Engines Ch. 9 And 10

Front 1

Describe the characteristics of synthetic lubricants.

Back 1

Advantages: fine lubrication qualities over that of petroleum based oils. Lower tendency to leave coking deposits, stronger chemical stability at high temps.
Disadvantages: very corrosive, limited shelf life of approximately six months.

Front 2

Define viscosity

Back 2

the property of a fluid that resists the force tending to cause the fluid to flow.

Front 3

Describe the functions of lubricants.

Back 3

To reduce the friction caused by metal to metal contact. Provide a film that permits surfaces to glide over one another with less friction.

Front 4

Describe the operation of a basic aircraft lubrication system

Back 4

to provide an adequate supply of clean oil to the bearings and gears at the proper pressure and temp., remove heat from the engine, and remove contaminants from the system.

Front 5

Describe the functions of the three subsystems of the aircraft lubrication system.

Back 5

Pressure subsystem: supplies lubricating oil from the tank to the main engine bearings and the accessory drives.
Scavenge subsystem: removes the oil from the main bearings and accessory drives through the oil coolers and returns it to the tank, completing the oil flow cycle
Breather pressurizing subsystem: connects the individual bearing compartments and the oil tank with the breather pressurizing valve to help minimize oil leakage.

Front 6

Describe the function of basic lubrication system components used on aircraft.

Back 6

Oil tank: stores the system oil supply and is normally located within or near the aircraft engine compartment.
-Gravity: ensures the pickup end is constantly immersed in the oil supply.
All oil tanks provide an expansion space and venting to ensure proper operation. Required to allow for both expansion of the oil due to heat absorption, and foaming due to circulation through the system.
Oil pump: supplies oil under pressure to the parts of the engine that must have lubrication.
-pressure: supply oil
-scavenge: scavenge oil
Oil pressure gauge: displays oil pump discharge pressure
Oil Temp gauge: displays oil temp prio to entering the engine bearing compartments
Filters: remove any foreign particles that may be present in the oil
Filter bypass valve: allows oil to flow around the filter element, should the filter get clogged.
Oil pressure relief valve: limits the max pressure in system. Valve is preset to relieve pressure by bypassing oil back to the pump inlet whenever pressure is exceeded.
Scavenge subsystem: removes oil from the main bearing compartments and accessory gear drives
Magnetic chip detector: warns pilot of metal contamination
Oil coolers: reduce temp of oil for re-circulation in system.
-air cooler: radiator type device, uses ambient air to cool oil
-fuel-oil cooler/heat exchanger: designed to cool the hot oil taken from the bearings and to preheat the fuel for combustion.
Oil Temp. Regulating valves: directs the flow of return oil into the fuel-oil heat exchanger to allow cooling to occur.
Fuel Temp. Sensing Switch: senses the exiting fuel's temperature. When temp is excessive, it sends an electrical signal to air-oil cooler doors, allowing air to pass through to cool the oil
Breather pressurizing subsystem: pressurizes the scavenge subsystem along with the oil tank to sea level pressure. Uses a breather pressurizing valve which consists of an aneroid operated valve and a spring loaded blow off valve. Pressurization is provided by compressor bleed air.

Front 7

Describe the types of accessories used on aircraft.

Back 7

Bleed air
Mechanically driven

Front 8

Describe how the accessories are driven.

Back 8

High and low pressure systems are used to drive aircraft and engine components or accessories while the interstage bleed valves are required to ensure compressor stability.
Compressor discharge air at high pressure and temp. is bled from the engine through ports or valves at intervals along the compressor case and at the end of the diffuser. It is ducted as a source of power

Front 9

Define interstage bleed air.

Back 9

It is ducted overboard to prevent compressor stall during certain periods of low thrust operation.

Front 10

Describe the starting sequence for a gas turbine.

Back 10

When the starter accelerates the compressor sufficiently to establish airflow through the engine, the ignition is activated and then the fuel is added. Must continue to accelerate the engine after light-off, and even after the engine reaches self-accelerating speeds.

Front 11

Describe the four types of abnormal starts.

Back 11

hot start: exceeding the max allowable temp for the turbine section during start
hung start: when the temp within the turbine section continues to rise, and the compressor rpm stabilizes below normal.
false start: occurs when compressor rpm stabilizes below normal, and the turbine temperature remains within limits.
Wet start: when the fuel-air mixture does not light off initially, but has capability to eventually ignite.

Front 12

Describe a DC Electric starter.

Back 12

Mechanically connected to the compressor and is mounted on either the engine accessory gear box or the front frameof the engine. A battery, auxilary power unit or external source may be used to supply electric current to the starter motor.

Front 13

Describe an Air Turbibe Starter

Back 13

(pneumatic starters) most common used on large gas turbine engines. A small, geared, air turbine motor is attached to the engine. Air is directed to the air turbine, which accelerates the compressor.

Front 14

Describe a basic aircraft ignition system.

Back 14

Normally used for gas turbine engines. Provides both high voltage and an exceptionally hot spark, which gives an excellent chance of igniting the fuel-air mixture at reasonably high altitudes.

Front 15

Describe the two types of ignitors.

Back 15

Annular-gap: protrudes slightly into the combustion chamber liner to provide an effective spark.
Constrained-gap: tends to jump in an arc which carries it beyond the face of the chamber liner. Consequently, it operates at a cooler temp. than that of the annular-gap plug.