11.10 Fuel Systems Flashcards
What does a fuel system usually consist of?
Tanks, pumps, filters, valves, lines and metering and monitoring devices.
What are rigid fuel lines made of?
Steel or aluminium alloy
What are the two basic types of fuel?
Reciprocating fuel (avgas)
Turbine fuel (Jet fuel)
How is AVGAS made?
Hydrocarbon compound refined from crude oil by a process called fractional distillation.
How is AVGAS different to jet fuel?
It is really volatile and extremely flammable with a low flash point.
What types of jet fuel are there?
Jet A1
Jet A
Jet B
What is the flashpoint of Jet A and A1?
43 to 65 degrees c
Which is better at the lower temp, A1 or A?
A1
What is the density of A1 and A at 15 degrees c?
0.81kg/litre
What three types of fuel tank are there?
Rigid removable
Bladder
Integral
What were many early fuel tanks made of?
Terneplate, a thin sheet of steel coated in lead or tin alloy.
What is a wet wing?
Integral tank design
What does NGS stand for?
Nitrogen generating system
What does the NGS do?
Designed to improve safety by reducing the risk of fuel tank explosions in aircraft. It does this by replacing oxygen in the fuel tanks with nitrogen
How does the NGS get nitrogen?
Extracted from the bleed air.
What four classifications of fuel leak are there?
Leak
Seep
Heavy seep
Running leak
How long is needed to monitor a leak?
30 mins
What area is classed as a stain?
19mm diameter
What area is classified as a seep?
19-38mm diameter
What area is a heavy seep?
38-101mm
What is SFAR 88?
Manages the safety, inspection and procedures of the fuel system and its components.
What is CDCCL?
Critical design control configuration limitations.
What does CDCCL control?
Refers to a feature of the fuel system design, for which integrity must be maintained to ensure that unsafe conditions do not develop.
What kind of components may you find as part of CDCCL?
Bonding leads
Harnesses and probes
Pumps
Access panels
Are CDCCL’s mandatory and how can they be changed?
Yes, only with approval from the NAA
What must the concentration of fuel vapours be kept below?
The lower explosive limit.
What is FQIS?
Fuel Quantity Indicating System
What four options does the selector valve have in a gravity feed system?
Shut off to the engine
Feed from the right wing
Feed from the left wing
Feed from both wings
What are large aircraft fuel systems split into?
Storage
Vent
Distribution
Feed
Indicating
What is a wobble pump?
Old school hand operated pump that delivers fuel backing up the engine driven pump.
What is the disadvantage of a wobble pump?
It requires fuel lines to be run through the flight deck.
How do vane type pumps regulate flow?
Adjustable pressure relief component
Centrifugal pumps are normally in the tank, what do they need if they are outside the tank?
Removal valve so that the pump can be removed without draining the fuel.
Depending on aircraft design what is the centrifugal boost pump used for?
EDP
What are fuel pumps cooled by?
The fuel flow
What do flapper valves allow?
Allow fuel to flow inboard to the pump.
What does an ejector pump do?
Ensure the pump always has liquid fuel at the inlet.
What is installed between the supply tanks and the engine fuel system to protect the engine-driven fuel pump and various control devices?
Low pressure filter
What are the three most common types of fuel filter?
Micron
Wafer screen
Plain screen
What size particles can a micron filter remove?
10-25 microns
What is the downside of micron filters?
They are easily clogged therefore a bypass is required.
What are the two weight limits that must not be exceeded?
Max take off
Max structural landing weight
What are fuel vent systems designed to do?
Relieve pressure in the fuel tanks and to allow proper flow of fuel.
What does the vent system maintain the pressure at?
Atmospheric
What can under pressurisation of the fuel tanks cause?
Component malfunction and engine fuel starvation.
What does not happen in an inflight fuel transfer?
Fuel is not moved from one tank to another, instead it is used to feed the engine until the levels are corrected.
For a ground fuel transfer what must the engineer do?
-Open the x feed valves
-Switch on boost pumps in tank which fuel is leaving
-Open defuel valve
-Open refuel valve for tank that is receiving
In a ground fuel transfer what does opening the defuel valve achieve?
Connects the engine feed manifold to the refuel manifold.
Fuel cross feed valves are motor actuated, what main parts do they have?
Valve body
Adapter and shaft
Actuator
What is the actuator in the fuel x feed valve?
28V DC
How many fuel flow indicators are there?
One per engine
Where is the temp sensor usually located?
Main fuel tank
Where are low pressure sensors located?
Boost pump inlet lines
What is a ratiometer type fuel quantity sensor?
The most common, uses a DC loop which utilises variable resistance to drive the indicator.
How do capacitance type fuel quantity sensors work?
Wired in parallel, as the level changes so does the capacitance of each one. A computer then sums the individual capcitances.
What is used to match the capacitance output with the pre calibrated indicator?
A trimmer
The amount of electricity stored in a capacitor depends on what 3 things?
Area of the plates
Distance between the plates
Dielectric constant
What is meant by the ullage?
Emptiness of the tank
What calculations does an ultrasonic fuel quantity system use?
Fillage = Total height - ullage
Valve in transit lights have what lighting states to indicate position?
Abnormal condition- Dim
Transit- bright
Normal- off
What two methods of refuelling are there?
Gravity overwing
Pressure
What are the main components of a typical refuelling system?
Couplings
Valves
Manifold
Diffusers
What three modes of pressure refuelling are there?
Manual
Automatic
Override
What is key before refuelling in manual mode?
Calculate the distribution
What pressure is pressure defuelling?
25 psi to 50psi
When will the FCMC start an aft transfer?
Landing gear and slats retracted
Trim tank not full
Inner tank above 6250kg
When will the aircraft do an automatic fuel transfer forward?
CG equals target
Inner tank less than 4000kg
