Lubrication Midterm Exam

Design Features Related to Lubrication

– Aircraft reciprocating engines are specially designed to support proper lubrication under all operating conditions using built-in features.

Drilled Oil Passages (Oil Galleries)

– Internal drilled passages in the engine block, crankshaft, and connecting rods that allow oil to flow directly to critical components.

Purpose of Oil Galleries

– Ensure continuous lubrication of even the innermost engine components.

Main Bearings

– Engine components that receive oil through drilled passages to reduce friction and wear.

Connecting Rod Bearings

– Bearings lubricated by oil galleries to support smooth rod movement.

Camshaft and Valve Mechanisms

– Engine components that receive oil through internal passages.

Grooved Bearings and Journals

– Bearings designed with grooves and holes that distribute oil evenly around the rotating shaft.

Oil Film

– A protective layer of oil that prevents metal-to-metal contact between moving parts.

Oil Jets and Sprays (Piston Cooling Nozzles)

– Oil spray nozzles aimed at the underside of pistons in some aircraft engines.

Purpose of Oil Jets

– Reduce piston temperature, prevent piston distortion, and improve engine cooling.

Proper Crankcase Design (Oil Control)

– Engine crankcase and sump shape designed to control oil flow effectively.

Crankcase Oil Functions

– Direct oil flow correctly, prevent excessive foaming, and allow easy drainage for scavenge pumps.

Breather System

– A system that prevents pressure buildup inside the crankcase.

Purpose of Breather System

– Allows oil to circulate smoothly without being forced out of seals and gaskets.

Lubrication Engineering Concept

– The engine is engineered specifically to support lubrication, not merely filled with oil.

Lubrication System Types

– Aircraft reciprocating engines use wet sump and dry sump lubrication systems.

Wet Sump System

– A lubrication system where oil is stored in the engine crankcase.

Wet Sump Oil Return

– Oil drains back into the sump by gravity after circulation.

Wet Sump Characteristics

– Simple, lightweight, but limited in oil capacity.

Dry Sump System

– A lubrication system where oil is stored in an external tank rather than in the crankcase.

Dry Sump Oil Circulation

– A pressure pump supplies oil while separate scavenge pumps return oil to the tank.

Dry Sump Advantage

– Allows more oil to be carried and performs better during sharp maneuvering.

Dry Sump Lubrication Components

– Major components that are also found in wet sump systems.

Oil Tank

– The oil reservoir in a dry sump system.

Oil Tank Requirements

– Must withstand vibration, flight loads, and allow oil expansion and foaming.

Oil Tank Positioning

– Positioned higher than the pump inlet to allow gravity feed.

Pressure Oil Pump

– An engine-driven, usually gear-type pump that delivers oil under pressure.

Pressure Pump Function

– Draws oil from the tank and sends it to lubrication points.

Regulating (Relief) Valve

– Limits oil pressure in the lubrication system.

Scavenge Pump

– A pump that returns oil from the crankcase and gear housings back to the oil tank.

Scavenge Pump Capacity

– Often larger than the pressure pump to prevent oil pooling.

Oil Filter

– Removes dirt, metal particles, and carbon from circulating oil.

Bypass Valve

– Allows oil to flow unfiltered if the oil filter becomes clogged.

Oil Cooler

– A heat exchanger that removes heat from the oil.

Oil Cooling Methods

– May use air cooling, fuel cooling, or dual systems.

Thermostatic Bypass Valve

– Controls oil flow through the cooler based on oil temperature.

Oil Passages and Tubing

– Carry oil from the pump to bearings, pistons, camshaft, and valves.

Engine Internal Galleries

– Distribute oil directly to lubrication points inside the engine.

Oil Pressure Indicator

– A cockpit instrument used to monitor oil pressure.

Oil Temperature Indicator

– A cockpit instrument used to monitor oil temperature.

Abnormal Oil Indications

– Help diagnose engine or lubrication system failure early.

Fuel System

– A group of components and lines designed to store, control, filter, and deliver fuel to the engine.

Fuel System Importance

– Ensures efficient and safe engine operation during all phases of flight.

Fuel System Purpose

– Delivers fuel to the engine, maintains pressure and flow, and ensures proper combustion.

Fuel System Failure Effects

– May cause loss of power, rough engine operation, or engine failure.

Fuel Storage Function

– Fuel is stored in strong, lightweight, corrosion-resistant tanks.

Fuel Supply Function

– Fuel flows to the engine by gravity or by engine-driven and electric pumps.

Fuel Filtration Function

– Removes dirt, rust, and water from fuel.

Fuel Measurement Function

– Controls and measures fuel flow based on throttle and mixture settings.

