15.10 Flashcards
Where does the lubrication system distribute oil to?
Engine bearings
Gearbox
What is the difference between wet and dry sumps?
The dry sump stores the oil in an external tank mounted on/near the engine
What do the wet and dry sumps do?
Recirculate the air whilst maintaining a constant pressure
What can the oil/lubrication system be divided into?
Full-flow and Constant pressure
What system has no way of regulation the oil pressure?
Full flow
In a full flow oil system, what does the oil pressure change with considering it has no means of being regulated?
N2 rotor speed (RPM and engine speed), The oil temperature and the flow areas downstream of the supply pump.
What rotor system is the supply pump driven by?
N2 via the gearbox
What happens as the N2 rotor speed increases?
There is higher flow so higher pressure oil
An increase of oil temperature leads to what sort of viscosity?
Lower viscosity
What does a decrease in oil temperature mean for the pressure?
Decreases
How can you detect a leakage in the oil system?
An increase in total flow area leading to a decrease in oil pressure
What happens if the leak is external?
A decrease in oil quantity and pressure (needs to move faster to compensate for quantity)
What prevents oil pressure from becoming too high?
Pressure relief valve
Where is the pressure relief valve installed in full flow?
Between delivery side and suction side
What is the constant pressure system also called?
The regulated pressure system
What does the constant pressure system have that the full flow system doesn’t?
Pressure regulating valve
What does the pressure regulating valve do in the constant pressure system?
It holds the pressure to a given value no matter the N2 rotor speed
FOR YOUR KNOWLEDGE, how does a full flow system work?
It reaches max pressure at idle then if it needs to exceed that, it will go beyond this making it inefficient
FOR YOUR KNOWLEDGE, how does a constant flow system work?
It reaches max pressure at idle and stays at this pressure even if the power is increased via speed via the N2 compressor
What is the purpose of the fuel systems discussed?
To deliver fuel to the nozzles
In what system do changes in the oil pressure have no effect on temperature?
Constant flow
What (in a constant flow unit) ensures that we have the same pressure regardless of engine speeds?
Pressure regulating system holding the pressure between the vent and the oil pressure
Why is the full flow system the most commonly used system?
It is simple and no adjustments are necessary
What are the two disadvantages of the full flow system?
System needs a large supply pump or relatively high oil pressure when the engines are at idle (leading to high oil pressure at high speeds.)
There is a significant increase in oil temperature after a power reduction (low flow rate)
What two types of cooling can engines use?
Air cooling
Oil cooling
Where is the air taken from for air cooling?
Early stages of compressor
What 3 things can air cooling be used to cool?
Turbine disc
Vanes
Blades
What does the oil require for lubrication?
An oil cooler
What does the use of cooling air reduce?
The quantity of oil to cool the bearings
What are the 4 subsystems that the basic lubrication system has?
Reservoir
Scavenge
Vent
Monitering
What is the purpose of the engine oil system?
To lubricate, cool and clean the bearing and gearboxes in the engine
What does system have the capability of doing to prevent ice formation in fuel?
Heat the engine fuel
What re the 3 subsystems of an oil system?
Storage
Distribution
Indicating
What is the oil tank made from?
Aluminium alloy with a silicone layer
What is the purpose of the silicone layer?
Fire resistance
What are the 2 ways to fill the tank?
Gravity
Pressure
How is gravity fill done?
Oil is added to the tank directly through the oil tank filler
How is pressure fill done?
Using a pressurised oil source connected to a filling manifold
The scupper (which surrounds the filler) has what purpose?
Catches spilled oil and drains it at the engine drain mast
What does a check valve prevent?
The discharge of air and oil when the cap is not correctly fitted
Where is the strainer and check valve located?
Bellow the filler cap
What is the purpose of the strainer?
Catches any large foreign particles during servicing
What is beneficial about the strainer for maintenance personnel?
Oil samples can be taken
What can you check the oil quantity with, that is positioned on the side face of the tank?
The sight glass
What is the primary source of oil cooling?
The fuel cooled oil cooler
How does the fuel cooled oil cooler work?
The oil cools as it heats the fuel
What operates when additional oil cooling is required?
Air oil heat exchanger
What is the single function of some oil pumps?
To supply or scavenge
What are the 2 most common oil pumps?
Gerotor
Gear
What are the 2 elements of the gear type pump?
Pressure
Scavenging
Some pumps have several elements, how are they configured?
1 or more elements of pressure and 2 or more for scavenging
How many elements does the gerotor pump contain?
2 (same as gear type)
How can the capacity of the elements be controlled?
By varying the size of the gerotor elements
Are each of the elements (pressure and scavenge) different or identical?
