High-G training
Encyclopedia
High-G training is done by aviators and astronauts who are subject to high levels of acceleration ('G'). It is designed to prevent a g-induced Loss Of Consciousness (abbreviated G-LOC
G-LOC
G-LOC, pronounced 'GEE-lock', is the abbreviation of G-force induced Loss Of Consciousness, a term generally used in aerospace physiology to describe a loss of consciousness occurring from excessive and sustained g-forces draining blood away from the brain causing cerebral hypoxia...

), a situation when g-forces move the blood away from the brain to the extent that consciousness
Consciousness
Consciousness is a term that refers to the relationship between the mind and the world with which it interacts. It has been defined as: subjectivity, awareness, the ability to experience or to feel, wakefulness, having a sense of selfhood, and the executive control system of the mind...

 is lost.
Incidents of acceleration-induced loss of consciousness have caused fatal accidents in aircraft capable of sustaining high-g for considerable periods.

The value of training has been well established during the decades since the 1970s and has been the subject of much research and literature, and training has contributed to extending pilots' G tolerance in both magnitude and duration. This training has allowed pilots and crews to more safely exploit the capabilities of high performance aircraft. This training will become more important as new weapons systems are fielded with even higher performance capabilities.

Training includes centrifuge, Anti-G Straining Maneuvers (AGSM), and acceleration physiology.

Overview

As g-forces increases, visual effects include loss of colour vision (grey-out), followed by tunnel vision (where peripheral vision is lost, retaining only the centre vision). If g-forces increase further, complete loss of vision will occur, while consciousness remains. These effects are due to a reduction of blood flow to the eyes before blood flow to the brain is lost, because the extra pressure within the eye (intraocular pressure
Intraocular pressure
Intraocular pressure is the fluid pressure inside the eye. Tonometry is the method eye care professionals use to determine this. IOP is an important aspect in the evaluation of patients at risk from glaucoma...

) counters the blood pressure. The reverse effect is experienced in advanced aerobatic maneuvers under negative g-forces, where excess blood moves towards the brain and eyes red out
Redout
A redout occurs when the body experiences a negative g-force sufficient to cause a blood flow from the lower parts of the body to the head. It is the inverse effect of a greyout or brownout, where blood flows away from the head to the lower parts of the body. Redouts are potentially dangerous and...

.

The human body has different tolerances for g-forces depending on the acceleration direction. Humans can withstand a positive acceleration forward at a higher g-forces than they can withstand a positive acceleration upwards at the same g-forces. This is because when the body accelerates up at such high rates the blood rushes from the brain which causes loss of consciousness.

A further increase in g-forces will cause G-LOC where consciousness is lost. This is doubly dangerous because, on recovery as g is reduced, a period of several seconds of disorientation occurs, during which the aircraft can dive into the ground. Dreams are reported to follow G-LOC which are brief and vivid.

The g thresholds at which these effects occur depend on the training, age and fitness of the individual. An un-trained individual not used to the g-straining maneuver, can black out between 4 and 6 g, particularly if this is pulled suddenly. Roller coasters typically do not expose the occupants to much more than about 3 g. A hard slap on the face may impose hundreds of g-s locally but not produce any real damage: a constant 15 g-s for a minute, however, may be deadly. A trained, fit individual wearing a g suit and practising the straining maneuver, can, with some difficulty, sustain up to 9g without loss of consciousness.

The human body is considerably more able to survive g-forces that are perpendicular to the spine. In general when the g-force pushes the body forwards (colloquially known as 'eyeballs in') a much higher tolerance is shown than when g-force is pushing the body backwards ('eyeballs out') since blood vessels in the retina appear more sensitive to that direction.

Early experiments showed that untrained humans were able to tolerate 17 g eyeballs-in (compared to 12 g eyeballs-out) for several minutes without loss of consciousness or apparent long-term harm.

G-suits

A G-suit is worn by aviators and astronauts who are subject to high levels of acceleration ('G'). It is designed to prevent a black-out and g-LOC (gravity-induced Loss Of Consciousness), due to the blood pooling in the lower part of the body when under G, thus depriving the brain of blood.

Human centrifuge training


Human centrifuges are exceptionally large centrifuge
Centrifuge
A centrifuge is a piece of equipment, generally driven by an electric motor , that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis...

s that test the reactions and tolerance of pilots
Aviator
An aviator is a person who flies an aircraft. The first recorded use of the term was in 1887, as a variation of 'aviation', from the Latin avis , coined in 1863 by G. de la Landelle in Aviation Ou Navigation Aérienne...

 and astronaut
Astronaut
An astronaut or cosmonaut is a person trained by a human spaceflight program to command, pilot, or serve as a crew member of a spacecraft....

s to acceleration above those experienced in the Earth's gravity.

The US Air Force at Holloman Air Force Base
Holloman Air Force Base
Holloman Air Force Base is a United States Air Force base located six miles southwest of the central business district of Alamogordo, a city in Otero County, New Mexico, United States. The base was named in honor of Col. George V. Holloman, a pioneer in guided missile research...

, New Mexico operates a human centrifuge. The centrifuge at Holloman AFB is operated by the aerospace physiology
Aerospace physiology
Aerospace physiology refers to effects on the human body caused by characteristics of the aerospace environment.This subject includes, but is not limited to, the following topics:* Spatial disorientation and airsickness* Vestibular system...

 department for the purpose of training and evaluating prospective fighter pilots for high-g flight in Air Force fighter aircraft.

The use of large centrifuges to simulate a feeling of gravity has been proposed for future long-duration space missions. Exposure to this simulated gravity would prevent or reduce the bone decalcification
Bone decalcification
Bone decalcification is the removal of calcium ions from the bone through histological process thereby making the bone flexible and easy for pathological investigation....

 and muscle atrophy
Muscle atrophy
Muscle atrophy, or disuse atrophy, is defined as a decrease in the mass of the muscle; it can be a partial or complete wasting away of muscle. When a muscle atrophies, this leads to muscle weakness, since the ability to exert force is related to mass...

 that affect individuals exposed to long periods of freefall. An example of this can be seen aboard the Discovery spacecraft the film 2001: A Space Odyssey
2001: A Space Odyssey (film)
2001: A Space Odyssey is a 1968 epic science fiction film produced and directed by Stanley Kubrick, and co-written by Kubrick and Arthur C. Clarke, partially inspired by Clarke's short story The Sentinel...

.

Man-rated centrifuges are made by AMST Systemtechnik in Austria (Austria Metall SystemTechnik), Latécoère
Groupe Latécoère
The Groupe Latécoère is an aircraft company based in Toulouse, France. Founded by Pierre-Georges Latécoère in 1917, the company was known in the past particularly for its seaplanes...

in France, Environmental Tectonics Corporation (ETC) and Wyle Laboratories in the USA.
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