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Note: All mounting hardware must be non-ferrous materials.
The MSU is a 3 axis magnetic sensor that is extremely sensitive to magnetic fields;
therefore, the use of non-magnetic materials to secure the MSU to the airframe is
required. The MSU requires 3 #10-32 socket head screws (i.e. MS16996-11 or
Series 300 Non-Magnetic Stainless Steel) torqued to 31.7 inch lbs. Aluminum or
brass screws may also be used provided that they are torqued appropriately.
NAS620-C10L Washers (or equivalent non-magnetic washers) may also be used with
the screws. The pattern for the mounting holes of the MSU is shown in Figure . The
mounting holes are slotted to allow the installer flexibility in aligning the direction of
flight axis of the MSU with the aircraft's longitudinal axis. The MSU must be installed
in the aircraft such that the forward direction of the MSU box is within ±0.5° of parallel
alignment with the aircraft's longitudinal axis.
The direction of flight (aircraft forward) is away from the cable assembly.
Note that the MSU mounting flange is 0.25" above the bottom of the MSU. An
aluminum bracket is recommended with a 3" round hole for the MSU.
The MSU should be mounted such that it is within 2 degrees of aircraft level.
Refer to Maintenance manual for the aircraft to determine aircraft level.
The MSU must be installed in the aircraft in a location where there is minimal
magnetic interference from other devices in the aircraft and in such a location where
physical excursions resulting from natural oscillations are minimal. To insure this, the
MSU must be placed as far away as possible from ferromagnetic metals such as iron,
cobalt and permalloy. It should also be placed as far away as possible from wires
carrying any significant current. Failure to install the MSU in a magnetically
friendly environment will result in heading errors which cannot be removed by
field calibration.
The following guidelines are recommended for MSU installation:
The MSU shall be mounted no closer than 10 ft to electric motor and relays.
The MSU shall be mounted no closer than 8 ft to ferromagnetic structures greater than 1
kg.
The MSU shall be mounted no closer than 4 ft to ferromagnetic structures less than 1 kg.
The MSU shall be mounted no closer than 4 ft to any electrical component/conductor
drawing in excess of 100mA.
The MSU shall be mounted no closer than 2 ft to any electrical component/conductors
drawing less than 100 mA.
Typical installation areas are the tail section or wing tips (See Appendix X). In rotor
craft, installation is usually below the main cabin or in the tail boom away from any
rotating ferromagnetic shafts. Installation of the MSU within 2 feet of the cabin is not
recommended due to potential interference that would affect the performance of the
device.
When mounting the MSU in the wing, it is recommended that the wing tip lights have
a dedicated power ground supplied through a twisted pair of wire back into the
fuselage as opposed to a ground reference back to airframe ground. This will prevent
current flow in the wing skin that may degrade the performance of the MSU.
OASIS Installation Manual
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