SPINAL INJURY CONTROL - Injury Biomechanics and Control: Optimal Protection from Impact - page 169

CHAPTER 5
SPINAL INJURY CONTROL
In this chapter, the technique developed in Chapter 4 is used to evaluate
the possibilities for reducing the risk of spinal injuries to an occupant of
a helicopter that has a hard or crash landing with a high vertical velocity.
Due to the impact of the landing, the occupant's vertebral column under-
goes a high longitudinal load that can lead to a severe spinal injury. To
avoid this injury, the occupant's seat should be equipped with shock isola-
tors that reduce the spinal load. Two configurations are considered for the
shock isolation system. In the first configuration, there is only one isola-
tor, a cushion between the seat pan and the occupant's lower torso, and
the seat pan is rigidly attached to the helicopter frame. In the second con-
figuration, in addition to the cushion, another shock isolator is introduced
between the seat pan and the airframe. This configuration represents the
three-component structure described in Section 4.2. The airframe, the seat
pan, and the occupant are regarded as the base, the container, and the object
to be protected, respectively. The limiting performance analysis of the heli-
copter's occupant shock isolation system is performed using the techniques
of Chapter 4. The dynamic response of the occupant's vertebral column to
the longitudinal impact load is modeled by a system of two bodies con-
nected by a spring and a dashpot with linear characteristics. The risk of
spinal injury is measured by the maximum magnitude of the force devel-
oped by the spring-and-dashpot element. This model is close to the DRI
model (Stech and Payne, 1969; Brinkley and Shaffer, 1970) which was
designed to evaluate the lower spine injury risk for a pilot leaving an air-
craft with an ejection seat. The control forces of the isolators are optimized