Can you hack the force?

  • Published
  • By Capt. Shawnee Williams
  • 71st Medical Group Aerospace Physiology
G-forces are always a factor in training aircraft such as the T-6 and the T-38. Vision changes, incapacitation and G-induced loss of consciousness are just a few of the physiological changes that can occur as a result of exposure to G-forces. Therefore, it is imperative that Joint Specialized Undergraduate Pilot Training students learn and understand how to overcome and sustain the G-forces. 

The first time most JSUPT students learn about the effects of acceleration on the body is during their initial training at Aerospace Physiology. Students are taught about the different types of acceleration and G-forces. More emphasis is placed upon positive and negative G-forces primarily due to the fact that these are the G-forces that student will most likely be exposed to in the aircraft. 

Positive G-forces act to push the blood towards the feet, consequently making it more difficult for blood to return to the heart. Exposure to positive Gs can cause blood pooling from 1-3 Gs, gray-out from 3-5 Gs, blackout from 4-5 Gs and unconsciousness at 5 or more Gs. 

Negative G-forces on the other hand act to push blood towards the head. In general, the human body does not have a very high tolerance for negative G-forces. Blood pooling starts to occur at 1G, vision is affected between -1 to -2.5 Gs, extreme discomfort at -2.5 to 3 Gs, and incapacitation at -3 or more Gs. 

Unfortunately, there is nothing the pilot can do to protect himself or herself from negative G-forces. However, there are two methods available to the student's for protection against positive G-forces: the anti-G suit and the Anti-G Straining Maneuver.

The G suit provides about 1 to 1.5Gs worth of protection. The G-suit is worn during every flight and automatically inflates in response to positive G-forces. The AGSM provides the greatest amount of protection against G-forces. The AGSM consist of two components: skeletal muscle tensing and cyclic breathing. When performed properly, the AGSM can provide against up to 4.5s protection. 

The first component of the AGSM involves contracting the muscles of the lower body and abdomen. This muscular contraction acts to compress the blood vessels in the lower extremities and helps to prevent blood from pooling. 

The second component is cyclic breathing. The breathing portion is performed by taking a full breath of air and trying to forcefully exhale against a closed glottis. Air exchanges should be performed every 3 seconds. Short, rapid air exchanges help to maintain intra-thoracic pressure, thus preventing a GLOC. 

Developing good habit patterns is a necessity in maintaining G-awareness. The entire AGSM should always be performed prior to G-onset. Failure to properly estimate the number of Gs and a poor AGSM could result in a GLOC or worse: loss of aircraft and loss of life.