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• Main Bearing - Has the critical function of supporting the main engine rotor.


  The number of bearings necessary for the proper engine support is for the most part, determined by the length and weight of the engine rotor.
• Oil Cooler - Provides additional cooling to the lubricating oil as it flows from the pump through the filter and into the engine.
• Many newer engines use hydraulic bearings, in which the outer race is surrounded by a thin film of oil.
• Plain bearings are also used in Gas Turbine Engine, they are sometimes called Sleeve or Journal Bearings.


  They are sliding bearings so they need adequate lubrication to float on oil for the reason that the shaft journal floats and slides on oil. They are also termed Hydro-Dynamic Bearings.
• The bearing housing usually contains an oil seal to prevent oil leaking from its normal path of flow.


  labyrinth seal is usually pressurized but the helical seal depends solely on reversed threading to stop oil leakage.
• carbon seals - These seals are usually spring loaded and are similar in material to those used as carbon brush in electrical motors.


  ball or Roller bearings - are fitted into the bearing housing and may have a self-aligning feature.
• The rotor shaft also provides the matching surface for the oil seal in the bearing housing. These machined surfaces are called “Sealing Land” and fit in rather close to the oil seal.


  metal Case Rubber Seal - This type of oil seal is made of various types of synthetic rubber materials. It is encased in various metals such as stainless steel,
• type II specification and are made with the following characteristics:

  • Vapor phase deposits
  • Load-carrying ability
  • Cleanliness
  • Bulk stability
  • compatibility
  • seal wear
• Vapor phase deposits—carbon deposits formed from oil mist and vapor contact with hot engine surfaces.


  Bulk stability—resistance to physical or chemical change resulting from oxidation. Permits long periods of serve operation without significant increase in viscosity or total acidity, the main indicators of oxidation
• Load-carrying ability — provides for heavy loads on the bearing systems of turbine engines.


  Cleanliness — minimum formation of sludge deposits during severe operation.
• Seal Wear — essential for the life of engines with carbon seals that lubricant properties prevent wear of the carbon at the carbon seal face.


  Compatibility — most turbine oil is compatible with other oils that meet the same military specification.
• Aircraft with turbine engines use a type of fuel different from that of reciprocating aircraft engines commonly known as Jet Fuel.


  Jet A - It is the most common turbine engine fuel available in the continental United States.
• Jet A-1 - By far the most common fuel for this reason is a wider family of jet fuels used to power all jet aircraft.


  Jet B It is a wide-cut fuel that is basically a blend of kerosene and gasoline.
• Jet A freezes at– 40°F and Jet A-1 freezes at– 52.6 °F.


  All grades of Jet Fuel are colorless or straw colored.
• fuel additives - are fuel-soluble chemicals added in small amounts to enhance or maintain properties important to fuel performance or fuel handling.


  additives are derived from petroleum based raw materials and their function and chemistry are highly specialized.
• Ice - can form in fuel tanks at the very low temperatures encountered at high altitude.


  The only FSII currently approved for Jet A, Jet A-1, and U.S. military fuels is di-ethylene glycol monomethylether (di-EGME).
• Metal Deactivator - These are chelating agents chemical compounds that form stable complexes with specific metal ions.


  The only approved metal deactivator is N,N´-disalicylidene-1,2-propane diamine.
• Antioxidants - work by interrupting this chain of reactions, preventing the formation of peroxides, soluble gums, or insoluble particulates.


  Peroxides - can attack elastomeric fuel system parts, gums can lead to engine deposits, and particulates can plug fuel filters.
• The approved antioxidants for aviation fuel are hindered phenols.


  Corrosion inhibitors - prevent free water and oxygen in the jet fuel from rusting or corroding these structures.
• Lubricity additives - are used to compensate for the poor lubricity of severely hydrotreated jet fuel.


  film - acts as a boundary lubricant when two metal surfaces come in contact.
• Conductivity additives are often referred to as static dissipator additives (SDA).


  When the additive is used, the conductivity of the fuel must be between 50 and 450 CU at the point of delivery into the aircraft.
• The only additive currently approved for use in jet fuel is Stadis®450, whose composition is proprietary.


  Tracer A® - can be used in Jet A and Jet A-1 to assist in detecting leaks in fuel handling systems.
• Biocides - are designed to kill microorganisms, which include bacteria and fungi (yeasts and molds) 


  Currently approved biocides are Biobor™ and Kathon™
• Prolonged or repeated contact of turbine oil with the skin can cause irritation and dermatitis.


  Information on established limits on exposure to turbine oil can generally be found in the material safety data sheets (MSDS).
• lubrications system in Gas Turbine

  • Dry-sump
  • wet-sump


  this type of lubrication system store the lubricating oil in the engine proper - Wet-sump engine
• this type of lubricating system utilize an external tank mounted on the engine or somewhere in the aircraft structure near the engine - dry-sump engines


  This pressure buildup is made possible by running the vent line through an adjustable check relief valve.
• oil pump - It is designed to supply oil under pressure to the parts of the engine that require lubrication, then circulate the oil through coolers as needed, and return the oil to the oil tank.


  two most common oil pumps are the gear and gerotor
• The gear-type oil pump has only two elements: one for pressure oil and one for scavenging.


  The gerotor pump - usually contains a single element for oil pressure and several elements for scavenging oil.
• oil filters - an important part of the lubrication system because they remove foreign particles that may be in the oil.


  The filtering element interior is made of varying materials including paper and metal mesh.
• filter bypass valve - prevents the oil flow from being stopped if the filter element becomes clogged.


  A regulating valve system controls the system's pressure to a limited pressure within the system.
• A relief valve is used to relieve pressure only if it exceeds the maximum limit for the system.


  Breather subsystems are used to remove excess air from the bearing cavities and return the air to the oil tank where it is separated from any oil mixed in the vapor of air and oil by the deaerator.
• thermostatic bypass valve - The purpose is to maintain proper oil temperature by varying the proportion of the total oil flow passing through the oil cooler.


  Check Valves - prevent reservoir oil from seeping (by gravity) through the oil pump elements and high-pressure lines into the engine after shutdown by stopping flow in an opposite direction
• Air oil coolers - are used in the lubricating systems of some turbine engines to reduce the temperature of the oil to a degree suitable for recirculation through the system.


  Two basic types of oil coolers in general use are the air-cooled and the fuel-cooled.
• fuel-cooled oil cooler - acts as a fuel oil heat exchanger in that the fuel cools the hot oil and the oil heats the fuel for combustion.

  deoiler - removes the oil from the breather air
• Magnetic chip detectors - are used in the oil system to detect and catch ferrous (magnetic) particles present in the oil.


  Chip detectors - are placed in several locations but generally are in the scavenge lines for each scavenge pump, oil tank, and in the oil sumps.
• A sight gauge indicates the oil level in the sump.


  A vent or breather equalizes pressure within the accessory casing.
• A magnetic drain plug may be provided to drain the oil and also to trap any ferrous metal particles in the oil.


  This plug should always be examined closely during inspections. The presence of metal particles may indicate gear or bearing failure.
• Provision may also be made for a temperature bulb and an oil pressure fitting