Support Systems

Question 1

State pascals principal

Answer 1

If pressure is applied at any point to that liquid in a closed system, that same pressure will be felt throughout the system.

Question 2

Describe mechanical advantage, and how it can be gained hydraulically.

Answer 2

The gain made whenever a small force is used to create a larger force.

As hydraulic fluid cannot be compressed, any pressure applied to it will be felt throughout the system. E.g. applying 1.1lb of pressure to the piston will cause 1.1lb of pressure to be felt throughout the whole system.

Question 3

Explain the advantages of using hydraulics to operate aircraft services.

Answer 3

• Relatively lightweight
• Efficient at transmitting force (not much lost due to friction)
• Minimal maintenance required

Question 4

What does hydraulic fluid do?

Answer 4

Assist with lubrication,cooling and to provide as little friction as possible.

Question 5

Differentiate between the three types of hydraulic oil (2,6,5)

Answer 5

Vegetable base

• prone to forming sludge and cause corrosion.
• BLUE in colour

Mineral base

• kerosene type petrochemical that has good lubrication qualities
• anti foaming and corrosion additives
• little changes in viscosity with temperature.
• Cannot be used with natural rubber seals
• very flammable
• RED

Synthetic

• Better at higher temperatures and pressures than other hydraulic fluids
• Almost flameproof
• Hydroscopic (attracts moisture) so must be handled carefully
• Is also very corrosive
• Coloured Purple, Green or Amber depending on the grade

Question 6

Describe the function of common hydraulic system components including:
(a) reservoir (unpressurised and pressurised)

Answer 6

(A) holds reserve of hydraulic fluid and protection for any leaks, provides an expansion chamber and helps purge air out.

Unpressurised - vented to atmosphere, typically used for small GA

Pressurised - for higher altitude and higher demands, ensures positive pressure to the pump, pressurised by nitrogen

(B)

Question 7

Describe the function of the pump and distinguish the different types. Hand, vane, gear, piston

Answer 7

Generates pressure within system and delivers it into the operating lines.

Hand pump
Double acting type, source of pressure if main pump not working. Typically used as backup

Vane type pump
Large volume, low pressure. Like a water wheel. driven off the engine

Gear type pump
Medium volume, pressure up to 1500PSI, driven off the engine.

Piston pump
Low volume per pump but pressure is up to 3500 PSI, a hydraulic system using pressure pump is likely to have multiple.

Question 8

Describe the function of pressure regulator

Answer 8

Prevent pressure build up and damaging components or causing a leak, it sets the hydraulic system’s operating pressure. Excess pressure is released back to the pump inlet or to the reservoir.

Question 9

Describe the function of the accumulators

Answer 9

Enables a hydraulic system to cope with extremes of demand using a less powerful pump, to respond more quickly to a temporary demand to smooth out pulsations.

Stores hydraulic pressure with the gas maintaining hydraulic pressure.

Question 10

What are the three types of accumulators?

Answer 10

Diaphragm accumulator

Bladder accumulator

Piston accumulator

Question 11

What are check valves

Answer 11

Prevent the reverse flow of fluid in a system. Also prevent loss of fluid from any leak upstream the valve

Question 12

What are pressure relief valves

Answer 12

Limits the amount of pressure in various parts of the system.

The last relief of any additional pressure you don’t want.

Question 13

what are selector valves

Answer 13

Change the way the piston actuates itself and is used to direct hydraulic fluid for system operation.

Initiates movement of actuators and controls direction of their movement.

Mechanical, electronic, or remote controlled.

Question 14

What are actuators

Answer 14

Used to convert pressure energy into mechanical force to do work.

Linear actuator (hydraulic jack) consists of a cylinder and piston which is attached to a piston rod.

Cylinder is attached to the airframe structure and this piston is attached to whatever component requires moving.

Question 15

What are filters

Answer 15

Part of system with the aim of removing all solid particles as contamination can affect your hydraulic system

Question 16

What are the types of hydraulic systems

Answer 16

Temporary pressure
- Where pressure is only developed in the system when required

Pressurised system
- maintained at all times within the hydraulic lines

Question 17

Describe the operation of temporary pressure systems (manual and open centre)

Answer 17

Manual pump control
- engine driven pump which draws fluid from the reservoir. if not required the fluid goes back to the reservoir.

When required though, pilot closes the pump control valve and actuates the system needed

Open centre system
- Minimises complexity of a hydraulic system for small and medium aircraft. Fluid circulates freely if not required.

When no system is needed, fluid flows from the reservoir through the open valves back to the reservoir.

Question 18

Describe the operation of pressurised systems

Answer 18

An accumulator maintains pressure in the system at all times. An unloading valve removes pressure from the pump when no service (gear, flaps, flight controls, etc) is being used

This valve allows the unneeded hydraulic fluid to flow back to the reservoir. When a service is activated, a valve is open and the pressure in the system decreases. The unloading valve will then allow hydraulic fluid from the pump to flow back into the system

Question 19

What are the use of pneumatic systems and when is it typically used.

Answer 19

Use of compressed air to actuate aircraft services.

Tend to be used for smaller applications not requiring a lot of force, such as de-icing boots.

