Lesson 5: Engine Lubrication And Cooling. Engine Lubrication And Cooling Principles of Engine...

Lesson 5: Engine Lubrication And Cooling

Engine Lubrication And Cooling

• Principles of Engine Lubrication

• Primary purpose is to reduce friction between moving parts.

• Liquid lubricants (oil) are used universally in aircraft.

• No metal to metal contact occurs.

• Friction and wear held to a minimum.



• Oil film acts as a cushion between metal parts.

–Crankshaft and connecting rods

–Shock-loading parts



• Absorbs heat from the parts.

–Pistons and cylinder walls.

• Forms a seal between the piston and the cylinder wall.

• Reduce abrasive wear.

–Picks up foreign particles and carries them to the filter.



• Reduces friction• Cushions• Absorbs heat• Cooling• Forms a seal• Reduces abrasive wear• Cleans


• Requirements & Characteristics Of Lubricants

• The Most important characteristic is its viscosity.

– The resistance of an oil to flow.

–High viscosity is oil that flows slow.

– Low viscosity is oil that flows freely.


How does temperature affect the viscosity of oil?


• Some Grades of oil become practically solid in cold weather.

– Increases drag

– Makes circulation difficult.

• Others become so thin at high temperatures that the oil film is broken.

– Rapid wear of moving parts.


• Flash Point And Fire Point

• Flash Point is the temperature at which a liquid will begin to give off ignitable vapors.

• Fire Point is the temperature at which there are sufficient vapors to support a flame.


• Cloud Point, Pour Point And Specific Gravity

• Cloud Point is the temperature at which its wax content, normally held in solution, begins to solidify and separate in to tiny crystals.

• Pour Point is the lowest temperature at which it will flow or can be poured.

• Specific Gravity is a comparison of the weight of the substance to the weight of an equal volume of distilled water.


• Aviation oils are classified numerically according to an approximation of their viscosity.

• Classified under an SAE (Society of Automotive Engineers) system.

• SAE divides all oils into seven groups according to viscosity at either 130° or 210° F.

• SAE 10 to 70 (SAE 20W)• “W” indicates that the oil is satisfactory oil for

winter use in cold climates.


• Lubricating Oil Types

• Straight Mineral Oil

• Ashless Dispersant

• Synthetic


• Straight Mineral oil

• Used in engines after overhaul or when new to facilitate wear-in or seating of piston rings.

• Often forms sludge when exposed to temperatures higher than normal.


• Ashless Dispersant (AD)

• Replaces mineral oil after the piston rings have seated.

• Less tendency to oxidize to carbon, or form ash deposits.

• Particles don’t clump together, forming sludge.

• Better lubricating properties than mineral oils.


• Oil Compatibility

Can different brands and grades of the same oil type be mixed?


• Oil Compatibility

If necessary in order to have proper operating oil levels, brands of the same type can be mixed.


• Internal Lubrication Of Reciprocating Engines

• Three Methods used

–Pressure

–Splash

–Combination Splash-And-Pressure


• Pressure-Lubrication

• A mechanical pump supplies oil under pressure to the bearings throughout the engine.

• Splash-Lubrication

• Used in addition to pressure lubrication on aircraft engines.


• Advantages of pressure lubrication system

• Positive introduction of oil to the bearings.

• Cooling effect caused by the large quantities of oil which can be circulated through a bearing.

• Satisfactory lubrication in various attitudes of flight.

From Reservoir To Filter


• Lubrication Systems

• Wet-Sump System

• Dry-Sump System


• Wet-Sump

• System consist of a sump or pan, in which the oil supply is contained.

• The sump or pan is attached to the bottom of the engine case.


• Wet-Sump

What are some of the disadvantages and advantages of the wet-sump system?


• Wet-SumpDisadvantages• Oil supply limited by sump.• Cooling is difficult.• Higher operating temperatures.• Not adaptable to inverted flying

Advantages• Requires no external parts and fittings to

complicate installation.• No second (scavenge pump) required.• Can be operated in much cooler temperatures.


• Dry-Sump

• Oil supply is carried in a separate tank.

• Scavenger pumps used to return the oil to the tank.

• Used in radial engines and engines capable of sustained inverted flight.

Dry-Sump


• Lubrication

System


• Engine Cooling Systems

• Why is excessive heat undesirable in internal combustion engines?


• Affects the behavior of the combustion of the fuel/air charge.

• It weakens and shortens the life of engine parts.

• It impairs lubrication.


• Engine Cooling Systems

• About one-fourth of the heat released in an engine is changed into useful power.

• Half of the heat goes out the exhaust, and the other is absorbed by the engine.

• Oil picks up some heat and transfers it to the airstream.

• The engine cooling system takes care of the rest.


• Cooling Fins

• Cooling fins increase the surface of a cylinder.

• This arrangement increases the heat transfer by radiation (from a jug to a barrel).

• Cylinders are normally replaced when a specified number of square inches of fins are missing.


• Cowling and baffles

• Designed to force air over the cylinder cooling fins.

• Direct the air close around the cylinders and prevent it from forming hot pools.

• Blast tubes direct jets of cooling air onto the bottom spark plug elbows.


• Temperature Controls

• Controls the air circulation over the engine.

• Keeps the engine from overheating on take off and getting too cold in high-speed low-power letdowns.

• Cowl Flaps, Augmenters


• Cowl Flaps


• Augmenters


• Cylinder Head Temperature Indicating System

• Consists of and indicator, electrical wiring, and a thermocouple.

• Thermocouple consists of two dissimilar metals connected by wiring to an indicating system. A voltage is produced when the temperature of the junction is different from the temperature where the dissimilar metals are connected.


• Pilot Responsibility

• Cowl Flaps?

• Power Settings?

• Airspeed?

• Fuel Mixture?


• Thermal Shock

• Occurs when engine parts that are operating at high temperatures are quickly cooled.

• Idle power, high airspeed, cool or cold air.

• Some parts are cooled much more rapidly then others. These parts shrink in size faster then the warmer, surrounding metals.

Lesson 5: Engine Lubrication And Cooling. Engine Lubrication And Cooling Principles of Engine...

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