Compass Questions ?

Hello,

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 answer.

Regarding the compass heading that shows in the glass displays:

How is it derived ?
GPS ?

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. ?

Thanks,
Bob

Hello Bob,

I'm unable to provide the answer as to the technology employed by
computer-generated displays to display magnetic information, but I would expect
something like a Hall device might be employed. As you implied, it could as
easily be derived from GPS data corrected for magnetic variation at the
particular location.

Magnetic/compass headings are not true, but magnetic. Navigation Sectional
charts http://skyvector.com/ are depicted in True coordinates, and the
pilot/navigator must correct for magnetic variation in drafting his flight
plan. ATC expects all course/heading numbers to be magnetic.

You'll find more information he
http://www.faa.gov/regulations_policies/handbooks_manuals/, and he
http://www.faa.gov/regulations_policies/handbooks_manuals/aviation/pilot_handbook/media/PHAK%20-%20Chapter%2015.pdf.

Hope that helps.

Best regards,
Larry Dighera



On Mon, 13 Jul 2015 18:36:54 -0400, Bob wrote:

Hello,

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 answer.

Regarding the compass heading that shows in the glass displays:

How is it derived ?
GPS ?

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. ?

Thanks,
Bob

In article , lid, Bob
says...

Hello,

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 answer.

Regarding the compass heading that shows in the glass displays:

How is it derived ?
GPS ?

Not sure what you really mean by glass display, but I'll assume old
school (real) compass - a magnetic pointer).

They point North! - magnetic north, always, of course!

I believe a LAME checks and swings the compass (Licenced Aircraft
Mechanical Engineer). (Ie. a mechanic! - but a plane mechanic! )
On doing so, they may adjust a placard beside the compass to indicate
local deviation, normally quadrants and sub-quadrants only. So maybe +1
for East for example. This is of course, local to each plane.

If not GPS, what ?

Is it then Magnetic or True ?

A compass always points magnetically.

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

Yes, both chart variation, and compass deviation (per above). On top of
that, there's wind to adjust for.

Does aviation use True or Magnetic when discussing or flying ?

Both of course. Charts are True, the compass is Magnetic.

--
Duncan.

Hi,

Thanks for replies and help.

What I was referring to are the new, modern, "glass" displays where most
everything shown is derived
from transducers located elsewhere.

e.g. when a display shows a Heading of, e.g., 075, it is of course
getting this info. from some kind of transducer, located elsewhere.

Is it derived directly from GPS ?
A Hall effect compass ?
or,... ?

Thanks again; interesting subject.

Bob
-------------------------------------------------------------------------------------------------------------

On 7/13/2015 6:36 PM, Bob wrote:
Hello,

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
answer.

Regarding the compass heading that shows in the glass displays:

How is it derived ?
GPS ?

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. ?

Thanks,
Bob

In article , lid, Bob
says...

Hi,

Thanks for replies and help.

What I was referring to are the new, modern, "glass" displays where most
everything shown is derived
from transducers located elsewhere.

e.g. when a display shows a Heading of, e.g., 075, it is of course
getting this info. from some kind of transducer, located elsewhere.

Is it derived directly from GPS ?
A Hall effect compass ?
or,... ?

Thanks again; interesting subject.

Well I'm not sure on that - perhaps others will reply. However,
cellphones usually use one or more magnetometers (hope I spelt that
right ). A GPS can't get a magnetic heading, only True.

I play with Arduino's a bit - and Googling 'arduino magentometer' gives
a few results, eg...
http://bildr.org/2011/01/hmc6352/
http://bildr.org/2012/02/hmc5883l_arduino/
http://eclecti.cc/hardware/hmc5843-m...ry-for-arduino

I *assume* that the compass in a glass display uses the same sort of
technology.

--
Duncan.

In article ,
, Dave Doe says...

In article , lid, Bob
says...

Hi,

Thanks for replies and help.

What I was referring to are the new, modern, "glass" displays where most
everything shown is derived
from transducers located elsewhere.

e.g. when a display shows a Heading of, e.g., 075, it is of course
getting this info. from some kind of transducer, located elsewhere.

Is it derived directly from GPS ?
A Hall effect compass ?
or,... ?

Thanks again; interesting subject.

Well I'm not sure on that - perhaps others will reply. However,
cellphones usually use one or more magnetometers (hope I spelt that
right ). A GPS can't get a magnetic heading, only True.

I play with Arduino's a bit - and Googling 'arduino magentometer' gives
a few results, eg...
http://bildr.org/2011/01/hmc6352/
http://bildr.org/2012/02/hmc5883l_arduino/
http://eclecti.cc/hardware/hmc5843-m...ry-for-arduino

I *assume* that the compass in a glass display uses the same sort of
technology.

Apologies to the apostrophe police - that's terrible!

--
Duncan.

Dave Doe wrote:
In article ,
, Dave Doe says...

In article , lid, Bob
says...

Hi,

Thanks for replies and help.

What I was referring to are the new, modern, "glass" displays where most
everything shown is derived
from transducers located elsewhere.

e.g. when a display shows a Heading of, e.g., 075, it is of course
getting this info. from some kind of transducer, located elsewhere.

