Lesson 5: Engine Lubrication And Cooling

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Lesson 5 Engine Lubrication And Cooling
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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.

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Engine Lubrication And Cooling

• Principles of Engine Lubrication
• Oil film acts as a cushion between metal parts.
• Crankshaft and connecting rods
• Shock-loading parts

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Engine Lubrication And Cooling

• Principles of Engine Lubrication
• 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.

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Engine Lubrication And Cooling

• Principles of Engine Lubrication
• Reduces friction
• Cushions
• Absorbs heat
• Cooling
• Forms a seal
• Reduces abrasive wear
• Cleans

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• How does temperature affect the viscosity of oil?

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• Lubricating Oil Types
• Straight Mineral Oil
• Ashless Dispersant
• Synthetic

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• Ashless Dispersant (AD)
• Replaces mineral oil after the piston rings have
  seated.
• Less tendency to oxidize to carbon, or form ash
  deposits.
• Particles dont clump together, forming sludge.
• Better lubricating properties than mineral oils.

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Engine Lubrication And Cooling

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

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Engine Lubrication And Cooling

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

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Engine Lubrication And Cooling

• Internal Lubrication Of Reciprocating Engines
• Three Methods used
• Pressure
• Splash
• Combination Splash-And-Pressure

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• 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.

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From Reservoir
To Filter
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Engine Lubrication And Cooling

• Lubrication Systems
• Wet-Sump System
• Dry-Sump System

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

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

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Engine Lubrication And Cooling

• Wet-Sump
• Disadvantages
• 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.

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Engine Lubrication And Cooling

• 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.

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Dry-Sump
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Engine Lubrication And Cooling

• Lubrication
• System

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Engine Lubrication And Cooling

• Engine Cooling Systems
• Why is excessive heat undesirable in internal
  combustion engines?

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Engine Lubrication And Cooling

• Affects the behavior of the combustion of the
  fuel/air charge.
• It weakens and shortens the life of engine parts.
• It impairs lubrication.

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling
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Engine Lubrication And Cooling

• 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

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Engine Lubrication And Cooling

• Cowl Flaps

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Engine Lubrication And Cooling

• Augmenters

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Engine Lubrication And Cooling

• 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.

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Engine Lubrication And Cooling

• Pilot Responsibility
• Cowl Flaps?
• Power Settings?
• Airspeed?
• Fuel Mixture?

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Engine Lubrication And Cooling

• 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.