Linkage Assemblies (Pilot and Gunner)

TM 9-1270-212-14&P

1-13. Electronic Interface Assembly (EIA).

The eyepiece can be adjusted vertically and laterally to

obtain eye coincidence and is spring-loaded to retract to the

NOTE

horizontal position when the detent iS released. The

eyepiece can be retracted either electrically by activating a

Except aS other Wise stated in the discussion

solenoid in the sight assembly or manually by pressing a

below, the contigurations of the EIAs used in

button on the sight housing.

HSS XM128 and HSS XM136 are identical.

c. The electrical connector (AlPI) on the helmet sight

The EIA (fig. 1-5) contains most of the electronic

assembly connects to a plug in the helicopter.

components, except for the helicopter-mounted controls

1-12. Linkage Assemblies (Pilot and Gunner).

and displays, necessary for the operation of the HSS. The

ElA is the point of interface between the HSS and the

Each linkage assembly consists of an arm assembly, a

helicopter interface control unit and contains a power

rear support, two rails, a front support assembly, and two

supply module, a power supply circuit card, eight buffer

mounting brackets (fig. 1-4). The carriage end of each arm

amplifier modules, four boresight potentiometers that

assembly travels on the rails and contains ball bushings for

connect to an amplifier circuit card, and circuit cards for

almost frictionless movement. A stowage bracket in each

BIT capability. The EIA used in HSS XM136 also contains

front support assembly holds the arm in an overhead

an azimuth bias circuit card containing the components

position when the arm is not in use. In addition, the front

necessary to compensate for the 5.5-degree left-azimuth

support of each linkage assembly contains a magnetic

angle at which the pilot linkage is mounted in the AH-1S

fixture into which the steel-fastener end of the arm

helicopter.

assembly is placed for a built-in-test (BIT) of the linkage

assembly and the EIA: this fixture is called the BIT bracket.

a. The power supply module is a dc-to-dc converter that

uses 28 volts dc from the helicopter prime 28-volt dc power

a. The forward end of each tubular arm asssembly

source to produce regulated 28 volts dc for the buffer

contains a round steel fastener that attaches to the

amplifiers and BIT circuitry.

magnetic receptacle at the top of the helmet sight assembly.

A pair of precision resolvers at the steel-fastener end of

b. The power supply circuit card functions with an

each arm and another pair at the carriage end provide for

input transformer to change 115-volt, 400-Hz ac to ac and

measuring the angular position of the helmet. Thus. with

dc vohagcs of various amplitudes.

the steel fastener attached to the helmet, the linkage

assembly can accurately determine the direction, both in

c. The buffer amplifier plug-in modules are used with

elevation and azimuth, its which the operator is looking,

the winding-compensated resolvers in each linkage assembly

i.e., the sight line to a target. Because of installation

to provide stable transformation ratios and phase shift

considerations, the pilot arm is 18 inches long and the

despite variations in temperature frequency.

gunner arm is 24 inches long. The gunner arm is bent

slightly to provide clearance within the helicopter cockpit.

d. The four boresight potentiometers provide a means

The resolvers are connected to the EIA by a coiled cable

of varying the amplitude and phase of small ac voltages for

that allows free movement of the carriage along the rails.

c o r r e c t i n g small system misalignments. These

The pilot-arm-assembly cable connects directly to the EIA;

potentiometers are mounted on the side of the EIA used in

the gunner arm assembly requires an extension cable to

HSS XM128 and in a small housing on the end of the EIA

reach the EIA. The resolvers require precision trimming

used in HSS XM136; as mounted in the helicopters, the

resistors, which must be mounted close to the resolvers to

potentiometers are in approximately the same location.

maintain system accuracy. These resistors are mounted on a

One of these potentiometers is used for azimuth adjustment

rectangular terminal board attached to the backshell of the

of the pilot linkage; one, for elevation adjustment of the

connector (inside the connector) at the end of each coiled

pilot linkage; one, for azimuth adjustment of the gunner

cable.

linkage; and one, for elevation adjustment of the gunner

linkage.

b. The two precision stainless steel rails are each 34

e. BIT circuitry includes logic. sequencing, and

inches long. The rear and front supports are secured to the

comparator circuits, as well as relays, reference voltage

mounting brackets, which secure the steel rails to the

helicopter overhead-canopy support members. The supports

sources, and external control switches. When externally

commanded, the circuitry tests each linkage assembly, its

are adjustable, to permit alignment of the rails during

system boresighting.

respective buffer amplifiers, and the power supply. Proper

1-6