In this post you will find answers to issues related to the Aircraft loading and centering, the load allowed in an aircraft or the relationship between the load and fuel of the same.
In aviation, too often the sentence that gives the title to this text is the key that reveals the final cause of a plane crash. Aircraft often have proportionally very small margins on both parameters, hence the importance of a careful calculation of the mass and balance’.
Keeping track of the aircraft’s load and balance will be equally necessary and important for both long (we recommend reading more about the longest commercial flights in the world) and short flights.
Differences between load and balance
The concepts of loading and centering, although they travel together and generally affect each other, should be considered separately. Only in this way will we understand exactly the role played by a correct calculation of them, and the importance of keeping below the maximum parameters recommended by the aircraft manufacturer.
Let’s start by defining what the maximum load of an aircraft is. The maximum load of an aircraft is the authorized weight of the goods it can carry when circulating in airspace.
On the other hand, the center of gravity of an aircraft is also commonly known as its center of gravity. These are some of the factors that can be considered essential for the safe and efficient operation of aircraft.
Being below the maximum load limits of the aircraft but totally off-centre can have consequences as dire as the opposite case of an overloaded aircraft, but within the limits of its centre of gravity.
Risks of overloading an aircraft
In short, the load is the weight we add to that of the empty aircraft which will complete the total weight at take-off. That is, the fuel needed for the flight; the motor oil, without which the engine plant of the aircraft could not work; the luggage or objects that travel with us on board, and finally ourselves.
This Total Take-Off Weight (WTO) cannot exceed the Maximum Take-Off Weight (MTOW) recommended by the manufacturer. It is therefore essential to know in detail the different weights of the various elements on board, while attached to the weight of the aircraft in empty will directly oppose, through the force of gravity, the ability to generate sustenance of the wings.
Going “over the top” also means a considerable increase in the need for acceleration at take-off, which translates into higher runway consumption by having to increase the take-off stroke and greater effort from the landing gear.
In flight, an excess load severely limits the manoeuvrability of the aircraft and the pilot’s ability to control it. The increase in stall speed means that any simple manoeuvre involves considerable difficulty and risk, and in the event of moderate or severe turbulence the structural strength of the aircraft is seriously compromised.
The landing with excess of load will require a greater speed of approach and the race will also be longer, so we will need a greater length of runway with the consequent risk if for whatever reason we need to make an engine and air. The braking capacity of the aircraft will also be considerably reduced.
To learn more about how cargo behaves and centering on planes we recommend reading more about the largest planes in the world.
Practical tips for calculating the load
Secure the load properly. Cargo movements, especially in the most compromising phases such as take-off and landing, can lead to extremely dangerous changes in the aircraft’s G.C.
Fuel consumption during the flight sometimes gradually alters the G.C. Let’s take it into account.
Flying alone and with little or no baggage, we must consider that our G.C. will always be a little advanced. Let’s keep this in mind.
Respect the maximum permissible loads in each area of the aircraft, according to the manufacturer’s manual.
The centering in the airplane
Once the process of determining how many kilos (or, if you prefer, pounds) of cargo we intend to carry has been completed, and once we are sure that the total weight is below the MTOW (Maximum Take Off Weight), or maximum take-off weight recommended by the manufacturer for the aircraft in question, we will have to decide how to place that weight inside the aircraft.
This is the concept of centering the load that so much affects the behavior of an aircraft in flight.
To do this, we must imagine the aircraft as if it were a scale, with one of the saucers on the nose and the other on the tail. The plane’s centre of gravity (C.G.) will coincide with the point of balance between the two.
The point of support where the entire weight of the aircraft is tilted, and whose limits are determined in each model during certification flights. The G.C., to guarantee the stability of the aircraft, is generally located in front of the aerodynamic centre. That is, the point where the lifting forces are exerted.
To calculate the position of the G.C. the manufacturer provides (we have already said that the plane must be considered as a balance) an imaginary line called “datum”, which divides the plane perpendicularly in two. In planes with a tricycle train this line usually coincides with the firewall.
As the load is placed far or near this “datum”, it will generate a “moment” that determines the maximum weight we can load at each point of the plane, which is lower the farther away from the datum.
Risks during the flight
It is essential to keep within the enclosure marked by the manufacturer in the centering table. Notwithstanding the way in which we distribute the different loads along the plane, always within the marked limits, it will determine the position of the G.C. with respect to the aerodynamic centre, by moving it forward or backward.
An advanced G.C. keeps a low angle of attack, and therefore less prone to stall, but be careful: It also makes rotation more difficult, increases wing loading and induced resistance, which translates into less range and higher fuel consumption.
When approaching and retrieving at the moment of the take-off, greater force must be exerted, and the risk of a take-off with a nose wheel (tricycle train) or a hood (tail slide) will be greater.
Flying (or trying to fly) with a delayed C.G. results in greater problems, if possible. Flying in these conditions implies a tendency to rearing which can lead to stall situations without warning, especially in turbulent weather conditions. Stall in these circumstances becomes much more difficult to steer and redirect. In the event of a spin-off, recovery is greatly complicated.
As we can see, it is always advisable to remain as close to a neutral G.C. as possible. However, a forward centre of gravity will always be preferable to one at the back of the plane.
Practical advice for centering the plane
As we have seen during the reading of the plane’s load and balance, excess weight, as well as for health, is not recommended for flight.
For this purpose (and not only to collect the excess weight) the airlines weigh the luggage. While it is easy to establish standardized average weights with passengers, it is impossible with luggage. A large suitcase can contain light objects, while a small briefcase can be full of heavy items.
Keep in mind when preparing the flight at the often ignored Density Altitude. With heat the response of the plane decreases as does its carrying capacity. This factor, together with an excess of load, increases the risk of having a scare.
From everything we have seen as a conclusion, we extract that it is very important to carry out a correct loading operation. The loading operation must be in accordance with the tables and graphs provided by the manufacturer and always within the limits assumed by the aircraft. All this is as important as not overdoing it.