Components & Brake Kinetic Energy - Aircraft Brakes - Airframes & Aircraft Systems #24

Summary

This 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

• 🅿️ The parking brake is a hydraulic system 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 is engaged by pulling the lever while holding down the foot pedals.
• 🔐 An electrical switch connected to the parking brake lever prevents fluid bleeding away from the brakes when the lever is engaged.
• 💧 A fully charged brake accumulator can hold the brakes fully on overnight, but the capacity varies depending on the aircraft.
• 🔄 Shuttle valves in the hydraulic system allow the highest pressure from either the manual or auto brake system to supply the brakes.
• 🛑 The anti-skid system modulates brake pressure to prevent wheel skidding, using speed tranches to sense incipient skids and adjust pressure accordingly.
• ⚙️ 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.
• ⚠️ Brake temperature indicators are essential for monitoring the health of the brake system, with different color codes indicating the temperature status of the brakes.
• 📊 The brake kinetic energy graph is divided into normal, caution, and danger zones, with specific actions and precautions associated with each zone.
• 🛫 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

00:00

🛫 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.

05:01

📊 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.

10:02

🛑 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.

Keywords

💡Parking Brake

The parking brake is a device used to secure an aircraft in place when parked, preventing it from rolling. Unlike car parking brakes, which are mechanical, aircraft parking brakes require hydraulic power to apply and hold the brakes. In the script, it is mentioned that the parking brake lever is spring-loaded to the off position, and it is applied by depressing the foot pedals and pulling the lever, which engages a latch pin to lock the pedals and maintain brake pressure.

💡Hydraulic Braking System

A hydraulic braking system in aircraft utilizes hydraulic power to operate the brakes. The script describes how the brakes are normally powered by one of the aircraft's hydraulic power systems, with an automatic switchover to an alternate system in case of low pressure. This system is crucial for applying the brakes effectively and safely during various flight operations.

💡Brake Kinetic Energy Graph

The brake kinetic energy graph is a tool used to estimate the amount of energy absorbed by the brakes during heavy usage, such as after an aborted takeoff. The graph helps pilots and maintenance crews to determine the necessary precautions and actions based on the energy absorbed. In the script, an example is given where the graph is used to calculate the energy absorbed during an aborted takeoff, leading to a reading in the 'danger zone'.

💡Anti-Skid System

The anti-skid system is designed to prevent the aircraft's wheels from locking up during braking, which could lead to skidding. The script explains that the system senses incipient skids and modulates brake pressure accordingly to maintain wheel traction. Each wheel has individual anti-skid protection, and the system can be monitored through electronic displays on modern aircraft.

💡Brake Accumulator

A brake accumulator is a device that stores hydraulic fluid under pressure to maintain brake function in the event of primary hydraulic system failure. The script mentions that the accumulator pressure gauge indicates system pressure when available, but if normal pressure is lost, it falls to the gas pre-charge pressure, indicating the use of the accumulator's stored fluid.

💡Shuttle Valves

Shuttle valves are components that direct the flow of hydraulic fluid to the brakes, allowing the system to use the highest available pressure source. As described in the script, they move to allow the system supplying the highest pressure, whether from manual or auto brake systems, to feed the brakes.

💡Brake Metering Valves

Brake metering valves regulate the flow of hydraulic fluid to the brakes, controlling the braking force. The script explains that these valves pass fluid freely through the anti-skid valves to the brakes unless a skid is detected, at which point the anti-skid system modulates the pressure.

💡Thrust Reversers

Thrust reversers are devices on jet engines that redirect engine thrust forward to help slow the aircraft down during landing. The script discusses how the number of serviceable engine thrust reversers can affect the amount of kinetic energy absorbed by the brakes, as factored into the brake kinetic energy graph.

💡Brake Temperature Indicators

Brake temperature indicators are systems that monitor and display the temperature of the brake assemblies. The script mentions both electromechanical and electronic display systems that can alert pilots and maintenance crews to high temperatures, which could indicate potential issues with the brakes.

💡High-Speed Braking

High-speed braking refers to the use of brakes during high-speed taxiing or after an aborted takeoff. The script explains that some accumulators have enough fluid to stop the aircraft from high speeds, while others are only sufficient for maintaining the parking brake. High-speed braking is a critical aspect of aircraft safety, especially in emergency situations.

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