G-suit

A g-suit, or the more accurately named anti-g suit, is a flight suit worn by aviators and astronauts who are subject to high levels of acceleration force (g). It is designed to prevent a black-out and g-LOC (g-induced loss of consciousness) caused by the blood pooling in the lower part of the body when under acceleration, thus depriving the brain of blood. Black-out and g-LOC has caused a number of fatal aircraft accidents.

If blood is allowed to pool in the lower areas of the body, the brain will be deprived of blood, leading to temporary hypoxia. Hypoxia first causes a greyout (a dimming of the vision), also called brownout, followed by tunnel vision and ultimately complete loss of vision 'blackout' followed by g-induced Loss Of Consciousness or 'g-LOC'. The danger of g-LOC to aircraft pilots is magnified because on relaxation of g there is a period of disorientation before full sensation is re-gained. A g-suit does not so much increase the g-threshold, but makes it possible to sustain high g longer without excessive physical fatigue. The resting g-tolerance of a typical person is anywhere from 3-5 g depending on the person. A g-suit will typically add 1 g of tolerance to that limit. Pilots still need to practice the 'g-straining maneuver' that consists of tensing the abdominal muscles in order to tighten blood vessels so as to reduce blood pooling in the lower body. High g is not comfortable, even with a g-suit. In older fighter aircraft, 6 g was considered a high level, but with modern fighters 9 g or more can be sustained structurally making the pilot the critical factor in maintaining high maneuverability in close aerial combat.

A g-suit is a special garment and generally takes the form of tightly-fitting trousers, which fit either under or over (depending on the design) the flight suit worn by the aviator or astronaut. The trousers are fitted with inflatable bladders which, when pressurized through a g-sensitive valve in the aircraft or spacecraft, press firmly on the abdomen and legs, thus restricting the draining of blood away from the brain during periods of high acceleration. In addition, in some modern very high-g aircraft, the Anti-g suit effect is augmented by a small amount of pressure applied to the lungs (partial pressure breathing), which also enhances resistance to high G. The effects of anti-g suits and partial pressure breathing are straightforward to replicate in a simulator, although only continuous g can be produced artificially in devices such as centrifuges.

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