Fuel and Air Mixing

– Fuel is mixed with air before entering cylinders in carburetor systems.

Gravity Feed Fuel System

– Fuel flows from the tank to the engine by gravity.

Gravity Feed Tank Location

– Fuel tank is located above the engine.

Gravity Feed Use

– Common in small, light aircraft.

Pump Feed Fuel System

– Uses pumps to deliver fuel to the engine.

Pump Feed Use

– Used when fuel tanks are below the engine.

Fuel Injection System

– Fuel is injected directly into each cylinder or intake port.

Fuel Injection Advantage

– Provides more precise fuel control and better efficiency.

Carburetor System

– Uses a carburetor to mix fuel and air in the correct ratio.

Carburetor

– A mechanical device that mixes fuel and air and delivers it to engine cylinders.

Carburetor Function

– Adjusts the fuel-air mixture depending on engine speed and power needs.

Aviation Gasoline (AvGas)

– Fuel specially refined for aircraft piston engines.

Volatility

– The ability of gasoline to change from liquid to vapor easily.

Purpose of Volatility

– Aids quick engine starting and proper fuel-air mixing.

Vapor Lock

– A condition caused by fuel that is too volatile.

Octane Rating

– A measure of fuel’s resistance to knocking or detonation.

Knocking

– Abnormal combustion that can damage engine components.

High Octane Fuel

– Can withstand higher compression without detonation.

100LL

– The most commonly used aviation gasoline today.

Energy Content

– The amount of power produced when fuel is burned.

High Energy Fuel

– Produces more engine power and better aircraft performance.

Freezing Point

– The temperature at which fuel begins to freeze.

Low Freezing Point Requirement

– Prevents fuel line blockage at high altitudes.

Fuel Stability

– The ability of fuel to remain chemically stable during storage.

Unstable Fuel Effects

– Can form gums and varnish that clog fuel systems.

Clean Burning

– The ability of fuel to burn completely.

Clean Burning Benefits

– Reduces carbon buildup, prevents spark plug fouling, and increases engine life.

Color Coding of AvGas

– A safety system used to identify correct fuel types and prevent fueling errors.

Carburetor

– A mechanical device used in aircraft reciprocating engines to meter, atomize, and mix fuel with air in the proper proportion for combustion under varying operating conditions.

Use of Carburetors in Light Aircraft

– Carburetors are still widely used because of their simplicity, reliability, and ease of maintenance.

Importance of Carburetor Knowledge

– Improper fuel–air mixture can lead to power loss, rough engine operation, carburetor icing, or engine failure.

Purpose of a Carburetor

– Provides the correct fuel–air ratio, atomizes fuel, delivers a uniform mixture, adjusts mixture for power and altitude, and ensures smooth engine operation.

Basic Principle of Carburetion

– The carburetor operates based on Bernoulli’s Principle, where increased air velocity causes reduced pressure that draws fuel into the airstream.

Bernoulli’s Principle

– As air velocity increases, pressure decreases.

Venturi

– A narrowed section of the carburetor that increases air speed and lowers pressure.

Venturi Effect

– The pressure drop in the venturi draws fuel from the float chamber into the airflow.

Carburetor Airflow Action

– Uses increased air speed and reduced pressure to draw fuel, which can lead to carburetor icing.

Jet Engine Inlet Function

– Slows air to increase pressure for stable airflow and efficient engine operation.

Float-Type Carburetor

– A carburetor that uses a float mechanism to maintain a constant fuel level and meters fuel using pressure differences in the venturi.

Float Chamber (Float Bowl)

– Stores fuel and maintains a constant fuel level for proper metering.

Float and Needle Valve

– Regulates the amount of fuel entering the float chamber based on fuel level.

Discharge Nozzle

– Releases fuel into the airflow at the venturi.

Throttle Valve

– Controls the quantity of fuel–air mixture entering the engine and regulates engine power.

Mixture Control

– Adjusts the fuel–air ratio according to altitude and engine operating conditions.

Operation of a Float-Type Carburetor

– Airflow through the venturi creates low pressure that draws fuel from the float chamber, mixes it with air, and delivers it to the engine.

Rich Mixture

– A mixture containing more fuel and less air, used during engine start and high power.

Lean Mixture

– A mixture containing less fuel and more air, used during cruise for fuel efficiency.

Effects of Improper Mixture

– Causes rough engine operation, overheating, spark plug fouling, and loss of power.

Factors Affecting Carburetion

– Air density, engine speed, temperature, and throttle position.

Air Density Effect

– Decreases with altitude and requires mixture adjustment.

Engine Speed Effect

– Higher RPM requires increased fuel and airflow.