Downloaded from https://www.everyspec.com ADS-79D-HDBK FIGURE G-1. GE T700 turboshaft engine G.4.2 Auxiliary Power Unit (APU). An auxiliary power unit is a small turboshaft engine (See Figure G-3) designed to supply pneumatic / hydraulic / electrical power to the aircraft and to start the aircraft main engines. A typical gas turbine APU for US Army aircraft is comprised of three main sections: Power Turbine section, Reduction Gearbox Assembly, and Controls/Accessories. The APU power turbine section is divided into the compressor and turbine assemblies. a. The compressor provides a source of compressed air for combustion and, depending on the application, bleed air for general aircraft use.
Air enters the compressor inlet, is compressed in a centrifugal impeller, the air is then discharged through a diffuser into the turbine plenum. b. The turbine or ―hot end‖ assembly consists of a turbine plenum, combustion chamber assembly, and turbine wheel assembly. The plenum serves as a receiver for compressor discharge air and as an enclosure for the combustion chamber. Compressed air is received by the turbine plenum and FIGURE G-2. Cross section of T700 directed through the combustion chamber, where fuel is introduced and burned. The hot gasses then flow into a radial fixed-area nozzle and a radial inflow turbine wheel. The turbine wheel drives the compressor and gearbox.
After passing through the turbine wheel, the gas discharges axially through a short diffusing tail pipe section. 115