Construction & System Operation - Aircraft Brakes - Airframes & Aircraft Systems #22
Summary
TLDRThe video script delves into the intricacies of aircraft wheel brakes, highlighting the challenge of heat dissipation due to the immense energy conversion during braking. It outlines the evolution from simple to complex hydraulic systems, the shift from steel to carbon in brake manufacturing for better heat management, and the importance of monitoring brake lining material to prevent brake fade and potential fires. The script also discusses the role of technological advancements in enhancing brake efficiency and the mechanisms of automatic brake wear adjusters.
Takeaways
- ✈️ Aircraft wheel brakes function by converting kinetic energy into heat through friction between a fixed and a moving surface.
- 🔥 The amount of heat generated when stopping large modern aircraft is enormous, presenting a significant challenge for heat dissipation.
- 🛫 Technological advancements like reverse pitch on propeller-driven aircraft and reverse thrust on jet engines, along with ground spoilers, help reduce the workload on brakes.
- 🔧 Aircraft now use plate or disc brakes operated by hydraulic systems, similar to those in cars but adapted for the unique demands of aviation.
- 🚗 Light aircraft use a braking system very similar to cars, with fixed friction pads gripping a rotating metal disc.
- 💡 The hydraulic system in larger aircraft is controlled by metering valves connected to the pilot's foot pedals, with primary and alternate hydraulic sources for redundancy.
- 🔩 Large aircraft increase braking surface area with multiple brake plates (rotors) and friction material layers (stators), improving braking ability and reducing temperatures.
- 🔄 Recent designs have segmented brake discs to improve heat dissipation, enhancing brake efficiency.
- 🏎️ Carbon is increasingly used in brake manufacturing due to its superior heat absorption and dissipation properties compared to steel, allowing for higher and longer-lasting braking performance.
- 🔍 Brake fade occurs when brakes overheat and lose their ability to slow the aircraft effectively, which is a critical safety concern.
- 🛠️ Automatic brake wear adjusters maintain a constant running clearance, compensating for wear and preventing brake drag, which can lead to excessive heat and potential brake failure.
Q & A
How do aircraft wheel brakes function?
-Aircraft wheel brakes function by using friction between a fixed surface and a moving one to bring an aircraft to rest, converting kinetic energy into heat energy.
What is the challenge faced by aircraft designers regarding brakes?
-The challenge faced by aircraft designers is dissipating the enormous amount of heat generated when stopping large modern aircraft, as the braking systems have to handle increasing speeds and weights of aircraft.
How do reverse pitch on propeller-driven aircraft and reverse thrust on jet engine aircraft assist in braking?
-They help reduce the work the brakes need to do by providing additional means of slowing down the aircraft, thus reducing the load on the wheel brakes.
What type of brakes are commonly used in aircraft?
-Aircraft now use plate or disc brakes operated by hydraulic systems as their means of slowing down or stopping.
How do hydraulic systems operate in aircraft brakes?
-On larger aircraft, hydraulic pressure controlled by metering valves connected to the foot pedals is used to operate the brakes, with a primary and an alternate hydraulic source available for redundancy.
What is the purpose of brake torque rods in aircraft undercarriage?
-Brake torque rods prevent the bogie from rotating about its pivot point during braking by counteracting the torque developed during the braking process.
Why are carbon brakes preferred in modern aircraft?
-Carbon brakes are preferred due to their superior heat absorbing and dissipating properties compared to steel, which allows for higher levels of braking and quicker turnaround times.
What is brake fade and how can it affect an aircraft?
-Brake fade is a phenomenon where brakes become too hot and are unable to absorb further energy, leading to a rapid diminishment in their ability to slow down the aircraft.
How do automatic brake wear adjusters function in aircraft braking systems?
-Automatic brake wear adjusters use springs to move the pressure plate back when the brakes are released, allowing the stator and rotor assemblies to move slightly apart, compensating for brake wear and maintaining a constant running clearance.
What is brake drag and what are its potential consequences?
