Lubrication And Cooling Flashcards
Functions Of Oil
Lubricate
Clean
Reduce wear
Seals
Protection from corrosion
Cooling
Required Oil Properties
Optimal Viscosity - high enough for lubricate but low enough to flow
High flash point - temperature at which oil gives off vapours
Low carbon forming tendencies
Discourage of sludge
Oil Grades (Saybolt)
Graded according to viscosity
Higher the temp the higher the grade
Wet Sump System
All of the oil carried in a sump within crankcase
Drawn from sump via suction filter
Requires greater quantity of oil to have supply
Utilises a gravity return system
High oil temp means viscosity is too low and lubricating layer too this
Dry Sump Tank
Oil held in a tank mounted remotely from engine
Pump provides more oil pressure than necessary - pressure can be guaranteed
Relief Valve in Dry Sump
Located after the OPP and functions to return oil to pump inlet if pressure too high
Disadvantages of wet sump
Limited amount of oil
Higher oil temps and shorter oil life
Not suited for radial and aerobatic a/c
+simple and cheap though
Dry Sump (4 pumps)
Oil pressure pump - draws oil from sump
Oil scavenge pump - in supply line
- capacity is OPP x 3
- supply oil has larger volume as mixes with air
Governor pump - engine lubricating oil used to change pitch of CSP
Feathering pump - electrically driven
Used to feather prop when engine fails
Oil Filter
Between Oil Pressure Pump and engine
Removes contaminants
Bypass valve required to ensure continuous flow if blocked
Suction Filter
High pressure filter to various placed jets to lubricate points and bearings
Dry Sump - Big end bearings pressure and light loaded components pressure
Big end bearings Fed with high pressure oil at 4 to 5 bars (60/70psi)
Fed with low pressure oil via pressure reducing valve (oil to camshaft)
Dry Sump Scavenge Pump
Pumps oil back to oil tank via oil cooler
More powerful than high pressure pump to ensure oil does not pool in sump
Oil Tank
Reserve of oil to allow for fluctuations in demand/thermal expansion/minor leaks
De-aerator plate - Dry Sump role
On oils return from engine/separate out air bubbles suspended in the oil
Hot Well - Dry sump role
On start when oil is cold and viscous oil drawn from hot well.
Refills with hot oil returning from engine so establishes a good circulation.
Coarse Filter - Dry Sump System
Cleans oil by trapping dirt/metals carried by oil
Magnetic Plugs - Dry Sump
Used for engine condition monitoring
Oil Pump
Engine driven/speed varies with engine RPM
Pump output increases at higher engine speed
Regulated by pressure relief valve
Low oil pressure at high RPM indicate worn oil pressure pump
Oil Cooler - Dry Sump/wet sump
Dry Sump - Fitted in return line between scavenge pump and oil tank
Wet Sump - Oil cooler fitted in pressure supply line
Anti surge valve - dry sump
Allows oil to bypass the cooler when it is cold and viscous
Doesn’t need to be cooled
Oil Temp Gauge - Dry Sump
Measures temp of oil in supply line after the cooler before the pressure pump
Oil Pressure Gauge
Measures oil pressure at outlet of pressure pump
Cold oil = more viscous = higher pressure reading
Warm oil = less viscous - lower pressure reading
Indicate within 30 secs of starting
Splash Lubrication
Spray oil onto moving parts across the crankshaft
Wet vs Dry Sump
Wet Positives/Negatives
+ Cheaper/Easier
+ Less parts
- inversion could lead to oil starvation
- greater quantity of oil needed to supply oil pump
- risk of excessive oil at high RPM
- not filtered or cooled
Dry Sump Positives/Negatives
+ oil contained separately
+ Filtered and cooled under all flight conditions
- more moving parts
Checking Oil Lvls Dry vs Wet
Dry check straight after shut down (start to drain back into engine)
Wet check 20 minutes to allow time for all to drain back to sump
Oil Consumption - What causes it?
Oil leaking past piston rings into cylinder then combusts with mixture and expelled from exhaust
Worn piston rings = greater consumption
Low viscosity = more escapes past oil control ring
Liquid Cooling System
Water + glycol through galleries in crank case and cylinder
Hot fluid piped to radiators using ram air to cool and then returning to engine
Thermostat valve controls engine temperature in cooled system
Air cooling systems
Air inlet directs air over engine via baffles (control flow)
Cowl flap open to increase cooling flow
Exhausted hot gas to atmosphere
Cylinder Head Temperature
Measures temp of cylinder usually the hottest on closet at is the hottest
Measured via thermocouple requires no electrical supply
Saybolt System to SAE No
SAE no will be around half of the Saybolt number
Oil Coring
Excessive cooling leading to congealed oil blocking system
Oil temp excessive and cooler flap open suspect coring
Close the cooler flap
Cowl Flaps
Regulate the flow of cooling air to the engine
Open at full power on a climb and close for a low power descent
Thermostat Valve
Controls engine temperature in liquid cooled system
Detonation causes
Low RPM with a high power setting
Hot well (Hot Pot)
Reduce time taken to raise the temperature of the oil when starting the engine from cold restrict quantity of oil in circulation
Anti Surge Valve
Fitted to bypass matrix on start when oil is cold and thick
Oil returning to oil tank is filtered by
Scavenge filter
Purpose of magnetic chip detectors
To find ferrous metallic particles in the oil to detect impending engine failure
