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. 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. Research commenced late in 1940, and a suit was designed with rubber sacs covered externally by inextensible material. The sacs automatically inflated when g forces increased during flying. The suit was developed at the Sydney Medical School. Cotton constructed the first human centrifuge in the Anderson Stuart Building at Sydney University under tight wartime security. The volunteers, young airmen, were strapped by their legs to the centrifuge and subjected to high g-force and monitored until black-out occurred. All lost consciousness. On February 19, 1942, the day of the major Japanese
bombing of Darwin, Cotton's suit was approved by the Allied war chiefs. The Americans soon issued orders for manufacture of a suit based on Cotton's design. The Cotton suit was later flight-tested in a Hurricane,
Kittyhawks, and Spitfires and provided about 2 g protection. It was examined by RAF Physiological Laboratory and the Royal Air Force ran competitive trials of the Cotton anti-g suit with the Frank g-suit that was already adopted in 1944. The Franks suit was self-contained, production contracts prepared and there was insufficient capacity to develop both simultaneously so the RAF was not able to take it on but recommended the RAAF did. The researchers were part of a team assembled at the Mayo Clinic investigating the effects of high-performance flight on military pilots, by studying the physiological effects of flight and how to mitigate them. They used a large
centrifuge to whirl riders and observe their blood pressures at the head and heart levels with special instruments. To prevent drops in blood pressure, the team designed an air bladder suit that inflated the pilot's calves, thighs, and abdomen. A primary contribution, allowing for the shift from pulsatile water-filled bladders to non-pulsatile air-filled bladders, made by the Mayo investigators was to show that maintenance of arterial pressure rather than
venous return was required to maintain perfusion of the eyes and brain. Prototypes of the GPS suits were known as the "arterial occlusion suit" or the Clark-Wood suit, named after Wood and Dave Clark (head of the David Clark Company who fabricated the early suits for the team at Mayo). Their efforts finally culminated with the release of the first US military design in late 1943: the GPS (gradient pressure suit) type fighter pilot's G-1 anti-g suit. The team subsequently worked on developing further, more advanced models in 1944 and beyond. Although uncomfortable and distracting to use, later research showed that military fighter pilots who wore g-suits survived and defeated their opponents in greater numbers than those who didn't. Modern g-suits meet the United States Air Force Standard CSU-13B/P and United States Navy Standard CSU 15 A/P. ==Uses==