Antenna Stabilization; Limits; Errors; Compensation - Telephonics RDR-1600 Pilot's Manual

Antenna Stabilization

9.0 ANTENNA STABILIZATION
Airborne radar antennas are stabilized to preserve a normal cockpit display
when the aircraft is climbing, descending or turning. When the aircraft
departs from straight and level flight, the stabilization system automatically
adjusts the antenna position to compensate for the change. Both limits and
errors associated with antenna stabilization are important to the pilot.

9.1 LIMITS

The limits of antenna stabilization are different for climbing or descending
and turning while climbing or descending. For straight ahead climbs and
descents, the limits are simply the mechanical stops at 30 degrees. When
turning, the tilt and bank angles determine the stabilization limits (the rule
of thumb is a total of 30 degrees) so moderate turns combined with mod-
erate climbs and descents will stay within limits.
Figure 9.1-1. Aircraft Pitching/Rolling ±30°

9.2 ERRORS

There are two sources of stabilization errors: acceleration and drift.
Accelerations and decelerations cause the gyro to precess in pitch. The
pilot may not notice a small temporary discrepancy between the altitude
indicator and visible horizon, but on the radar screen the antenna pitch pre-
cession will appear as an exaggeration of the desired tilt. Drift errors
(appearing on the attitude indicators pitch and roll precession accumulate
in turns) disappear slowly after the aircraft returns to straight and level.
Gyro precession errors directly affect radar stabilization and the quality of
the return displayed on the screen.
40 RDR-1600 Pilot's Guide

9.3 COMPENSATION

There are some compensations the pilot can use for antenna stabilization
errors. When the system has been operating properly in level flight, the pilot
may be able to correct for ground return showing on one side and not the
other by tilting the antenna up until all ground returns are cleared. During
takeoff, the pilot can raise the antenna tilt to clear the ground returns
caused by gyro acceleration error, then as the airplane stops accelerating,
readjust the antenna tilt back toward level. Adjusting antenna tilt is also the
remedy for ground returns that appear because of gyro precession in a pro-
longed turn. Good operating practices include:
• Adjust radar and obtain weather picture before takeoff
• Compensate antenna tilt for gyro precession
• Evaluate weather in the immediate sphere of operation
• Do not "over-scan" weather targets
• During excessive aircraft maneuvers, recognize the limitations of
stabilization
TM106101(8/01) TM106101(8/01)
Antenna Stabilization (Cont.)
RDR-1600 Pilot's Guide 41