AVIM 103D Dependant Brakes
Brake Assemblies
Multi disc assemblies
Commonly use carbon braking disc
Still use steel wearing discs
These systems are designed to withstand very
extreme temperature, and weather operating
conditions
The various discs can be solid, segmented,
slotted, internal or external tangs or notches
Brake Assemblies
In every case they will index alternately to the
inside or the outside, with one side being
attached to the gear and the other a part of
the wheel
These will have an even distribution of
pistons in the complete circumference of the
brake disc assembly
Brake Assemblies
Multi disc
assemblies
Brake Assemblies
Multi disc
assemblies
Brake Assemblies
Multi disc
assemblies
Brake Assemblies
Multi disc assemblies
B-1
Rockwell
Bomber
Carbon
Steel
This is the 33 SC Bendix wheel typically installed on all WWII military Beech's and C
model aircraft. This was a drum style brake just like the drum brakes in your car...older
car that is...
This wheel is easily identified by the teardrop cutouts between the spokes. The 33SC
wheels and tires are quite rare these days also because the tires and inner tubes are
nearly impossible to find. They sure look good and there are several of us that want to
get together to have a run of fresh tires made. The cost is substantial so the more
people we have to help fund this the more cost effective it will be for us all.
Inboard side Bendix 33SC wheel.
Bendix 33SC drum brake assembly.
Thin steel
stationary discs
and thin bronze
rotating discs
Do not set
parking brake
when brake is
hot; wait 10 to
15 minutes for
brake to cool.
Figure 1-10 Automatic adjusters with torque-less
bushings depend on a pre-set friction between the grip
collar and the pin to assure proper return action.
Figure 1-11 Automatic adjusters with torque-type
bushings require a specified torque on the adjusting nut
to compress the friction sleeve around the pin
Figure 1-14 Return
mechanism for
multiple-disk brake
using a helical
spring to pull the
pressure plate back
when the brake is
released.
Figure 1-15
Return
mechanism for
an executive jet
multiple-disk
brake using a
Belleville washer
for the return
spring
Figure 1-20 If a single-disk brake does not have a return
system, a determination of the lining wear can be made by
measuring the distance between the disk and the edge of
the housing with the brake applied.
Figure 1-21 Disk stack wear of a multiple-disk brake may be determined
either by measuring the distance between the edge of the spring housing
and the end of the adjusting pin, or by measuring the distance between the
back of the pressure plate and the edge of the brake housing. Both
measurements are made with the brake applied.
Mig 21 Tire, Wheel, Brake
Off-Aircraft Inspection/Servicing
• AN MS and Special bolts and other hardware
– Visual, dimensional and magnetic particle inspection
• Inlet and bleeder adapter
• Torque tube and pressure plate
– Visual, dimensional and magnetic particle inspection
• Piston Housing
– Visual, dimensional and fluorescent penetrant
inspection
– Pistons, seals, backup rings and insulators
Off-Aircraft Inspection/Servicing
• Stationary and rotating discs
– Thickness, wear, cracks at relief slots
– Tangs and slots
– Loose rivets and pads that are curled
– Glazed pads
• Self-adjusters
– Visual and magnetic particle inspection
Back plate
Torque Tube and
pressure plate
Figure 1-22 Wear
pads subjected to
high heat may thin
and curl along their
edges.
