Aircraft Engine Lubricants

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Questions and Answers

What is the primary reason for using a lubricant in an aircraft engine?

To protect against corrosion
To reduce friction between moving parts (correct)
To cool the engine
To clean the engine

What is the primary difference between aviation piston engine oils and jet engine oils?

Piston engine oils are used for turbojet engines while jet engine oils are used for turboprop engines
Piston engine oils are synthetic while jet engine oils are petroleum-based
Piston engine oils are petroleum-based while jet engine oils are synthetic (correct)
Piston engine oils are used for outdoor protection while jet engine oils are used for internal storage

What happens when two metal parts with peaks and valleys rub together?

The metal surfaces are smoothed out
The metal surfaces become magnetized
The metal is worn away from the surfaces (correct)
The metal surfaces merge together

What is the purpose of inhibitors in aviation?

To provide outdoor protection or internal storage (A) Signup and view all the answers

What type of lubricants are used for turbojet, turboprop, or turbofan engines?

Either mineral-based or synthetic lubricants (A) Signup and view all the answers

How does the oil reduce friction between moving parts?

By wetting the surfaces and filling in the valleys (D) Signup and view all the answers

What is the purpose of the oil cooler in an aircraft engine?

To give up the heat from the combustion process to the outside air (C) Signup and view all the answers

What are greases composed of?

Mineral or synthetic base oils with metal soaps or organic thickeners (D) Signup and view all the answers

What is the result of the metal-to-metal contact between moving parts?

Increased wear (B) Signup and view all the answers

What is the main characteristic of speciality lubricants?

They are miscellaneous products with specific uses (C) Signup and view all the answers

What is the primary factor that determines the type of lubricant used in an aircraft engine?

The engine design and operating conditions (A) Signup and view all the answers

What is the viscous nature of oil used for in an aircraft engine?

To seal and cushion the moving parts (C) Signup and view all the answers

What is the general rule for applying oil to bearing surfaces?

Apply a quantity of oil sufficient to cover the bearing surfaces (B) Signup and view all the answers

Why did sodium soap greases tend to get washed out of the system?

Because they were soluble in water (C) Signup and view all the answers

What type of thickeners are used in high-temperature applications?

Non-soap thickeners, such as modified clays or organic compounds (C) Signup and view all the answers

What is the purpose of wiping the lubricating point clean and dry before applying oil or grease?

To prevent the accumulation of dirt or foreign matter (B) Signup and view all the answers

What is an example of a modified clay thickener used in some greases?

Microgel™ (D) Signup and view all the answers

What is the purpose of using inorganic fillers, such as molybdenum disulphide and graphite, in some greases?

To provide extremely high-temperature performance (D) Signup and view all the answers

What is a potential hazard of using an injector needle to inject grease?

It can inject grease into the hand or finger if it slips off the grease point (A) Signup and view all the answers

What is a characteristic of a zerk (hydraulic) fitting?

It has a push-on coupler that is more secure (C) Signup and view all the answers

What is the purpose of penetrants in aviation?

To free seized parts (A) Signup and view all the answers

What type of locations are dry lubes typically used in?

Turbine engine fan blades (D) Signup and view all the answers

What is a common outcome of a finger injury caused by an injector needle?

The finger will become swollen, stiff, and gangrenous (C) Signup and view all the answers

How are penetrants and inhibitors typically approved?

By the aircraft manufacturer and/or operator (B) Signup and view all the answers

What is the primary function of a grease gun?

To lubricate bearings at high pressure (C) Signup and view all the answers

Why are manual grease guns preferred for certain airframe lubrication tasks?

They minimize the risk of over greasing (B) Signup and view all the answers

What is the purpose of priming a new nozzle before its first use?

To ensure proper grease flow (A) Signup and view all the answers

What is the typical pressure range of a manual grease gun?

Several thousand psi (D) Signup and view all the answers

What is the purpose of dedicating a grease gun to a single type of grease?

To prevent contamination of different greases (B) Signup and view all the answers

What is the consequence of over greasing bearings?

Forcing grease into adjacent areas, causing damage (B) Signup and view all the answers

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Study Notes

Aero Engine Oils

Piston engine oils are typically mineral petroleum oils, either straight mineral or blended with additives, including part synthetic multi-grade oils.
Jet engine oils for turbojet, turboprop, and turbofan engines can be mineral-based or synthetic, with an emphasis on synthetic for modern engines.

Greases

Greases are formulated with mineral or synthetic base oils combined with metal soaps or organic thickeners, providing versatility in lubrication.

Inhibitors

Inhibitors protect parts from corrosion and can be oils, solvent compositions, pastes, or additives, effective for outdoor conditions and during storage.

Specialty Lubricants

Specialty lubricants cover various products such as gear oils, instrument oils, damping fluids, anti-seize compounds, and dry lubricants, catering to specific lubrication needs.

Lubricant Properties

Aviation lubricants are categorized into piston-engine oils and jet engine oils, each tailored to the physical and chemical requirements of respective engines.
Aviation piston engine oils primarily use petroleum base stocks, while modern gas turbine oils are predominantly synthetic.

Functions of a Lubricant

Reduces friction by forming a film between metal parts, allowing smoother movement and minimizing wear.
Provides cooling by absorbing heat from engine components and circulating heated oil to cool down.
Seals and cushions between moving parts, protecting against contaminants and ensuring optimal operation.

Oil Viscosity and Application

Oil viscosity is crucial for maintaining a protective film, determined by the clearance between moving parts.
Application of grease requires ensuring components are clean and dry to prevent contaminants while avoiding excessive accumulation.

Types of Greases

Early greases were thickened with calcium soap; sodium soap greases were later introduced but were prone to water washout.
Modern applications utilize water-resistant thickeners like barium, lithium, and aluminum compounds, and for high temperatures, non-soap thickeners or inorganic fillers like molybdenum disulfide are employed.

Safety with Lubrication Tools

Injuries can occur with injector needles if they slip, while zerk fittings offer a safer alternative for providing grease to components.
Grease guns are designed to inject pressurized grease into bearings, available in various types including manual and pneumatic versions.

Grease Gun Operation

A manual grease gun delivers about 1.5 grams of grease per pump stroke, with a lever mechanism engaging a zerk fitting for efficient application.
Each grease gun should be dedicated to a specific grease type to prevent cross-contamination and ensure proper lubrication practices, particularly to avoid over-greasing and damaging components nearby.

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