3 - Fuel

Question 1

What are jet fuels comprised of?

Answer 1

Mix of liquid hydrocarbons, all kerosene based

Question 2

What is wide-cut fuel? What designator does it have? What is its volatility/flash point?

Answer 2

Jet B, essentially a mix of kerosene and gasoline.
Low flash point, high volatility.

Question 3

What is the % of kerosene/gasoline in Jet B?

Answer 3

30% kerosene 70% gasoline

Question 4

Where are Jet A, A-1, B, JP5 used? What colour are they?

Answer 4

A-1, most of world
A, mainly USA
B, very cold climates, low flash/freeze point
JP5, a/c carriers, high flash (safety consideration)

All straw coloured or colourless

Question 5

What is the difference between Jet A and Jet A-1?

Answer 5

Jet A has a higher freeze point

Question 6

What colours are the stickers for jet fuels (3)

Answer 6

All white writing/black sticker

Jet A, black background
Jet A-1, grey background
Jet B, yellow background

Question 7

What is volatility and what 2 factors is it characterised by?

Answer 7

The tendency to vaporise

1. Vapour pressure
2. Distillation profile

Higher volatility fuel will have greater vapour pressure and lower initial distillation temperatures (easier starting esp in cold wx)

Question 8

What are the advantages of low volatility?

Answer 8

Reduces vapour lock, evaporative losses, flammability

Question 9

Where do you identify what fuel an aircraft requires? are there any legal requirements?

Answer 9

Sticker next to filler required by law, POH, AFM, Tech log

Question 10

What are the 3 main variations of fuel tanks? What are the properties of each?

Answer 10

Rigid
- require space in structure for installation
- usually riveted/welded al-alloy
- can be covered in rubber coating (shock ab)

Bladder
- thin fabric impregnated with neoprene (or other impenetrable material)
- along with rigid must be restrained
- common as aux tank for large a/c

Integral
- inside of portion of structure sealed during manufacture and becomes fuel tank

Question 11

Why are some fuel tanks pressurised? What source would be used to do so?

Answer 11

To reduce vaporisation and provide positive pressure to the system pumps.

Engine bleed air or ram air.

Question 12

What is the purpose of a NACA duct?

Answer 12

Provide slight positive pressure to fuel vent so fuel is not drawn out in flight.

Question 13

What do fuel vents allow for?

Answer 13

Lets air out of the tank during climb and in during descent, and for refuelling.

Must be controlled in pressurised tanks (valves).

Question 14

Why is water contaminated fuel an issue? Is there anytime when it typically isn’t?

Answer 14

Dissolved water generally isn’t a issue

Free water can cause engine damage or failure, freeze and block filters/flow, and facilitate corrosion and microbial growth

Question 15

How is water checked for/removed from tanks?

Answer 15

It is denser than fuel so sits at the bottom of the tank, a telescopic pipe is used to check the fuel

Question 16

What is a sight glass?

Answer 16

Clear plastic or glass tube open to the fuel tank, fills to the same level of fuel as is in the tank.

Can have a float and indicating rod instead of fuel.

Question 17

How does a drip type indicator operate?

Question 18

How does an electrical ratiometer fuel indicator operate?

Answer 18

The movement of a float in the fuel tank moves a connecting arm to the wiper on the variable resistor in the tank. Resistor is wired in series with one of the coils in the radiometer type indicator.

As the resistance changes (float moving) the current to the coils changes, varying the magnetic field which the indicator points to.

Question 19

How does an electronic capacitance indicator operate?

Answer 19

Several variable capacitance transmitting probes are installed in a tank (metal), they extend the whole depth of the tank. The concentric plates are open so fuel can sit at the same level as the tank, fuel or air acts as a dielectric transmitting electric force as the fuel level changes.

The probes are wired in parallel, as the level of fuel changes the capacitance of each probe changes. The capacitance of all probes is totalled and fed to a fuel computing unit/indicator.

Question 20

What units does a electrical capacitance indicator give?

Answer 20

Mass, can give mass and/or volume

Question 21

What are the advantages of electrical capacitance indicators?

Answer 21

• No moving parts in tank
• Even during changes in attitude the reading will be accurate (reads total capacitance)

Question 22

What is the purpose of a fuel jettison?

Answer 22

Allows crew to jettison (dump) fuel, lowering ac weight.

The boost pump moves fuel from the tank to the manifold, where it flows away from the aircraft through dump chutes in the wingtips.

Question 23

What is the purpose of a fuel cross-feed system?

Answer 23

Individual fuel systems on a ME a/c are interconnected, fuel from any tank can be fed to any engine. Provides flexibility for fuel management.

Question 24

What order are fuel tanks consumed? Why?

Answer 24

Centre tank, wings from inboard to outboard.

Outboard tanks provide bending relief.

Question 25

What are the purpose of auxillary (boost) pumps? What type is most common?

Answer 25

ensure positive pressure to the engine driven pump, aid in starting, crossfeeding, jettison

electrically driven centrifugal

Question 26

What is the purpose of an engine driven pump?

Answer 26

Deliver a continuous supply of fuel at the proper pressure to the engine.

Question 27

How does a constant displacement, rotary vane type engine driven pump operate?

Answer 27

If the outlet pressure is too high the bypass valve plate lifts snd fuel is returned to the pump inlet.

If the inlet pressure is higher than outlet the bypass valve plate lowers and fuel passes through.

Question 28

What is the purpose of a jet pump? How does it operate?

Answer 28

To scavenge fuel from the low points of the tank and ensures the boost bump surge box is always full for the pumps. Uses Venturi effect.