Aircraft Systems Flashcards
1
Q
Pascal’s principle
A
Pressure applied to an enclosed incompressible fluid will be transmitted without a change in magnitude to every point of the fluid and to the walls of the container.
The pressure at any point in the fluid is equal in all directions.
2
Q
Mechanical advantage
A
The advantage we can get by using a mechanism to transmit force
3
Q
Gaining mechanical advantage hydraulically
A
- Using Pascal’s principle
- A small force can move a heavier object
4
Q
Advantages of aircraft hydraulic systems
A
- Relatively lightweight
- Efficient at transmitting force
- Minimal maintenance required
5
Q
Hydraulic pumps
A
- What hydraulic systems are powered by
- Engine or auxiliary power unit driven
- Pumps create hydraulic pressure by forcing the hydraulic fluid through the system
6
Q
Vane type hydraulic pump
A
- Designed to move large volume at low pressure.
- Change the volume between adjacent vines due to the rotor’s eccentric mounting positions
- Efficiency decreases with increasing fluid viscosity
7
Q
Geared type hydraulic pump
A
- Fluid is moved from the inlet to the outlet around the casing
- When the teeth of the gears engage on the discharge end of the pump, the amount of space decreases, causing medium volume of fluid to be expelled
- Susceptible to wear and tear
8
Q
Piston type hydraulic pump
A
- Used in larger aircraft
- Rotating cylinder made to move pistons up and down generating suction at the inlet and discharge pressure at the outlet
9
Q
Hang type hydraulic pump
A
- Mainly used in GA aircraft as a backup in case of system failure
10
Q
Open centre hydraulic system
A
- Hydraulic fluid circulates freely from the reservoir through the open valves and back to the reservoir
- The selector valve redirects the fluid to move to the actuator
- Requires relatively low hydraulic pressure to operate
11
Q
Pressurised system
A
- Accumulator maintains pressure in the system at all times
- unloading valve removes pressure from the pump when no service 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 he pressure in the system decreases
- Unloading valve allows the hydraulic fluid from the pump to flow back into the system
12
Q
Mineral base hydraulic oil
A
- Petrol based
- Anti-corrosion
- Anti-foaming
- Little change to viscosity with temperature
- Cannot be sued with rubber seals (corrosion)
- Flammable
- RED
13
Q
Vegetable based hydraulic oil
A
- Blend of castor and alcohol
- Have been used on older aircraft
- Not suitable for higher pressure systems
- Prone to smudging and causing corrosion
- BLUE
14
Q
Synthetic based hydraulic oil
A
- Made from Organophosphates = alcohol + phosphoric acid
- Perform better at higher temperatures and pressures
- Almost flameproof
- Hydroscopic (attract and retain water)
- Very corrosive
- GREEN, PURPLE, AMBER
15
Q
Pneumatic system
A
- Use of compressed air to actuate aircraft services
- Similar to hydraulic system
- However, doesn’t transfer pressure as well as hydraulic fluid
- Air is unlimited
- Lighter and simpler than hydraulic
- No fire hazard
- Air tight seals and tracing leaks
- Not suitable for heavy equipment
- Precise control is not possible
16
Q
Operation of a pneumatic system
A
- Compressed air is drawn from the bleed air valve and is compressed using an air compressor.
- Air from the source is cooled down through an intercooler
- Compressed air passes through a metal filter
- Air pressure in the system is controlled by a pressure regulartor
- Compressed air is distributed through out the aircraft via pneumatic lines
Pneumatic systems can also be used for emergency situations.
17
Q
Thermo-couple fire warning system
A
- Two types of metal that when heated, produce a small voltage
- Once the voltage reaches a certain level is triggers a relay switch which will activate the fire warning system
- Is a probe, so can only detect fire when the flame or the heat reaches the probe
- Doesn’t require an external source of electricity
18
Q
Bi-metallic switch fire warning system
A
- Two strips of different metal stuck together
- When heated, one metal strip will expand faster than the other resulting in them both bending.
- It then makes contact with a switch which closes the fire warning circuit
- Can only detect fire if it is right next to it
Fire detection systems usually use multiple thermo-couple or bi-metallic probes arranged in parallel
19
Q
Continuous loop fire warning systems
A
- Conducting wire passing through a conducting casing
- wire is connected to a power supply and the case is connected to the earth
- When heated is applied, the thermistor material looses its resistance capability and a connection is made between the central wire and the case
20
Q
Fire extinguishers - CO2 fire extinguisher
A
- Well suited for electrical and liquid fires caused by fuel or hydraulic fluid.
