Components & Brake Kinetic Energy - Aircraft Brakes - Airframes & Aircraft Systems #24
Summary
TLDRThis lesson delves into the intricacies of aircraft parking brakes and hydraulic braking systems. It explains how the parking brake operates, requiring hydraulic power and a lever mechanism to apply pressure. The script also covers the brake kinetic energy graph, crucial for assessing energy absorption post-braking events, and the brake temperature indicating system, which monitors heat generated during braking. The lesson highlights the importance of correct braking techniques, including the use of anti-skid brakes, spoilers, and reverse thrust, for safe landings on limited runways.
Takeaways
- đ żïž The parking brake is a hydraulic system used to maintain pressure at the brakes when the aircraft is parked without chocks.
- đ§ The parking brake lever is spring-loaded to the off position and is engaged by pulling the lever while holding down the foot pedals.
- đ An electrical switch connected to the parking brake lever prevents fluid bleeding away from the brakes when the lever is engaged.
- đ§ A fully charged brake accumulator can hold the brakes fully on overnight, but the capacity varies depending on the aircraft.
- đ Shuttle valves in the hydraulic system allow the highest pressure from either the manual or auto brake system to supply the brakes.
- đ The anti-skid system modulates brake pressure to prevent wheel skidding, using speed tranches to sense incipient skids and adjust pressure accordingly.
- âïž The brake kinetic energy graph helps pilots determine the amount of energy absorbed during braking, which is crucial for decision-making after high-energy events like aborted takeoffs.
- â ïž Brake temperature indicators are essential for monitoring the health of the brake system, with different color codes indicating the temperature status of the brakes.
- đ The brake kinetic energy graph is divided into normal, caution, and danger zones, with specific actions and precautions associated with each zone.
- đ« Proper landing techniques, including correct approach speed and touchdown, are crucial for a safe stop, especially when combined with anti-skid braking, ground spoilers, and reverse thrust.
Q & A
What is the primary function of the parking brake in an aircraft?
-The parking brake is used to maintain pressure at the brakes when the aircraft is parked without chocks.
How is the parking brake applied in an aircraft?
-The parking brake is applied by depressing the foot pedals and then pulling the parking brake lever while holding the lever in position, which releases the pedals and locks the lever in the engaged position, thus applying full pressure to the brakes.
What is unique about the parking brake system in aircraft compared to cars?
-Unlike cars, the aircraft parking brake requires hydraulic power to apply and hold the brakes. It is not a simple mechanical device like the handbrake found in cars.
How does the electrical switch connected to the parking brake lever function?
-When the parking brake lever is engaged, the electrical switch operates, closing a valve in the anti-skid system return line, preventing fluid from bleeding away from the brakes.
What is the role of the brake accumulator in the aircraft's braking system?
-The brake accumulator maintains pressure to the brake system when both normal and alternate hydraulic sources are unavailable. It ensures that the brakes can be held fully on overnight or stop the aircraft from high speeds, depending on the system design.
What does the brake kinetic energy graph represent and how is it used?
-The brake kinetic energy graph indicates the amount of kinetic energy absorbed during braking, which is represented in millions of foot-pounds. It is used to determine the amount of energy absorbed and to guide decisions regarding precautions and actions to be taken after significant braking events like aborted takeoffs or landings.
How does the anti-skid system in aircraft work?
-The anti-skid system senses impending wheel skidding and modulates the brake pressure accordingly. When skidding is detected, it commands the respective anti-skid valve to release the brake pressure and then apply reduced pressure to prevent further skidding.
What is the purpose of the brake temperature indicating system?
-The brake temperature indicating system monitors the temperature of each individual wheel's brakes and alerts the crew if the temperature exceeds predetermined levels, indicated by an amber or red light, helping to prevent brake overheating and failure.
How does the shuttle valve system between manual and auto brake systems function?
-The shuttle valves move to allow the system supplying the highest pressure, whether manual or auto, to supply the brakes. This ensures that the brakes receive the maximum available hydraulic pressure for effective braking.
What actions should a pilot take to ensure a safe stop on a limiting runway?
-A pilot should use correct approach speed, touch down at the correct place on the runway, apply anti-skid braking immediately after touchdown, deploy ground spoilers promptly, and select reverse thrust without delay to ensure a safe stop.
Outlines
đ« Aircraft Parking Brake and Hydraulic Braking System Overview
This paragraph introduces the operation of the aircraft parking brake and the components of a typical hydraulic braking system. It explains how the parking brake works, requiring hydraulic power to apply and hold, and how it is engaged by depressing foot pedals and pulling the parking brake lever. The paragraph also covers the role of the brake accumulator in maintaining brake pressure and the anti-skid system's function in preventing wheel skidding. Additionally, it discusses the brake kinetic energy graph and the brake temperature indicating system, which are crucial for assessing the energy absorbed by the brakes and making informed decisions after operations like aborted takeoffs or landings.
