Figure 3-10.--Comparison of the physical characteristic of piano-convex lens and Fresnel lens.

area. This assembly contains a local gyro, gimbaled

pump to 1400 psi, filtered, and piped to the power supply

platform, hydraulic cylinders, and electrically operated

output line where it is available to the external system

servo valves. More information on the stabilized plat-

through a shutoff valve. On the return line, fluid is

form is given later in this chapter.

returned from the external system to the reservoir at a

reduced pressure of 75 psi. A shutoff valve is also used

in this low-pressure line. Electrical power is obtained

PRINCIPLES OF LENSES USED IN THE

from ship's power system and connected through the

GSI SYSTEM

motor controller and junction box. This assembly is

located as close as possible to the stabilized platform. It

There are two types of lenses used in the optical

provides hydraulic fluid at 1400 psi to the hydraulic

portion of the GSI system: the Fresnel lens and the

actuator on the stabilized platform. The motor and con-

lenticular lens. A discussion of the principles of the

troller operate on 440-volt, 3-phase received from

piano-convex lens is provided so the physical charac-

normal ship's power supply. The temperatures witches

teristics of this type of lens may be compared with the

(not shown) operate the OVERTEMP light on the

physical characteristics of the Fresnel lens.

remote control panel. Also, a pressure switch in the

hydraulic pump discharge line will close at 1200 psi. If

PLANO-CONVEX LENS

not closed, the pressure switch will de-energize the

electronic panel assembly on low oil pressure.

A piano-convex lens has a plane, or flat, surface and

Hydraulic fluid heaters in the oil reservoir maintain the

a spherical surface. This type of lens is a positive, or

temperature at approximately 70F5.

collective, lens; that is, a lens in which the light rays are

collected at a focus to form an image. The radius of the

TRANSFORMER ASSEMBLY

spherical surface of the lens is known as the radius of

curvature.

The transformer assembly is a weathertight

enclosure mounted within 3 feet of the stabilized plat-

FRESNEL LENS

form. An interconnecting cable, which is part of the

transformer assembly, connects the transformer

The Fresnel lens is a lightweight and relatively thin

assembly to the GSI. This assembly is located as close

sheet of transparent Lucite material. The refraction of

as possible to the stabilized platform. Its purpose is to

light rays by the Fresnel lens is collective, as in a

step down the voltage for the source light (GSI) from

piano-convex lens; however, the Fresnel lens differs

115 volts ac to 18.5 volts ac.

from a piano-convex lens, as shown in figure 3-10. One

surface of the Fresnel lens consists of a number of

GLIDE SLOPE INDICATOR

stepped facets. These facets are circular, concentric

ASSEMBLY

grooves that extend from the center of the lens to the

edges. The slope of each facet is independent of the

The GSI assembly consists of two major sub-

slope of all other facets. These slopes are designed to

assemblies: the mounting base assembly and the

provide a perfect focus of the light rays that pass through

indicator assembly. The indicator assembly is supported

the lens. Thus, the Fresnel lens provides an advantage

in the mounting base assembly, which is mounted on the

over a piano-convex spherical lens in that the plano-

stabilized platform. The incoming system cable con-

convex spherical lens causes spherical aberration of

nects at the rear of the right-hand heater compartment.

The mounting base assembly provides the means to

accurately position the indicator assembly in relation to

the landing pad. The mounting base is then secured in

this position by the retractable plunger. Indicator eleva-

tion is controlled by the elevation adjustment knob. The

GSI sits in the trunnions of the mounting base assembly.

STABILIZED PLATFORM

ASSEMBLY

Figure 3-10.--Comparison of the physical characteristic of

The stabilized platform assembly is mounted to the

ship's deck in close proximity to the helicopter landing

piano-convex lens and Fresnel lens.

3-7