- Don’t leave residue that might harm sensitive equipment
- Aren’t commonly found in aircraft cabin as they displace oxygen and present a risk of asphyxiation.
21
Q
Methyl bromide fire extinguisher
A
- Extensively used in aviation due to its excellent fire suppression properties and its low residue output
- Safe around aircraft electronics
- Typically used in cargo bays and engine compartments
- Very toxic - not used in cockpit or cabin
22
Q
Dry powder fire extinguisher
A
- Powdered extinguishing agent expelled under pressure
- It blankets the fire and interrupts the chemical reaction of the fire
23
Q
Fire extinguisher system
A
- Fire extinguishing agents are stored in cylinders
- Discharge of the agent can often be controlled to provide an initial burst to extinguish the fire and then a slower sustained release to prevent reigniting.
24
Q
Safety features on high pressure cylinders.
A
- Pressure gauge - indicates the pressure of the agent inside the cylinder. Used to verify that the cylinder is charge and read for use
- Pressure relief valve - valve opens to release pressure if it exceeds a specified limit, preventing the cylinder from bursting in case of overpressure
25
Q
Ice accumulation dangers
A
- Lift reduction, increasing the stall speed
- Control problems, control surfaces are harder to move, reducing effectiveness.
- Weight increase, reducing performance and increasing fuel consumption
- Decreased engine performance, reduces engine power
- Instrument malfunction, blocked pitot tubes and static vents
- Visibility reduction
26
Q
Ways of detecting ice
A
- Visually looking
- Vibrating probe
27
Q
Anti-icing systems
A
- Prevent the formation of ice
- Heating surfaces
- Generated electrically or divert hot air from engines
28
Q
De-icing systems
A
- Remove ice
- Inflatable rubber boots on leading edges of wings and tail surfaces
- De-icing fluids
29
Q
Mechanical de-icing
A
- Inflatable boot on leading edges and tail surfaces
- Uses pneumatic system
- Breaks bond between ice and boot’s surface
- Disrupt smooth airflow over the wind which can reduce lift and increase drag momentarily
30
Q
Fluid de-icing
A
- AKA weeping wings of TKS systems provide an active method of preventing the accumulation of ice on an aircraft.
- Typically used for anti-icing, but also function as de-icing
- Built on leading edges of aircraft
31
Q
Thermal de-icing
A
- AKA heated surface anti-icing or bleed air anti-icing
- Hot air is bled off from the compressor section of the engines and directed to the surfaces that need to be kept free of ice
32
Q
Windscreen wipers
A
- Generally only fitted of IFR traffic as they need to be able to fly in heavy rain
33
Q
What else repels water droplets?
A
- Hydrophobic film
- Chemically treated windscreens
- Nozzles which sprat a rain repellent onto the windscreen when needed.
34
Q
Bonding strips
A
- Used in aircraft to electrically bond together different components
- To provide a path for electricity to travel safely between different parts of the aircraft
35
Q
Static discharge wicks
A
- On trailing edges of aircraft to eliminate static electricity
- Can cause issues with the aircraft’s communication and navigation systems by creating electrical noise, can cause sparks of electrical discharge
36
Q
Ways oxygen can be stored
A
- Liquid form (LOX)
- Gaseous form (ABO) in a high pressure bottle
37
Q
What does oxygen do when the oxygen system is in use?
A
- Oxygen flows through a regulator that reduces the pressure
38
Q
Constant flow regulator
A
- Simplest deign
- Oxygen will constantly flow at a set rate, regardless of you inhaling or exhaling and regardless of altitude
- When flying lower, the system provides too much oxygen resulting in a waste
39
Q
Diluted demand regulator
A
- More complex system that uses oxygen more efficiently
- Controlled by an aneroid capsule
- Sense is the pilot is inhaling or exhaling providing a flow of oxygen only when inhaling
40
Q
Pressure demand regulator
A
- Works in the same way as a diluted demand but offers a greater pressure to “force” the oxygen into the lungs
- can make is harder to exhale and can be exhausting after awhile.
41
Q
portable oxygen
A
If the crew needs to move around while being under oxygen.
42
Q
Pressurised vs. unpressurised
A
- Unpressurised above 10,000ft - supplementary oxygen is required
- Pressurised only need supplementary oxygen in case of a decompression.
