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Compass Questions ?

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Old July 15th 15, 09:56 PM posted to rec.aviation.piloting
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Default Compass Questions ?

Dallas wrote in

Bob wrote:

Regarding the compass heading that shows in the glass displays:

The heading information from the PFD comes from a directional gyro. The
directional gyro's drift is constantly corrected (slaved) by a magnetic
compass located in the tailcone on the airplane. The output of this compass
is electrically "enhanced" and amplified through a "flux gate".

Bottom line: A very accurate, stable, compass reading that never needs

And to expand on that a bit...


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Old September 5th 15, 11:53 PM posted to rec.aviation.piloting
Brian Whatcott
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Default Compass Questions ?

Oh my, a reasonable question, attracting answers over the next two days,
of which just one had it right - and that referred to the AHRS
attitude heading system. What used to be an expensive collection of
gyros and accelerometers is now commercially available (for model
aircraft and drones) for $20 on up. Glass cockpits can often select
heading in TRUE or MAG form.

For those of us flying on the cheap, a moving map application like APIC
from Approach Systems (an update costs $10) loaded on a personal
assistant like the HP IQue which cost around $300 when new uses its
internal GPS to provide a track made good (over the ground) which can be
presented as Mag or True. It is convenient to set the direction
indicator to the MAG track indicated, though this ignores the difference
between Heading and Track - the former being needed to make good the
latter, despite a crosswind.


Brian W

On 7/13/2015 5:36 PM, Bob wrote:

Not a Pilot, but always interested in the engineering aspects.

This question came up, and I realize that I am not sure of a correct

Regarding the compass heading that shows in the glass displays:

How is it derived ?

If not GPS, what ?

Is it then Magnetic or True ?

Does the Pilot have to correct for variation/declination changes during
a flight ?

Does aviation use True or Magnetic when discussing or flying ?

etc. ?



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