brakes, the control circuit energizes to operate the
opening solenoid of the control valve. Pressure is
sent to the actuating cylinders, extending the speed
brakes. To close, the opposite solenoid energizes,
repositioning the control valve and directing pressure
to the retract side of the actuating cylinders, closing
the speed brakes.
When you depress or pull the manual override
handle to operate the speed brakes, a plunger
manually positions the control valve to direct pressure
to the actuating cylinders. The spring bungee
connected to the manual control lever returns the
manual override handle assembly to the neutral
position when the handle is released. If electrical
power is applied while the manual override handle is
actuated, the system will remain in the position
selected by the handle. If the handle is released, the
system actuates to the position selected by the control
switch on the throttle lever. The speed brakes cannot
be stopped at intermediate positions between fully
closed and fully open. The restrictor in the open line
restricts return fluid flow from the actuating cylinders
when the speed brakes are being closed.
If the hydraulic system fails, the check valve in
the pressure line traps pressure between the control
valve and the actuating cylinders. If the speed brakes
are open, this pressure will hold them open. If the
speed brakes are actuated to the closed position, the
pressure in the system will shift the primary slide in
the control valve. This movement will relieve the
trapped pressure and allow the speed brakes to close
from the air load against them.
A blowback relief valve, installed in the hydraulic
return line, allows for automatic retraction of the
speed brakes under high air loads. When the speed
brakes are open, the force of the airstream against the
surfaces tends to force them closed. The force builds
up the hydraulic pressure in the speed brake system.
When the pressure reaches a maximum of 3,650 psi, it
relieves through the blowback relief valve.
Wingtip Type
The wingtip speed brake system is an electrically
controlled and hydraulically operated system. It
operates either alone or with the fuselage speed
brakes. See figure 9-41.
Figure 9-41.—Wingtip speed brake control system.
9-47