-Brake drag occurs when the brakes do not release fully, which can generate excessive heat and potentially lead to brake fade or even a brake fire.
How is the remaining brake lining material checked in multiple disk brake systems?
-The most popular method is by checking the amount that the retraction pin or wear indicator pin extends from the spring housing with the brakes selected on.
Outlines
🛫 Aircraft Wheel Brakes and Heat Dissipation Challenges
This paragraph introduces the fundamental concept of aircraft wheel brakes, which operate on the principle of friction between a fixed and a moving surface to decelerate and stop the aircraft. It highlights the significant amount of heat generated during braking, especially in large modern aircraft, and the historical challenge this poses for designers and scientists. The paragraph also discusses the evolution of braking systems, including the use of reverse pitch on propeller-driven aircraft and reverse thrust on jet engines, as well as ground spoilers to reduce the workload on brakes. The focus then shifts to the components of a typical aircraft braking system, emphasizing the use of plate or disc brakes operated by hydraulic systems. The description includes the operation of light aircraft brakes, which are similar to car brakes, with fixed friction pads and a rotating metal disc. The hydraulic system's role in applying pressure to the brake pads is explained, along with the function of toe brake pedals and the differential braking capability. The paragraph concludes with a discussion on the construction of brakes in larger aircraft, which use multiple brake plates and friction material to increase surface area and braking efficiency.
🔧 Advances in Brake Technology and Maintenance
This paragraph delves into the technological advancements in aircraft brake systems, particularly focusing on heat dissipation and the evolution of brake disc plate design. It explains how the change from a single continuous rotating plate to a segmented plate has improved heat dissipation and increased brake efficiency. The use of carbon in brake manufacturing is discussed due to its superior heat absorption and dissipation properties compared to steel, which allows for higher and more sustained braking levels and quicker turnaround times. Despite the higher cost and shorter lifespan of carbon brakes, their advantages are considered to outweigh the disadvantages, leading to their widespread use in modern aircraft. The paragraph also addresses the issue of brake fade, which occurs when brakes become too hot to absorb further energy, leading to a rapid loss of braking ability. It describes the function of brake adjusters, which use springs to maintain a constant running clearance and compensate for brake wear. The importance of monitoring brake lining material thickness is emphasized to prevent excessive wear or overheating, which could lead to brake fade or even a brake fire. The paragraph concludes with methods for gauging the remaining depth of brake lining material, including the use of retraction pins, wear indicator pins, and wear gauges.
🏁 Understanding Brake Materials and Maintenance Indicators
The final paragraph summarizes key points about aircraft brake systems, emphasizing that they are typically hydraulically operated and that brake discs can be made from either steel or carbon. It reiterates the efficiency and heat management advantages of carbon brakes over steel, despite their higher cost and quicker wear. The paragraph also touches on the critical issue of brake fade, which can severely impact braking performance. Lastly, it underscores the importance of understanding the function of automatic brake wear adjusters and the various methods used to indicate when maintenance is required, ensuring the continued safety and reliability of aircraft braking systems.
Mindmap
Keywords
💡Friction
💡Kinetic Energy
💡Heat Dissipation
💡Reverse Pitch
💡Reverse Thrust
💡Hydraulic Systems
💡Brake Pads
💡Brake Disc
💡Brake Torque Rods
💡Carbon Brakes
💡Brake Fade
Highlights
Aircraft wheel brakes use friction to convert kinetic energy into heat energy to stop the aircraft.
Heat dissipation is a major challenge for aircraft designers due to the enormous amount of heat generated during braking.
Improvements in braking systems are necessary as aircraft become faster and heavier.
Reverse pitch on propeller aircraft and reverse thrust on jet engine aircraft help reduce the workload on brakes.
Aircraft now use plate or disc brakes operated by hydraulic systems for slowing down or stopping.
Light aircraft use a braking system similar to cars, with fixed friction pads and a rotating metal disc.