Semi-Boosted Brakes
Boost assisted brakes hydraulic systems are
not independent of each other
The mechanical action of the operator does
some of the work
Engine driven hydraulics do the rest of the
work
SemiBoosted
Brakes
Power Boosted Brakes
Similar to semi-boosted in theory, the
operator's actuating force is not part of the
brake actuating force
They are similar to the independent brakes in
that left pedal operates left brake, and right
pedal operates right brake
They operate by diverting a controlled
amount of hydraulic fluid from the engine
driven pump to the brake assemblies
Power Boosted Brakes
In some large aircraft systems the nose gear
will also have braking capabilities
If both pedals are being applied equally the
nose brake will assist braking
In theory of operation they are also similar to
the differential follow-up steering devices
They are dependent on the aircraft hydraulic
system for operating power
Power Boosted Brakes
The braking function calls for the operator to
apply a fixed amount of pedal travel to get a
fixed amount of braking
As long as the pedal remains in the same
position you should get the same amount of
braking
Power Boosted Brakes
Although hydraulic valves can regulate they
still either let fluid flow or don't let it flow,
based upon a fixed amount of travel
By modifying the valves to be self adjusting
using balancing springs, and pressure
differential changes across the spool valve, we
create a valve system that will allow a fixed
amount of fluid flow for a fixed amount of
pedal travel
No Boost Brakes
No Boost Brakes
No Boost Brakes
Power Boosted Brakes
Engine driven pump
Power Boosted Brakes
Engine driven pump
Power Boosted Brakes
Engine driven pump
Power Boosted Brakes
Engine driven pump
Power Boosted Brakes
By modifying the valves to be self adjusting
–using balancing springs
–pressure differential changes across the
spool valve
–we create a valve system that will allow a
fixed amount of fluid flow for a fixed
amount of pedal travel
Power Boosted Brakes
Pressure Ball-Check Brake Control Valve
Very similar to PBCV
Instead of a spool for valving it uses a piston
and a check-ball
Instead of two coiled balanced coil springs it
uses one coil spring and a flexing lever
The application of hydraulic pressure on the
piston springs closes the check-ball
Power
Boosted
Brakes
Pressure Ball-Check
Brake Control Valve
Power Boosted Brakes
Hydraulic fluid source, High pressure
Power brake control valves
Pedal assemblies and linkage
Control valves
Emergency Pneumatics
Anti skid
Air/oil transfer tube
Deboosters
Emergency valve
Shuttle valves
Pressure cylinder
Power Boosted Brakes
Hydraulic Check
Valve
Power Boosted Brakes
Hydraulic
pressure
accumulator
Power Boosted Brakes
Hydraulic
pressure
manifold
Power Boosted Brakes
Hydraulic
return manifold
Power Boosted Brakes
Power Brake
Control Valves
Power Boosted Brakes
Anti Skid Control
Valves
Power Boosted Brakes
Debooster
Assemblies
Power Boosted Brakes
Shuttle Valves
Power Boosted Brakes
Brake Assemblies
Power Boosted Brakes
Emergency pneumatic manifold
Power Boosted Brakes
Air / oil transfer tube
Power Boosted Brakes
Emergency
Brake Valve
Power Boosted Brakes
Emergency Pressure Cylinder
Power Boosted Brakes
Debooster Assemblies
Much like an electronic transformer, trading
pressure for volume instead of voltage for
current
As the debooster reaches the maximum range
of its travel a pin opens a through flow check
valve allowing full pressure to reach brakes:
used for emergency situations such as a leak
Power Boosted Brakes
Debooster
Assembly
Power Boosted Brakes
Debooster
Assembly
Power Boosted Brakes
Debooster
Assembly
Power Boosted Brakes
Lockout Debooster Assemblies
Much the same as a normal debooster except
it can be locked to a closed through flow state
when the debooster piston reaches full
extention
It must be manually set to open via pin
handle
This allows for a complete lock out of each
brake in the event of t major leak
• Decreases pressure to the brake
• Provides a large volume of fluid
to the brake
• Provides for rapid release of the
brake
Power Boosted Brakes
Shuttle valve
Keeps the normal brake hydraulic system
separated from the emergency system during
normal operation
Will allow brake system to swap to an
alternate pressure source during emergency
braking
Power Boosted Brakes
Air / oil transfer tube
This is a tank full of oil that will be fed into the
hydraulic system during emergency brake
operations
The oil is forced into the system by gas
pressure from an emergency discharge bottle
In principle it is very similar in operation to a
pressure accumulator
Power Boosted Brakes
Air / oil transfer tube
Gas In
Oil Out
Power Boosted Brakes
Air / oil transfer tube
Gas In
Oil Out
Power Boosted Brakes
Air / oil transfer tube
Gas In
Oil Out
Anti Skid Brakes
The main purpose of aircraft anti-skid is to
maximize braking effectiveness during all
braking conditions
The basic operation is to monitor all wheel
rotation speeds
When a difference begins to occur the
offending brake is automatically deactivated
slightly, until it comes back up to speed
Anti Skid Brakes
Will prevent the aircraft from touching down
with the brakes on
Will reduce the possibility of tire hydro
planeing
Generally does not operate under 20 mph
Usually has several common components
found on most vehicles that use anti skid
Anti Skid Brakes
Used exclusively on aircraft with power brake
systems
Some form of wheel speed sensor, usually
one for each braked wheel
Some form of brake servo valve, usually one
for each braked wheel
Some form of electronic control unit, often
internally independent for each wheel
Anti Skid Brakes
To prevent an inadvertent locked wheel
during touchdown the systems leaves the
brakes fully released until the WOW switch is
moved to ground
Two basic types of wheel speed sensors are
an A/C sine wave signal generator, and a D/C
voltage generator.
