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October 11/02
Revision 8
2. Description of Subsystems, Units and Components:
A. Windshield Heat System:
The windshield heat system automatically maintains front windshield and
side window temperature for deicing and defogging. It is designed in such
a manner that no single failure can cause total loss of windshield heat. It is
not required for bird strike protection. The system consists of the following
units and components:
• Heating Media
• Temperature Sensors
• Windshield Heat Controllers
• Windshield Heat Control Switch(es)
• Window Heat Advisory Lights
(1) Heating Media:
The left and right front windshields are constructed as laminates of
three panes of glass and two interlayers. The outer pane is
constructed of very thin but very strong glass. Should the glass be
fractured, heating for that windshield will be lost. A conductive
coating is applied on the inside surface of the outer pane. A bus bar
at the top and bottom of each windshield distributes AC power from
the associated windshield heat controller to the conductive coating.
Two temperature sensors are also imbedded in each windshield.
The left and right side windows constructed as laminates of two
acrylic layers with one interlayer and an Aircon heating mat
sandwiched in between. A bus bar at the top and bottom of each
window distributes AC power from the associated windshield heat
controller to the heating mat. Two temperature sensors are also
imbedded in each window.
(2) Temperature Sensors:
As stated above, two temperature sensors are imbedded in each
windshield and window. They are normally referred to as the No. 1
and No. 2 sensors. Both sensors are connected to the windshield
heat controller section serving that windshield/window. The
windshield heat controllers use the No. 1 sensor for thermostatic
control of the window. Should the No. 1 sensor circuit short or open,
the windshield heat controllers switch to the No. 2 sensor with no
interruption of service or notification to the flight crew. Should the
No. 2 sensor then fail, the windshield heat controllers disable heat to
that window and notify the flight crew by extinguishing the window
heat advisory light.
On airplanes SN 1000 through 1155 having ASC 3 and ASC 275,
SN 1156 through 1203 having ASC 275 and airplanes SN 1204 and
subsequent, a temperature sensor test switch is incorporated. The
switch is installed on the right-hand radio rack and is labeled W/S
SENSOR TEST. With the windshield heat control switch(es)
selected ON (OFF legend extinguished) and the TEST switch
placed in either the SENSOR #1 or SENSOR #2 position, the
associated sensor for each windshield and window is tested.
Results of the test are obtained by observing the window heat
OPERATING MANUAL
PRODUCTION AIRCRAFT SYSTEMS 2A-30-00
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October 11/02
Revision 8
advisory lights. An illuminated advisory light confirms an operative
sensor. If the advisory light does not illuminate, the light itself should
be checked using the annunciator lights test switch. If the light tests
satisfactorily, then a faulty sensor can be suspected and reported.
(3) Windshield Heat Controllers:
Two dual-unit heat controllers regulate AC power to the windshield
and window heating media. The Left Front/Right Side (LF/RS) heat
controller governs left front windshield and right side window
heating; the Right Front/Left Side (RF/LS) heat controller governs
right front windshield and left side window heating. Windshield/
window temperature is maintained at 90-100°F (32-38°C) by the
controller. Sensor monitoring and switching is also performed by the
heat controller.
Remote Control Circuit Breaker (RCCB) logic units are incorporated
as connection and protection devices for each window. Should a
window draw current in excess of a preset value, the RCCB will
disconnect that window by causing the system circuit breaker to
pop.
On airplanes SN 1183 and subsequent, the Electrical Load Warning
System (ELWS) is capable of automatically shedding windshield
heat, if ON, to protect APU generating capabilities. At or above
34,000 feet (pressure altitude sensed by the Air Data Computer), the
ELWS processor will automatically shed windshield heat based on
the bus being powered by the APU alternator, i.e., RF/LS heat
controller if the APU alternator is powering the Left Main AC bus,
LF/RS heat controller if the APU alternator is powering the Right
Main AC bus. Once at or below 32,000 feet PA, windshield heat is
automatically restored.
Power for control and heat is provided by Left and Right Main AC
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湾流4操作手册 Gulfstream IV Operating Manual 2(55)
