIPTION
ENGINE
The Pratt & Whitney Canada Inc. PT6A-114A 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. It provides a
compression ratio of
7.0:l.
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
shafi 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.
(Continued Next Page)
U.S. 7-45