Oil Systems And Cooling Systems

Question 1

Explain the main function of an engine oil system

Answer 1

Lubricate - limits component wear and temperature from friction
cool - pumped through out engine and heat absorbed by oil and dissipated
clean - foreign materials are picked up by oil and removed by the filter.

Question 2

What are the secondary functions of oil

Answer 2

Sealing and cushioning.

Question 3

Describe the effect of temperature on the viscosity and lubrication qualities of oil

Answer 3

Different grades have different viscosities and decreases with an increase in temperature.

Question 4

Compare the features of the ashless dispersant (AD) oils used in piston aero- engines with straight mineral oil and detergent oils.

Answer 4

Mineral
•Prone to oxidation, sludge and carbon deposits, which clogs pipes, filters

• Detergent
• Clean the engine, but form metallic ash compounds, which clogs pipes and filters
• Ashless Dispersant (AD)
• Doesn’t form carbon, sludge or ash deposits

Question 5

With respect to oil grades, differentiate between the commercial aviation numbers and SAE ratings

Answer 5

SAE rating system (Society of Automotive Engineers)

An aircraft flight manual may show the oil to be used in SAE rating system, in aviation we use the “commercial aviation number” for oil
•80 grade oil = SAE 40
•100 grade oil = SAE 50

Question 6

Differentiate between a wet sump and a dry sump oil system

Answer 6

Wet sump (very common in aircraft engines)
•The oil accumulates in the sump at the bottom of the engine. There is no oil tank
•Not ideal for aerobatic aircraft

• Dry sump
• There is an oil tank, and the sump is much smaller
• The oil is pumped into a tank, from which it is pumped around the engine

Question 7

What are the components of an oil system? (6)

Answer 7

Scavenge pump 
Oil pump
Oil cooler
Oil tank (dry sump system only)
Filter
Pressure relief valve

Question 8

How does a dry sump work? include how the function of these things:

• Engine driven oil pump, pressure relief valve
• oil galleries
• oil gauges
• oil sumps and scavenge pumps
• oil cooler
• oil tank and filter

Answer 8

Oil is stored in a tank when not circulating and pumps are used to scavenge the oil from the bottom of the sump and back into the seperate oil tank.

Engine driven-gear oil pumps are used in dry-sump.

A scavenge pump is used to lift the oil from the sump to the oil tank and a main pump is used to provide oil at pressure through the oil galleries.

Oil pressure relief valve is incorporated into the system on the engine side of the main fuel pump and when oil pressure reaches a limit valve will open and divert oil back to the pump inlet to control the pressure.

Oil gauge indicates oil pressure provide by oil pump.

Oil filters remove any solid particles of foreign matter such as grit or carbon from the oil as it circulates.

Question 9

How does a wet sump work? include how the function of these things:

• Engine driven oil pump, pressure relief valve
• oil galleries
• oil gauges
• oil sumps and scavenge pumps
• oil cooler
• oil tank and filter

Answer 9

Oil is stored in a tank when not circulating and pumps are used to scavenge the oil from the bottom of the sump and back into the seperate oil tank.

Wet sump system only the main pump is required, being used to draw its supply of oil directly from the sump.

Oil pressure relief valve is incorporated into the system on the engine side of the main fuel pump and when oil pressure reaches a limit valve will open and divert oil back to the pump inlet to control the pressure.

Oil gauge indicates oil pressure provide by oil pump.

Oil filters remove any solid particles of foreign matter such as grit or carbon from the oil as it circulates.

Question 10

Explain the need for periodic oil changes.

Answer 10

Oil filters build up debris over time and therefore reach a maximum, so they should be changed every 50 hours.

Question 11

Describe the likely results of operating an engine with:
(a) incorrect oil type;
(b) incorrect oil quantity.
(C) overtighten dipstick

Answer 11

Oil quantity checked prior to every flight
Too little – risk of engine damage and failure
Too much – can cause compression issues

Do not over-tighten the dip stick - pressure build up

Do not mix oil grades – different viscosities = different lubrication

Question 12

Describe the likely causes of:

(a) low oil pressure;
(b) high oil pressure;
(c) high oil temperature.

Answer 12

Low oil pressure - low oil, scavenge pump failure, faulty gauge, oil leak

High oil pressure - faulty oil pressure relief valve

High oil temperature - engine too warm or overheated

Question 13

Explain the relationship between a fluctuating or low oil pressure reading accompanied by a rise in oil temperature and what to do

Answer 13

The most likely reason is a serious issue with the lubrication system.

Land as soon as possible If the engine runs out of oil, and the above symptoms would match an oil leak and an overheating engine, the engine will seize

Question 14

Describe the actions the pilot should take in oil system malfunctions.

Answer 14

High oil temperature - open cowl flaps if fitted, reduced throttle setting and consider an early landing.

Low oil pressure - land ASAP

Question 15

Explain the reasons why excessively high engine temperatures and rapid cooling must be avoided

Answer 15

Excessive high temperatures can damage engine components and potentially cause detonation.

Rapid cooling causes shock cooling which leads to cracked cylinder heads, engine blocks and the engine ages at a faster rate.

Question 16

Describe the ways in which heat from the combustion process is dispersed from a typical aero-engine.

Answer 16

They are typically air cooled but some have water cooled cylinder heads.

Air cooled uses intake ducts, propellor slipstream, ram air, ducts and baffles.

Question 17

In a typical aircraft engine, explain the function of:

(a) cowling ducts and baffles;
(b) cooling fins;
(c) pilot-operated cowl flaps;
(e) radiator;
(f) intercooler.

Answer 17

(A) placed to direct a smooth flow of cooling air through the fins around each cylinder to ensure they’re cooled evenly.
(B) around cylinder heads to increase distance of cooling
(C) cooling at high power and can be adjusted by the pilot, only closed in cruise
(F) only found on super or turbocharged engines as they warm the engine faster.

Question 18

Explain the general engine handling techniques for maintaining engine temperatures within the proper range, for aircraft:

(a) without CHT (cylinder head temperature) gauge or cowl flaps;
(b) fitted with CHT gauge and cowl flaps.

Answer 18

(A) unable to determine temperature of the engine, so avoid running engine on ground for long periods at high power settings, climbing at high power, low speed for long and descending with throttle closed for long times
(B) monitor engine temperature and if it is going out of range open cowl flaps to appropriate amount.

Question 19

When should cowl flaps typically be opened and closed?

Answer 19

Open for takeoff
partially open for climb
closed during cruse
and closed during a low power descent