đ Understanding Brake Kinetic Energy and Temperature Indicators
This section delves into the brake kinetic energy graph, which is used to determine the amount of energy absorbed by the brakes during operations like aborted takeoffs. The graph is entered with parameters such as all-up weight, brake application speed, and serviceable engine thrust reversers, and it outputs the absorbed energy in millions of foot-pounds. The output is divided into three zones: normal, caution, and danger, with each zone having associated actions and precautions. The paragraph also discusses brake temperature indicators, which are used to monitor the temperature of individual wheel brakes and can be displayed on electromechanical or electronic screens. The importance of consulting the brake kinetic energy graph before taking action after heavy braking events is emphasized.
đ Safe Landing and Braking Techniques
The final paragraph focuses on the techniques for a safe landing and stopping the aircraft on a runway, especially in limiting conditions. It highlights the importance of using the correct approach speed, touching down at the right spot on the runway, and applying anti-skid braking immediately after touchdown. The use of ground spoilers to increase brake efficiency by dumping lift from the wings is also mentioned. The paragraph concludes with the advice to select reverse thrust promptly to aid in stopping the aircraft. The discussion serves as a guide for pilots to ensure safe landings and effective use of the braking system.
Mindmap
Keywords
đĄParking Brake
đĄHydraulic Braking System
đĄBrake Kinetic Energy Graph
đĄAnti-Skid System
đĄBrake Accumulator
đĄShuttle Valves
đĄBrake Metering Valves
đĄThrust Reversers
đĄBrake Temperature Indicators
đĄHigh-Speed Braking
Highlights
The parking brake is used to maintain pressure at the brakes when the aircraft is parked without chocks.
The parking brake lever is spring-loaded to the off position and requires hydraulic power to apply and hold the brakes.
To apply the parking brake, foot pedals are depressed and then the parking brake lever is pulled while holding the lever.
An electrical switch connected to the parking brake lever prevents fluid bleeding away from the brakes when engaged.
A fully charged brake accumulator has enough fluid to hold the brakes fully on overnight.
The typical wheel brake system is powered by one of the aircraft's hydraulic power systems with automatic switchover to an alternate system in case of low pressure.
The accumulator pressure gauge indicates system pressure when hydraulic system pressure is available.
Shuttle valves are placed between the manual and auto brake systems to allow the highest pressure system to supply the brakes.
The anti-skid system protects the wheel from further skidding by releasing and then applying reduced brake pressure.
Brake kinetic energy graphs help determine the amount of energy absorbed during braking, which is crucial for decision-making after high-energy events.
Brake temperature indicators are used to monitor the temperature of each individual wheel's brakes.
Older aircraft use electromechanical indicators, while modern aircraft display brake temperatures on electronic screens.
Brake temperature indicators can trigger an Amber high temperature warning or a red brake overheat warning if temperatures exceed certain thresholds.
The brake kinetic energy graph is used to read off the amount of kinetic energy absorbed during braking events.
Actions and precautions associated with the normal, caution, and danger zones of the brake kinetic energy graph are of interest to pilots.
A safe stop begins with a good landing, using correct approach speed and touchdown location, followed by the immediate application of anti-skid braking.
Ground spoilers should be deployed immediately after touchdown to dump lift from the wings and improve brake efficiency.
Reverse thrust should be selected without delay to assist in stopping the aircraft.
Transcripts
this lesson will explain the operation
of the parking brake and then we will
look at the components that make up a
typical hydraulic braking system
the brake kinetic energy graph will be
described as well the brake temperature
indicating system
King break is used to maintain pressure
at the brakes when the aircraft is
parked without chocks normally once
chocks are fitted the brakes can be
released
parking brake is not a mechanical device
such as this found on your car it
requires hydraulic power to apply and
hold the brakes
the parking brake lever is spring-loaded
to the off position to apply the parking
brake the foot pedals are depressed
then the parking brake lever is pulled
whilst holding the lever in position the
pedals are then released this allows the
latch pin on the pedal mechanism to
engage with the pole on the lever
mechanism locking the pedals down and
the lever in the engaged position thus
keeping the brake metering valves open
applying full pressure to the brakes
an electrical switch connected to the
parking brake lever operates when the
lever is in the engaged position closing
a valve in the anti-skid system return
line preventing fluid bleeding away from
the brakes
a fully charged brake accumulator will
have sufficient fluid to hold the brakes
fully on overnight
to release the parking brake the pedals
are depressed allowing the lock pin to
release from the pole and the lever to
spring forward
the typical wheel brake system shown
here has all the features and components
we have discussed so far
the brakes are normally powered by one
of the aircraft hydraulic power systems
system B with automatic switch over to
an alternate system system a in the
event of low pressure in system B
when both normal and alternate brake
hydraulic sources are unavailable an
accumulator will maintain pressure to
the brake system
the accumulator pressure gauge is on the
gas side of the accumulator
provided hydraulic system pressure is
available it will read system pressure
however if normal system pressure is
lost and the brakes are operated the
accumulator pressure will fall until all
fluid in it is used up the gauge will
then read the gas pre-charge pressure
the non-return valve will prevent
backflow to the pumps in some systems
the accumulator has sufficient fluid to
stop the aircraft from high-speed but in
others it only has sufficient fluid to
