12.32.4. Explain the term viscosity.
Viscosity = “Stickiness”
– high viscosity = thick and slow flowing oil
– low viscosity = thin and readily flowing oil
Excessively high temperatures reduce the viscousity and so the effectiveness of the oil as a lubricant
12.32.2. State the functions of an engine lubrication system.
Lubrication
– oil provides a thin film between moving surfaces
– this avoids metal to metal contact between moving parts
– avoids high friction forces and subsequent high temperatures
– avoids excessive wear on those parts
Cooling
– oil pumped under pressure goes through pipes and galleries to areas where needed
– this flow of oil is used to assist in cooling all parts of the engine
– absorbs heat generated in piston skirts, cylinder walls and main bearings
– heat is then dissipated via oil cooler
Cleaning
– the flow of oil will collect up dirt, grit and combustion products, metal flakes
– oil goes through a filter which removes solid contaminants from the oil.
12.30.8. Explain the importance of aircraft earthing during refuelling.
The aircraft and the fuelling equipment and components should be at the same electrical potential to avoid the possibility of a spark during refuelling
12.30.6. State the general rules for fuelling of aircraft, including the special precautions for the use of drum stock, and plastic containers.
1) Check the fuel is the correct type and grade
2) Position aircraft as far away from buildings and other aircraft as possible – if too windy apply park brake
3) Ensure engine not running and ignition switches OFF
4) Adhere to the No Smoking rule
5) Keep passengers / observers clear
6) Before starting the refuel – make sure the aircraft and fuelling equipment are electrically bonded together and earthed
– make sure bonding clip attached to aircraft before fuel caps removed
7) Do not refuel if an electrical storm is in the vicinity
8) Avoid resting the full weight of the refuelling nozzle on the intake neck of the tank – can result in cracking if done regularly
9) If conditions are wet / dusty try to avoid these contaminating the fuel
10) Once refuelling is done ensure the filler caps are refitted and properly locked in place
11) Complete the FUELLING DOCUMENTATION
12.30.4. Describe the procedure to be used for a fuel drain check.
1) Use a clean glass container and drain a small quantity of fuel – 50 – 100 mls from each fuel drain valve and the strainer drain valve.
2) Fuel strainer drain is found at the lowest point in the whole fuel system
3) Any water present should appear as small globules at the bottom of the container – other impurities will be darker coloured (be aware that it is possible to get all water in the container, so be aware of the colour of the drain sample)
4) If the check is negative from each drain then empty the contents into a suitable receptacle
5) Do not tip the contents back into the aircraft tank
6) If the check is positive – carry out further checks – seek guidance from instructor or maintenance engineer
12.30.2(c) . fuel tank construction and associated limitations.
– separate fuel tanks are located in each of the wings or in some aircraft in the fuselage. Some tanks use rubber bladders to contain the fuel, others seal the joints in a section of the airframe construction.
– incorporates an expansion space and vent above the level of the filler cap
– this enables the fuel to expand when warmed and excess pressure to be vented overboard
– filler caps are accessed from above the wing or on the fuselage as appropriate.
– overflow drain is fitted
12.30.2(b) . fuel quantity indicators;
– electronically operated fuel gauges are in the cockpit
– callibrated to be most accurate in the straight and level attitude
– if possible always back up reading by a visual check of the contents of the fuel tanks during pre-flight inspection using a dipstick.
12.30.2(a) . fuel tank, sump, drain point, supply line standpipe, vents, overflow drain;
Fuel tank
– Contains the aircrafts fuel.
Sump
– A low spot in the tank where contaminants (mostly water) can drain to.
Drain point
– A valve/tap in the sump through which contaminants can be drained.
Supply line standpipe
– the entry point of the fuel supply line. Normally stands up above the bottom of a sump in order to prevent contaminants from entering the supply line.
Vents
– incorporated to compensate for pressure changes caused by temperature changes which cause air/fuel in the tank to expand and contract.
Overflow drain
– allows fuel to drain if expansion or overfilling results in an excess of fuel in the tank.
12.30.2. Describe the function of the following components of a simple fuel system:
12.28. Fuel System Components