Fuel

Question 1

what is the normal type of fuel used in aircraft?

Answer 1

aviation gasoline or AVGAS.

Question 2

what are the grades of AVGAS? (4)

Answer 2

MOGAS 91 - PURPLE
MOGAS 95 - ORANGE/YELLOW
AVGAS 100LL - LIGHT BLUE/CYAN
AVTUR/JET A1 - STRAW COLOURED/CLEAR

Question 3

how do you read OCTANE? (e.g AVGAS 100LL)

Answer 3

100 is the octane number, the higher the better resistance to detonation or knocks.

LL means low lead. low lead content is 2mL per imperial gallon or one part per 2250

Question 4

if a fuel has a mix of 87% octane and 13% heptane normal what does this mean? and how can you improve it?

Answer 4

it’s graded as 87 octane. to improve fuel octane rating, Tetra Ethyl Lead (TEL) can be added.

Question 5

what is the max amount of TEL that can be added?

Answer 5

5.5ml per imperial gallon or one part per 800 for avgas.

Question 6

what does OCTANE 100/130 mean?

Answer 6

means that 100/130 AVGAS has an octane rating of 100 at the lean power settings and 130 at rich settings.

Question 7

how does a gravity feed system work?

Answer 7

gravity moves the fuel from the tank to the carburettor.

fuel flow is maintained due to gravity and so long as the pressure provided is 150% of the maximum flow rate required there’s no need for a fuel pump.

Question 8

fuel systems typically have what?

Answer 8

four arrangements and is normally set to both but if an imbalance occurs, manually selecting the one with more help.

Question 9

how do pressure systems work?

Answer 9

fuel is drawn from tanks and is routed via the fuel selector valve. which is then directed to the strainer via two fuel pumps. first is electrically driven and the second is an engine-driven pump.

In normal flight engine-driven pump supplies fuel under pressure to the carburettor. a fuel line also runs to the fuel pressure gauge in the cockpit. if the engine pump fails, the engine stops so the electric pump must be switched on immediately.

Question 10

when is the electric fuel pump switched on? and what can it do? (6)

Answer 10

• normally during critical stages of flight like takeoff and landing and at flights below 1000ft.
• Provides fuel for starting
• electrically driven
• purge fuel lines of vapour lock
• may prime cylinders
• supply fuel if engine driven pump fails

Question 11

what are in the tanks of pressure systems?

Answer 11

float type content units that may have direct reading fuel quantity transmitters not requiring power that sends information to fuel quantity gauges on the instrument panel.

Question 12

what is unusable fuel?

Answer 12

fuel in the tank(s) that is not considered to be accessible for running the engine

e.g if tank has 10 gallons, if the level falls to that of the outlet, there may be as 1 gallon left in the tank and that’s referred to as unusable fuel, so that means only 9 gallons are usable. the fuel gauges only read usable fuel

Question 13

what do the numbers mean at the of different fuel?

Answer 13

fuel grade - below a figure of 100 they’re known as octane rating and above they’re known as performance number.

Question 14

what are the three different types of fuel?

Answer 14

AVGAS - used for light aircraft
MOGAS - used for motor vehicles like cars
AVTUR - used by jet turbine aircraft.

Question 15

what are the characteristics of AVGAS? (4)

Answer 15

• Can cause damage if used in older lower compression engines.
• labelled red
• dyed blue
• higher quality control than MOGAS

Question 16

what are the characteristics of MOGAS? (4)

Answer 16

• may cause detonation in AVGAS designed planes
• labelled purple
• dyed purple for 91 and yellow for 95
• vapourises more easily than AVGAS causing vapour locks

Question 17

what are the characteristics of JET A1/AVTUR?

Answer 17

• straw or clear coloured
• kerosene smell
• damage AVGAS planes
• labelled black

Question 18

what can using MOGAS in AVGAS aircraft lead to? (3)

Answer 18

• leads to vapour locks in the engine
• the engine will produce less power which contributes to detonation
• spark plugs can foul.

Question 19

what is the most common contaminant in fuel?

Answer 19

water

Question 20

how can contaminants be avoided? (3)

Answer 20

condensation can occur at night inside the tank (if near empty) so keeping them full overnight minimises the chance.

