At the front of the engine, the inlet housing forms an annular
airflow path to the inlet guide vanes (IGV) which are variable on the
T55L11A engine.
An airflow path is between the inner diameter of the housing
and the base contours of the compressor stages. The compressor rotor
has seven axial and one centrifugal stage compressor. The diffuser
channel contains radial vanes which straighten the airflow from the
centrifugal compressor. These vanes increase the static air pressure
to its highest pressure at the diffuser exit. Air passes into the
combustor section where its flow direction is changed twice. Flowing
rearward from the diffuser, the air surrounds and enters the
combustor liner through holes and louvers, and 28 swirl cups reverse
the airflow direction for the first time. Each swirl cup contains a
dualorifice, fuelatomizing nozzle. As combustion occurs, the hot
expanding gases move forward to the curl assembly, again reversing
the flow. The T55L7 uses 14 "T" cane vaporizer tubes to inject the
fuel for combustion.
The gas flow is directed by the first and second stage nozzles
to the twostage gasproducer (GP) turbine. The T55L7C engines use
a singlestage GP turbine. These turbines are attached to the rear
of the compressor rotor shaft and extract the energy required to turn
the compressor.
From the second stage turbine of the L1A engine, the gas flow
continues through the power turbine (PT) section. Most of the
remaining energy of the hot gases is extracted by the twostage PT
and is transmitted by the power shaft to the power output shaft.
After the expanding gases have passed through the PT section they are
exhausted to the atmosphere through the exhaust duct.
5.4.
MODEL COMPARISON
The T55 series gas turbine engines are used to power the CH47
Chinook helicopter. The CH47B is powered by either the Lycoming
T55L7, 7B, or 7C turboshaft engines. The CH47C is powered by
either T55L7C or T55Lll engines.
Basically, the Lycoming T55 series engines are of the same
design and differ only in shaft horsepower and internal details. The
T55L7 and 7B engines are rated at 2,200 shp at normal power and
2,650 at military power. The T55L7C engine is rated at 2,400 shp
at normal power, 2,650 at military power, and 2,850 at maximum power.
The T55L11 engine is rated at 3,000 shp at normal power, 3,400 at
military power, and 3,750 at maximum power.
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