Wet Tail – Fuel is stored in Tail not only for storage, but to adjust the C.G. position.
Wet Wings – Fuel is stored in Wings.
Each tank is vented into the Atmosphere to equalize the Pressure in fuel tanks with the Atmospheric Pressure.
If Vents are clogged pressure on top of the fuel will decrease & fuel flow will decrease & Eng. may fail.
Fuel Vent Heaters – provided to prevent Vents from clogging due to icing.
Each fuel tank has Sump – to collect impurities
Drain – is used to drain impurities.
Fuel in the Sump is the Unusable Fuel.
Fuel tanks have Baffle Plates – to prevent Surging of fuel.
A fuel filter is provided to collect impurities, if filter gets Clogged, a fuel fitter by pass line is provided (Now fuel will not be filtered).
Fuel filter also has a Sump & Drain.
There is another Drain provided at the lowest point in the fuel lines.
Fuel Cocks – allows/stop Fuel Flow to the Engine.
Electrical (Booster) Mechanical (Engine Driven Pump)
In big Aircrafts– Fuel Cocks are not in the cockpit, but can be operated from the cockpit.
Low Pressure Cocks – is placed before Engine Driven Fuel Pump.
High Pressure Cock – is placed after Engine Driven Fuel Pump.
If Low Pressure Cock is switched off. Engine stops, after some time, because some amount of fuel has already gone at the Engine Driven Pump.
If High Pressure Cock is switched off Engine stops immediately.
Booster Pump is before the Engine Driven Pump.
It is an Emergency Unit, and is intended to be used in the condition when a EDP fails, therefore all critical stages of flt Take off, Landing etc. they are kept ON.
1) Booster Pump helps to remove Vapor Locks
2) Removes Fuel Imbalance in the Wings, which is very critical in case an Engine fails in a Multi Engine Aircraft.
3) In some a/c as height increases gravity of fuel decrease, therefore fuel flow decreases & because of this reason the Booster Pumps are kept ON to supply fuel under press to the engine above a Specified Altitude (Booster pumps are fitted in the fuel tanks).
Therefore, in case of Electric failure Booster Pumps will not be available & Aircraft has to Descend to a lower altitude so that constant flow of fuel through gravity feeding is available.
Vapor lock forms due to the presence of fuel vapor into the fuel lines – they prevent Gravity flow of fuel.
Causes of Fuel Vapors –
1) High Volatile Fuel (Gasoline is very highly Volatile as compared to the Turbine fuel).
2) High Temperature of Fuel
3) Lower Atmospheric Pressure. At Low Pressure Boiling point of fuel decrease, therefore In Simla, (High Altitude, Low Pressure) H2O boils at low Temperature.
4) Slushing of Fuel due to Turbulence.
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Fuel content garages:
1) Float Type
2) Float Type with Electric Indication
3) Electrical gauges – they are Capacitance type of Fuel Gauges.
Capacitor – Prevents flow of Current & in turn gets charged up.
As fuel decrease capacitance continues to decrease.
Electrical Gauges gives Weight of the Fuel & not Volume.
Di-electric – that substance in Capacitor which prevents flow of Current.
Fuel Pressure Gauges – measures Pressure after Engine Driven Pump & before High Pressure Cock.
It indicates Pressure of fuel going into the engine.
If fuel pressure decreases Engine fails.
Fuel press Annunciator (Warning Light) glows if fuel pressure decreases.
Fuel Flow Indicator – Indicates Rate of Fuel Flow in each Engine.
Fuel Totaliser – gives total value of fuel left in all the tanks.
Fuel content gauges are unreliable in low Content ranges, therefore Fuel Totaliser is more reliable.
Fuel Heaters – are used to heat the fuel to prevent freezing of any H2O in the fuel.
Fuel Temperature Gauges – Indicate when to switch ON and OFF the heat.
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Fuel heaters
1) Oil to Fuel Heat Exchanger – Hot oil is used to heat fuel & it also causes the Oil Temperature to decrease.
2) Air to fuel – Hot oil from Engine compressor is used to heat fuel
Specific gravity – S.G of fuel depends upon Temperature of fuel
If Temperature increase S.G decreases
Weight of fuel depends upon S.G. of Fuel
Warm fuel is Light in Weight.
Cold fuel is Heavier in Weight.
Fuel Contamination – is mainly caused by H2O Vapor.
Fuel can hold H2O vapor in the dissolved form.
Amount of H2O vapor held by the Fuel depends upon Temperature of fuel.
Higher the Temperature more H2O Vapor can be dissolved.
H2O can be reduced from fuel by reducing Temperature of the fuel.
In night when Temperature falls, H2O Vapor Condenses and forms H2O, which settles at the bottom of the Wing. During starting of the Engine it gives a rough running or may even cause Engine failure. Therefore Drains are provided, because H2O is heavier it tends to settle at the bottom of fuel tanks, drain in provided at lowest point in the line. .
In night when temperature is ejected to fall, fuel tanks on filled to the top, to prevent Fuel Condensation.
If the fuel in the tank is low the air above the fuel in fuel tank will cause a drop in Temperature fuel tank walls will become Cold & Condensation will take place.
Condensation is a process of Water Vapor turning into Liquid.
Filling tanks to full after last sortie of the day will decrease Fuel Condensation.
Water being heavier then air will settle at the bottom of the Wing & cause rough running or even Engine failure. Therefore, fuel tanks are Drained before first flight of the day to drain any water accumulated at the bottom of the wing.
In night when temperature is expected to fall fuel tanks are filled to the top after last sortie of the day, to prevent Fuel Condensation & Eliminate any airspace above fuel.
If Temperature increases, Fuel Expands, Volume increases.
Fuel Additives
Isopropyl Alcohol – decreases the Freezing Temperature of fuel.
Ethylene Glycol Monoethyle Eather – absorbs the Water Vapor dissolved in the fuel.
Then additives must be added in specified percentage.
These additives are added to the fuel because Microbiological bacteria can form in the fuel tanks, & can go along with the fuel to the engine & cause problems.
Dip stick – to measure fuel from top of tanks.
Drip stick – is a stick, which when pulled down, comes lower & fuel starts Dripping out of stick as it happens you stop & read the markings.
Drip Stick is a Hollow Stick.
When Temperature is expected to rise if fuel tanks are full, As Temperature increases Density decreases Fuel expands Fuel Volume increases. It will cause fuel to overflow the tanks.
Maximum Payload– is that Payload that can be carried in an Aircraft subject to Structural Limitations.
is the difference between Zero fuel Weight – Empty Weight.
Empty Weight – 27,000 lbs
Mon Zero fuel wt – 28,000 lbs
Maximum Takeoff Weight – 44,000 lbs
Therefore payload here is 28,000 – 27,000 = 11,000 lbs.
Zero fuel Weight restriction comes due to Wing Root Restrictions.
Lift provides upward force, causing stress on the wings. Therefore fuel in the wings give a downward force, counter acting this upward force.