Pneumatics

Question 1

What do large gas turbine a/c use for their pneumatic system

Answer 1

Engine bleed air

Question 2

Small a/c have a pneumatic system driven by

Answer 2

A vacuum pump driven by the engine via a quill shaft

Question 3

What is quill drive designed to do if the torque load becomes excessive

Answer 3

Designed to shear if the torque load becomes excessive

Question 4

Some older turboprop and piston engined a/c use pneumatics for

Answer 4

L/d gear

Brakes

Flaps

Question 5

Moisture separator

Answer 5

Prevents ice buildup which could come from moist air - takes the moisture out

Question 6

Desiccator

Answer 6

Picks up any excess moisture after the moisture separator

Question 7

When is the emerg system used - pneumatics blower system

Answer 7

When the isolation valve is closed

Question 8

Adv and disadv of an air pressure system

Answer 8

Won’t run out

More dangerous - high pressure system - you can’t see if there is a leak

Cheaper, simpler and lighter

Question 9

Blower

Answer 9

Sucks air in - compressor

Question 10

Mass flow control valve - blower system

Answer 10

Controls the mass flow to maintain the correct amount in the cabin - will send a signal to the spill valve to open/close to maintain the correct mass of air

Question 11

Choke valve purpose and how it works

Answer 11

Located in the cabin blower system - purpose - raise the temp of the air if required

How - applying a back pressure to the blower

Question 12

Pack valve

Answer 12

Controls the air conditioning - either on/off

Question 13

How does the a/c regulate the mass flow for an a/c using bleed air for pneumatics

Answer 13

Mass flow controller sends a signal to the variable metering orifice which opens and closes to maintain the correct mass flow

Question 14

Bleed air is fed from

Answer 14

From the LP stages of the Hp compressor

From the engine compressor

Question 15

Bleed air is cooled by

Answer 15

An air conditioning pack

Question 16

Isolation valve

Answer 16

Allows each pneumatic system to work in isolation - once opened one engine can supply both engines

Question 17

HPSOV

Answer 17

Designed to open slowly on eng start to prevent a surge of air pressure - also req to close quickly to stop smoke and fumes reaching the cabin

Question 18

Materials for pneumatics

Answer 18

Plastic and fibre glass for low pressure systems

Stainless steel for high pressure systems

Question 19

Normal cause of overpressure - pneumatics

Answer 19

Usually caused by the failure of the high pressure shut off valve - sensor drives the valve shut

Question 20

Safety device to prevent overheat

Answer 20

Electrical temp switch downstream of the bleed air control valve will close the valve

Question 21

Overheat action by the pilot - pneumatics

Answer 21

Close the bleed switch and then open the isolation valve to make up for the lost system - allows 1 engine to supply both a/c packs

Question 22

Light a/c obtain hot air from and the possible risk

Answer 22

A heat exchanger wrapped around the exhaust this is then mixed with cold air - risk of carbon monoxide

Can also receive to air from a combustion heater

Question 23

Combustion heater

Answer 23

Burns fuel to generate heat and warm the air

Separated heating to keep you warm

Takes heat from the fuel the tanks and burns it

Question 24

Safety devices required with a combustion heater

Answer 24

Automatic fuel shutoff

Adequate fire protection

Question 25

Purpose of air conditioning

Answer 25

To supply a constant delivery of clean air, to the cockpit and cabin, within a set temp range

Question 26

What is conditioned air

Answer 26

Air which is treated for pressure and temp

Question 27

Do we control humidity

Answer 27

No

We take all the water out and put a little back in

Question 28

Fresh air requirements

Answer 28

1 pound of fresh air per seat per min under normal circumstances

0.5 pound of fresh air per seat per min following a failure of any part of the system - lowest is can be

Between 18 - 24*C

Question 29

At 40,000ft the humidity is about

Answer 29

1-2%

Ideally it should be about 30%

Question 30

Carbon monoxide contamination not to exceed

Answer 30

1 part in 20,000 - legal limit

Question 31

Bootstrap (air cycle) system consists of

Answer 31

In the specific order of 
Primary heat exchanger (precooler)
Compressor 
Secondary heat exchanger (intercooler)
Turbine 

It is the combined effect of the secondary heat exchanger and the turbine = cooling

Question 32

Bootstrap system is most efficient at

Answer 32

High mass flow values

Question 33

Cold air unit/air cycle machine in a bootstrap system is made up of

Answer 33

Compressor, shaft, turbine

Question 34

When stationary/slow in the air - how does the a/c provide ram air

Answer 34

Uses a fan powered by an electric motor - electrically driven of by a third wheel on the cold air unit

Question 35

2 types of water separators and where it is located

Answer 35

Impingement or centrifugal

Located downstream of the turbine/ air cooler

Question 36

Centrifugal water separator

Answer 36

Air-driven fan throws water outwards - water is drained and collected

Question 37

Impingement water separator

Answer 37

Moisture sticks to the cold collector tubes and collects at the bottom

Question 38

How does the humidifier work

Answer 38

Same as a carburettor- air tube - sucks water out and into the airflow

Question 39

What is the recirculating fans

Answer 39

Draws air from underfloor area through filters and is reintroduced into the conditioned distribution system - prevents stagnation

Question 40

What is gasper air

Answer 40

Cold conditioned air supplied to the pax through punkah louvres

Question 41

Trim air

Answer 41

Low pressure, high temp air

Allows us to control different temps in each cabin