Skyhawke Hanger

Question 1

What is the purpose of a large a/c electrical system?

Answer 1

Generate, regulate and distribute electrical power, same as a light a/c.

Question 2

What differences are there between light and heavy a/c electrical systems?

Answer 2

More than one system (for redundancy) and can be a mixture of AC/DC circuits.
AC more common, largely due to lightweight alternator attached to each engine and greater power demands. They also have smaller gauge wire.

Question 3

What purposes are fuses, CB and overload switches?

Answer 3

Prevent current overload.

Fuses melt, CB pop (reset once), overload switches are on/off switches.

Question 4

What is an essential bus?

Answer 4

System where electrical power supply is routed through a common bar, which is attached to various electrical components.
Purpose is so that electrical systems are broken down into channels and therefore prioritised in case of reduced supply of power.

Question 5

What 3 types of bus bar are there?

Answer 5

Parallel, split or split-parallel.

Question 6

What use is DC power? What is the major problem with DC power in a/c?

Answer 6

Is the way batteries are charged, but also powers some components. However, AC power is supplied so is rectified by using full wave rectifier.
DC circuits have own bus bar so can be isolated from AC circuits.

Question 7

Is AC possible from DC?

Answer 7

Yes, if necessary can be done by operating a static inverter from DC battery.

Question 8

What must be done before AC generators can be connected in parallel?

Answer 8

Output voltage, frequency and phase of rotation of all generators are the same.

Question 9

Will an emergency lighting system work in case of electrical failure?

Answer 9

Yes, needs to be armed and is auto activated.

Question 10

What purpose is a CSD?

Answer 10

A constant speed drive is required to produce a constant frequency power supply of approx 400hz.
An alternator output frequency is determined by rotation of armature which is driven by the engine, which does not operate at a constant speed. Hence the need for a CSD (works of CFF flyweights balanced by springs).

Question 11

What is the most common CSD used?

Answer 11

Hydro mechanical.

Mechanical governors maintain rotation speed for this type.

Question 12

What should happen in case of generator/gearbox malfunction? (In terms of CSD)

Answer 12

Disconnect engine drive from CSD by pulling “GEN DISC” switch. Once disconnected can’t be reset.

Side note) pull switch activates solenoid which pulls dog clutch switch open, breaking connection.

Question 13

What is the CSD/generator combo called on Airbus/Boeing?

Answer 13

Integrated drive generators (IDG) Boeing.

Integrated constant speed drive (ICSD) Airbus.

Question 14

Purpose of aircon and pressurisation system?

Is cargo compartment pressurised?

Answer 14

Supply conditioned air for heating/cooling of cockpit/cabin & a safe/comfortable environment.
Some compartments (avionics) require aircon to prevent condensation from heat build up.
Cargo compartments are usually pressurised (but not always air conditioned). Can be air conditioned for animals.

Question 15

What is the approx cabin altitude? What is the issue with this?
How is the cabin pressurised? At what rate?

Answer 15

8000ft.
Pressure differential between cabin and outside pressure altitude. As 8000ft is standard, further a/c climbs the greater the differential.
Cabin air outflow (outflow valve centrally located in cabin) less than air con inflow (usually from engines— air con unit) until they match at desired cabin pressure. This is normal ops. Can’t be excessive so that passengers feel uncomfortable (cabin pressure controller… determined by rate controller).
0.26PSI/min climb, 0.16PSI/min descent.
To certify, cabin PD max must be doubled without failure.

Question 16

What is the target PD?
What happens if over pressurisation occurs?
What about if cabin px

Answer 16

8.9PSID.
A positive pressure relief valve opens automatically at a predetermined value set on the ground so cabin pressure never exceeds a given value.
This is not allowed to happen so a negative pressure relief valve is set at 0.5PSI so cabin pressure is never below the outside pressure.
These are located at the rear of the a/c.

Question 17

What is a dump valve? Where is it located?

What components make up the safety valve?

Answer 17

Dump valve drops any residual pressure on landing, activated by landing squat switch (WOW) but can be manually activated too. Located front of a/c.
 X3 Dump (emergency depressurisation), negative/positive pressure relief valve.

