plane, subjecting it to clockwise acceleration. It also causes the
horizontal canal to move to a vertical position, subjecting it to a
deceleration. This multiple stimuli will result in the false perception of
rolling in a clockwise direction.
(b) Rolling head onto left shoulder. Assume the pilot is in a
pitching attitude at a constant velocity and rolls his head onto his left
shoulder. Here he will experience a false sensation of yaw in addition to
the sensations induced by the true movements of his head and the aircraft.
e. Oculogravic Effect. The body is not equipped with sensors capable
of informing the brain of all the different linear accelerations acting upon
it. Instead, utricles and saccules transmit composite information of the
direction, magnitude and resultant vector. The false sensations that we get
because the otolith organs are unable to distinguish between the earth's
gravity and other superimposed linear accelerations are called the
oculogravic effects.
(1) Sensation of down: In 1820, it was discovered that a person on a
merry-go-round tended to lean to the center of the rotation to bring the
long axis of the body in line with a perceived vertical. This is explained
by the increased stimulation of the nervous epithelium within the otolith
organs resulting from both the increased magnitude and direction of the
force vector. This stimulation from centrifugal force gives the sensation
that down is to the outside. Simultaneously, as the individual begins to
align with the newly perceived vertical the illusion is intensified.
Carried to the extreme, as the rate of spin becomes great enough to exceed
the force of gravity, the perceived vertical would be 90 degrees from the
actual vertical.
(2) Sensation of nose-high attitude: During World War II, in
reporting on a series of night takeoff accidents, the Royal Air Force found
that forward acceleration caused the sensation of a nose-high attitude.
Pilots who were actually flying level or in a gentle climb would nose the
aircraft over and crash. The mechanism at work here is the same as the
merry-go-round illusion.
(3) Perceived nose-up attitude: Night takeoff accidents usually
occur as the pilot accelerates the aircraft forward at the rate of 32 feet
per second per second. Here a I G inertial vector pulls the otolith
membranes to the rear. The 1 G gravity vector which is always present will
combine with the 1 G inertial force to create a 1.4 G resultant force vector
pointing diagonally to the rear and down (Figure 19). The pilot perceives
up to be in the opposite direction to the resultant force vector and when
the aircraft is level will feel the nose is pitched up at an angle of 45
degrees. By correcting for this perceived nose-up attitude he pushes the
aircraft into the ground at an angle of 45 degrees. Oculogravic effects are
not experienced if adequate outside references are available; however, bad
weather and darkness make a pilot considerably more susceptible to them.
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