Identical
Where is an oil pressure regulating valve incorporated into the oil system?
On the pressure side
When is a pressure relief valve more of a pressure regulating valve?
When pressure in the system is kept in certain limits
When would a large turbofan oil system not have a regulating valve?
Because the system varies with rpm and engine speed
When is a relief valve especially important?
When oil coolers are involved because they are thin walls and easily ruptured
When is a bypass valve included in an oil system?
When an oil cooler is involved
What is the purpose of the bypass valve?
To maintain proper oil temperature and pressure
What 2 things does the bypass valve vary the proportion of oil flow passing through?
The oil cooler and the filter
What are screens in the suction lines used to protect?
Oil pumps
When would lubrication system screens protect the oil nozzles?
If the supply filter is bypassed (called the last chance filter) they are upstream of the oil nozzles
What 4 things do filters have in terms of construction?
A filter housing
Removable cover
Bypass valve
Clogging indicators
When is the system called the hot tank system?
If the oil cooler/ heat exchanger is installed in the supply line
Why is it called the hot tank system?
Because the oil is not cooled before entering the oil tank
When is the system called a cold tank system?
When the oil cooler is installed in the scavenge line
Why is it called a cold tank system?
Because the oil is called before it returns to the tank
What are the 2 mains types of oil coolers?
Fuel cooled
Air cooled
What are the advantages of fuel cooled oil coolers?
They are efficient and small
What aircraft are air cooled oil coolers used on?
Turboprop engines and APUs
What are the main components of a typical fuel cooled oil cooler?
Housing
Cover
Core
How many scavenge pumps are there?
7
What is the purpose of the scavenge pumps?
To remove oil from the bearings and gearboxes
What is in the external gearbox that removes air overboard from the scavenge oil?
A breather
Where is a de-aerator installed?
At the inlet for the scavenge wheel
What is the purpose of the de-aerator?
Separates air from incoming scavenge oil
What does the air leave the oil tank via?
The vent line
What can happen if the tank filler cap is removed during present HP air?
Hot oil can spill out the tank
How long is the HP air present for after engine shutdown?
5 mins
What does the oil indication monitor?
Quantity
Condition
Pressure
Temperature
What are the 2 types of transmitters used for indication?
Capacitance type
Reed switch type
What is the principle of the capacitive level measurement based on?
The capacitance change of the capacitor
What is the upper and lower of the capacitance transmitter?
The upper part has electronic components for a capacitance measurement (measuring the capacity) and the lower part is immersed in oil and has 2 concentric tubes
What does the Reed type transmitter consist of?
A metal tube with a float inside and a multi switch assembly
What activates the internal switch assembly?
Permanent magnets
When the tank is full, where is the float?
The upper limits
What changes with the switch?
Resistance
What do oils contain to boost their performance?
Additives
What does SOAP stand for?
Spectrometric
Oil
Analysis
Program
Where does the engine oil carry particles from the bearings and the gears to?
Filters and the lubrication system
What is monitored by the debris monitoring system?
The quantity, size and type of material for indication of internal wear of lubricated parts
What size particles does a scavenge oil filter element catch?
more than 0.0015
What happens to the particles caught in the filter?
They are removed and sent for testing
What size particles can SOAP analysis find?
0.001-0.02mm (so small they cannot be caught in normal oil filters)
What is the disadvantage of SOAP?
Filter element is not changed often, but when it is it takes time
When are SOAP samples taken periosdically?
When the engines are shut down
Where are oil samples for SOAP taken from?
The oil tank
What is an advantage of magnetic chips?
Theyre less time consuming
Easier
What do magnetic chip detectors a catch?
Metal particles that are attracted to the magnet
How are magnetic chip detectors checked?
Manually and on some aircraft they are electronically monitored
What happens to resistance when particles connect to the magnet?
It decreases
What is the resistance between the two chip detector magnets monitored by?
The electric control unit (ECU)
Where can the oil quantity be checked at?
Sight gages or ECAM/EICAS
What does the siphoning effect do to the flow of oil from the tank to the gearbox?
Makes it slower
What is installed to prevent the siphoning effect on a oil system?
An anti-siphon device
On engines without anti-siphon what is the time interval after engine shut-down that you can check the oil quantity in the tank?
Between 5 and 20 minuets
How long should you wait before opening the oil tank filler cap?
5 minuets
If you can smell fuel when opening the filler cap, where is a leakage indicated?
In the fuel cooled oil cooler
What 2 things can the oil system be replenished using?
Oil cans (gravity)
Oil servicing (pressure)
Where can details of the required oil type be found?
On a label close to the oil tank filler cap
Because monitoring the oil consumption of the engine is important, what must you enter into the logbook?
Quantity of oil added to the tank