Question 18

What can be selected on the cockpit environmental system panel?

Answer 18

Simple as OFF, NORMAL, RAM.
Can set different temperatures in cockpit/cabin sections.
Cabin pressure controller, rate selector, landing altitude selector, baro pressure selector, emergency controls and warning lights in conjunction with CWP.
If APU a an operate the panel this option will be available.

Question 19

Describe how a refrigerant works to cool a cabin

Answer 19

Heat can be added/removed from a refrigerant without changing its temperature during a state change.
As a refrigerant turns from a liquid to vapour in doing so requires heat energy so absorbs this heat from the cabin. This gas then turns back into a liquid, giving off heat but outside the a/c cabin and returns to the a/c cabin to absorb more heat in a continuous cycle.

Question 20

Name the most common refrigerant used in a/c. Why is this the most common?

Answer 20

R-12 (AKA Freon-12, Genetron-12, Isotron-12, Ucon-12).
It is a stable compound at low and high temperatures and does not react with any substance in the air con system (ie rubber for hoses/seals). Is colourless and basically odourless.
Note: is a different substance if the number is different.

Question 21

What two types of O2 systems are available in an emergency?

Give a brief explanation of both

Answer 21

Continuous flow is the simplest. Flow is immediate and continuous.
Pressure demand has a diluter-demand regulator which provides O2 but only as person breathes in, prolonging duration of O2 supply. It also dilutes the O2 with suitable amounts of atmospheric air at all altitudes below 34000ft further prolonging supply.

Question 22

Where is the diluted-demand system more commonly found?

What should the O2 system be set to in case of smoke/contaminate in the cockpit?

Answer 22

On the flight deck as prolonged supply is more beneficial until a suitable altitude has been reached. Continuous for PAX.
Should be set to 100% O2.

Question 23

What are the advantages/disadvantages of a chemical O2 system?
What about a gaseous?

Answer 23

A: Lightweight, less maintenance, less equipment (less space consumed)
D: Greater fire risk, not tamper proof, won’t turn off

Gaseous are the opposite.

Question 24

What systems are onboard to protect against fire?

Answer 24

Overheat, smoke and fire protection systems.

Where fire protections can be broken into detection and extinguishing systems.

Question 25

What type of fire system is usually found in toilets and some cargo compartments?

Answer 25

Eutetic head (squib) which melts at 70-75*C so extinguishing agent can leave the bottle.

Question 26

What types of extinguishing agents are there? How do they work?

Answer 26

Water: cools fire and displaces O2 (no electrical fires)
CO2/N (insert cold gases): displaced O2 (electrical fires)
Dry chemical/powder: smothers fire so excludes O2 (any type of fire-not used in cockpit)
Halogenated hydrocarbons: chemically interferes with combustion

Question 27

Explain why halogenated hydrocarbons are the fire extinguishers of choice in a cockpit.
Any disadvantages?

Answer 27

AKA freons (HALON 1301/1211).
Low toxicity.
Is more effective at lower concentrations, so can put out fires without depriving people of O2.
No residue if left after fire.
Effective on all fire types.
Can be contained in personnel compartments as compact.

Availability issues as environmentally damaging to ozone.

Question 28

How does a single wire thermal switch work?

Answer 28

28V DC is applied to both paths and if an overheat alarm/fire occurs which closes a switch, the path is complete creating a circuit. This arrangement means one open circuit and system will still provide fire protection at all the fire surveillance points.
A test switch tests entire loop.
Short circuit will provide false alarm.

Question 29

How does a pneumatic fire protection system work?

Answer 29

Tube contains a gas which will expand as fire heats up gas. At a given temp the pressure of the gas will overcome a check valve pressing on a diaphragm which contacts an alarm sensor (completes circuit).
As the temperature drops the gas pressure will drop and diaphragm pushing air back and alarm is no longer activated.

Question 30

How does a smoke detector system work?

Answer 30

Utilise photoelectric cells with light directed towards them. If there is sufficient smoke it refracts the light so the sensor does not pick up on this light and therefore rings a bell.

