500  Air Inlet Door Actuator Installation 
Feb 15/70  Figure 401 (Sheet 2) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  49-15-31 Page 403 

C. Position actuator on bracket. Shim if required using 0.062 inch laminated shim.
D. Install actuator attaching bolts, washers, and nuts.
E. Position pushrod bearings on actuator arms and install connecting bolts, nuts, and washers.
F. Connect electrical plug to actuator.
G. Position BATTER SWITCH to ON and remove placard.
H. Position master switch to OFF.
I. Test and adjust APU air inlet. Refer to 49-15-0.

G00093
Air Inlet Door Actuator Installation  500 
49-15-31 Page 404  Figure 401 (Sheet 3) BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Feb 15/70 

APU ENGINE - DESCRIPTION AND OPERATION
1. General
A.  The APU engine provides bleed air for the pneumatic power and shaft power for driving the engine accessories and the electrical generator. The engine is basically a gas turbine. It consists of a compressor section, a turbine section and an accessory drive section (Fig. 1).
B.  Static or ram air enters the compressor plenum. The air is compressed by a first stage impeller, by a second stage impeller, and discharged into the turbine plenum. From the turbine plenum, compressed air enters the combustion chamber where fuel is added, and the air-fuel mixture ignited. The gases of combustion then flow into the turbine where the gas energy is converted into useful mechanical power. The mechanical power is used to drive the engine compressor and the ac electrical generator. When required, the bleed air for pneumatic power is obtained from the turbine plenum.
2.  Compressor Section
A.  The compressor section is the source of compressed air for the engine turbine. It consists of a two stage centrifugal type compressor and the compressor plenum. The two compressor stages are connected by crossover ducts. One impeller and one diffuser constitute a compressor stage. The first stage impeller is a double entry type (two similar impellers back-to-back); the second stage impeller is a single-entry type. Both impellers have a common shaft. The shaft is mounted in two pressure lubricated bearings. The accessory end of the shaft is splined to mate with the accessory drive section quill shaft. Seals are used to prevent excessive amounts of turbine gas from entering into the lubrication system.
3.  Turbine Section
A.  The turbine section provides the means of burning the air-fuel mixture and extracting mechanical power from the gases of combustion. The turbine section consists of a turbine wheel, a torus assembly, a nozzle assembly, a turbine plenum assembly, and a combustion chamber. The turbine wheel is a radial inward-flow type. It is attached to the same shaft carrying the compressor impellers. The plenum chamber serves as a receiver for the compressor discharge air and as an enclosure and heat shield for the turbine end of the unit. The torus assembly mates with the discharge end of the combustion chamber and directs the combustion gases into a series of nozzles. The nozzles guide the combustion gases from the torus assembl y into the turbine wheel. The single combustion chamber is formed by integral portions of the plenum and torus assemblies and incorporates a combustion chamber liner and cap. The combustion chamber liner provides a combustion area. It is perforated to control the burning rate and the location of the flame. Mounting pads are provided on the cap for mounting the fuel atomizer and igniter plug.
500 
Aug 15/67  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  49-21-0 Page 1 

4.  Accessory Drive Section
A.  The accessory drive section reduces the high turbine speed to lower values to drive the components necessary for the engine operation and to drive the ac electrical generator. It is located at the compressor end of the engine. The accessory drive section consists of a gear train enclosed in a housing. The gear train receives its power from a quill shaft splined to the compressor impellers and turbine wheel shaft. The gears in the accessory drive section are spray lubricated. Refer to APU Lubrication System, 49-91-0.
B.  The accessory drive housing provides mounting pads for the fuel control unit, starter motor, cooling air fan, centrifugal switch, oil pump, and ac electrical generator. For description of the accessories, refer to APU Fuel System, 49-31-0; APU Ignition and Starting System, 49-41-0; APU Cooling Air System, 49-51-0; APU Engine Controls, 49-61-0; APU Lubrication System,  49-91-0; and AC Generation System, Chapter 24.
　
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