航空飛機氣動通用系統(tǒng)英文培訓(xùn)課件-

PNEUMATICSGeneralPneumatics,

from

the

Greek

?νευματικ??(means

-

coming

from

the

wind)Pneumatics

was

firstdocumented

in

60

A.DPascal"s

principle,

states

thatpressure

is

constant

throughouta

static

fluid.Pneumatics

are

generally

used

for applications

involving

less

force

than hydraulic

applications.Pneumatics

may

be

contrasted

with hydraulics,

which

uses

incompressible liquid

media

such

as

oil

or

water

instead of

air.Air

is

compressible,

is

considered

to

be

a fluid,

and

most

industrial

applications

use approximately

80

to

100

pounds

persquare

inch

(psi)

gauge

pressure,

ascompared

to

hydraulics

which

arecommonly

used

from

1,000

to

5,000

psi,and

in

some

cases

10,000

psi

and

higher.Both

pneumatics

and

hydraulics

are applications

of

fluid

power.

Physical pneumatic

principles

conclude

that

the pressure

that

forms

in

compressible

liquids can

be

harnessed

to

a

high

potential

of power.Pneumatic

systems

can

provides

compressedair

at

a

constant

flow

rate

to

air

conditioningunits,

where

its

temperature

is

controlled

andit

is

ducted

into

the

cabin.Pressurization

systems,

restricts

the

escape

of air

from

the

cabin

to

maintain

proper pressurization

in

the

cabin.The

pneumatic

system

also

provides compressed

air

for

engine

starting.The

engine

compressors,

auxiliary

power

unit, or

a

ground

unit

can

be

used

to

supply

the pneumatic

system.

The

pneumatic

manifold

is normally

supplied

from

the

engines.

The

APU or

an

external

air

source

may

also

be

used.Instructionalpurposes

onlyPNEUMATICS

-

APPLICATIONSAPPLICATIONSSome

examples-Pressurization-Anti-ice-De-ice-Rain

removal-Lift

enhancement-Air

conditioning-Engine

starting-Pneumatic

braking-OtherPressurizationPressurized

air

for

the

cabin

comes

from

the

compressorstages

in

the

aircraft"s

jet

engines.

Moving

through

thecompressor,

the

outside

air

gets

very

hot

as

it

becomespressurized.

The

portion

drawn

off

for

the

passenger

cabiis

first

cooled

by

heat

exchangers

in

the

engine

struts

anthen,

after

flowing

through

ducting

in

the

wing,

is

furthcooled

by

the

main

air

conditioning

units

under

the

floorthe

cabin.The

cooled

air

then

flows

to

a

chamber

where

it

is mixed

with

an

approximately

equal

amount

of

highly filtered

airfrom

the

passenger

cabin.

The

combined outside

and

filtered

air

is

ducted

to

the

cabin

and distributed

through

overhead

outlets.Compared

to

other

modes

of

transport,

office

buildings andother

enclosed

spaces

occupied

by

large

numbersof

people,

today"s

jetliners

provide

an

environment

this

superior

in

many

respects.

For

example,

in

theheating

and

cooling

seasons,

most

office

buildingsprovide

a

far

lower

percentage

of

outside

air

--

often

alow

as

20

percent

or

even

less.

In

addition,

buildingstypically

have

a

much

lower

air-change

rate,

andthey"re

seldom

equipped

with

high-efficiency

filters

lthose

found

in

airplanes.A

further

advantage

for

airplane

passengers:

theoutside

air

that

enters

jetliner

cabins

at

cruisingaltitudes

is

generally

much

cleaner

than

what

isavailable

for

ventilating

buildings

and

surface

modesof

transportation.Studies

have

confirmedthe

overall

safety

and

effectiveness

of

cabin

air

systems.

One

of

the

studies, conducted

for

the

U.S.

Government,

was

the

most comprehensive

of

all.

It

involved

an

independent

testing service

taking

air

samples

on

92

randomly

selected

airline flights.

The

levels

of

pollutantssuch

as

fungi

and

bacteria were

found

to

be

similar

to

or

lower

than

thoseencountered

in

normal

indoor

environments.

Also,

levels

ofcarbon

dioxide

were

found

to

average

less

than

one-thirdthe

limit

recommended

by

the

American

Conference

ofGovernmental

Industrial

Hygienists.

Studies

conducted

byBoeing

and

by

airlines

have

shown

similar

results.Anti-iceAir

acquired

from

engine

bleed

air

is

used

to

prevent ice

formation

by

using

the

heat

energy

of

the

air

to heat

the

surrounding

surface"s

above

freezing. However

this

system

draws

power

from

the

engine thereby

reducing

thrust

potential.

