Partial supination versus Gz protection

Visual and loss of consciousness endpoints during 2 G/s onset G forces sustained for 5 s in 14 and for 10 s in 27 untrained pilots indicated high tolerances when upright, and increases of greater than 3 G when supinated to 60 degrees. Protection against visual symptoms of only 1.1 G when tilted 60 degrees and especially none when experienced subjects were tilted 45 degrees from vertical were unexpected results in 1942. Subsequent findings by others of slight decreases in tolerance at 30 degrees are contrary to hydrostatic basis of G tolerance. Presumably factors other than heart to brain distance (e.g., increased intracranial and intraocular pressures) affect G tolerance when subjects are supinated 30 degrees. We conclude that the apparent increased incidence of G-LOC since the incorporation of 30 degrees seat in F-16 and other fighters in mid-1970's supports the current relevance of these data and suggests that all aircrew should follow the lead of veteran test pilots who sit upright in preparation for and during high G maneuvers (10).