Section II. DESCRIPTION AND DATA - TM-9-1270-212-14-P0017

TM 9-1270-212-14&P

Section II. DESCRIPTION AND DATA

assemblies are mounted at a 0-degree azimuth angle. For

1-9. Subsystem Description.

HSS XM128, the pilot linkage has a down pitch angle of 4

degrees and the gunner linkage assembly has a down pitch

The HSS is a helmet-directed sighting subsystem that

angle of 8 degrees. In the HSS XMl36 installation (fig. 1-2,

interfaces with the gun turret and the telescopic sight unit

view B), the EIA is mounted horizontally, the gunner

(TSU) of the TOW missile subsystem in the AH-1S(Mod)

helicopters(fig. 1-2). The HSS

linkage assembly is mounted at a 0-degree azimuth angle,

and AH-1S

and the pilot linkage assembly is mounted at a 5.5-degree

operates from power supplied by the helicopter and con-

left-azimuth angle. For HSS XM136, the pilot linkage has a

sists of the following assemblies:

pitch angle of 0 degrees and the gunner linkage has a down

pitch angle of 11.5 degrees.

Helmet sight (2)

c. The four potentiometers (used for boresighting

Pilot linkage

adjustments) are on the right side of the EIA used in HSS

XMl28 and in a smaJl housing on the end of the EIA used

Gunner linkage

in HSS XMl36. The bonding jumper on the EIA used in the

HSS XM136 is approximately twice as long as that on the

Electronic interface

EIA used in HSS XMl28. The EIA used in HSS XM136 has

an azimuth bias circuit which compensates for the

Extension cable.

5.5-degree offset of the HSS XM136 pilot linkage.

a. The HSS enables the helicopter pilot and

1-11. Helmet Sight Assembly.

copilot/gunner (hereinafter referred to as gunner) to rapidly

acquire visible targets and to direct either the gun turret or

The helmet sight assembly (fig. 1-3) is a lightweight

the TSU to those targets. The helmet-mounted optical sight

aluminum visor housing with a magnetic receptacle

extends over the operator's right eye, and an illuminated

containing a reed switch attached near the top rear and a

reticle pattern is projected into the optical sight.

sight assembly attached to the front. The aluminum visor

Electromechanical linkages sense the helmet position and

generate sight-line signals, which are processed by the

housing is precision attached to the SPH-4 helmet when the

existing visor cover is removed. For initial installation, an

electronic interface assembly (EIA) and used to control the

installation kit containing special fasteners and tools and a

angular position of the turret or the TSU.

small visor knob is furnished with each helmet sight

assembly.

b. Either operator can command the gun turret or TSU

by means of operator-selectable cockpit switches. When

a. The magnetic receptacle holds the steel fastener on

necessary, the gun turret and TSU can be commanded

the front of the arm assembly (fig. 1-4) in place and a latch

simultaneously by the pilot and gunner, respectively.

insures against inadvertent separation. In an emergency, the

1-10. Differences Between Models.

latch allows separation of the steel fastener and magnet at

an axial force of approximately 20 pounds. The magnetic

a. There are two models of the HSS, HSS XM128 (used

receptacle contains a reed switch that senses the presence of

in the AH-1S(Mod) helicopter) and HSS XM136 (used in

the steel fastener. The reed switch closes when the steel

the AH- 1S

helicopters). All of the differences,

fastener is attached and opens when separation occurs.

mechanical and electrical, between the two models result

from differences in HSS installation in the helicopters. The

b. The sight assembly consists of a sight housing and an

only major item that differs between the two models is the

eyepiece. The sight housing contains a lamp assembly

EIA. The helmet sight assemblies, pilot and gunner linkage

(containing three 5-volt lamps), a reticle, and a lens system.

assemblies, and extension cable are identical and inter-

Th sight housing projects the reticle pattern, focused at

changeable between models.

infinity, into a beam splitter within the eyepiece. The beam

splitter superimposes the reticle pattern on the normal

eyepiece image. A detent in the sight housing holds the

b. In the HSS XM128 installation (fig. 1-2, view A), the

eyepiece down in the sighting position over the right eye.

EIA is mounted vertically, and the pilot and gunner linkage

1-3