Special Features; Chapter 1. Description/Operation; Section 1. Description; General - Hobart JET-EX 4 Operation And Maintenance Manual

CHAPTER 1. DESCRIPTION/OPERATION

SECTION 1. DESCRIPTION

1. General

The Jet-Ex 4 unit covered in this manual (Figure 1) is a gasoline engine driven, self-contained generator
set manufactured by Hobart Brothers Company, Power Systems Group, Troy, Ohio U.S.A. The basic
unit is identified by a Specification Number 7005, plus a dash number which defines a specific configura-
tion. The Series number, plus the dash number, make up the Specification Number.
Specification No. 7005-1 covers a stationary, skid mounted unit rated at 28.5 Volts DC output. It is
equipped with a sheet metal canopy and hinged engine compartment door. The unit is also equipped with
a mechanical governor. Various options are available for use with the basic unit. These options are listed
in paragraph 2.B. below.
The basic generator set is designed to generate and deliver 28.5 volts DC power to an aircraft when its on-
board generators are shut down. In addition to poviding continuous, regulated power to the aircraft, the
unit is designed for starting any fixed-wing aircraft or helicopter which is equipped with an external 28.5
volt DC power receptacle. Refer to Figure 2 for complete Specifications and Capabilities.

2. Special Features

A. Standard
The "Soft-Start" current limiting feature, recommended by most engine manufacturers, provides the
operator with a control which limits the inrush current to the aircraft engine's starter. When the opera-
tor presets this control, the generator will provide constant voltage to the preset currrent value. As
more current is applied beyond the preset current value, the voltage will decrease to a minimum of 14
volts DC, after which the voltage will remain constant as more current may be delivered beyond the
preset current value. Limiting inrush current is recommended by most engine manufacturers to pro-
tect the aircraft engine's starter shear section. The current limiting control is continuously adjustable
from 300 amperes, which is recommended for helicopter and small turbine starting, to 1600 amperes,
required for starting larger aircraft engines when the control is turned fully clockwise.
Additional features include a mechanical governor which maintains the engine speed at 2600 RPM at
no load, an all-electric engine overspeed protection device which shuts down the engine by opening
the ignition circuit if the engine speed reaches 3200 RPM.
May 20/89
OM-2049
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