(e)
Linear Variable Differential Transducer (LVDT)
1) The actuator piston LVDT functions as a linear follow-up transmitter for closing the loop around the EHSV. It is operated by the actuator piston. The LVDT provides a feedback voltage to the yaw damper modules that varies directly with linear motion. This feedback is used to null the servo loop. The LVDT is not a line replaceable unit.
(f)
The electrical connection to the yaw damper servo is provided by one external and two internal connectors. One internal connector is used for the solenoid valve and the other for the EHSV. These electrical pins are mated when the solenoid or EHSV is bolted in position.
(g)
The solenoid valve on each servo is controlled by the auto-disengage relay in the yaw damper modules. When 28 vdc is applied, the valve opens and arms the yaw damper system. The servo valve opens in proportion to a dc command signal from the yaw damper modules. The LVDT is excited by 26 vac, 400 Hz and provides a feedback voltage signal proportional to the linear position of the actuator piston.
E. AIRPLANES WITH -122 YDM AND SUBSEQUENT YDM DASH NUMBERS;
Modal Suppression Accelerometer
(1)
The modal suppression accelerometer provides the yaw damper module with lateral acceleration data of the aft end of the aircraft. This data aids the yaw damper module in controlling the yaw and turn coordination of the aircraft.
(2)
The modal suppression accelerometer is composed of a detection circuit that consists of a cantilever surrounded on both sides by metal plates. The cantilever moves with the changing lateral velocity of the aircraft. An output signal is produced by comparing the difference of the spacial gaps between the metal plates and the cantiliver.
3. Operation_________
A. Functional Description
(1) Yaw Correction Requirements (Fig. 6)
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MAINTENANCE MANUAL
Yaw Correction Requirements
Figure 6
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(a) Sideslip 1) An airplane is defined to be in sideslip when the airplane heading is not aligned with the flight path. The sideslip angle is the angle between airplane heading and the flight path. Airplane sideslip is caused by unstable air conditions, aerodynamic instability, or banking without coordinating rudder movement. When the airplane sideslips, it flies yawed and a side force tends to retard the sideways velocity. This damping force comes largely from increased drag on the faster moving wing, the fuselage, and vertical stabilizer. Damping and the vertical fin tends to correct the sideslip by "weathercocking" the airplane.
2) When a sideslip condition is present, the airflow on the forward wing goes from an outboard point on the leading edge to an inboard point on the trailing edge. The airflow on the trailing wing goes from an inboard point on the leading edge to an outboard point on the trailing edge. This results in an increase in angle of attack of the forward wing relative to that of the trailing wing. A difference in angle means a difference in lift on the two sides of the airplane that induces a rolling moment.
(b) Dutch Roll 1) Dutch roll is a common oscillatory condition encountered due to low drag high speed aerodynamic design and turbulance which can be created by air mass instability. If this condition is allowed to persist, it causes considerable discomfort. If the airplane experiences a side force causing yaw relative to the flight path, sideslip is produced. The change in direction of relative wind causes one wing to produce more lift than the other, thus inducing roll.
2) The yaw induced roll and weathercocking moment combine to induce yaw in the opposite direction of the roll. This produces an uncoordinated turn. The change in direction of relative wind causes one wing to produce more lift than the other, causing the wings to level. The airplane then banks back in the other direction and repeats the cycle with oscillating motion. The frequency of this oscillation is in the range from 0.5 to 0.1 Hz.
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