Gravity suits, also known as G-suits, are specially designed garments worn by aviators who undergo rapid accelerations, such as fighter pilots and astronauts. The suits apply pressure to the stomach and legs and prevent blood from rushing away from the brain during acceleration. This process allows the wearer to endure higher sustained gravitational forces for longer periods of time.
G-suits are more accurately called anti-G suits, since their purpose is to counter the effects of G-force on the human body. G's are measurements of acceleration expressed in multiples of the force of gravity. Results reveal the amount of stress being placed on an accelerating body due to inertia. One G is the force gravity exerts on a person on the surface of the earth.
An individual's resistance to G-force is based on several factors. Generally, an average human can endure between three and five sustained G's before blacking out, which is referred to as G-induced loss of consciousness (G-LOC). G-LOC is caused by lack of blood flow to the brain, essentially starving it of oxygen.
Pilots and astronauts can withstand much higher G-loads with the help of resistance training and G-suits. To put the amount of stress in perspective, during a typical commercial flight, passengers would probably never experience more than one and a half G's, yet fighter pilots might experience around nine G's when coming out of a sharp dive.
G-suits typically consist of tightly fitting pants that contain inflatable sacs. These sacs are sensitive to the amount of G-force being exerted and will fill with liquid or pressurized air to prevent too much blood from flowing down the axis of the body. G-suits may be worn outside or inside the flight suit, depending on the model.
The first G-suit was developed by a team at the University of Toronto in 1941. Led by Dr. Wilbur R. Franks, the team found that they could cushion the effects of G-force by wearing a garment consisting of a layer of water between two sheets of rubber. In testing, however, this system proved to be bulky and uncomfortable. In 1944, the U.S. Air Force and Navy, in cooperation with the Mayo Clinic and Berger Brother's Company, designed a new model G-suit using compressed air which was more successful. This model became known as the Berger suit, and later models tended to follow the same basic design.
In the 2000s, however, Swiss inventor Andreas Reinhard and the German company Autoflug developed a new style, which is called the LIBELLE G-Multiplus®. It is a full-body suit, made with a hybrid material composed of flame-resistant Nomex® and Kevlar® that is run through with channels of a water-based liquid. As G-forces increase, the liquid channels contract, pulling the material of the suit along with them, effectively acting as a vice. This model has been successfully tested at up to 12 G's.