Vega AHRS-1 / AHRS-3 / MAG-1 Operating Manual
Page 10
Slip Sense:
Select if you want the slip to have a high sensitivity or a low sensitivity setting.
Slip Zero:
This function allows you to set your slip indicator to exactly zero even if your aircraft tends to fly slightly wing down. The
procedure is to place the aircraft in a stable, straight and level attitude during calm flight conditions and then select this
function. To cancel the correction, place your sensor absolutely horizontal (use a spirit level) and select the function
again.
Speed Unit:
Select the speed unit.
Speed:
Enter the cruising speed of your aircraft. This speed is transmitted to the attitude sensor for aiding purposes if the GPS
speed is not available.
Pitch Marker:
This enables or disables the pitch markers on the horizon display.
CAN Address:
Select the CAN address of the SP-X attitude sensor.
Couple Coeff (AHRS-3 only):
This is a number from 1 to 10. “1” is the default.
This number determines how “strongly” the AHRS will force the gyro derived horizon estimate to coincide with that of the
accelerometer based level calculations which are based on gravity.
“1” causes a very slow correction. This is the normal state and used most often.
“10” is the highest correction speed. This is usually used if the AHRS is used in unfavorable conditions.
Background:
Gyros can only tell you if you are rotating around any axis (you have three of them). Gyros cannot tell your attitude, they
can only tell you how your attitude is changing.
Accelerometers can tell you your attitude – but only if you are not accelerating. That includes a turn as this involves accel-
eration (constant change of direction). In addition accelerometers will react to any movement of your aircraft caused by
turbulence etc.
So – basically accelerometers can sometimes tell you your attitude while gyros can tell you how your attitude has
changed – but with errors as measurements are never 100% accurate – so the longer you rely only on the gyros the
worse it gets.
To a large extent the AHRS can estimate accelerations acting on your aircraft as it knows the aircraft's velocity. This
means it can estimate a reasonably valid attitude from the accelerometers that is “noisy” even in accelerated flight. For
this to be possible it has to assume how your aircraft moves through space. So it is mostly correct but sometimes not.
The coupling coefficient allows you to trade between the two.
Usually a panel mounted AHRS is affected by vibrations from engines (gyros don't like vibrations). This is the largest error
source for a typical AHRS. If your installation suffers from that a higher coupling number may assist as gyro errors are
larger than normal.
If this does not help you will have to either try and reduce vibrations affecting the panel or install an external AHRS like
the SP-7 or high grade SP-9. This allows locating the AHRS in a more suitable and protected area. If the AHRS-4 detects
an external AHRS it will automatically use it. External AHRS is connected onto the CAN bus.