Basic Engine Construction

CHAPTER TWO

T-34C AIRCRAFT SYSTEMS FAMILIARIZATION WORKBOOK

202.

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

550 shaft horsepower (SHP) (1315 ft-lbs. torque), however, normal NATOPS operation is

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

accessories. The PT6A-25 has four main sections: compressor, combustion, turbine, and exhaust.

Figure 2-1 Basic Engine Construction

Compressor Section

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