Figure 12-30.-Typical single disc brake installation.
replace the lost fluid. Since the fluid passing through the
piston shaft acts on the large piston head, the piston will
move up, allowing the ball check valve to seat when
pressure in the brake assembly becomes normal.
When the brake pedal is released, pressure is
removed from the inlet port, and the piston return spring
moves the piston rapidly back to the top of the debooster.
This rapid movement causes a suction in the line to the
brake assembly, resulting in faster release of the brake.
EMERGENCY BRAKE SYSTEM
On all aircraft except those equipped with
independent-type brake systems, an emergency brake
system is provided. On some aircraft a pneumatically
operated emergency system is provided. Others have a
reserve hydraulic system; an emergency hydraulic
reservoir retains a sufficient supply of hydraulic fluid
for manual operation of the brakes in case no hydraulic
power is available.
The power boost brake system, described earlier, is
equipped with a pneumatically operated emergency
system. The emergency system consists of a T-handle,
compressed air bottle, air release valve, and pressure
gauge.
The system is operated by pulling the T-handle. This
releases the compressed air stored in the air bottle. Air
pressure unseats the shuttle valves at the air inlet ports
and seats the hydraulic pressure ports. Air pressure is
then applied directly to the brakes.
Once air pressure has been applied, the brake can
be released only by depressing a button on the air release
valve. Brake systems must be bled after using the
emergency pneumatic systems, and the air storage bottle
must be serviced with the specified amount of dry
compressed air or nitrogen. A pressure gauge indicates
the amount of air in the bottle, in pounds per square inch
(psi).
BRAKE ASSEMBLIES
Learning Objective: ldentify the various types
of brake assemblies.
Brake assemblies commonly used on naval aircraft
are the single disc, dual disc, multiple or trimetallic disc,
and segmented rotor. The single and dual disc types are
more commonly used on small aircraft; the multiple or
trimetallic disc types are normally used on medium–
sized aircraft; and the segmented rotor types are
commonly found on heavier types of aircraft.
SINGLE DISC BRAKES
The single disc brake is very effective for use on
smaller types of aircraft. Braking is accomplished by
applying friction to both sides of a rotating disc-the disc
being keyed to the landing gear wheel. There are several
variations of the single disc brake; however, all operate
on the same principle and differ mainly in the number
of cylinders and the types of brake housing. Brake
housings may be either the one piece or divided type.
Figure 12-30 shows a single disc brake installed on an
aircraft, with the wheel removed. The brake housing is
attached to the landing gear axle flange with mounting
bolts.
12-35