Some

aircraft direct

this

bleed

air

over

the

front

windshield

for

ice prevention

as

well

as

the

leading

edges

of

the

wingand

tail

surfaces.Instructionalpurposes

onlyDe-iceAir

acquired

from

engine

bleed

air,

vacuum

pumps,

or air

compressors

to

remove

ice

formation

by

using pressure

of

the

air

to

inflate

“boots”

on

the

flight critical

areas

of

the

aircraft.

The

“boots”

inflate break

the

surface

cohesion

of

the

ice

so

the

forward motion

of

the

aircraft

can

blow

it

off.Rain

removalAir

is

acquired

from

engine

bleed

air,

vacuum

pumps,

or

aircompressors

to

remove

rain

from

the

windshield.

This

highvelocity

air

“blows”

away

any

water

that

may

come

in

contwith

that

surface.Instructionalpurposes

onlyLift

enhancementAir

acquired

from

engine

bleed

air,

vacuum

pumps,

or air

compressors

is

directed

to

critical

lift

areas

of

t wing

and

control

surfaces

to

strengthen

theboundary air

next

to

the

wings

surface.AIR

CONDITIONINGAir

conditioning

systems

generate

cool

air

to

the

cabinavital

equipment.

The

source

of

this

cool

air

is

either

inform

two

systems;Freon

based

gas

system.Driven

by

electric

or

mechanical

drive

systemClosed

systemUses

Freon

as

the

heat

transfer

agentAir

based

gas

systemDriven

by

bleed

air

from

the

jet

engines,

or

auxiliary

sourceOpen

systemUses

outside

air

as

the

heat

transfer

agentThe

air

is

compressed,

reaching

the

maximum

pressure

andtemperature

in

the

cycle,

by

a

centrifugal

compressor,

driven

bybleed

air

from

the

jet

engines.

The

hot

air

is

directed

to

aexpansion

turbine

where

it

isexpanded.Thisexpansion

causesthe

air

to

cool

without

a

change

in

pressure.

The

air,

now

cooledis

directed

to

a

mixing

chamber;

here

hot

air

from

the

bleed

airsystem

is

mixed

with

cold

air

from

the

recycling

machine

forentry

to

the

cabin.AIR

CYCLE

DEVICEBASIC

AIR

CYCLE

DEVICEMixing

BoxDrive

TurbineBleed

AirCabin

AirCEDTCold

AirHot

AirCompression and

Expansion

TurbinesInstructionalpurposes

onlyInstructionalpurposes

onlyEngine

startingAir

CartX-bleedEngine

startingInstructionalpurposes

onlyAir

CartX-bleedPneumatic

BrakingThe

pneumatic

braking

system

is

an

alternate

system

and is

a

way

of

providing

pressure

to

main

brakes

in

the

event of

hydraulic

system

failure

installed

on

various

aircrafThere

is

no

anti

skid

or

differential

braking

available

f the

pneumatic

source.

A

pneumatic

brake

control

valve operated

by

a

handle

on

the

captain"s

instrument

panel opens

andmodulates

air

bottle

pressure

to

a

transfer

tub Pressurized

hydraulic

fluid

from

this

tube

is

routed

toa shuttle

valve

on

each

mainwheel

brake.

The

shuttle

valve moves

to

block

the

hydraulic

pressure

port

of

the

main brake

line

and

permits

fluid

from

this

tube

to

apply

the brakes.

Pneumatic

braking

is

only

used

when

hydraulic pressure

is

lost.Instructionalpurposes

onlyOther

ApplicationsDiscussA

few

questions…..1.

Air

conditioning

units

(open

system)

useoutside

air

as

the

heat

transfer

agent.True

/

False1.

Air

conditioning

units

(open

system)

useoutside

air

as

the

heat

transfer

agent.True2.

Pneumatics

are

generally

used

for

applications involving

force

than

hydraulic

applicationMore

/

Less2.

Pneumatics

are

generally

used

for

applications involving

force

than

hydraulic

applicationLess3.

Anti-skid

or

differential

braking

will

not

be available

when

using

pneumatic

brakes.True

/

False3.

Anti-skid

or

differential

braking

will

not

be available

when

using

pneumatic

brakes.True4.

A

centrifugal

compressor,

compresses

air

to increase

its

&

.4.

A

centrifugal

compressor,

compresses

air

to increase

its

Pressure

&

Temperature.5.

Some

aircraft

anti-ice

systems

draw

powerf