T-34C AIRCRAFT SYSTEMS FAMILIARIZATION WORKBOOK
BASIC ENGINE CONSTRUCTION
The T-34C aircraft is powered by a PT6A-25 turboprop engine, built by Pratt and Whitney. It is
a reverse-flow type with inverted flight capabilities. This engine is flat rated at a maximum of
limited to 425 SHP (1015 ft-lbs. torque).
The primary purpose of the engine is to provide the motive force to turn the propeller through the
reduction gearbox. The secondary purpose is to supply power to drive the engine-driven
Figure 2-1 Basic Engine Construction
The compressor section consists of the compressor inlet case, compressor, and diffuser. The
compressor inlet case directs outside air to the compressor. A circular foreign objective damage
(FOD) screen to prevent foreign object ingestion covers the entrance. The air is then compressed
at a 7:1 ratio by a three-stage axial compressor and a single-stage centrifugal compressor. These
compressors are assembled as an integral unit and driven by the compressor turbine.
The air leaves the compressor via diffuser vanes (pipes) and enters the diffuser where the pressure is
further increased. This high pressure air is then delivered to the combustion chamber. Through tap-
offs the diffuser also provides P3 fuel control reference air and bleed air for cockpit heating.
2-2 BASIC ENGINE CONSTRUCTION