Aircraft Lubrication Systems - Vocabulary Flashcards

Vocabulary flashcards covering key terms and concepts from the aircraft lubrication lecture notes.

Lubricant

A substance (typically oil) whose primary purpose is to reduce friction between moving parts by circulating a thin oil film in the engine.

Oil film

A continuous layer of oil that keeps moving surfaces apart to prevent metal-to-metal contact; friction becomes internal fluid friction.

Friction

Resistance to motion between moving surfaces; in engines it includes sliding, rolling, and wiping friction.

Sliding friction

Friction when one surface slides over another (as in plain bearings); surfaces are not perfectly smooth.

Rolling friction

Friction produced when a roller or sphere rolls over a surface; generally lower than sliding friction and used in antifriction bearings with balls between races.

Wiping friction

Friction that occurs between gear teeth under high loads; lubricant must withstand these loads.

Cushioning

The oil film acts as a cushion between metal parts, protecting bearings from shock loading.

Sealing

Oil forms a seal between piston and cylinder wall to prevent gas leakage from the combustion chamber.

Oil cooling

Oil circulating through the engine absorbs heat; can account for up to about 50% of total engine cooling.

Cleaning/Dispersant

Oil cleans by carrying particles to a filter; dispersant keeps particles in suspension, aiding filtration.

Corrosion protection

Oil coating protects internal parts from corrosion; important to prevent rust during operation and shutdown.

Life blood of the engine

A common phrase referring to engine oil, essential for performance and extending time between overhauls.

Viscosity

Resistance of an oil to flow; high viscosity = thick, low viscosity = thin; affected by temperature.

SAE rating

Viscosity grade system (e.g., 10 to 70); groups oils by viscosity at specified temperatures; does not indicate quality.

Saybolt Universal Viscometer

Instrument that measures viscosity by timing the flow of 60 cm³ of oil through an orifice at a set temperature.

Winter designation (W)

Letter W in SAE numbers (e.g., 20W) indicates suitability for winter use; not the same as dispersant-related W.

Ashless dispersant

A type of dispersant additive that helps keep contaminants in suspension without leaving ash deposits.

API gravity scale

API system for oil gravity; API numbers relate to density and can be converted to specific gravity with charts.

Specific gravity

Ratio of an oil’s weight to the weight of an equal volume of water; examples: SG around 0.9 corresponds to 7.2 lb per gallon.

Dispersant

Additive in oil that keeps particles in suspension so filters can remove them.

Viscosity index

A number describing how resistant oil viscosity is to temperature changes; higher VI means less change with temperature.

Flash point

Temperature at which oil begins to emit ignitable vapors; fire point is the temperature where vapors ignite.

Cloud point

Temperature at which oil’s wax content solidifies and crystals form, making the oil appear cloudy.

Pour point

Lowest temperature at which oil will flow or be poured.