Yaw Damp System. A yaw damp system is
provided to aid the pilot in maintaining 'directional
stability and increase ride comfort. The system may be
used at any altitude and is required for flight above
17,000 feet. It must be deactivated for takeoff and
landing. The yaw damp system is a part of the autopilot.
Operating instructions for this system are contained in
Chapter 3. The system is controlled by a YAW DAMP
switch adjacent to the ELEV TRIM switch on the pedestal
Rudder Boost System. A rudder boost system is
provided to aid the pilot in maintaining directional control
resulting from an engine failure or a large variation of
power between the engines. Incorporated in the rudder
cable system are two pneumatic rudder boosting servos
which actuate the cables to provide rudder pressure to
help compensate for asymmetrical thrust.
During operation, a differential pressure
valve accepts bleed air pressure from each engine.
When the pressure varies between the bleed air systems,
the shuttle in the differential pressure valve moves toward
the low pressure side. As the pressure difference reaches
a preset tolerance, a switch closes on the low pressure
side which activates the rudder boost system. This
system is designed only to help compensate for
asymmetrical thrust. Appropriate trimming is to be
accomplished by the pilot.. Moving either or both of the
bleed air valve switches on the overhead control panel to
PNEU & ENVIRO OFF position will disengage the rudder
Condition levers must be in LOW
IDLE position to perform rudder
The system is controlled by a switch
located on the extended pedestal placarded RUDDER
BOOST ON OFF (fig. 2-8), and is to be turned on before
flight. A preflight check of the system can be performed
during the run-up by retarding the power on one engine to
idle and advancing power on the opposite engine until the
power difference between the engines is great enough to
activate the switch to turn on the rudder boost system.
Movement of the appropriate rudder pedal (left engine
idling, right rudder pedal moves forward) will be noted
when the switch closes, indicating the system is
functioning properly for low engine power on that side.
Repeat the check with opposite power settings to check
for movement of the opposite rudder pedal. The system
is protected by a 5-ampere circuit breaker, placarded
RUDDER BOOST, located on the overhead circuit
breaker panel (fig. 2-27).
With brake de-ice on, rudder boost
may be inoperative.
2-40. FLIGHT CONTROLS LOCK.
towing the aircraft or starting
engines. Serious damage could
result in the steering linkage if
towed by a tug with the rudder lock
Positive locking of the rudder, elevator and aileron
control surfaces, and engine controls (power levers,
propeller levers, and condition levers) is provided by a
removable lock assembly (fig. 2-19) consisting of two
pins, and an elongated U-shaped strap interconnected by
a chain. Installation of the control locks is accomplished
by inserting the U-shaped strap around the aligned control
levers from the copilot's side; then the aileron/elevator
locking pin is inserted through a guide hole in the top of
the pilot's control column assembly, thus locking the
control wheel. The rudder is held in a neutral position by
an L-shaped pin which is installed through a guide hole in
the floor aft of the pilots rudder pedals. The rudder
pedals must be centered to align the hole in the rudder
bellcrank with the guide hole in the floor. Remove the
locks in reverse order, i.e., rudder pin, control column pin,
and power control clamp.
2-41. TRIM TABS.
Trim tabs are provided for all flight control surfaces.
These tabs are manually activated, and are mechanically
controlled by a cable-drum and jack-screw actuator
system, except the right aileron tab which is of the fixed
bendable type. Elevator and aileron trim tabs incorporate
neutral, non-servo action, i.e., as the elevators or ailerons
are displaced from the neutral position, the trim tab
maintains an "as adjusted" position. The rudder trim tab
incorporates anti-servo action, i.e., as the rudder is
displaced from the neutral position the trim tab moves in
the same direction as the control surface. This action
increases control pressure as rudder is deflected from the