maintain the parking brake overnight
there are shuttle valves placed between
the manual and auto brake systems these
will move the cross to allow whichever
system is supplying the highest pressure
to supply the brakes
the hydraulic fluid from the brake
metering valves or the auto brake valve
passes freely through the anti-skid
valves to the brakes unless an incipient
skid is sensed by the anti-skid system
we'll speed tranches mounted in the
axles transmit wheel speed inputs to the
anti-skid control unit each wheel is
provided individually with anti skid
protection
when skidding is initially detected the
anti-skid controller adaptive pressure
bias modulation circuit commands the
respective anti-skid valve firstly to
release the brake pressure then to apply
a reduced pressure to protect the wheel
from further skidding
many aircraft have a system fitted
whereby whenever the landing gear is
selected up the wheel brakes are
automatically applied to stop the wheels
rotating in the wheel wells
during the application of brakes a
considerable amount of energy is
absorbed this energy is released in the
form of heat which must be dissipated
the break packs wheel assembly's and
tires are capable of absorbing a certain
amount of heat before they fail
some method of determining the amount of
energy absorbed will facilitate
decisions regarding precautions and
actions to be taken after an aborted
takeoff a landing or simply taxing the
aircraft around the airfield
one such method is the brake kinetic
energy graph a graph similar to this one
will be found in your particular
aircraft performance manual
the graph is entered with all up wait
and break application speed in knots
corrected for wind
and then factored for the number of
serviceable engine thrust reversers and
airfield altitude
the graph will then indicate the amount
of kinetic energy absorbed in millions
of foot-pounds this figure is not of
much interest to pilots
however the graph output is also split
into three zones the normal caution and
danger zones
it is these zones and the actions and
precautions associated with them but the
pilot is interested in
the actions and precautions for the
three zones are listed here you can take
a moment to read them but bear in mind
that they will vary from aircraft type
to aircraft type
as an example we will use an aborted
takeoff at a weight of 280 thousand
pounds stopping from a speed of 125
knots with no wind and one reverser
operating at an airfield with a pressure
altitude of 2,000 feet the graph is
entered with the weight 280,000 pounds
we move across to the reference line
then up the guide lines until the 125
not line is intercepted
we then move across to the reverses
reference line and up to intercept the
one reversal operating point
we now move the cross to the altitude
reference line then up to intercept the
2,000 feet point finally we move to the
right to read off the break kinetic
energy absorbed 27 million foot-pounds
as this was an aborted takeoff no two
applies meaning we need to add five
which brings it to 32 so we are in the
danger zone
many aircraft are fitted with brake
temperature indicators older aircraft
have electromechanical indicators while
our more modern aircraft the
temperatures can be displayed on one of
the electronic display screens
sensors are arranged to sample the
temperature of the brakes of each
individual wheel and their output is
sent to the indicator panel
here you can see a system typical of
that used on many older aircraft the
indicator has two pointers labeled left
and right
aircraft has four wheels on each bogie
they are represented on the group of for
mechanical push switches only one of
which can be depressed at a time
each switch allows the brake temperature
of a pair of wheels to be displayed on
the indicator
for instance if the left forward push
button was pressed in then the gauge
would now be reading the temperature of
the front pair of wheels on the Left
bogie
the break temperatures of all wheels are
constantly monitored by the system if
the temperature of any brake assembly
rises above a predetermined level then
an Amber high temperature indicator
light illuminates
by cycling through the switch positions
the operator will be able to locate the
wheel brake which is triggering the
alarm
[Music]
should any brake temperature go even
higher there is another trigger point at
which a red brake overheat caption will
illuminate
on aircraft with a central warning
system the break over heat warning will
normally be repeated on it
there is a push button for testing the
system when it is pressed and held the
indicated temperature for the selected
pair of wheels will rise by about 100
degrees
shown here is the system used by Airbus
all of the landing gear information is
brought together on one electronic
screen
the break temperatures normally appear
in green changing to Amber with the
caution light if the temperature exceeds
300 degrees Celsius
this system also has the facility to
monitor the anti-skid system
the bars appear when the system is armed
and the release Annunciations appear
when the anti-skid is operating and
releasing break pressure
break temperature indicators are a
useful guide for the crew
however after heavy breaking in the
event for instance of an aborted takeoff
it can take some considerable time 10
minutes or more before the energy
absorbed by the whale tire and brake
assembly manifests itself on the
temperature gauge it is important that
in such a case the brake kinetic energy
graph is consulted before a course of
action is decided upon
there are a number of aids available to
youth the pilot to help you bring the
aircraft to a safe stop on a limiting
runway in marginal conditions
however these all need to be used
correctly
a safe stop begins with a good landing
this means using the correct approach
speed
and touching down at the correct place
on the runway
Paul anti-skid braking should be applied
immediately after touchdown
do not use cadence braking that is to
say do not pump the brake pedal up and
down
the ground spoilers should be
immediately deployed not so much for
their stopping assistance but more for
the fact that they dump the lift from
the wings putting more weight on the
wheels allowing the brakes to operate
more efficiently
finally reverse thrust should be
selected without delay
you
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