Cabin Atmospheric Control Systems

8/3/2019 Cabin Atmospheric Control Systems

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Cabin Atmospheric ControlSystems

By: Eric Spoor

Information in this section was taken from:Transport Category Aircraft Systemsp.2-1through 2-25Aircraft Maintenance and Repairp.506-548


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Cabin Atmospheric

Control Systems Heating Systems Cooling Systems Pressurization Systems Oxygen Systems


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Heating Systems

Exhaust Heating Systems Combustion Heater Systems Electric Heating Systems Bleed Air Heating Systems


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Exhaust Heating Systems

Exhaust heating systems are thesimplest of aircraft heating systems andare used on most light aircraft

The systems components includeo A heater muff around the exhaust stackso An air scoop to direst ram air into the heater

muffo Ducting to carry the heated air into the cabin


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Combustion Heater Systems

Combustion heaters or surfacecombustion heaters are often used toheat the cabin of larger, more expensiveaircraft

This type of heater burns the aircrafts

fuel in a combustion chamber or tube todevelop required heat

Air flowing around the tube is heated

and ducted to the cabin


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Electric Heating Systems

These systems provide cabin heat whenthe aircraft is on the ground and enginesare not running

Electric heaters are often used on smallturbo-prop aircraft

Air is taken from the cabin, passed overelectric heater coils, and returned to thecabin


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Bleed Air Heating Systems

Bleed air heating systems are used onunpressurized turbine-engine aircraft

Extremely hot compressor bleed air isducted into a chamber where it is mixedwith ambient or recirculated air to cool

the air to a useable temperature This air mixture is then ducted into the

cabin


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Bleed Air Heating Systems

(cont.)

This system contains several safetyfeatureso Temperature sensors prevent excessive heat

from entering the cabino Check valves to prevent a loss of

compressor bleed air when starting theengine and when full power is required

o Engine sensors eliminate the bleed system ifthe engine becomes inoperative


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Cabin Cooling Systems

Aircraft-cooling systems are used to coolair inside the aircraft for passenger andcrew comfort

There are two basic methods of coolingcabin air, they are:o Freon Vapor-Cycle Cooling Systemso Air-Cycle Cooling Systems


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Vapor-Cycle Cooling

Systems Vapor-cycle cooling systems are used

on reciprocating-engine aircraft and insome small turboprop aircraft

This is a closed system that uses theevaporation and condensation of freon

to remove heat from the cabin


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Air-Cycle Cooling Systems

Air-cycle cooling systems are used onmodern large turbine-powered aircraft

These systems use the compressionand expansion of air to adjust thetemperature in passenger and crew

compartments


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Cabin Pressurization

Systems Cabin pressurization provides a

comfortable environment for passengersand crew while allowing the aircraft to flyat higher altitudes

Flying at high altitudes is more fuel

efficient and it allows the aircraft to flyabove most undesirable weatherconditions


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Aircraft Structures

If an aircraft is to be pressurized, thepressurized section (pressure vessel) must be

strong enough to withstand operationalstresses

In general, the maximum altitude at which anaircraft can fly is limited by the maximum

allowable cabin differential pressureo Cabin differential pressure is the pressure

difference between ambient air and the air insidethe pressure vessel


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Aircraft Structures (cont.)

The stronger the aircraft structure, the higherthe allowed differential pressure will be

General cabin pressure differentials allowed bydifferent aircraft types:o Light aircraft approx. 3-5 psio Large reciprocating-engine aircraft approx. 5.5 psio

Turbine-powered transport aircraft approx. 9psi


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Sources of Pressurization

The source of aircraft pressure variesdepending on the type of engineinstalled on the aircraft and aircraftdesign

Although the specific method of

pressurizing cabin air varies betweendifferent aircraft, pressurization is alwaysdone, in some form, by the aircraft

engines


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Reciprocating Engines

Reciprocating engines can pressurize cabin airthrough the use of:o Superchargerso Turbochargerso Engine-driven air pumps

The use on superchargers and turbochargers

for pressurized air:

o May introduce fumes and oil into the cabin airo Greatly reduces engine power output


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Turbine-engines

Turbine-engine aircraft usually utilizeengine bleed air for pressurization

In these systems, high pressure air isbled from the turbine-enginescompressor

This also causes a reduction in enginepower but it is not as significant of a loss


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Independent Cabin

Compressors Some aircraft use independent cabin

compressors for pressurization which are used

to eliminate the problem of air contamination Independent cabin compressors are driven byeither:o The engine accessory sectiono Turbine-engine bleed air These compressors may use one of two types

of pumps:o Roots-type positive displacement pumpso

Centrifugal cabin compressors


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Pressurization System

Components Heat exchanger

o used to cool the hot pressurized air to a usable

temperature Outflow valveo primary cabin pressure control, regulates the

amount of pressurized air that is allowed to exit thecabin

Safety valve (positive pressure relief valve)o prevents cabin over-pressurization by opening

automatically at a predetermined pressure


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Pressurization System

Components (cont.) Negative pressure-relief valve

o Prevents cabin pressure from going below

that of the ambient air Dump valve

o Releases all cabin pressure when aircraftlands

o Often controlled by landing gear squat switch


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Oxygen Systems

Oxygen systems are required on aircraftthat operate for extended periods above10,000 ft

The two types of oxygen systems areused on private and commercial aircraft

are:o Stored-gas Oxygen Systemso Chemical or Solid State Oxygen Systems


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Stored-Gas Oxygen Systems

Stored-gas oxygen systems use oxygencylinders (bottles) to hold the aircrafts

oxygen supply Oxygen bottles may be:

o high-pressureo

low-pressure


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Stored-Gas Oxygen Systems

High-pressure bottleso Contain oxygen at 1800psio Green in color

o Labeled Aviators Breathing Oxygen

Low-pressureo Contain oxygen at 450psio Yellow in coloro Labeled Aviators Breathing Oxygen


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Chemical or Solid State

Oxygen Systems There are many advantages of using

solid-state oxygen systemso Safeo Lower in cost than stored-gas systemso Comparatively maintenance free

Cabin Atmospheric Control Systems

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