(2)
To do the standby compass swing check by towing the airplane around check points, do this task: Magnetic Heading Reference System -Maintenance Practices (AMM 34-21-00/201).
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ALL 01 Page 401 Apr 25/9734-22-01
Standby Compass Location
Figure 401
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STANDBY ATTITUDE REFERENCE SYSTEM - DESCRIPTION AND OPERATION
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1. General_______(See figures 1 and 2.)
A. The standby attitude reference system (SARS) provides a visual display of basic airplane roll and pitch attitude. The system is in continuous operation during flight but normally functions as an emergency backup system in event of inertial navigation system or power system failure. The system receives 28 volts dc for operation through the STBY ATT IND ciruit breaker on electronic circuit breaker panel P7. Power to the system is from the battery bus. During emergency operation the battery bus is automatically switched to receive battery power for operation of the system.
B. One system is installed, consisting of a standby attitude indicator (SAI) mounted on the center instrument panel, and a static inverter, mounted in the upper equipment center beneath the flight engineer's station.
2. Standby Attitude Indicator
__________________________
A. The standby attitude indicator consists of a 115-volt ac, 3-phase vertical gyro suspended in a two degree-of-freedom gimbal system which is, in turn, connected to a drum type roll and pitch attitude display. The system displays approximately 90 degrees of freedom in climb, 80 degrees of freedom in dive, and 360 degrees of freedom in roll.
B. The gyro system utilizes a spinning ball type device to automatically erect the gyro at turn-on. A caging control knob on the front of the instrument operates a mechanical erector to accelerate the erection process. This same knob is also used to adjust the airplane symbol relative to the horizon line on the drum display.
C. A power supply failure indicator monitors power to the gyro motor and causes a warning flag to appear if power is lost.
3. Static Inverter
_______________
A. The static inverter accepts 28-volt dc power and converts it to the 115-volt, 400-Hz ac, 3-phase power required by the standby attitude indicator. The inverter is a solid-state unit.
4. Operation (Fig. 3)
_________
A. Functional Description
(1)
The static inverter receives 28-volt dc power and converts it into 115-volt 400-Hz ac power through a solid-state multivibrator network
(2)
Three-phase power from the inverter is supplied to the three-phase gyro motor through both coils of the flag motor. When current is flowing equally through the two flag motor coils, the power failure flag is torqued out of view. Power loss to or an open circuit in any phase of the gyro motor will cause an unbalance of currents in the flag motor coils which allows a spring to pull the power failure flag into view.
EFFECTIVITY
ALL 12 Page 1 Oct 10/7334-24-00
LUBBER LINE
POWER FAILURE WARNING FLAG
HORIZON LINE
AIRPLANE
CAGING CONTROL
FLIGHT ENGINEER'S CONSOLE
STANDBY ATTITUDE INDICATOR
A
Standby Attitude Reference System Component Location Figure 1
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(3) The standby attitude indicator incorporates a roll brake that engages whenever power is removed from the indicator. The brake maintains the sphere within 70 degrees of level attitude after gyro spin-down. This provides easier caging of the gyro to level due to the limited travel required. The roll brake is also associated with the OFF flag "in view" stop. When power is first applied to the indicator, the spin-up gyro wobble often increases tension on flag "in-view" stop causing the flag to remain in sight. This can be prevented by briefly pulling the caging knob to relieve this tension after power application.
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