1 - The Black Vault

THE COMBAT TALON WEAPONS SYSTEM
it did not extend all the way to it, pivoted around
that point. The AN/APQ-115 had provisions for
three set clearances—250, 500, and 1,000 feet. Its
computer allowed any altitude to be selected between
the preset clearances by rotating the clearance
select knob. For the AN/APQ-122 radar, four
set clearances were available—250, 500, 750, and
1,000 feet. On the APQ-122 radar, clearances
other than the four preset ones were not available
to the flight crew (fig. 13).
, t -hi" "V I ■—'Id LI !■ J
a/-'- '^^ rij':r._h. ur
^|- CLI^H-IC"
,i\ T I . Uh. I' - i-T.c ^L •.
p iiimh rr -nr'-.^.i£. i
U. J-'l,Mr-i
':i1k:-^ •/.•.^•'-r--- m.-_V.h
Figure 15. Obstacle Warning Template (Source: 1st SOW, CTF
Student Study Guide, Hurlburt Field, Fla., 23 June 1991.)
TsiEL.*-^ ;iiEr fjs Z-: :. :-—r^c :■■ ;— ITLZTJJJCE
Figure 13. Template Shift Due to A Change in Set Clearance
(Source: 1st SOW, CTF Student Study Guide, Hurlburt Field,
Fla., 23 June 1991.)
Two additional zones were incorporated into
the TF template and played a significant role
during TF operations. A blanking zone, which
extended in front of the aircraft 750 feet to
1,000 feet, had a two-fold purpose. First, it gave
the radar the necessary recovery time between
transmissions; and second, it cut out close-in
side lobe targets, which could cause erroneous
climb commands. A second zone, the obstaclewarning
zone, was an area within the template
that, when penetrated by an obstacle, triggered
a visual and an audible obstacle warning (figs.
14 and 15).
Si-= h^
'^—r
To:; --■
I— JOO-J'
?L?_i.'i.i:; ii.-.m
-CH-
Figure 14. Radar Blanking Zone (Source: 1st SOW, CTF
Student Study Guide, Hurlburt Field, Fla., 23 June 1991.)
Terrain-Following Radar Operation
The pilot was the primary controller of the terrainfollowing
radar. He was the only one who could
select the terrain-following or terrain-avoidance
modes, thus overriding selections made by the
right navigator. With the pilot’s selector switch
in the MAP mode, the right navigator controlled
operating modes on all three indicators. By moving
his selector switch from MAP to TA, TF, or
cross scan (CS), the pilot routed X band radio frequency
energy to the TF antenna and, on pre-
MOD-90 aircraft, controlled the modes of his and
the left navigator’s indicators, with only one exception.
The E squared presentation of the TF
mode was not available to the left navigator.
Therefore, whenever the pilot was in this mode,
the left navigator’s indicator displayed the KA
band precision ground mapping (PGM) mode,
provided that the mode was selected by the right
navigator. The right navigator could not display
TF, TA, and CS modes on his indicator and was
limited to the KA band’s PGM as long as the X
band was being controlled by the pilot. As part of
the MOD-90 upgrade in the late 1980s, both the
left and right navigators were given increased ca -
pability to view the selected TFR presentation
concurrently with the pilot. During TF flights
both frequency bands could be employed, each
transmitting from a different antenna. The pilot
would normally monitor the E squared presentation*
on his indicator, the left navigator would
monitor TA presentation, and the right navigator
would provide navigational information from the
precision ground mapping display (fig. 16).
__________
*In radar terminology, the E scan represents the vertical sweep of the antenna (up and down), and the left and right sweep is the range. For
Combat Talon application, the range was originally “exponential,” thus the E squared designation. Later modifications to the radar included digital
scanner converter (DSC) TF display, which was actually an E scan, but the range was logarithmic.
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