From the face of a young girl, suddenly turned into an old woman and returned to the beginning. The effects of G-forces on the human face can mostly be seen on the muscles and temporary changes in appearance, but they actually do much more to our bodies.
Acceleration is measured in units of gravitational force, abbreviated in English as the G force (gravity – gravity). Normally on the ground, people experience a force of gravity of 1G. When flying around, diving or doing a vertical loop, the upper limit G force that the pilot can experience reaches 7.5 to 8G, when launching the parachute even exceeds 10G, exceeding the endurance limit of a well-trained and physically fit pilot. During the jet pilot’s parachute jump, the phenomenon of unconsciousness (fainting) often occurs although the pilot’s great overload time is only about 1-2 seconds. This is also the reason why so many fighter pilots flying over the sea in an emergency need to parachute to escape often encountering a lot of danger when in this case of temporary fainting.
Gravity is an accelerating force. This means it acts on objects to change their velocity. All bodies exert a gravitational force on each other, and this force is unique because it can act over very large distances. On and near planet Earth, our planet’s gravity is so great because Earth has so much mass that all other gravitational forces are essentially insignificant. This force has been calculated to be approximately 9.82 m/(s^2) , and is commonly referred to as ‘g’, as you may recall from high school physics class.
It is important to note that according to Newton’s Second Law of Motion, F = ma, the force of gravity is closely tied to the mass of an object and changes proportionally to this value. For example, the gravitational force on the moon (an object much smaller than the Earth) is only 1.62 m/(s^2). Gravity is the reason why objects fall to the surface of the Earth, and also the force that airplane wings have to resist to create lift. When the lift of an airplane is greater than the force of gravity, controlled flight becomes possible as the Wright brothers demonstrated to the world in 1903.
The human body, like the rest of life on Earth, has adapted to life on land, in which we are constantly exposed to Earth’s gravity (g). For simplicity, let’s call this standard gravity of the Earth (9.82 m/s^2) 1G. However, in pilot flights, they may encounter situations where there is more or less of this 1G constant.
Accordingly, the physiology of their bodies will all be affected and react to the change in G force. When an airplane is flying towards the Earth and exerts thrust on that path of motion, it is accelerating at that rate plus 1G (9.82 m/s^2). As the same plane accelerates out to escape the surface of the Earth, the sum of the acceleration forces will be the difference from the thrust and 1G.
Accordingly, the force G acts on the human body in different axes (or directions). They are usually described as the x, y, z axes. Each has a positive (+) or negative (-) direction, where the positive direction is downward in the same direction as the Earth’s gravity and vice versa.
Gx is described as the force acting on the body from the chest to the back; Gy is a force exerted from shoulder to shoulder, and it is encountered during an aileron roll (an aerobatic movement in which the aircraft makes a 360° turn). Aerobatic pilots frequently encounter this type of G-force and are still able to safely and accurately control the aircraft. Gz is the force of gravity acting on the vertical axis of the object – parallel to the spinal cord.
So, how do these forces affect the body’s ability to function? The axis most relevant to this is Gz, because the G force transmitted along this axis occurs frequently in flight and also has a significantly larger physiological impact. Acceleration in the Gx axis is commonly experienced by astronauts during space shuttle launches. The Gy acceleration is less relevant, but it is also gaining more attention due to the development of newer generation fighters with omnidirectional propulsion such as the F-22 and F-35. For simplicity, the term ‘G’ in the rest of the article is usually applied only to forces in the Gz axis.
The circulatory system is most significantly affected by the increased G force during flight. Even at 1G, a person’s blood pressure during a stroke will have the highest pressure in the lower extremities (legs) and lowest in the brain (in the skull) due to gravity. Because our bodies have adapted to the 1G environment, we have built mechanisms to compensate for this difference. And when the G-force is increased, the upper physiological phenomenon is magnified, and the blood pressure difference between the skull and the lower part of the body becomes larger and leads to significant cerebral hypoxia (no blood = no oxygen). The end result is unconsciousness.
In aeronautics, this is known as G-LOC, or G-induced loss of consciousness, and to this day it remains a major cause of loss of control in both fighter aircraft and aircraft. military combat and civil aerobatics. For example, during the 1990s, the US Air Force lost about one aircraft per year due to G-LOC.
In addition to the effects on circulation, the increased G-force disrupts respiration by diverting blood to the base of the lungs, deflates the small air sacs (called alveoli), and creates ventilation/pump incompatibility. blood due to air remaining in the upper part of the lungs, where there is very little blood flow.
Other less severe effects of G-forces are musculoskeletal pain (usually limited to the back and neck) and small bruises called petechiae caused by broken capillaries. This usually occurs in gravity-dependent areas of the body and is known as the Geasles.
To somewhat limit the impact of G-forces, pilots are often dressed in special protective clothing as well as oxygen masks. In addition, they often have to undergo large G acceleration training to prevent unconsciousness during flight.
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