A g-suit, or 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 have caused a number of fatal aircraft accidents.
Operation If blood is allowed to pool in the lower areas of the body, the brain will be deprived of blood. This lack of blood flow to the brain 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-force there is a period of disorientation before full sensation is regained. 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.
Design 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 (positive pressure breathing), which also enhances resistance to high g. The effects of anti-g suits and positive pressure breathing are straightforward to replicate in a simulator, although only continuous g can be produced artificially in devices such as centrifuges. Various designs of g-suit have been developed. They first used water-filled bladders around the lower body and legs. Later designs used air under pressure to inflate the bladders. These g-suits were lighter than the liquid-filled versions and are still in extensive use. However, the Swiss company Life Support Systems AG and the German Autoflug collaborated to design the new Libelle suit for use with the Eurofighter Typhoon aircraft, which reverts to liquid as the medium and improves on performance. The Libelle suit is under consideration for adoption by the United States Air Force.
History As early as 1917, there were documented cases of pilots' loss of consciousness due to g (G-LOC) that were referred to as "fainting in the air". The recognition that the tight turns required of RAF High Speed Flight pilots taking part in 1920s Schneider Trophy races causing blackouts meant a restriction to 4 g to limit them to "grey out" with only partial loss of vision. In 1931 a professor of physiology, Frank Cotton, from the University of Sydney described a new way of determining the center of gravity of the human body. This made it possible to describe the displacement of mass within the body under acceleration. Cotton had recognised the need for an anti-gravity suit during the 1940 Battle of Britain. It was estimated that 30% of pilot deaths were due to accidents, including black-out. Supermarine Spitfires, in particular, were capable of rapid turns that generated high g-forces, causing black-out when diving to fire or avoid enemy fire. With the development of higher speed monoplane fighters in the late 1930s, acceleration forces during combat became more severe. As early as 1940 some aircraft had foot-rests above the rudder pedals so that the pilot's feet and legs could be raised during combat in an attempt to minimize the negative effects of high speed turns. Large rudder deflections were often not necessary during such manoeuvres, but being able to cut inside the opponent's turning radius was.
Franks g-suit Wilbur R. Franks had suggested water-filled system in 1938 and in the absence of government funding he built a prototype – sized on himself – with private funding, but his work was limited by availability of a suitable aircraft. In 1940 the UK provided a Supermarine Spitfire to aid his research. The first g-suits were developed by a team led by Franks at the University of Toronto's Banting and Best Medical Institute in 1941. The suits were manufactured by the Dunlop company and first used operationally in 1942 by pilots of 807 Squadron Fleet Air Arm (FAA) flying Supermarine Seafires during the Operation Torch invasion of North Africa. These devices used water-filled bladders around the legs; two Marks (versions) were developed:
Franks Mark I suits were used by RAF Hawker Hurricane and Supermarine Spitfire pilots; Franks Mark II suits were used by the United States Army Air Forces and Royal Canadian Air Force pilots. Adoption of the suit by the RAF was limited, as there was concern about pilots exceeding the stress limits of their aircraft and the possibility of revealing its existence to the enemy.
… excerpt ends here. Continue reading the full article.
