Applications Index : Aerospace
Piloting Display
There is a trend in experimental aircraft instrumentation towards electronic
flight information displays due to their versatility and ability to clearly provide more
information in a small space. An attitude indicator of this type needs an electronic signal
from a solid-state attitude and heading gyro such as is provided by the Watson Industries' AHRS-E304.
Solid-state gyros are used because mechanical gyros have a very short life,
typically a few thousand hours. The mean time between failure (MTBF) for the Watson
Industries gyro package is many tens of thousands of hours. This is a safety issue since
a more reliable gyro sensor system will result in fewer accidents related to avionics
failures.
Watson Industries has the ideal sensor package for this application. The
Watson Attitude and Heading Reference System (AHRS-E304) outputs bank elevation, heading,
roll rate pitch rate and yaw rate. This provides the attitude indicator with all the
necessary information on aircraft attitude and dynamics.
Technical Challenges:
Sustained dynamic maneuvers, and high rates are always possible during
flight. All the sensors in the attitude indicator system must have a range that is wide enough to
track all the motions involved. When performing a sustained maneuver such as circling a
location, bank errors due to centrifugal force
could build up in the system. To correct this problem, a velocity input to the AHRS is
required. The velocity data is used with the turn rate to calculate the centrifugal force
and remove its effects from the system. Velocity is normally transmitted to the Attitude
and Heading Reference System via an analog voltage, but we have options available for the
sensor to receive velocity digitally as well.
The heading output for the AHRS-E304 is referenced to the magnetic heading
provided by an internal magnetic compass. This means that any extraneous magnetic fields
in the vicinity will induce heading errors. Installation in an aircraft can be difficult
because of the magnetic environment. Aircraft can have steady state magnetic fields of
over 400 milliGauss. Considering that the Earth's field is only about 650 milliGauss,
considerable heading errors can result. These vehicles also have motors, relays, batteries
and high current carrying conductors that create highly variable magnetic fields that can
induce heading errors. Finding a mounting location that is magnetically clean is key to
solving this issue.
Watson Industries has rate gyros with enough range
for any higher-rate maneuvers. We strongly encourage you to read our
magnetometer mounting location paper
for more information on finding the best place to install your AHRS. We also provide free
software for calibrating the AHRS internal compass after it has
been installed to help to remove any remaining heading errors that may result from its mounting
environment.
Watson Experience:
Watson Industries has been manufacturing sensor packages for use in attitude indicators since 1995.
Requirements:
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Roll Rate: |
±200°/sec |
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Pitch: |
±100°/sec |
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X, Y, and Z Acceleration: |
±10g |
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Airspeed Input - The possibility of sustained dynamic maneuvers requires airspeed be
read into the sensor to allow calculation of and correction for those dynamics. The
standard input format is an analog voltage. A digital airspeed signal from GPS or
another source is available as a custom option. |
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Magnetically clean installation location |
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Installation digital compass calibration |
Applicable Products:
Typical Options:
We are able to accommodate your custom needs. Go to our
custom product modifications page
for a listing of the most common custom options we support.
Custom options for this application:
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Digital airspeed input from GPS or other source. |
