The importance of weight distribution

Nowadays, airplanes allow us to move large loads in an efficient, safe and prompt way. Pilots, thus, have to be aware of how much the aircraft weighs and where the load is located.

These calculations are what are known as loading and balance and mass and balance. In fact, among the exams student pilots have to take, they have the subject of ‘Mass and Balance’.

Weight definitions

When preparing a flight, pilots refer to different weights. Some of these are:

  • Empty weight: This is the weight of an airplane and its installed equipment, e.g. (radio, fire extinguishers, first aid kits, etc).
  • Maximum weight with zero fuel: This indicates the maximum weight the plane can load without taking into account jet fuel.
  • Take-off weight: This is the total weight of the plane at the time of take-off.
  • Landing weight: This is the total weight of the plane upon landing. On a normal flight, it corresponds to the take-off weight minus the used-up fuel.

Mass vs Weight: Are these the same thing?

Although in regular speech we don’t really take it into consideration, mass and weight of an object are not the same. Every object has a fixed mass but its weight will change according to its location.

Weight is the result of multiplying mass by gravity but gravity is not fixed. For example, Earth’s surface gravity is 9.8m/s², whereas Mars´ is 3.71m/s² and Jupiter’s is 23.12m/s².

This means an object with a mass of 10kg on Earth will have a weight of 98 Newtons (N) in Mars, 37.1N in Mars and 231.2N in Jupiter.

Does the mass and balance of an aircraft affect its gravity centre?

Of course, it does! According to where the load is located, its gravity centre is going to change from one location to another. It’s fundamental for pilots to know the location of the airplane’s gravity centre as its manoeuvrability will be very much affected.

A gravity centre close to the nose of the airplane will make it very stable when flying, however, it will require more force on the controls to manoeuvre. The fuel consumption will also increase and so will stall speed.

On the other hand, a rear centre of gravity reduces the stability of the airplane despite increasing manoeuvrability and reducing fuel consumption and stall speed.

Pilots have to know the load, mass and balance of an aircraft

The behaviour of airplanes is not always the same; and weight has a lot to do with these changes. A heavier aircraft will need more thrust force and a longer runway for take-off. It will also have a higher stall speed and will also use more of the runway for landing.

Due to all of these, prior to each flight, pilots have to fill in load and balance graphs. In them, the weight of the plane has to be indicated, its on board fuel, the weight of the passengers and load, as well as indicting the temperature and altitude of the airport, so that the landing and take-off distances are obtained.

To conclude, it is of great importance for pilots to know all the weights the aircraft carries so they can optimise routes and altitudes and reduce flying time in fuel.