Construction & System Operation - Aircraft Brakes - Airframes & Aircraft Systems #22

Summary

The 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

00:00

🛫 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.

05:01

🔧 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.

10:03

🏁 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.

Keywords

💡Friction

Friction is the force that resists the relative motion or tendency of such motion of two surfaces in contact. In the context of the video, friction is crucial for aircraft wheel brakes to function, as it is the interaction between the fixed and moving surfaces that helps convert kinetic energy into heat, thereby slowing down or stopping the aircraft.

💡Kinetic Energy

Kinetic energy is the energy possessed by an object due to its motion. The video discusses how aircraft brakes work by converting the aircraft's kinetic energy into heat energy through friction, which is a fundamental principle in the operation of braking systems.

💡Heat Dissipation

Heat dissipation refers to the process of removing excess heat from a system to prevent overheating. In the video, it is highlighted as a significant challenge for aircraft designers due to the enormous amount of heat generated when stopping large modern aircraft.

💡Reverse Pitch

Reverse pitch is a technique used on propeller-driven aircraft where the angle of the propeller blades is adjusted to push air forward, helping to slow the aircraft down. The video mentions this as one of the methods to reduce the workload on the brakes.

💡Reverse Thrust

Reverse thrust is a mechanism used in jet engine aircraft to redirect the engine's thrust forward, which assists in deceleration. The script explains that this, along with other methods like ground spoilers, helps to reduce the work that brakes need to do.

💡Hydraulic Systems

Hydraulic systems use fluid power to transmit energy for various mechanical functions. In the video, hydraulic systems are described as the means by which aircraft brakes are operated, highlighting their importance in the braking process.

💡Brake Pads

Brake pads are the components that press against the brake disc or rotor to create friction and slow down the vehicle. The video explains that in aircraft braking systems, brake pads are made of inorganic materials and are used in conjunction with a metal disc to slow down or stop the aircraft.

💡Brake Disc

The brake disc is a part of the braking system that rotates with the wheel. It is pressed against by the brake pads to create the friction necessary for slowing down or stopping the aircraft. The video describes how the friction pads bear on or grip a metal disc, which is a key component in the braking mechanism.

💡Brake Torque Rods

Brake torque rods are components that prevent the undercarriage bogie from rotating about its pivot point during braking. The video mentions these as a recent technological advancement that helps manage the torque developed during braking.

💡Carbon Brakes

Carbon brakes are a type of brake system used in aircraft, made from carbon composite materials. The video points out that carbon brakes have superior heat absorption and dissipation properties compared to steel brakes, allowing for higher braking levels and quicker turnaround times, despite their higher cost and shorter lifespan.

💡Brake Fade

Brake fade is a phenomenon where the braking effectiveness is reduced due to overheating of the brake components. The video explains that if the brakes become too hot, they cannot absorb further energy, and their ability to slow down the aircraft diminishes rapidly.

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