82011-IM, REV J
Sandel SG102 & MT102 Installation Manual
Page 1-2
1.3
General Information on Strapdown AHRS
When used as a DG replacement, the SG102 differs in certain key characteristics from the electro-
mechanical gyro it replaces which affect the installation. It must be remembered that the SG102 is a
strapdown AHRS and this means it is installed like an AHRS - even if it is used or thought of as a
directional gyro.
A strapdown AHRS is composed of three sensors in a Roll-Pitch-Heading orientation. When the
aircraft is level it is easy to visualize its operation as each of the three sensors senses the movement in
its own axis. However, the operation of the AHRS gets complicated as the aircraft maneuvers. For
instance in a 90 degree bank what was the Pitch sensor is now the Heading sensor; the Heading sensor
is now the Pitch sensor. This sensor translation occurs at every intermediate attitude. In order for this
process to work properly, the SG102 itself must be precisely aligned with the aircraft axis; otherwise
changes in roll may induce like small changes in pitch, and vice-versa. Very small misalignments will
wash out during operation, but large misalignments will cause improper operation.
A mechanical DG has no such requirement as it is gimbaled and will level itself to gravity on startup
and stay level during most flight maneuvers. This means that a mechanical DG installed non-level
will work properly; however installing with the SG102 without checking the mechanical alignment
will
not
work. Make sure the SG102 is mechanically aligned! Once correctly installed the SG102
mounting base is designed to allow removal and replacement of the SG102 without realignment.
The 4-quadrant compass calibration (part of the ground test procedure) is important for correct system
operation. Do this carefully! The benefit of doing this calibration correctly is the SG102 will be more
accurate in heading, especially during maneuvers, than a mechanical DG.
1.4
SG102 Features
The SG102 is intended for use in airplanes or helicopters to provide stabilized primary magnetic
heading to compass indicators, flight control and director systems, or other aircraft systems requiring
stabilized heading information.
The SG102 provides output heading data in the following formats:
Heading Format
SG102
SG102/D
MOD1
MOD2
ARINC 407 (XYZ)
X
X
-
ARINC 429 (LOW SPEED)
X
X
X
ARINC 429 (HIGH SPEED)
-
X
X
RS-232 Stormscope™
X
X
X
Quadrature Stepper
X
X
-
The SG102 incorporates a single 26 pin “D” connector with a Positronics latch. Additionally, the
SG102 MOD 1 and MOD 2 (P/Ns SG102-000, -100, -200) is signal and plug compatible with the
Bendix/King KG102 electromechanical directional gyro used in the KCS55 compass system.
Contact the factory with any questions about interfacing to specific equipment not covered in the
installation drawings.