The fuel system typically has a sump at the bottom of each tank collecting any contaminants that are heavier than fuel can collect. a check of fuel via taking fuel samples through the fuel drain should be done before each flight and after refuelling to check for contaminants.

if present show check with instructor or engineer.

Question 21

what are the disadvantages to a gravity feed system?

Answer 21

• extreme attitude changes can affect fuel flow. if gravity can’t assist the fuel into the carburettor, it’ll be deprived of fuel and cause engine failure.
• vapour locking. where fuel vapourises in the fuel lines prevent fuel from flowing.

Question 22

what is the use of the priming system?

Answer 22

to assist with starting the engine when it’s struggling to do so such as during cold days.

Question 23

how does a priming system work?

Answer 23

pumping fuel into most of the cylinders. operated from the cockpit with either a hand pump or electric activated it bypasses the carburettor and injects fuel directly into the cylinders.

Question 24

what is incorporated into most fuel systems and what do they do?

Answer 24

fuel filters and fuel strainers.

they are the last opportunity to stop impurities from entering the carburettor.

Question 25

what is normally at the bottom of each fuel tank?

Answer 25

sumps where any impurities heavier then fuel can collect. drain cock fitted at the lowest point allowing pilots to collect samples of fuel to find potential contaminants.

Question 26

why are fuel vents important?

Answer 26

allow atmospheric pressure to be maintained above the fuel as its being consumed during the flight. preventing a partial vacuum from developing in the tank which could lead to the collapse of the tank or fuel starvation.

Question 27

during pre-flight what should be done with fuel vents and filler cap?

Answer 27

check if secured tightly. vents aren't blocked or obstructed.

Question 28

what do baffles do?

Answer 28

stop fuel from sloshing and moving quickly from one end to the other. As if they were to move around it would mean the COG to suddenly move and would cause problems.

Question 29

Fuel lines from each tank will meet together where? and what does this allow a pilot to do?

Answer 29

meet together at the fuel selector which is operated from the cockpit. allows the pilot to choose whether the fuel is on or off and in some aircraft will allow for the pilot to select individual tanks.

Question 30

what does a fuel quantity gauge do? and how does it work?

Answer 30

tells you how much fuel remains in the tank. some might have a mechanical float with an arm or it may have a system that measure the capacitance from sensors in the tank.

Question 31

what does a fuel flow metre or fuel pressure gauge do?

Answer 31

allows a pilot to assess the fuel flow from the tanks to the engine.

Question 32

what is a cross feed system?

Answer 32

a system where if you have two or more fuel tanks and two engines you can decide whether to draw from one tank or both to engine 1 or 2.

Question 33

what are the general rules when refuelling? (7)

Answer 33

- park brake let off so that in the event of a fire it can be pushed away. - nobody inside aircraft if refuelling with avgas - engine and ignition off - no smoking - earth aircraft - hold nozzle in a way so that the weight of the hose is not resting on the aircraft and stressing the skin - look at nozzle and make sure its clean before putting in.

Question 34

what is the general procedure when conducting a fuel drain check?

Answer 34

during pre-flight inspection check for any fuel contaminants using an approved container to take a sample from fuel drain. any water will be seen at the bottom. never tip fuel sample back in, for the risk of contaminating the fuel. if contaminants are visible take another two samples and check if still present, if so consult engineer.

Question 35

when should a fuel drain check take place?

Answer 35

before flight and after refuelling, but refuelling you should wait 20 minutes to let contaminants work their way to the bottom.

Question 36

what should be considered when using drumstocks? (3)

Answer 36

# fill drum up so minimal air is left in the sum as fuel can be contaminated by water, dust and rust. store drum on its side so that the bung is completely covered with fuel. when uplifting fuel from a drum, the use of a filter can help keep contaminants out of your fuel system.

Question 37

refuelling from drumstocks what should you consider

Answer 37

stand drum upright but tilted slightly and chock it with the high side positioned at 12 o'clock, bung at 3 and vent at 9. allow drum to stand undisturbed for at least 10 minutes prior to fueling to let any internal contaminants settle out. connect the bonding lead from the drum to the aircraft before opening any fuel caps, and leave it in place until all fuel caps have been replaced.

Question 38

what are the considerations with non approved plastic containers?

Answer 38

with non approved plastic containers, a static charge can build on the container and this charge can then jump to another object causing a spark. this spark can ignite the fumes of the fuel being used.