Question 20

Advantages of pneumatic systems

Answer 20

• Air is unlimited
• Light weight - both the air and a pneumatic system are light
• Simplicity - reasonably simply construction
• No fire hazard

Question 21

Disadvantages of pneumatic system

Answer 21

• Not suitable for operation of large or heavy
• Air tight seals – these would be very difficult to obtain and maintain
• Tracing leaks – extremely difficult
• Compressed air is ‘springy’ and as such not suitable for use where precise control of something is required, and the springiness results in a delay in operating controls –undesirable in some cases

Question 22

Describe the operation of a typical pneumatic system

Answer 22

Compressor, compresses air which then goes into the unloading valve incase theres too much pressure, the excess air is then sent to ground charging valve.

A moisture separator is used to seperate any excess moisture due to compression which is then sent to a desiccant to get rid of the moisture.

Goes through a filter and to a one way check valve, then to a primary bottle and emergency then into whatever item is used to move.

Question 23

Describe the typical operation of hydraulic systems

Question 24

Distinguish between anti-icing and de-icing systems

Answer 24

Anti-ice
- prevents before ice form

De-ice
- used after ice has formed

Question 25

Describe use of mechanical ice protection systems

Answer 25

Inflation and deflation of deicing boots. Air supplied by an engine driven air pump or by bleed air. Operation should be delayed until ice has reached 5mm depth as thinner ice may not crack and fall off, But don’t delay too long either or the ice may not be able to be removed

Question 26

Describe use of fluid ice protection

Answer 26

Melt ice by lowering its freezing point. Only a limited amount of de-icing fluid can be carried and is usually used for propellers and windscreens,

Question 27

Describe use of thermal ice protection

Answer 27

Heat is used to melt and keep ice away Can be heat from engine bleed air or by electrical heating, Activated prior to icing conditions being encountered. Common electrically heated components are pitot tubes, windscreens and propellers

Question 28

Describe typical systems for: (A) ice detection (b) windscreen heating; (c) rain clearance.

Answer 28

Ice detection •Ice can be detected visually, however, larger aircraft also have an ice detection system •Optical transducer on the aircraft which measures the opactity and reflective index of liquid on the probe •If it detects ice, a notification is made in the cockpit Windscreen heating •A thin heater element is placed between the layers of windscreen glass •A thermostat is included as over heating of the windscreen may lead to fatigue and cracking Rain clearance ``` Fitted to some light twin aircraft, and most larger aircraft •Several types of systems in use •Windscreen wipers •Bleed air •Chemical applied to the windscreen ```

Question 29

Describe the performance reductions associated with - ice accumulation - operation of anti-iced and de-ice equipment

Answer 29

Ice - increase weight therefore higher stall speed, more drag. Stability and controllability of the aircraft. - if not used, ice may not be able to be removed.

Question 30

Explain the function and operation of: (A) static discharge wicks (B) bonding strips

Answer 30

(A) to allow static charge to go back into the atmosphere. Typically found on trailing edges. They’re built up with hundreds of carbon fibres enclosed in a flexible wrapping. (B) to keep all parts of an aircraft at the same static charge. Consist of braided low-resistance metal strips or an adhesive tape.

Question 31

Describe the operation of the three typical fire detection system

Answer 31

Thermocouple - two dissimilar metals are used and when heated will produce a small voltage which is fed to a relay which trips a circuit activating the warning. Bi-metallic strip - armature made of two different metals are used, these will expand at different rates, causing it to bend which closes a circuit which then closes a relay activating the warning. Continuous loop - thermistor material contained within a wire running inside the aircraft. If the thermistor materials reaches a certain temperature, it’ll conduct electricity and trip a relay. The thermistor stops conducting electricity if temp reduces to normal.

Question 32

Explain any precautions taken when using common fire extinguishers and describe typical fire extinguishing systems

Answer 32

Carbon dioxide •For cargo compartments and engine bays, sometimes in the cabin Methyl Bromide •Highly toxic and being phased out of service. For engine bays only Dry powder •Commonly found in hand held extinguishers, and for use in the cabin * Halon (“halogenated hydrocarbons”) * Being phased out as it destroys the Ozone layer. Banned for new systems since 1994 •Hydrofluorocompounds (HFCs)

Question 33

What is found within the engines and the APU sometimes?

Answer 33

Extinguishing agent is kept in pressurised bottles.

Question 34

Describe the function of a cockpit fitted or portable oxygen system

Answer 34

When Oxygen is carried on an aircraft, it can be installed (fixed) in place or a portable system •Generally the only place with fixed Oxygen will be the cockpit •Portable systems can be used by flight attendants, or by pilots if Oxygen is only carried on some flights (eg: dropping skydivers

Question 35

Principle of operation of constant flow oxygen systems

Answer 35

Simplest, cheapest, commonly found in GA aircraft •Consists of tank/s, a regulator and delivery hose manifold •O2 is stored at around 2200 psi, reduced by the regulator to 20-75 psi •Built in systems have the manifold installed in the aircraft •Portable systems may have the manifold as part of the regulator •A flow indicator gives a visual indication that the system is providing O2 •Same flow rate regardless of the altitude

Question 36

Principle of operation of altitude adjustable oxygen

Answer 36

Similar to a Constant Flow system except that the flow of O2 can be adjusted by the user, depending on the altitude •Not a common feature but where it exists and is used, it saves on O2 consumption

Question 37

Principle of operation of altitude compensating oxygen

Answer 37

Similar to an Altitude Adjustable system except that the flow of O2 is regulated automatically based on cabin altitude •More expensive system so generally only found on more expensive aircraft