Garmin GRS 77, Руководство по установке

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GRS 77/GMU 44 Installation Manual Page 2-5
190-00303-10 Revision L
2.5.1 GRS 77 AHRS Mounting
Only part number 011-00868-20 GRS 77H units can be installed in helicopters.
The GRS 77 includes an extremely sensitive strap-down inertial measurement unit. It must be mounted
rigidly to the aircraft primary structure. Do not use shock mounting. Shock mounts used for other types
of inertial systems are not acceptable for the GRS 77 AHRS. The mounting system must have no
resonance with the unit installed that would cause DO–160D vibration levels to be exceeded. (See the
GRS 77 Environmental Qualification Form). Vibration outside of these limits may result in degraded
accuracy.
The supporting plate must be rigidly connected to the aircraft primary structure through strong structural
members capable of supporting substantial loads. Avoid areas that are prone to severe vibration (e.g.,
areas close to engine mounts and landing gear).
The GRS 77 should be mounted within 13 feet (4.0 meters) longitudinally and 6.5 feet (2.0 meters)
laterally of the aircraft center of gravity. The mounting location for the GRS 77 should be protected from
rapid thermal transients, in particular, large heat loads from nearby high-power equipment.
The GRS 77 mounting rack should be leveled to within 3.0° of the aircraft level reference, and an aircraft
leveling and offset setting procedure carried out prior to flight. (This procedure is described in Section 5.)
Alternatively, if the mounting rack can be guaranteed level to within 0.25° of the aircraft level reference,
the aircraft leveling and offset setting procedure is not required.
The GRS 77 mounting rack’s forward direction must be aligned in heading to within 1.0° of the aircraft
forward direction. (The arrow symbol on the rack points forward.)
Some metal structures of the GRS 77 may become magnetized if closely exposed to permanent magnets.
While this will not affect the GRS 77 itself, it may slightly affect nearby magnetic instruments in the
aircraft (whiskey compass). Ordinary use of magnetic screwdrivers to tighten the GRS 77 fasteners will
not cause problems, but non-magnetic screwdrivers are preferred. Avoid placing the GRS 77 within 1
inch of magnetically mounted antennas, speaker magnets, or other strongly magnetic items.
For installations with multiple GRS 77 AHRS units, note that the slip/skid indications associated with the
AHRS units may differ slightly depending upon the heading misalignments between the AHRS units. For
example, a 2-degree difference in heading alignment between two AHRS units will result in a one-eight
trapezoid difference in the slip/skid indications when in a steady 15-degree nose-up climb. Reducing the
heading misalignment between AHRS units will reduce this effect approximately proportional to the
misalignment angle.
Figure 2-1. GRS 77 and Mounting Rack
NOTE