Wing oversweep can only be obtained with the
Electronic Control
aircraft weight on the wheels. Wing oversweep, shown
A wing sweep under electronic control is initiated
in figure 16-39, reduces the amount of space required
at the throttle quadrant. Four modes are
for spotting the aircraft. A wing sweep self-test can
available-automatic, aft manual, forward manual, or
only be performed while the wings are overswept.
bomb manual. Selection of these modes causes the air
SPEED BRAKE SYSTEM
data computer to generate wing sweep commands
consistent with the aircraft speed, altitude, and
Speed brakes are hinged, movable secondary
configuration of the flaps and slats. The commands are
control surfaces used for slowing down the speed of the
applied through the wing--flap glove-vane controller
aircraft by increasing the profile drag. These surfaces
to the wing sweep control drive servo. They are
are also called "dive brakes" or "dive flaps." On some
converted to mechanical rotary force. This force,
aircraft, they are hinged to and faired with the sides of
transferred to the wing sweep/flap and slat control box,
the fuselage or they are attached to the wings. On the
causes the wing sweep hydraulic control valve to
F/A18 aircraft the speed brake is located on the top, aft
operate hydraulic motors that are driven by the flight
end of the fuselage between the vertical stabilizers.
and combined hydraulic power systems to sweep the
Regardless of their location, their purpose is the same.
wings. The flight hydraulic power system positions the
right wing, and the combined hydraulic power system
Fuselage Type
positions the left wing. A synchronizing shaft (fig.
16-38) interconnects the wings to ensure symmetrical
The fuselage speed brake system is normally
operation. If a hydraulic system fails, it provides the
electrically controlled and hydraulically operated. See
driving force for sweeping the wing affected by the
figure 16-40. In an emergency, it can be controlled
failed system.
manually.
Wing sweep commands generated by the air data
The brake surfaces are installed on the sides of the
computer are limited by the configuration of the
aft portion of the fuselage below and forward of the
auxiliary flaps, maneuver flaps, and slats. With the
horizontal stabilizer. They hinge at their forward end.
auxiliary flaps extended, wing sweep is limited to
When in the closed position, they fit flush with fuselage
21.25 degrees. The maneuver flaps, with or without
skin. An elevator speed brake interconnect provides a
slats extension, limit wing sweep to 50 degrees. To
connection between the left-hand speed brake and the
prevent structural damage to the wings during
aircraft nose down elevator control cable. When the
negative-g conditions, wing sweep is interrupted to
speed brakes open, the cable pulls and provides a nose
prevent wing sweep changes until the negative-g
down action to counteract the tendency of the aircraft to
condition no longer exists. In the automatic mode, the
assume a nose up condition.
wings are positioned at a rate of 7 degrees per second.
The speed brakes may be actuated by the
two-position, spring-loaded-to-neutral control switch
Mechanical Control
on the throttle lever or by the manual override control
When wing sweep is under mechanical control, the
handle. When operating the switch to open the speed
wing sweep handle positions the wings through the
brakes, the control circuit energizes to operate the
wing sweep/flap and slat control box. Because the
opening solenoid of the control valve. Pressure is sent
minimum wing sweep limiting is not available under
to the actuating cylinders, extending the speed brakes.
mechanical control, the wings can be swept to an
To close, the opposite solenoid energizes, reposition-
adverse position that could cause damage to the wings.
ing the control valve and directing pressure to the
Mechanical control is used for emergency wing sweep
retract side of the actuating cylinders, closing the speed
and wing oversweep.
brakes.
During emergency wing sweep, the wing sweep
When you depress or pull the manual override
handle, mechanically coupled to the wing sweep/flap
handle to operate the speed brakes, a plunger manually
and slat control box through a cable assembly,
positions the control valve to direct pressure to the
positions the wings. The wing sweep can be returned to
actuating cylinders. The spring bungee connected to
electronic control by repositioning the wing sweep
the manual control lever returns the manual override
handle to the stowed position.
handle assembly to the neutral position when the
16-44