The friction pads are made of inorganic material and the plates are forged steel with a case-hardened surface.
Hydraulic pressure from the slave cylinder behind the piston is used to push the brake pad against the disk.
The force applied to the brake pads is proportional to the effort applied to the toe brake pedal.
Larger aircraft use hydraulic system pressure controlled by metering valves for braking.
Multiple brake plates, known as rotors, are used to increase the braking surface area and reduce temperature.
The rotating brake plates or rotors revolve with the wheel, while the stationary pad assemblies remain stationary with the axle.
Brake torque rods prevent the undercarriage bogie from rotating during braking.
Technological advancements have led to the design of brake discs with interconnected segments for improved heat dissipation.
Carbon is often used for brake units due to its superior heat absorbing and dissipating properties compared to steel.
Carbon brakes are lighter than steel but have a shorter life and are more expensive.
Break fade occurs when brakes become too hot and cannot absorb further energy, reducing their effectiveness.
Automatic brake wear adjusters maintain a constant running clearance and compensate for brake wear.
Break drag can generate excessive heat and may lead to early brake fade or even a brake fire.
Monitoring the thickness of brake lining material is crucial for preventing excessive wear or overheating.
Transcripts
in common with most breaking systems
aircraft wheel brakes function by using
friction between a fixed surface and a
moving one to bring an aircraft to rest
converting kinetic energy into heat
energy
the amount of heat generated in stopping
a large modern aircraft is enormous
the problem of dissipating this heat has
been a challenge to aircraft designers
and scientists for many years
breaking systems have been improved but
aircraft have got faster and heavier
making heat dissipation a constant
problem
the use of reverse pitch on propeller
driven aircraft and reverse thrust on
jet engine aircraft plus the use of
ground spoilers has helped reduce the
work the brakes need to do but even with
these the need for powerful brakes still
exists
in this the first in a set of three
lessons on wheel brakes the components
that make up a typical aircraft braking
system will be described
aircraft now use plate or disc brakes
operated by hydraulic systems as their
means of slowing down or stopping
light aircraft use a very similar system
to that used on cars it consists of a
pair of fixed friction pads bearing on
or gripping a metal disc which rotates
with the wheel
the friction pads are made of an
inorganic material and the plates are a
forged steel with an especially case
hardened surface
with no pressure applied to the toe
brake pedal the pads are knocked away
from the disk by the action of it
rotating
if pressure is applied to the toe brake
pedal hydraulic pressure will build up
in the slave cylinder behind the piston
this pressure will cause the piston to
move over within the caliper unit
pushing the brake pad against the disk
the reaction of the right hand brake pad
pushing against the disc will cause the
caliper unit to move in the opposite
direction
carrying the left hand pad with it until
the disc is squeezed between the two
pads
the force apply to the brake pants will
be proportional to the effort applied to
the toe brake pedal the toe brake pedals
can be applied together or if
differential braking is required for
ground maneuvering the toe brakes can be
used separately
when break pressure is released
imperfections in the rotating brake disc
once again cause the brake pads to move
apart so that the residual braking
effect is minimal
on a simple light aircraft system the
pilot is able to apply sufficient
pressure to the pedal with his foot to
operate the brakes and slow the aircraft
down
however on larger aircraft the pressure
required to operate the brakes is
greater than can be generated by the
pilots feet so aircraft hydraulic system
pressure controlled by metering valves
connected to the foot pedals is used
there will be a primary
and an alternate hydraulic source
available the alternate source often has
independent pipe work
there may also be an accumulator for use
in the case of total hydraulic system
failure
large aircraft the braking surface is
increased by using multiple break plates
known as rotors
BAM which between layers of friction
material mounted on assemblies known as
status
this greatly increases the surface area
thus increasing the braking ability and
helping to reduce the brake temperature
in this sort of construction the
rotating brake plates or rotors are key
to revolve with the outer rim of the
wheel
and the stationary pad assemblies or
status carrying the friction material
are key to remain stationary with the
axle
the actuating Pistons
are housed in a fixed talk plate they
push on the sliding pressure plate
