The first thing to bear in mind is that aviation fuels are classified into two main groups: AVGAS and jet fuels.
Fuels for internal combustion piston engines are AVGAS, while fuels for turbine engines are Jet Fuels.
But let’s look at each of them in more detail below.
Jet fuels are used in turbine engines, such as those used in commercial aircraft. Although there are several subtypes, the most common is Jet-A1, also called paraffin.
Jet-A1 is a very efficient fuel that generates high power with relatively low fuel consumption. Moreover, it is not only used as a fuel, but also as a coolant for the engine oil.
For the combustion of Jet-A1 to take place, i.e. for it to ignite, a minimum temperature of 38°C is required.
As explained above, there are many subtypes of Jet Fuels and, after Jet-A1, the best known is Jet-B, which is the most commonly used in cold climates.
As with Jet Fuels, there are several subtypes of AVGAS, the best known of which is AVGAS 100 LL.
Fuels used in general aviation are focused on safety rather than power. Bear in mind that most are single-engine aircraft, so it is essential that there are no problems during flight.
In addition, AVGAS fuels are very efficient, as their weight is minimal compared to the energy they generate, and they have very little waste.
The octane rating, or octane number of a given fuel, is the anti-knock power of the fluid. OK, let’s take it one step at a time.
Detonation is when the fuel does not burn progressively inside the cylinder, but instantaneously. Detonation must be avoided at all costs, as it damages the engine and significantly reduces the power output.
The higher the octane rating of a fuel, the greater its resistance to detonation. More efficient engines, i.e. those using a higher compression ratio, need fuels with a higher octane rating.
While Jet-A1 is clear, or straw-yellow, AVGAS can be red, green or blue, depending on the subtype of fuel.
In fact, the different colours of AVGAS are not actually the colours of the fuel itself, but rather pigment is added to quickly identify which one is being used.
🔴 AVGAS 80 is red.
🟢 AVGAS 100 is green.
🔵 And AVGAS 100 LL is blue.
Before the first flight of the day, it is essential to drain the aircraft. What is this and what is it done for?
Well, draining the aircraft consists of taking a small sample of fuel to check that there is no water or sediment present.
In addition, this process is used to check that the fuel lines leading to the engine are not blocked.
If water is found in the sample, the process must be repeated until no more water is found. You can see how it is done in our post about the Diamond DA20 preflight check. You will learn a lot of things… Promise!
With the aim of reducing emissions, the use of so-called SAFs (Sustainable Aviation Fuels) is being promoted.
SAFs are made from waste, generally used oils and greases, which are deoxygenated and hydroprocessed to obtain a pure product to combine with traditional hydrocarbons.
Iberia has already incorporated the use of PBS in some of its flights with the Airbus A320Neo; we are talking about an 85% reduction in emissions.
Of course, not all aircraft can hold the same amount of fuel, but here are some examples.
The Airbus A320, the most widely used short-haul aircraft in Europe, has a maximum capacity of 27,200 litres of fuel. Amazing, isn’t it? Well, wait for it.
The world’s largest passenger jet, the Airbus A380, needs just over 200,000 litres to fill its tanks!
Bearing in mind that the fuel tanks of our cars have a capacity of between 45 and 65 litres, the figures are even more incredible, aren’t they?
The wings of commercial aeroplanes have an interior lining which turns them into a watertight tank to be filled with fuel; this is what is known as wet wing.
You may be asking yourself why inside the wings and not somewhere else, right? It’s really quite simple.
Just like everything else in aviation, there’s not only one motive for something, but various reasons, some of which are as follows:
As a general rule, the centre of gravity in commercial aeroplanes is situated between the leading and trailing edge of the wing, therefore aiding also with its stability.
Now you know where fuel is carried in commercial aeroplanes you may be asking yourself where our own planes do.
Commercial aircraft have a system that allows the engines to be fuelled from the main fuel tank, although pilots can manually indicate whether they want fuel from another tank to be used.
Additionally, they have cross-feed valves, which allow any engine to be fed from any tank. These are only used in the event of an incident or if there is an imbalance between tanks.
In our aeroplanes, it’s slightly different.
Now that you know which type of tank is most commonly used by commercial aircraft, let’s review the other types that exist:
There are two methods of delivering fuel from the tank to the engine.
You’ve probably seen videos or photos of planes refuelling in flight. This is one of the most complicated manoeuvres in the world because, not only does the pilot have to fly very close to another plane, but also have to set up the necessary couplings.
But don’t worry, that’s the job of military pilots! Commercial aircraft have large enough fuel tanks to be able to fly from one destination to another without the need for in-flight refuelling.
But, as this is a rather interesting topic, let’s look at the types of in-flight refuelling that can be done.
The basket is the most common mode and, as the name suggests, it is a basket that is deployed with a hose, which must be inserted into the aircraft stand.
The other in-flight refuelling system is the boom. It consists of a telescopic boom that is controlled from the aircraft and, as with the basket, must be inserted into the aircraft mount.
To facilitate the manoeuvre, the tanker aircraft has an operator who provides feedback to the pilots to make accurate contact.
