Aviation Powerplant Oil and Fuel Systems

Flashcards covering viscosity properties, oil system types, lubrication methods, engine mechanics, and fuel metering adjustments from the lecture notes.

Viscosity

The resistance to flow characteristic of a liquid, where oil that flows slowly is described as having a high viscosity.

Saybolt Universal Viscosimeter

A device used to measure oil viscosity for grading by heating the oil and measuring the time it takes for $60\,cc$ of it to flow through a calibrated orifice.

SAE

Society of Automotive Engineers; the organization responsible for identifying oil viscosity designations by number.

Flash Point

The temperature at which a liquid begins to give off ignitable vapors.

Fire Point

The temperature at which there are sufficient vapors to support a flame, which occurs at a higher temperature than the flash point.

Cloud Point

The temperature at which the wax or paraffin content in oil begins to solidify and separate into crystals.

Pour Point

The lowest temperature at which an oil flows or can be poured.

Straight Mineral Oil

Oil with no additives that has a tendency to oxidize at high temperatures; used mainly on new or newly overhauled engines.

Ashless-Dispersant

The most common aviation oil that does not form ash deposits and contains additives such as anti-wear and anti-foam.

Wet Sump

An oil system where all the oil is contained in the engine crankcase integral oil tank; it is simple and lightweight but difficult to cool.

Dry Sump

An oil system with a separate oil tank, well suited for radial engines, requiring more components like a scavenge pump.

Pressure Lubrication

Oil distribution where oil under pressure flows through passages to components like bearings, the camshaft, and crankshaft main journals.

Splash Lubrication

Lubrication produced by the movement of internal parts such as the crankshaft and gears, affecting cylinder walls and cam lobes.

Spray Lubrication

Lubrication where oil is forced through aimed nozzles, typically used in large engines.

Oil Dilution

A process for cold climates where fuel is injected into the oil pump prior to shutdown to thin the oil for easier circulation during the next start.

Thermostatic Bypass Control Valve

A valve in the oil cooler; when it is open, the oil bypasses the cooler and no cooling occurs.

Gear Type Pump

The most common oil pump consisting of two mesh gears that move a fixed volume of fluid per revolution of the pump.

Constant Displacement

A pump characteristic where a fixed volume of fluid is moved per each revolution of the pump.

Gerotor Type Pump

A pump with a spur or drive gear rotating inside a housing where oil is drawn in as space increases and forced out as space decreases.

Piston Stroke

The total distance a piston travels between the outward and inward limits within a cylinder.

Four Stroke Operation

An engine cycle that requires $2$ complete revolutions for the four strokes to occur.

Valve Timing

The specific point at which the intake and exhaust valves open and close.

Valve Overlap

The occurrence when both the intake and exhaust valves are open simultaneously around TDC.

Detonation

Uncontrolled explosion of the fuel/air mixture in the cylinder causing high temperatures, pressures, and engine knocking.

Pre-ignition

Premature ignition of the fuel/air mixture before the spark plug fires, often caused by hot spots like an overheated valve edge.

Compression Ratio

Calculated by dividing the Total Volume (at $BDC$) by the Clearance Volume (at $TDC$).

Journals

Crankshaft parts supported by bearings that allow the crankshaft to rotate freely and support it within the crankcase.

Crankpins

The locations on the crankshaft where the connecting rods attach.

Intake Valve

The entry point for air or air/fuel mixture, made of chrome, nickel, or tungsten steel with a smaller diameter shaft than the exhaust valve.

Exhaust Valve

The valve through which gases leave the cylinder, made of Inconel, silicon-chromium, or cobalt-chromium.

Metallic Sodium

A substance found inside the exhaust valve's larger diameter shaft that melts to transfer heat from the valve face to the stem.

Exhaust Valve Lead

The occurrence when the exhaust valve opens before bottom dead center ($BDC$).

Exhaust Valve Lag

The occurrence when the exhaust valve closes after top dead center ($TDC$).

Intake Valve Lead

The occurrence when the intake valve opens before top dead center ($TDC$).

Intake Valve Lag

The occurrence when the intake valve closes after bottom dead center ($BDC$).

Venturi Pressure Differential

A condition in a carburetor where intake air passes through a venturi creating $P1 > P2$, causing fuel to flow.

Rich Mixture

A ratio such as $11:1$ that has more fuel, cooler running temperatures, and may lead to plug fouling and ash deposits.

Lean Mixture

A ratio such as $16:1$ that has less fuel, hotter running temperatures, and a higher EGT.

Updraft Carburetor

The most common aircraft carburetor type, defined by the upward direction of airflow.

Butterfly Valve

Another name for the throttle valve that controls the amount of air passing through the carburetor.

Carburetor Idle Mixture Adjustment

An adjustment where turning the screw clockwise Leans the mixture and counter-clockwise makes it Rich.

Back Suction Mixture Control

A system where closing the vent valve eliminates pressure differential to stop fuel flow reaches the idle cut-off position.

Accelerator Pump

A component that pushes fuel out of a chamber and discharge nozzle when the throttle is opened rapidly to prevent a lean stumble.

Discharge Check Valve

A valve in the accelerator pump that prevents the siphoning of fuel from the chamber out of the discharge nozzle.

Pump Inlet Check Valve

A valve in the accelerator pump that prevents fuel from being pushed back into the float chamber.

Power Enrichment

A system that increases fuel flow at power settings above cruise to help dissipate excess heat, operating in parallel with the main metering jet.

Economizer

A system that works only at cruise settings to lean out the mixture and enhance fuel economy by bleeding atmospheric pressure.

Blocked Air Bleed Hole

A condition in a fuel nozzle that causes increased fuel flow.

Bendix Idle Rise

On a Bendix system, the idle mixture is set correctly if the engine shows an RPM rise of $25-50\,RPM$ before shut down.

Unmetered Pressure

The fuel pressure checked at idle RPM, adjusted via the relief valve on the pump.