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

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Joseph R. Licina
authorized to use ANVIS. The IHADSS visor would not support the
ANVIS mounting bracket, so a custom visor bracket kit was developed to
mount the standard ANVIS SPH-4 visor assembly on the IHADSS helmet.
The available mounting points on the IHADSS helmet for the ANVIS visor
produces a downward tilt of the ANVIS such that the pilots have to
constantly tilt their head backwards for straight ahead viewing with the
ANVIS even with the ANVIS tilt adjustment in the maximum up position.
The guidance for the use of ANVIS in the AH-64 is to mount either the
ANVIS or the HDU on the helmet, but not both. However, many of the
Apache aviators mount both, which increases the head supported weight to
> 6.5 lbs.
The Apache helicopter uses a near infrared laser range finder and
designator that is not eye safe. To initially protect the Apache
crewmembers, laser protective spectacles, plano or with correction with
KG-3 glass were fielded. The KG-3 glass appears slightly grey tinted and
with 3-mm thickness provides approximately 80% visual transmittance with
> 4.0 optical density (O.D.). To interface with the HDU, the right lens of
the standard aviator frames was reduced in size and reshaped. To further
reduce the effect on the FOV of the HDU, the right lens of this modified
spectacle was typically increased in pantoscopic tilt (i.e., pitched down).
At the same time, a development program was initiated to produce visors
with laser protection to replace the spectacles. Unfortunately, the only
suitable technology was dye or absorptive materials which may affect the
ballistic protection of polycarbonate, and significantly reduces visual
transmittance and induces color properties. Because of the proliferation of
ruby lasers for range finders and designators by the former communist
block, the laser protective spectacles and visors included dyes to absorb red
wavelengths. The visible transmittance was further reduced to less than
40% with a green tint. With the possibility of using laser wavelengths that
match the sensitivity wavelengths of the eye, the absorptive dye technology
for laser protection produces visible transmittance that are both
unacceptable to the aviator for night flight and block the wavelengths
emitted from the instrument panel, head down displays and position lights.
Limited ballistic protection for the eyes has been available with the
initial fielding of the SPH-4 aviator helmet with the polycarbonate visors
in 1970. The visors will not stop bullets, but will reduce the injuries from
spall and flash fires. At present, no other clear optical material provides the
degree of ballistic protection for a given thickness as polycarbonate.
Therefore, we anticipate that polycarbonate visors will be used for future
HMD systems.