control actuator to reposition the load-feel bungee and
achieve hydraulic-powered actuation of the ailerons.
At the same time, the actuator operates the cable drum
mechanism. The cable drum mechanism operates the
jack screw mechanism to reposition the follow-up
trim tab to aerodynamically maintain the aileron
surface in a position corresponding to that achieved
by the hydraulic actuation.
The tab movement does not control the lateral
trim of the aircraft while normal powered flight is
maintained. This is accomplished by the hydraulic-
powered displacement of the ailerons. When the
manual flight control system is used, the follow-up
trim tab position introduced during powered
operation becomes effective and maintains the same
trim as that provided by the powered operation.
With the power system disconnected, further
hydraulic trim control ends, and all future trim inputs
are achieved through aerodynamic effect. This
function depends upon selective follow-up tab
position. Engaging the AFCS controls the trim
actuator by electrical inputs.
Aircraft without trim tabs achieve lateral trim by
repositioning the lateral control surfaces as necessary
to achieve a balanced lateral flight condition. The
trim actuator, located in the aileron trim and mixing
linkage, normally acts as a series-connected,
fixed-length rod in the aileron control system. The
trim control switch on the stick grip controls the
actuator length.
Shortening or retracting the trim
actuator (trim button to the right) supplies a left wing
up input into the aileron control system linkage.
Extending the actuator supplies a left wing down
input. The trim actuator changes the neutral position
of the aileron mechanism, allowing the control
surfaces to deflect and trim the aircraft without
moving the control stick.
Longitudinal Trim
Longitudinal or pitch trim can be accomplished in
several ways.
On aircraft with a nonmoveable
horizontal stabilizer, trim could be provided by a trim
tab arrangement or deflection of the elevators in much
the same manner as described for the lateral trim
systems.
Aircraft with a movable horizontal stabilizer and
elevators are longitudinally trimmed by changing the
angle of incidence of the stabilizer.
Moving the
four-way trim control switch on the stick grip fore or
aft will raise or lower the leading edge of the
stabilizer to provide the angle of incidence necessary
for balanced flight.
An electric trim motor and
actuator arrangement provides movement of the
stabilizer.
Aircraft that use a movable horizontal stabilizer
for longitudinal control trim do so by varying the
neutral position of the control linkage, which, in turn,
moves the surface. For example, longitudinal trim is
provided by varying the position of the artificial-feel
bungee, repositioning the linkage, and setting up a
new neutral position for the stabilizer linkage.
Anytime a new neutral is introduced by the trim
actuator, the power valve shuttle is displaced. The
stabilizer assumes a new neutral location, changing
Figure 9-42.—Aileron trim control system.
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