LUBRICATION AND COOLING

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LUBRICATION AND COOLING
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FUNCTIONS OF ENGINE OIL

• Lubrication (Primary function)
• Wear-reduction
• Protection
• Cooling
• Cleaning
• Corrosion protection
• Hydraulic action

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Lubricating Oil Properties

• Gravity
• Flash Point
• Viscosity
• Cloud Point
• Pour Point
• Carbon-Residue Test
• Ash Test
• Precipitation number

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Gravity

• The gravity of petroleum oil is a numerical value
  which serves as an index of the weight of a
  measured volume of this product

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Flash Point

• The flash point of an oil is the temperature to
  which the oil must be heated in order to give off
  enough vapor to form a combustible mixture above
  the surface that will momentarily flash or burn
  when the vapor is brought into contact with a
  very small flame.

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Viscosity

• Viscosity is technically defined as the fluid
  friction of an oil
• To put it more simply, it is the resistance an
  oil offers to flowing
• Heavy-bodied oil is high in viscosity and pours
  or flows slowly
• Oils are typically classified by viscosity. SAE
  30 is a reflection of the oils viscosity. The
  higher the number the higher the viscosity.

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Multiviscosity Oils

• When you see a W on a viscosity rating it means
  that this oil viscosity has been tested at a
  Colder temperature. The numbers without the W are
  all tested at 210 F or 100 C which is
  considered an approximation of engine operating
  temperature. In other words, a SAE 30 motor oil
  is the same viscosity as a 10w-30 or 5W-30 at
  210 (100 C).
• The difference is when the viscosity is tested at
  a much colder temperature. For example, a 5W-30
  motor oil performs like a SAE 5 motor oil would
  perform at the cold temperature specified, but
  still has the SAE 30 viscosity at 210 F (100 C)
  which is engine operating temperature. This
  allows the engine to get quick oil flow when it
  is started cold verses dry running until
  lubricant either warms up sufficiently or is
  finally forced through the engine oil system. The
  advantages of a low W viscosity number is
  obvious. The quicker the oil flows cold, the less
  dry running. Less dry running means much less
  engine wear.

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Cloud Point

• The cloud point is the temperature at which the
  separation of wax becomes visible in certain oils
  under prescribed testing conditions
• When such oils are tested, the cloud point is
  slightly above the solidification point

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Pour Point

• The pour point of an oil is the temperature at
  which the oil will just flow without disturbance
  when chilled

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Carbon-Residue Test

• The purpose of the carbon-residue test is to
  study the carbon-forming properties of a
  lubricating oil.

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Ash Test

• The ash test is an extension of the
  carbon-residue test
• If an unused oil leaves almost no ash, it is
  regarded as pure
• The ash content is a percentage (by weight) of
  the residue after all carbon and all carbonaceous
  matter have been evaporated and burned

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Precipitation number

• The precipitation number recommended by the ASTM
  (American Society for Testing and Materials) is
  the number of milliliters of precipitate formed
  when 10 mL of lubricating oil is mixed with 90 mL
  of petroleum naphtha under specific conditions
  and then centrifuged

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Lubricating Oil Types

• Straight Mineral Oil
• Ashless Dispersant Mineral Oil
• Synthetic Oil
• Mineral/Synthetic Blends

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Straight Mineral Oil

• Straight mineral oil is one of many types of oil
  used in aircraft reciprocating engines
• It is blended from selected high-viscosity-index
  base stocks
• These oils do not contain additives, except for a
  small amount of pour-point depressant for
  improved fluidity at cold temperatures
• Often used after engine overhaul or when new to
  facilitate seating of the piston rings (wear-in).

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Ashless Dispersant Oil

• Most aircraft oils other than straight mineral
  oils contain a dispersant that suspends
  contamination such as carbon, lead compound and
  dirt
• The dispersant helps prevent these contaminants
  from gathering into clumps and forming sludge or
  plugging oil passageways

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Synthetic Oil

• Because of the high operating temperatures of
  gas-turbine engines, it became necessary to
  develop lubricants which would retain their
  characteristics at temperatures that cause
  petroleum lubricants to evaporate and break down
• Synthetic lubricants do not break down easily and
  do not produce coke or other deposits

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Multiviscosity Oil

• In certain circumstances, all single-grade oils
  have short comings
• In cold-weather starts, single grade oil
  generally flows slowly to the upper reaches and
  vital parts of the engine
• Multigrade oils have viscosity characteristics
  that allow for better flow characteristics at
  engine start

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Characteristics of Aircraft Lubricating Oil

• It should have the proper body (viscosity)
• High antifriction characteristics
• Maximum fluidity at low temperatures
• Minimum changes in viscosity with changes in
  temperature
• High antiwear properties
• Maximum cooling abilities
• Maximum resistance to oxidation
• Noncorrosive

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Characteristics of Lubrication Systems

• Pressure Lubrication
• Splash Lubrication and Combination Systems
• Principal Components of a Lubrication System
• Oil Capacity

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Pressure Lubrication

• In a pressure lubrication system, a mechanical
  pump supplies oil under pressure to the bearings
• Oil flows into the inlet of the pump through the
  pump and into an oil manifold which distributes
  it to the crankshaft bearings

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Splash Lubrication and Combination Systems