The A/C type control box has an internal
signal converter. Probably a rectifier circuit
Anti Skid Brakes
The wheel servos operate by releasing brake
fluid pressure back to return, until the wheel
comes back up to speed
They then start reapplying the brake to a
lessor degree, attempting to achieve
maximum braking action
Using a linear elector motor that deflects fluid
flow, the valve spool is position by varying
degrees of fluid pressure
Anti Skid Brakes
The computer control unit is able to sense
when a wheel is begging to change speed and
predicts impending skid
By using data from the other wheels, and
remembering the what the wheel speed was
prior to slippage it can determine when the
wheel is back up to proper speed
Anti Skid Brakes
Since the aircraft is decelerating it is actually
looking for a change in the rate of deceleration of
any given wheel
There are various different activation thresholds
for different systems, but it is common for these
modern systems to be reacting within several
hundredths of a second
All systems include operator indication and self
test functions
Figure 3-14 The
anti-skid test
switch sends a
simulated wheel
spin-up signal
into the control
box through the
wheel speed
sensors.
Figure 3-13 When the
brake pedals are
depressed with the
airplane on the ground,
both brake lights
should illuminate,
indicating that both
brakes are receiving
pressure
Anti-Skid Highlights
Electro-hydraulic system
Armed by a cockpit switch
Electric AC or DC wheel speed sensors
Operates just below the skid point at an impending
skid
• Warning lamp illuminates when the system off or
during a system failure
• Skid sensed – control valve relieves pressure from
brake
• Touchdown protection through squat switch – no
signal sent to control box
•
•
•
•
Variable
reluctance AC
generator
Permanent
magnet
surrounded by a
pick up coil
Exciter ring
mounted in
hubcap
Permanent magnet
generator
Output voltage directly
proportional to the
rotational speed.
No converter in the
control unit
Touch Down Protection
Wheel speed senor generates signal to make control
valve send full brake pressure to brake
Wheel speed greater than 20 MPH
Aircraft on ground; speed less than 20 MPH,
pilot has full brake control
Converter necessary for AC wheel speed
sensors
Ground System Test
• Simulates wheel lock-up, release and
restoration of brakes:
– Cockpit anti-skid switch “ON”
• Depress pedals – left and right brake lights
illuminate
• With pedals still depressed, press test
switch – lights remain on; switch released
– brake lights extinguish and then
illuminate
Fight System Test
Aircraft configured for landing
– Cockpit anti-skid switch “ON”
Simulates touch down protection feature:
• Depress pedals – left and right brake lights
remain off
Simulates normal brake function:
• With pedals still depressed, press test
switch – lights illuminate as long as switch
depressed
Tweak Test - Wheel Speed Sensor
Simulates skid
followed by normal
braking:
• Remove hub cap
• With brake
applied, spin sensor
blade
• Brake will
momentarily
release, then
reapply
DC Wheel Speed Sensor Tweak Test
• Remove wheel hub cap to expose sensor
blade.
• With anti-skid switch “ON” and brake applied,
give blade sharp spin with your finger.
• In a properly operating system, brakes
momentarily release then reapply.
• If the sensor fails the tweak test, check the
resistance using a sensitive ohmmeter.
Figure 3-16 If a
wheel-speed
sensor fails the
tweak test, the
resistance of
the coil should
be measured
with an
accurate
ohmmeter
DC Wheel Speed Sensor Resistance Test
• Remove cable
connector and
measure resistance of
armature while slowly
rotating blade 3600.
• Uniformity and
amount of resistance
through blade travel
should be within
maintenance manual
specifications.
DC Wheel Speed Sensor Polarity Test
• Place meter on lowest DC voltage scale; attach
positive lead to pin “B” and negative lead to
pin “A”.
• Tweak blade in clockwise direction viewed
from drive end.
• Meter should read upscale.
Control Box
• Check by substitution method
– Swap cables
• Problem changes sides – control box
defective
• Problem remains on same side – wheel
speed sensor or control valve defective
Control Valve
• Measure control valve coil resistance using
sensitive ohmmeter
– Resistance within specification, control
valve parts are defective
B757 HYDRAULIC CONTROL PANEL
B757 CONTROL
B757 NOSE LANDING GEAR
B757 NWS
B757 MAIN GEAR
B757 PROXIMITY SWITCH
B757 BRAKE SYSTEM
B757 ANTI-SKID
B757 AUTOBRAKES
B757 AUTOBRAKES
Anti-corrosion Sealant
B787 Electric Brake
B737-800 Brake Change
B737-800 Brake Change
B737-800 Brake Change
B737-800 Brake Change
Beechcraft Super King Air
END OF
SECTION
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