Engines Ch. 3 Cooling & Lubrication

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Why is oil between moving parts?

Oil acts as a lubricant, reducing friction and wear between moving parts, which helps prevent overheating and prolongs engine life.

4 functions of oil

clean, cool, lubricate, seal,

other functions of oil

protects from rust, heats fuel, changes prop pitch,

Viscosity

a fluids resistance to flow, oil labeled with numbers,

Saybolt Universal Viscometer

measures how fast a fluid flows, oil categorized by SAE system, W means good for winter use.

flash point

temp a liquid gives off ignitable vapours

fire point

enough ignitable valors to have a continuous flame

cloud point

low temp where wax contents solidify and cloud

pour point

lowest temp it can still be poured

specific gravity

weight of oil vs. weight of distilled water at a given temp 

Straight Mineral Oil

used on new or overhauled engines to wear in engine, not as effective

Ashless dispersant oil

main oil, replaces mineral oil, forms less sludge

synthetic oil

avoided as its untested

pressure distribution (oil sprayers)

oil pump delivers pressurized oil to parts

splash distribution (oil pan)

oil distributed as parts move and splash, often used together with oil sprayers

Wet sump

oil is stored and splashed in a pan, no external parts, hard to cool, bad for inverted

Dry Sump

oil in external tank and pumped to engine, more parts, gets oil everywhere

heat wasted

60-70% heat wasted, half remaining is exhaust, other half must be dispelled by engine

1 gallon of avgas can boil

75 litres of water

Cooling Fins

increase surface area exposed to air

cowling shape

shaped to guide air to cylinders

baffles

in cowling to guide airflow, blast tubes add air

Winter fronts

block some air to prevent cooling

cowl flaps

allows air out so more can enter in slower flight

augmenters

shorter exhaust pipe, allows more air out to let more air in.