• Although pressure lubrication is the principle
  method of lubrication on all aircraft engines,
  some engines use splash lubrication also
• Splash lubrication is never used by itself
• All lubrication systems are pressure systems or
  combination pressure/splash systems

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Components of Lubrication Systems

• Plumbing for Lubrication Systems
• Temperature Regulator (Oil Cooler)
• Oil Viscosity Valve
• Oil Pressure Relief Valves
• Oil Separator
• Oil Pressure Gauge
• Oil Temperature Gauge
• Oil Pressure Pumps
• Scavenge Pumps
• Oil Dilution System

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Plumbing for Lubrication Systems

• Oil plumbing is essentially the same as is used
  in oil and hydraulic systems
• When the lines will not be subject to bending,
  aluminum tubing is used
• Synthetic hose is often used near the engine and
  other places on the aircraft that are subject to
  vibration or other movement

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Temperature Regulator (Oil Cooler)

• An oil temperature regulator is designed to
  maintain the temperature of the oil for an
  operating engine at the correct level
• These regulators are often called oil coolers
  since cooling of engine oil is one of their main
  functions

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Oil Viscosity Valve

• The oil viscosity valve is generally considered a
  part of the oil temperature regulator unit and is
  employed in some oil systems
• The viscosity valve consists essentially of an
  aluminum alloy housing and a thermostatic control
  element
• The oil viscosity valve works with the oil cooler
  valve to maintain a desired temperature and keep
  the viscosity within required limits

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Oil Pressure Relief Valves

• The purpose of the oil pressure relief valve is
  to control and limit the lubricating pressure in
  the oil system
• This is necessary to prevent damage caused by
  excessive system pressure and to ensure that
  engine parts are not deprived of fuel due to a
  system failure

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Oil Separator

• Air systems where oil or oil mist is present may
  require the use of an oil separator
• These are often used on vacuum pump outlets
• The oil separator contains baffle plates which
  cause the air to swirl and it deposits on the
  baffles

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Oil Pressure Gauge

• An oil pressure gauge is an essential component
  of any engine oil system
• These gauges generally use a bourdon tube to
  measure the pressure
• They are designed to measure a wide range of
  pressures

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Oil Temperature Gauge

• The temperature probe for the oil temperature
  gauge in the oil inlet line or passage between
  the pressure pump and the engine system
• On some installations the temperature probe is
  located in the oil filter housing
• These are normally electric or electronic

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Oil Pressure Pumps

• Oil pressure pumps may either be of the gear type
  or vane type
• The gear type pump is used in the majority of
  reciprocating engines and uses close fitting
  gears that rotate and push the oil through the
  system

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Scavenge Pumps

• Scavenge pumps are driven in the same manner as
  the pressure pumps but have a greater capacity
• This higher capacity is because the oil in the
  sump is foamy which means it has a much greater
  volume than air-free oil

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Oil Dilution System

• The purpose of the oil dilution system is to
  provide thinner oil during engine start
• This allows faster lubrication of engine
  components
• Oil dilution is accomplished by pumping a small
  amount of fuel into the oil

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Sludge Chambers

• Some reciprocating engines have sludge chambers
  which are in the hollowed out connecting-rod
  journals
• These journals accumulate carbon sludge and dirt
  particles as they are designed to
• During engine overhaul these must be replaced

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Typical Lubrication Systems

• Oil System for Wet-Sump Engine
• Oil System for Dry-Sump Engine
• Oil Tanks

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Wet Sump System

• In a wet sump system the oil is housed within the
  crankcase.
• This is not possible in a turbine engine
  application because of the high operating
  temperatures.

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Oil Tanks

• Dry sump engine lubrication systems require a
  separate tank for each engine system
• These tanks can be constructed in three different
  ways
• Welded sheet aluminum
• Riveted aluminum
• Stainless steel
• Some aircraft are equipped with synthetic rubber
  tanks

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Troubleshooting

• Symptom Oil pressure decrease, oil temp.
  increase.
• Cause loss of oil causing temp. to rise, engine
  failure imminent.
• Action reduce power to maximize engine life.

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Troubleshooting

• Symptom Oil pressure decrease, oil temp. steady
• Cause Oil pressure gauge malfunction.
• Action monitor engine instruments.

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Troubleshooting

• Symptom Slight drop in oil pressure, steady or
  slight rise in oil temp.
• Cause possible filter blockage, by-pass valve
  restricts flow.
• Action inform maintenance.

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Usage Monitoring

• It is important to monitor oil usage trends in
  order to detect problems before they become
  critical.
• Each company will have specific trend monitoring
  procedures.

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Engine Cooling Systems

• Cowling
• Baffles
• Cooling fins
• Cowl flaps
• Augmenters

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Liquid Cooled Cylinder
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Air Cooled Engine
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Engine Cooling Airflow
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Pilot Handling

• It is the pilots responsibility to ensure engine
  operating temperatures remain in the normal
  operating range.
• Temperature can be controlled by adjusting
• Cowl flaps
• Power setting
• Airspeed
• Fuel mixture

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Thermal Shock

• Thermal shock occurs when an engine operating at
  high temperatures is allowed to cool quickly.
• Some parts cool more rapidly than others and
  causes stress cracks in the cylinder head.
• Pilot handling can prevent thermal shock by
  avoiding rapid power reductions, especially in
  cold outside air temps.