Lubrication System

Dry-Sump:

• Oil is contained in a separate tank, and circulated through the engine by pumps
• These tanks are always larger than the oil it is meant to contain to compensate for thermal expansion
• An oil pump also supplies oil pressure in a dry-sump system, but the source of the oil is located external to the engine in a separate oil tank
• After oil is routed through the engine, it is pumped from the various locations in the engine back to the oil tank by scavenge pumps
• Dry-sump systems allow for a greater volume of oil to be supplied to the engine, which makes them more suitable for very large reciprocating engines
• Most jet engines will consist of a dry sump design
• When checking the oil level on an dry-sump engine that has been sitting idle, readings may be inaccurate unless rotated (or "burped")
  • Refer to your POH

  Lubrication System Components:

  Oil Filter:

  • The oil filter is responsible for screening the oil for foreign debris
  • Oil filters accomplish this by pushing oil through a one or more screens or paper filters

    Oil Screens:

    • There are two types of oil screens:
      • Pressure Screens, or;
      • Suction Screens

      Suction Screens:

      • Suction screens are screens placed before the oil pump in the lubrication system , filtering out the largest contaminents before they enter delicate system components

      Pressure Screens:

      • Pressure screens filter finer particulates, down to 60 microns

      Paper Oil Filters:

      • Paper oil filters are a newer technology in which paper completes the functions of an oil screen

      Oil Filler Cap/Dipstick:

      • The oil filler cap/dipstick used to measure oil quantity is usually accessible through a panel in the engine cowling [ Figure 2 ]
      • If the quantity does not meet the manufacturer's recommended operating levels, oil should be added
        • If oil is unexpectedly low, the source of oil burn/leak should be investigated

        Oil:

        • The type of oil required may vary on numerous atmospheric and operation conditions, as stipulated by the aircraft operations manual [ Figure 1 ]
        • The AFM/POH or placards near the access panel provide information about the correct oil type and weight, as well as the minimum and maximum oil quantity
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      • The loss of engine oil pressure would lead to engine vibrations, RPM would decrease, and the engine would eventually seize
      • Viscosity: the ability of a liquid to resist flow

      Heat Management:

      • A critical purpose of engine oil is to help manage cooling
      • This occurs by cool oil moving through warm areas, picking up the heat, and dissipating it through a radiator

      Oil System Gauges:

      

      • System is monitored through pressure and temperature gauges [ Figure 3 ]

      Oil Pressure Gauge:

      • The oil pressure gauge provides a direct indication of the oil system operation [ Figure 3 ]
      • It ensures the pressure in pounds per square inch (psi) of the oil supplied to the engine
      • Green indicates the normal operating range, while red indicates the minimum and maximum pressures
      • There should be an indication of oil pressure during engine start
      • Refer to the AFM/POH for manufacturer limitations

      Oil Temperature Gauge:

      • The oil temperature gauge measures the temperature of oil [ Figure 3 ]
      • It is usually measured after passing through the oil cooler
      • A green area shows the normal operating range and the red line indicates the maximum allowable temperature
      • Unlike oil pressure, changes in oil temperature occur more slowly
      • This is particularly noticeable after starting a cold engine, when it may take several minutes or longer for the gauge to show any increase in oil temperature
      • Check oil temperature periodically during flight especially when operating in high or low ambient air temperature
      • High oil temperature indications may signal:
        • Plugged oil line or cooler
        • low oil quantity (possible engine failure)
        • Defective temperature gauge

        Oil/Lubrication Malfunctions/Emergencies:

        • Oil consumption depends primarily upon the efficiency of the seals
        • Oil can be lost through internal leakage, and, in some engines, by malfunctioning of the pressurizing or venting system
        • Increases in oil temperature are not always associated with a drop in oil pressure, nor a rise in CHTs

        Low Oil Pressure:

        • Low oil pressure can be caused by an oil leak which leads to lack of oil in the system, or an ineffective oil pump
        • These emergencies can be particularly detrimental when flying an aircraft utilizing a constant-speed propeller

        Low Oil Pressure Primary Indications:

        • Oil pressure will indicate low

        Low Oil Pressure Secondary Indications:

        • Rising Cylinder Head Temperatures (CHT)
        • Oil temperature may rise (if the pressure drops rapidly then it is less likely you will have a corresponding temperature indication
        • Rough engine indications

        Low Oil Temperature:

        Primary Indications:

        • Oil temperature will indicate low

        Secondary Indications:

        High Oil Temperature:

        High Oil Temperature Primary Indications:

        • Oil temperature will indicate high

        High Oil Temperature Secondary Indications:

        • Other temperatures will indicate high
        • Possible smoke
        • Low oil pressure
        • High RPM

        High Oil Temperature Considerations:

        • Open cowl flaps, if equipped

        Oil Leaks:

        • Oil on windscreen may come from engine or propeller

        Oil System Inspections:

        Inspecting the oil system is not a routine check, but rather a detailed review of aircraft engine health

        Oil Inspection:

        • Pilots should inspect the oil as part of the pre-flight checklist
        • Inspecting the oil is critical in determining the quantity and condition of oil
        • Oil should never go below the Pilot Operating Handbook specified minimum quanty
        • The color of the oil is a reflection of oil age and engine health
          • New, clean oil should be light in color
          • Dark oil is generally the result of contaminates and oxidation after many hours of operation
            • Too dark is a judgement call based on the amount of hours of use
            • Dark oil may be due to bad piston seals
            • Smaller sumps should therefore be changed/drained more often

            Oil Filter Inspection:

            • It is never required, but pilots who own their airplane may elect to inspect the oil filter for tell-tale signs of wear
            • Oil filters are designed to bypass, if clogged, but are only meant to last for the life of the oil
              • Oil filters should be changed with every oil change
              • Changing an oil filter often also allows for consistent engine health trend analysis

              Private Pilot (Airplane) Operation of Aircraft Systems Airman Certification Standards:

              • Objective: To determine the applicant exhibits satisfactory knowledge, risk management, and skills associated with safe operation of systems on the airplane provided for the flight test.
              • References: FAA-H-8083-2 (Risk Management Handbook), FAA-H-8083-3 (Airplane Flying Handbook), FAA-H-8083-23 (Seaplane, Skiplane, and Float/Ski Equipped Helicopter Operations Handbook), FAA-H-8083-25 (Pilot Handbook of Aeronautical Knowledge); POH/AFM
              • Note: If K1 is selected, the evaluator must assess the applicant's knowledge of at least three sub-elements
              • Private Pilot Operation of Aircraft Systems Lesson Plan