(4)
The rate gyro senses the rate of change of the airplane yaw attitude. It generates an ac output voltage with the magnitude and phase a function of the angular yaw rate and direction of the motion. The gyro consists of a small, viscous-damped, single degree-of-freedom gyro composed of a motor and rotor, gimbal, signal pickoff, torsion bar and viscous damper. With a yaw rate, a precessional torque is developed by the gyro which displaces the gimbal. The torsion bar and viscous damper, attached to the gimbal, try to restrain it. The pickoff rotor, also attached to the gimbal, rotates within a stator which contains both primary (excitation) and secondary (output) windings. The angular position of the pickoff rotor due to the yaw rate determines the magnitude and sense of the output voltage.
(5)
On airplanes with yaw damper coupler part No. 4030952-906 installed, yaw acceleration signal derived from the yaw rate gyro is used to provide improved ride quality characteristics. In addition, a roll signal from vertical gyro is used to provide turn coordination.
(6)
The yaw computer provides for amplification and shaping of the rate signals for operation of the yaw damper hydraulic transfer valve and synchronizes the signal chain prior to engagement.
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B. Yaw Damper Controls
(1)
The yaw damper controls consist of circuit breakers, an engage switch, a disengage warning light, a test switch, and a yaw damper indicator.
(2)
Yaw damper power is supplied through two circuit breakers located on the main load control center (P6-2). One circuit breaker is for 115 volts ac and the other is for 28 volts dc.
(3)
The YAW DAMPER ENGAGE switch is located on the overhead panel (P5) and is the solenoid held type. When the engage switch is placed to the ON position, and if the yaw damper engage interlocks are satisfied, the solenoid will hold the switch engaged. The yaw damper is then in the yaw damping mode.
(4)
Whenever the yaw damper is, or becomes, disengaged, the amber light, labeled YAW DAMPER, on the overhead panel (P5-3) will illuminate steadily. The MASTER CAUTION lights and the FLT CONT master caution annunciator light, located on the light shield, will also illuminate.
(5)
The YAW DAMPER TEST switch and indicator are located on the center panel (P2). When the yaw damper is operative; i.e., engaged and hydraulic power available, if the test switch is actuated, a test voltage is applied to the yaw damper coupler that torques the rate gyro. As the gyro is displaced, its output signal is sent through the normal signal chain and the rudder will deflect. The position transducer on the rudder power control unit senses the rudder displacement from neutral and sends a signal to the indicator which shows rudder deflection. If the test switch is placed left, L position, the bar on the indicator should deflect left and if the switch is placed right, R position, the bar should deflect right. In flight, the indicator shows rudder deflection from neutral resulting from yaw damper inputs.
(6)
The yaw damper coupler provides control signals to the solenoid valve and transfer valve and receives feedback signals from the position transducer. Yaw damper hydraulic power is supplied by the B hydraulic power system.
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C. Position Transducers
(1) There is a linear position transducer mounted on the rudder power control unit. The transducer supplies a rudder position feedback signal to the yaw damper coupler. The transducer is a variable reluctance transformer which is excited by 26 volts ac. The magnitude of the output signal varies directly with the length of the input stroke and the phase of the signal changes with the direction of the stroke from the center null position.
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D. Transfer and Solenoid Valve
(1)
The transfer and solenoid valve control hydraulic flow for yaw damper control at the rudder power control unit.
(2)
The yaw damper solenoid valve is mounted on the rudder power control unit. It is a solenoid actuated valve that is energized when the yaw damper is engaged and it supplies hydraulic power to the transfer valve.
(3)
The transfer valve, also mounted on the rudder power control unit, converts the yaw damper electrical signals into hydraulic flow to move the rudder. The unit consists of a torque motor which moves either a flapper valve or a jet pipe assembly which regulates the hydraulic flow to the control valve.
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