In flight verification of the inversion illusion.

Pilots' sensations of orientation while pushing over (bunting) are inconsistent. We flew 13 aircrew or naive subjects individually in a Hawk or Hunter jet training aircraft. With sun visor down and eyes closed, each was asked to report what the aircraft was doing. After unaccelerated level flight for 30 s, the aircraft was accelerated in level flight from 200 to 250 kts at +0.15 to +0.25 Gx, and gently pulled into a stable 250-kt, 3000 ft/min climb. After 30 s, it was pushed to -1 G during 3 s. Minus 1 G was then held for a further 3 s. Of 30 maneuvers, 14 produced sensations of inversion in 9 of 13 subjects. Two subjects reported feet-up rotation to the inverted; one felt a rotation of indeterminate direction; five felt sudden inversion. This illusion was experienced by 3/3 naive non-pilots, 6/8 pilots, and 0/2 test pilots. We conclude that the "inversion illusion" exists, and that the postulated sensation of backward rotation is often not perceived.