1. PURPOSE. Because acrobatic flying subjects pilots to gravitational effects (G's) that can impair their ability to safely operate the aircraft, pilots who engage in aerobatics, or those who would take up such activity, should understand G's and some of their physiological effects. This circular provides background information on G's, their effect on the human body 3 and their role in safe flying. Suggestions are offered for avoiding problems caused by accelerations encountered in acrobatic maneuvers.

2. BACKGROUND. Acrobatic flying demands the best of both aircraft and pilot. The aircraft must be highly maneuverable, yet tolerant of G-loads. The pilot must possess skill and physiological stamina. He or she must be daring, yet mindful of the aircraft's limitations as well as his or her own. Federal Aviation Administration (FAA) Advisory Circular No. 91-48, “Acrobatics-Precision Flying with a Purpose,” dated June 29, 1977, discusses some of the airworthiness and operational aspects of aerobatics, but does not consider biomedical factors. The most important of these biomedical factors is the pilot's response to accelerations (or G-loading). The major physiological effects of G-loading vary from reduced vision to loss of consciousness. The pilot who understands these effects will be better able to cope with them so that he or she can continue the sport of acrobatic flying.

3. HISTORICAL CONSIDERATIONS. Aerobatics is said to have started in 1905 when Daniel J. Maloney at Santa Clara, California, in a glider descending from a tethered balloon, did a “side-somersault,” probably a roll. Later, another pilot, in the same glider, performed both left and right "side-somersaults." A number of unintentional and deliberate maneuvers were performed in the early years of powered flight but the star performer was the Frenchman, Peguod. In 1913, Peguod jumped from his aircraft in the first demonstration of the use of a newly designed parachute; as he descended, he watched the unpiloted Bleriot go through a number of bizarre maneuvers that he thought might be repeated by a competent pilot. Later, Peguod astonished onlookers with such maneuvers as vertical S's, inside loops, inverted half-loops with rolls, etc. Contrary to the comment in a leading flying publication of the day that “Peguod-ing is not to become fashionable in the French Army,” acrobatic flying became an essential part of combat flying in World War I.

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