2A-27-30: Yaw Flight Controls System:
1. General Description:
The purpose of the yaw flight controls system is to provide the crew with a means
of controlling aircraft movement about the vertical axis when aircraft speed allows
aerodynamic use of the rudder. The rudder is a manually and electrically
controlled, mechanically actuated, hydraulically boosted airfoil located on the
trailing edge of the vertical stabilizer. Total rudder travel is 22 degrees in either
direction. Rudder movement is depicted on the FLIGHT CONTROLS synoptic
page.
Movement of the aircraft around the yaw axis is accomplished by the movement
of the rudder pedals which transmit inputs through conventional mechanical
linkage (cables and bellcranks) to displace the rudder. A dual hydraulic actuator
boosts inputs to the rudder surface. The rudder can be operated without the
assistance of the hydraulic actuator. In the event of a loss of both normal hydraulic
systems, the Auxiliary Hydraulic (AUX) system can also supply power to the
rudder actuator in flight through the selection of the STBY RUD (Standby Rudder)
switch on the lower portion of the pilot’s flight panel.
2. Description of Subsystems, Units and Components:
A. Automatic Hardover Prevention System:
Automatic hardover prevention is incorporated into the rudder boost
actuator. Switches monitor inputs to, and outputs from, the rudder actuator.
If the inputs and outputs disagree for 0.5 second or longer, hydraulic
pressure to the affected side of the actuator is shut off and a message is
displayed on the Crew Alerting System (CAS) display. The rudder is still
operative, but without benefit of the affected side’s hydraulic boost. The
rudder hardover prevention system receives power from the Right
Essential DC bus.
B. Redundant Hydraulic Power Sources:
Hydraulic power to the rudder actuator is normally provided by the L SYS
and R SYS. In addition, the AUX system can also supply power to the
rudder actuator in flight through the selection of the STBY RUD switch.
C. Automatic Overload Limiting System:
Force modulating valves within the rudder actuator provide protection of
the aircraft rudder against overload. Rudder surface movement is limited
by these valves when airspeeds increase airloads against the rudder.
When the hinge movement limit is reached, force-modulating valves shift,
reducing pressure to the limit actuator load output. This action causes a
logic-computed (blue RUDDER LIMIT) advisory message to be displayed
on CAS. Any further input force at the pedals cannot further displace the
rudder.
In addition to rudder limiting, hydraulic pressure to the rudder actuator is
monitored. Should a pressure differential between the L SYS and Right
Hydraulic System (R SYS) exceed 700-1000 psi, or a single summed
output pressure of less than 500 psi be detected, a blue SINGLE RUDDER
advisory message is displayed on CAS.
D. Standby Rudder System:
(See Figure 7.)
In the event of dual hydraulic system failure in flight, a Standby Rudder
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-27-00
Page 17
May 22/01
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