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2. Air Inlet Ducts
A. The air inlet ducts supply static air on the ground and ram air in flight. The ducts consist of the air diffuser duct, the compressor air inlet duct, and the accessory cooling air duct. The air diffuser duct is located inside the fuselage aft of the rear pressure bulkhead on the right side (Fig. 1). The forward end of the duct is attached to the fuselage where the APU air inlet door is located. The aft end of the duct is connected to the airplane right torque box. The torque box functions as an air collector. The air supply is routed into two ducts from the torque box, the compressor air inlet duct and the accessory cooling air duct. Both ducts are rigidly attached to the torque box and remain with the airplane at the time of the APU engine change. The compressor air inlet duct is rectangular in shape. It is attached to the flange of the APU compressor plenum with a quick action lock. For the description of the accessory cooling air duct, refer to 49-51-0, Accessory Cooling Air System.
3. Air Inlet Door
A. The air inlet door controls the air supply to the APU. It is triangular in shape and is located at the right side of the fuselage forward of the right horizontal stabilizer. A vortex generator, located on outer surface of door, provides increased ram air flow to air inlet when APU is operated in flight (Fig. 1). The door is hinged at the forward end, opening inward, and is operated by two pushrods and an electrical actuator. The door does not fully close, thus allowing APU air inlet pressure to be greater than tail pipe pressure at all times.
4. Air Inlet Door Actuator
A. The air inlet door actuator opens and closes the APU air inlet door. The actuator is of the rotary type. It consists of a gear train and a worm gear set, enclosed in a housing. Two output shafts are integral with the worm gear. Two actuator arms, which operate the air inlet door pushrods, are attached to the output shafts. Driving the actuator is a dc, split field, series wound motor. The motor is reversible and equipped with a magnetic brake. The motor operation is initiated by the APU master switch and terminated by either of the two limit The actuator is attached to the structure inside the fuselage aft of the rear pressure bulkhead. (Fig. 1.).
502
Aug 15/77 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 49-15-0 Page 1
Air Inlet Duct and Door 502
49-15-0Page 2 Figure 1 BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. Jun 20/84
APU AIR INLET - ADJUSTMENT/TEST
1. General
A. The APU air inlet adjustment/test consists of adjusting the air inlet door pushrods for door alignment, the door switch plunger for travel distance and the vortex generator flap for efficient ram air flow into inlet. The switch and vortex generator flap must be adjusted each time the door position is altered by either removal or realignment. A test is provided for the air inlet door alignment but no test can be performed for the door switch plunger travel distance because of the installation characteristics of the switch.
B. Adjustment of the vortex generator flap requires that adjustments and checks be made both inside and outside of airplane.
2. APU Air Inlet Adjustment
A. Air Inlet Door Alignment Adjustment
(1)
Prepare for Air Inlet Door Alignment Adjustment
(a)
Check that BATTERY SWITCH is ON.
(b)
Position APU master switchh to ON.
(c)
After door is fully open, position BATTERY SWITCH to OFF and placard.
WARNING: SERIOUS INJURY CAN RESULT WHILE MEASURING DOOR ALIGNMENT IF BATTERY SWITCH IS ON AND APU MASTER SWITCH IS INADVERTENTLY PPOSITIONED OFF.
(d)
Open stabilizer trim access door 3701 to gain access to air inlet door actuator.
(2)
Adjust Air Inlet Door Alignment
(a)
Measure door alignment when door is fully open. Refer to view 2, Fig. 501.
(b)
Remove nuts, washers and bolts connecting pushrods to actuator arms (Fig. 501).
(c)
Loosen one pushrod rod end bearing locknut.
(d)
On basis of approximately 0.02 inch travel per half revolution of rod end, rotate rod end until door alignment would be within limits as shown in view 2, Fig. 501.
(e)
Tighten pushrod rod end bearing locknut.
(f)
Perform steps (c) thru (e) for other pushrod rod end.
(g)
Position pushrods on actuator arms and install connecting bolts, nuts, and washers.
(h)
Position BATTERY SWITCH to ON and remove placard.
(i)
Position master switch to OFF.
(j)
Measure door alignment when door is closed. Refer to view 2, Fig. 501.
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