Girish Linganna
The term ‘g-force’, commonly referred to as ‘force’, is used to gauge the acceleration exerted by the gravitational pull of Earth on an entity or a person.(Acceleration means change in the velocity of an object, which could be an increase or decrease in speed, or a change in the direction of motion).
It is worth emphasizing that the lowercase letter, ‘g’, is used to distinguish it from the gravitational constant, ‘G’, and is written in italics to distinguish it from the unit of weight measurement, ‘gram’.
The two most familiar forces of gravity are 0 g, which is felt in environments without gravity, and 1 g, which is the force experienced by any object on Earth at or above sea level.
How Does g-force Work?
Let us consider the example of riding in a car, which is an experience well-known to almost everyone. Whenever a car changes speed or direction, we feel the effects of g-forces.
These g-forces are experienced longitudinally when the car accelerates or brakes, causing us to move backwards or forwards, and laterally when the car changes direction, causing us to move from side to side. The intensity of these g-forces increases with the strength of the change in speed or direction.
G-force when flying aeroplane
To make an aeroplane fly, an amount of g-force equivalent to its weight must be applied upwards. This process may seem easy, but it is crucial that all necessary steps are taken to ensure a safe flight.
The training of pilots includes learning how to manage g-forces effectively.
G-forces and aeroplane pilots
Pilots experience significant impacts of g-forces, which can affect their physical abilities. For instance, during a 60° turn, a pilot weighing 80kg will experience a weight increase to 160kg, making it challenging to move their limbs. However, pilots undergo extensive training to manage these effects.
When experiencing intensely strong g-forces, a phenomenon, known as a ‘blackout’, may happen. This occurs when blood flows towards the lower body, leading to a temporary loss of vision that may last a few seconds. This has been depicted in the movie, Top Gun: Maverick.
In military aviation, pilots frequently encounter g-forces and, therefore, wear specialized suits that apply pressure to the lower body, preventing blood from flowing downward. This is not a concern in commercial aviation where g-forces are typically minimal.
Military and aerobatic pilots have the ability to endure up to 10 g-forces with proper training and methods. It is essential for them to acquire the necessary skills to withstand such intense physical stress.
On an ordinary roller-coaster ride, the human body can usually tolerate up to 5 g-s. However, military pilots and astronauts need to undergo rigorous g-force training to prepare their bodies for up to 9 g-s.
If the g-s go beyond this limit, it can lead to g-induced loss of consciousness (g-LoC) that results in the diversion of blood from the brain, thereby causing pilots to lose control of their planes.
Training to Withstand g-force
Most individuals have experienced a tingling feeling in their stomach while rapidly descending in an elevator, which is caused by the gravitational or g-forces acting on their body. This same sensation can also be felt while riding roller-coasters or driving down steep inclines.
When you first experience it, it may come as a surprise. But, after a few repetitions, your body will adapt and you will not feel anything. This same process applies to pilots who undergo training to endure g-forces. As they accumulate more hours of flying experience, the impact of g-forces lessens significantly.
The Army utilizes rotating machines that spin rapidly to enable pilots to experience the impact of g-forces during simulations.
How to Calculate g-forces
When a pilot initiates a turn, the g-forces on their body increase. But how does the pilot determine the magnitude of the g-forces? The answer is there exists a formula that links the aircraft’s pitch degrees during the turn to the g-forces produced.
This formula is 1/cos(alpha) = g-forces, where alpha is the pitch degree of the aircraft.
If you input values into the formula, you can find that a 45° turn equals 1.41 g, whereas a 60° turn equals 2 g.
However, a pilot need not bother with these calculations while flying because most aeroplane come fitted with g-force meters.
Positive g-forces, negative g-forces
There are two types of g-forces, which are positive and negative g-forces.
Positive g-forces are produced during turns or steep ascents, resulting in the accumulation of blood in the lower parts of the body.
When we use the controls with a forward force or during steep descents, negative g-forces are generated, which have the opposite effect of positive g-forces and cause blood to flow towards the head.
Negative g-forces can be the most unpleasant and challenging to endure since they are not a regular part of our daily experiences.
Plane categories according to g-forces they can withstand
Just like human beings, different aircraft have different capabilities to withstand g-forces. To account for this, there are multiple categories of aircraft.
Normal
Maximum positive: 3.8 g
Maximum negative: -1.52 g
Utility
Maximum positive: 4.4 g
Maximum negative: -1.76 g
Acrobatic
Maximum positive: 6 g
Maximum negative: -3 g
Commercial aircraft
Maximum positive: 2.5 g
(2 g if the flaps are extended)
Maximum negative: -1 g
To prevent excessive loads, pilots must be aware of their aircraft’s limitations. Furthermore, aircraft maintenance requirements become more specific as g-forces increase.
The author is Defence and Aerospace analyst.
Disclaimer: Views expressed are personal and do not reflect the official position or policy of Financial Express Online. Reproducing this content without permission is prohibited.