the stator and rotor assemblies are
fitted between the pressure plate and a
fixed thrust plate
when the brake is applied hydraulic
pressure pushes the actuating Pistons
squeezing the rotors and stators between
the pressure plate and the thrust plate
the harder the brake pedal is pressed
the greater will be the braking force
applied to the pressure plate by the
Pistons
on aircraft with undercarriage bogies
the torque developed during braking will
attempt to rotate the bogie about its
pivot point this is prevented by brake
torque rods attached to the landing gear
leg
recent technological advancements in
heat dissipation have resulted in the
design of the brake disc plates being
changed from a continuous rotating
single plate to a plate constructed of
many interconnected individual segments
with the heat dissipation property has
been greatly improved thus increasing
brake efficiency
carbon is now often used for
manufacturing brake units because it has
much better heat absorbing and
dissipating properties than steel this
allows higher levels of braking to be
maintained for longer it also allows for
quicker turnarounds as it is not
necessary to wait so long for the brakes
to cool before taking off again
carbon brakes are also much lighter than
equivalent steel units
the disadvantages are their increased
cost and shorter life
however the advantages outweigh the
disadvantages and they are now found on
most modern aircraft
if in spite of all of this the brakes
become too hot they will not be able to
absorb any further energy and their
ability to slow down the aircraft
rapidly diminishes
this phenomenon is termed break fade
each break unit is fitted with break
adjusters would use Springs to move the
pressure plate back when the brakes are
released allowing the stator and rotor
assemblies to move slightly apart the
internal construction of the brake
adjuster assemblies allows them to
maintain a constant running clearance
when the brakes are off there by
automatically compensating for brake
wear
retraction pin is connected to the
pressure plate and is a tight fit in the
friction bush which is part of and moves
with the guide assembly
when the brakes are released the spring
will pull the guide the pin and the
pressure plate to the left allowing the
stator and rotor assemblies to move
slightly apart
when the brakes are applied the pressure
plate will pull the pin and guide
assembly to the right until the guide
reaches the end of its travel
if further movement is required because
of pad where the pin will be pulled
through the friction bush
when pressure is released the spring
will pull the guide pin and pressure
plate back to the left until the guide
assembly once again reaches the end of
its travel thus maintaining a constant
running clearance if the return spring
inside the adjuster assembly ceases to
function or if the unit is wrongly
adjusted then the brakes may not release
fully
this is termed break drag
break drag will generate a lot of heat
and could be responsible for brake fade
occurring sooner than it otherwise would
or even for a brake fire
it is important that the thickness of
the brake lining material is carefully
monitored
two little break lining material
remaining may mean that the disk of a
single brake system becomes excessively
worn or grooved or on a multiple disk
break the remaining material overheats
and erodes extremely quickly
on multiple disk brake systems the most
popular method of gauging the depths of
brake lining material remaining is by
checking the amount that the retraction
pin or the wear indicator pin as it is
sometimes called extends from the spring
housing with the brakes selected on
the minimum amount that the pin can
extend beyond the housing for the brakes
to remain in service will be laid down
by the manufacturer
on systems where the retraction pin is
located inside the housing a wear gauge
can be used to check the distance that
the pin has moved within the housing
the wear gauge is held against the
housing and the rod is screwed in until
it touches the retraction pin
the maximum distance that the rod is
permitted to extend will once again be
laid down by the manufacturer
an alternative method which can be used
if no retraction pins are fitted to the
system is that if it is accessible the
amount of clearance between the back of
the pressure plate and the brake housing
can be measured again with the brakes
applied
the main points to be taken from this
lesson are that aircraft brake systems
are normally hydraulically operated and
the discs are manufactured from either
steel or carbon
carbon brakes are more efficient and
heat up less than steel however they are
more expensive and we're more quickly
you should understand the problem of
break fade and finally you should
understand the function of automatic
break where adjusters and the methods
used for indicating where
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