Fuel/fuel Systems

Question 1

Two basic fuel systems

Answer 1

Gravity fed
Pump fed

Question 2

Gravity fed

Answer 2

High wing aircraft
Fuel pressure decreases as fuel is consumed
Required to have pressure that supports 150% maximum flow required
Fuel strained prior to reaching carburettor

Question 3

Gravity fed pros and cons

Answer 3

Cons
Changes in attitude have major effect on fuel flow (direction of gravity)
Low operating pressures susceptible to vapour lock (fuel to vapour) which decreases pressure

Pros
Cheap

Question 4

Pump fed

Answer 4

Low wing aircraft
Main components…
Fuel tank
Fuel strainers and filters
Tank selector valves
Engine driven pump
Auxiliary pump
Primers
Priming systems

Question 5

Fuel tanks

Answer 5

Usually in wings
Aluminium fabric synthetic rubber
Evenly distributes weight of fuel
Have…
Filler caps
Expansion space (for fuel expansion due to heat)
Vents (to vent and get air in to replace fuel)
Baffles (prevent fuel surging and provide tank strength) (metal plate with holes)
Sumps and drains (lowest points of tank collects contaminates)
Standpipe (tank to engine pipe, elevated to reduce impurities to engine)
Fuel quantity detectors (mechanical or float)

Question 6

Fuel strainers and drains

Answer 6

Fuel filtered 3 times before reaching carburettor
1 at tank outlet for major contaminants (water dirt)
2 lowest point in system (contaminants drained)
3 before carburettor or injection system (fine gauze for smaller contaminants)

Question 7

Tank selector valve

Answer 7

Selects tank capable of shutting off fuel to engine
Must be easily accessible
Cannot allow for inadvertent selection

Question 8

Engine driven pump

Answer 8

Connected to engine automatic operation w engine running
Delivers fuel at constant pressure (pressure relief valve recirculates excess to start of pump)
Boost pump for engine not running
Vane type most common
Bypass valve for failure of engine pump

Question 9

Aux pump

Answer 9

For starting, purging lines, priming cylinders and fuel injected engines, backup pump
Must allow for 120% engine demand

Question 10

Priming system

Answer 10

In tandem with carburettors
Additional fuel for starting
Hand pump or electric valve
More w cold engine less with hot
Off after ignition

Question 11

Engine temp start limits

Answer 11

90-120 warm
120+ hot

Question 12

Engine fire during start

Answer 12

Starter ….. keep winding
Tank selector …… off
Fuel pump ……. Off
Throttle …… open

If fire continues
Master switch …….. off
Abandon aircraft

Question 13

Fuel

Answer 13

Petrol- hydrocarbons

Question 14

Volatility

Answer 14

Ease with which liquid vaporises
High volatility vaporises easily (vapour lock)

Question 15

Anti Knock rating

Answer 15

Ability to resist knocking

Question 16

Octane

Answer 16

Refers to anti Knick rating
ISO octane has best rating
Octane 100 = same as iso octane

Question 17

Performance numbers

Answer 17

Tetra ethyl lead increases anti Knock rating above 100
Produces more power before detonation

Question 18

Fuel types

Answer 18

Mogas cars
Avgas aviation more regulation and less volatile than mogas and higher octane (green 100)
Avtur (jet A1) aviation turbine (straw coloured)

Higher fuel grade increases chance of plug fouling and corrosion
Lower fuel grade increases detonation and is illegal

Question 19

Causes of inflight engine failure

Answer 19

Fuel - contamination, starvation, pump failure, exhaustion
Air- intake blockage
Spark - magneto failure
Mechanical - mechanical, propeller

Question 20

In flight engine failure actions

Answer 20

Tank selector ……. Change tanks
Mixture …… full rich
Fuel pump …… on
Alternate air ……. Open
Ignition ……. Both