Is it derived directly from GPS ?
A Hall effect compass ?
or,... ?

Thanks again; interesting subject.

Well I'm not sure on that - perhaps others will reply. However,
cellphones usually use one or more magnetometers (hope I spelt that
right ). A GPS can't get a magnetic heading, only True.

I play with Arduino's a bit - and Googling 'arduino magentometer' gives
a few results, eg...
http://bildr.org/2011/01/hmc6352/
http://bildr.org/2012/02/hmc5883l_arduino/
http://eclecti.cc/hardware/hmc5843-m...ry-for-arduino

I *assume* that the compass in a glass display uses the same sort of
technology.

Apologies to the apostrophe police - that's terrible!

--
Duncan.

The display in a glass panel is GPS course. You need a magnetic compass to know
your heading. The difference between the two is wind correction, magnetic
variation and compass deviation.

While I don't doubt that someone could create a device that would send
magnetic heading info to a glass panel, it would have to be some obvious
secondary display. You want to be looking at your true course if you want
to get from A to B.

--
Don Poitras

In article , , Don
Poitras says...

Dave Doe wrote:
In article ,
, Dave Doe says...

In article , lid, Bob
says...

Hi,

Thanks for replies and help.

What I was referring to are the new, modern, "glass" displays where most
everything shown is derived
from transducers located elsewhere.

e.g. when a display shows a Heading of, e.g., 075, it is of course
getting this info. from some kind of transducer, located elsewhere.

Is it derived directly from GPS ?
A Hall effect compass ?
or,... ?

Thanks again; interesting subject.

Well I'm not sure on that - perhaps others will reply. However,
cellphones usually use one or more magnetometers (hope I spelt that
right ). A GPS can't get a magnetic heading, only True.

I play with Arduino's a bit - and Googling 'arduino magentometer' gives
a few results, eg...
http://bildr.org/2011/01/hmc6352/
http://bildr.org/2012/02/hmc5883l_arduino/
http://eclecti.cc/hardware/hmc5843-m...ry-for-arduino

I *assume* that the compass in a glass display uses the same sort of
technology.

Apologies to the apostrophe police - that's terrible!

--
Duncan.

The display in a glass panel is GPS course. You need a magnetic compass to know
your heading. The difference between the two is wind correction, magnetic
variation and compass deviation.

While I don't doubt that someone could create a device that would send
magnetic heading info to a glass panel, it would have to be some obvious
secondary display. You want to be looking at your true course if you want
to get from A to B.

The OP is asking about just about such a device. And it's clear they do
exist in a glass display (a compass that is).

Take for example, the Cessna website. If you navigate to say the Cessna
TTx - and check out the glass Avionics section, and look at Equipment
Details (rather than Standard Features), it specifies a Magnetometer ...
"GMU-44 Magnetometer (dual)"

Albiet a compass is almost obsolete and uncessary with todays navigation
equipment, but let's not forget runways - still lined up and named
magnetic. Makes me wonder when that will change.

--
Duncan.

Dave Doe wrote:
In article , , Don
Poitras says...

Dave Doe wrote:
In article ,
, Dave Doe says...

In article , lid, Bob
says...

Hi,

Thanks for replies and help.

What I was referring to are the new, modern, "glass" displays where most
everything shown is derived
from transducers located elsewhere.

e.g. when a display shows a Heading of, e.g., 075, it is of course
getting this info. from some kind of transducer, located elsewhere.

Is it derived directly from GPS ?
A Hall effect compass ?
or,... ?

Thanks again; interesting subject.

Well I'm not sure on that - perhaps others will reply. However,
cellphones usually use one or more magnetometers (hope I spelt that
right ). A GPS can't get a magnetic heading, only True.

I play with Arduino's a bit - and Googling 'arduino magentometer' gives
a few results, eg...
http://bildr.org/2011/01/hmc6352/
http://bildr.org/2012/02/hmc5883l_arduino/
http://eclecti.cc/hardware/hmc5843-m...ry-for-arduino

I *assume* that the compass in a glass display uses the same sort of
technology.

Apologies to the apostrophe police - that's terrible!

--
Duncan.

The display in a glass panel is GPS course. You need a magnetic compass to know
your heading. The difference between the two is wind correction, magnetic
variation and compass deviation.

While I don't doubt that someone could create a device that would send
magnetic heading info to a glass panel, it would have to be some obvious
secondary display. You want to be looking at your true course if you want
to get from A to B.

The OP is asking about just about such a device. And it's clear they do
exist in a glass display (a compass that is).

Take for example, the Cessna website. If you navigate to say the Cessna
TTx - and check out the glass Avionics section, and look at Equipment
Details (rather than Standard Features), it specifies a Magnetometer ...
"GMU-44 Magnetometer (dual)"

Albiet a compass is almost obsolete and uncessary with todays navigation
equipment, but let's not forget runways - still lined up and named
magnetic. Makes me wonder when that will change.

--
Duncan.

You're right. I was wrong. It makes sense that the glass HSI would need
to work like the mechanical one and that gets set manually to the
current compass setting.

--
Don Poitras

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
adjustment.

--
Dallas