Helmet-Mounted Displays: - USAARL - The - U.S. Army

Biodynamics 203
exceed the mechanical retaining forces. The U.S. Navy, with the
introduction of Cats Eyes NVG for their fixed-wing community, developed
a pyrotechnically activated detachment mechanism. This device was
activated when it received an electrical signal at the beginning of an
ejection sequence. This signal activated a squib which performed the
mechanical release of the Cats Eyes goggles.
A device similar to the Cats Eyes automatic release device could be
incorporated into the rotary-wing community, but a sensor would have to
be used to sense the crash onset and initiate device release. Such a sensor
is being developed by the Program Manager-Air Crew Integrated Systems
(PM-ACIS) for activation of the helicopter air bag restraint system.
Pursuing such an approach to reduce the head borne weight during crashes
introduces system complexities, increases technical risk, and raises
program costs. The determination of when the device should be detached
is not a trivial issue, and actual crash acceleration data are generally not
available upon which to base such determinations. Generally, a portion of
such an automatic device remains on the helmet. The trade between the
amount of weight being removed versus the amount being retained may
become negligible if the design is not optimized.
Current frangibility (breakaway) design requirements are that when
subjected to an acceleration of 9 G or less in any vector within the limits
described in Figure 7.10, the designed frangible components shall not
separate. However, separation must occur for acceleration of 15 G or
greater. During breakaway, the frangible components should not come in
contact with the wearer’s forehead, eye sockets, or facial regions at any
acceleration level (Rash et al., 1996).