Question 31

How does the engine nacelle fire extinguishing system work?

Answer 31

Bottle is pressurised to 500-600PSI. A relief valve is a fusible disk which ruptures if it overheats. Can also be activated in the cockpit by an electrical current sent to contractor which detonates an explosive cartridge which shatters a disk allows the discharge of extinguishing agent.

Question 32

What is an issue with control effectiveness at high speeds?

Answer 32

The control effectiveness so great that the flexibility of structures may result in twisting of the wing about torsional axis.
To avoid this, control surfaces can be split. Used in tandem at low speeds but individually (usually inboard ailerons or “flaperons/elevons”) at high speeds.
This is automatically done at high speeds computed by ADC.

Question 33

What extra consideration is there for primary/secondary control surfaces of a swept wing?

Answer 33

Primary controls sometimes require not just split controls but multiple control surfaces.
Secondary controls sometimes require all moving wingtips/tail fins and flying tail planes.

Question 34

When are lift augmentation devices used? Name the common types.

Answer 34

At low speeds and during T/O and landing to reduce speeds/distance.
Slats, slots, flaps and Fowler flaps.

Slotted flaps create a greater negative pressure gap which creates suction to pull control surface back into place.

Question 35

What is a problem with power boosted controls in transonic flight?

Answer 35

Shockwaves can form on the control surface, causing buffeting and these forces are fed back into the control system.
To prevent these forces from reaching the pilot, a power operated irreversible control system is required.

Question 36

How does a power boosted flight control system work?

How many hydraulic systems do modern a/c have?

Answer 36

Flight controls actuate control valves which direct hydraulic fluid to control surface actuators/servo valves known as power control units (PCU).
The pilot actually has no direct feel of flight controls forces so an artificial “q” feel is required to create proportional feel.
Modern a/c have 3 hydraulic systems as redundancy.

Question 37

How does fly by wire work?

Answer 37

Position transducers convert flight control movement to analogue electrical signals, which are sent to actuator control electronics. They are converted to digital signals and sent to flight computers so pilot inputs can be analysed to be sure they are inside flight envelope and adjusted if they are not.
Can be operated by IFS providing auto flight control and feed flight control position to data recorder.

Notes) flight control-CPU-electric signal-actuator

Question 38

Is autoland sensitive?

Answer 38

Some aspects have reduced sensitivity and response rate or are even inhibited.
Glideslope sensitivity is reduced below 200ft RA, 100ft RA AoA protection inhibited so flare can occur.
The pitch trim is often wound back to give elevator sufficient power for flare, so if AP disengaged then large pilot force required.
GA mode is inhibited at 5ft RA.

Question 39

Describe difference between fail passive and fail operational

Answer 39

Fail operational: has capability to tolerate failure of a components and be able to complete an auto land. This is because of 3 coupled AP which are monitored/compared. If 1 AP fails other 2 will work in fail passive. Because of such redundancy, these systems can work in very low vis landings.
Fail passive: 2 AP which are monitored/compared. If one fails/outside of limits both will disengage auto with warning. However, the a/c must be able to remain in steady flight following disengagement so a manual landing can be done. HUD make transition to manual flight less critical so can potentially reduce minima further as these landings are not authorised for very low vis landings.

Question 40

Describe the basic principal of alternator

Answer 40

Stator around rotor which spins. Current generated in stator.
DC required to excite coil.

Question 41

How many rods do the kiddie/fen wall fire detection systems have? What type of fire detection system is it?

Answer 41

Kiddie 2.
Fenwall 1.
Continuous detection

Question 42

What are Lindberg and systron donned systems examples of?

Answer 42

Pressure type fire detection systems (continuous).

Question 43

Benefits of AC?

Answer 43

More economically transmitted over long distances.
Lighter alternator… therefore simple, small and easy to maintain.
Less arcing so need to replace CB less.
Greater power for unit size.
Smaller gauge wire.

Question 44

What is temperature?

Answer 44

Measure of effect of heat on substance.

Question 45

What determines the aerodynamic force on a control surface?

Answer 45

Deflection and dynamic pressure (speed)