Vertical Card Compass
Wood
dip errors that a normal wet compass would have? Are they OK for IFR
flight?
Thanks...
Brad Wood
N39ER
AA5B
Bob Gardner
positive. They do exhibit Northerly Turning Error, but considerably
damped compared to a wet compass. Dip is hardly noticeable. Their
biggest advantage is that they don't jump around in turbulence.
Bob Gardner
Robert Scott
> How does a vertical card compass work? Does it have the same magnetic
> dip errors that a normal wet compass would have?
It may be useful to point out that northerly turning and
acceleration/deceleration errors are not peculiar to any particular
kind of compass, but are, by necessity, inherent in any compass
that measures the earth's magnetic field and attempts to report
the direction as projected onto the plane that is perpendicular
to apparent gravity.
Bob Scott
Ann Arbor, Michigan (email: rscott (at) wwnet (dot) net )
(My automatic return address is intentionally invalid.)
sdd...@yahoo.com
Bob Gardner <bob...@halcyon.com> wrote:
> My experience with vertical card compasses is one hundred percent
> positive. They do exhibit Northerly Turning Error, but considerably
> damped compared to a wet compass. Dip is hardly noticeable. Their
> biggest advantage is that they don't jump around in turbulence.
>
I concur as to above except that I think biggest advantage is that
presentation is same as on a DG, so you don't have to change thinking
switching from dg to whisky compass.
> Bob Gardner
>
> Wood wrote:
>
> > How does a vertical card compass work? Does it have the same magnetic
> >
> > dip errors that a normal wet compass would have? Are they OK for IFR
> > flight?
> >
> > Thanks...
> >
> > Brad Wood
> > N39ER
> > AA5B
>
>
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Larry Dighera
electronic compass based on the Hall Effect should not have errors
associated with geomagnetic dip nor acceleration.
On Wed, 15 Jul 1998 19:18:57 GMT, Rober...@noplace.com (Robert
Scott) wrote:
>It may be useful to point out that northerly turning and
>acceleration/deceleration errors are not peculiar to any particular
>kind of compass, but are, by necessity, inherent in any compass
>that measures the earth's magnetic field and attempts to report
>the direction as projected onto the plane that is perpendicular
>to apparent gravity.
There is no expedient to which a man will not resort
to avoid the real labor of thinking.
Sir Joshua Reynolds
Mark Mallory
: While the statement below may be true of mechanical compasses, an
: electronic compass based on the Hall Effect should not have errors
: associated with geomagnetic dip nor acceleration.
This is true only if the compass is mounted on a gyro-stabilized (or
equivalent) platform that is maintained parallel to the earth's surface
at all times, regardless of pitch and/or bank of the aircraft. A
Hall-Effect compass mounted directly to the aircraft will have
essentially the same *turning* errors (due to magnetic dip) as would a
Whiskey compass.
Angelo Campanella
>It may be useful to point out that northerly turning and
>acceleration/deceleration errors are not peculiar to any particular
>kind of compass, but are, by necessity, inherent in any compass
>that measures the earth's magnetic field and attempts to report
>the direction as projected onto the plane that is perpendicular
>to apparent gravity.
With ONE important qualification:
NORMAL compasses are arranged to have the compass card (carrying the magnet)
lay more or less horizontal. This is arranged by having the center of gravity
(read carefully please!) of the suspended card below the center of support.
At lattitudes away from the equator (us), the dip angle is considerable. At
40 degres north it is about 40 degrees fromt he horizontal.
A neutrally balanced card, were it to exist, would really want lay parallel to
the dip angle (not 'flat'). But the center of gravity, being below the center
of support, will exert a torque as a result of this 'not parallel to the dip
angle' effect, thus placing the center of gravity to be NOT under the center
of support. East-west acceleration or turns from north or south will result in
a turning torque on the card, thus producing the well known turning error
offsets.
The VERTICAL Card compass just MIGHT have this lower CG arrangement to a
lesser extent or not at all. In that case, the turning error will be
correspondingly less or removed. I've though about this for many years. But I
never figured out how to keep the compass card in place with no centering
forces available.
Comments, Please.
Ang.
Robert Scott
The theoretical problem is that the magnetic force vector is
3-dimensional but the desired compass indication is 2-dimensional,
being comprised of just an angle between 0 and 360 degrees. In
order to reduce the 3-dimensional magnetic force vector to a vector
in a 2-dimensional plane, an assumption needs to be made as to which
plane to use. Once we identify a plane, then the compass projects
the magnetic force vector onto that place to get the compass
indication. The operation of the mechanical whiskey compass
that Angelo accurately described in a previous posting causes the
magnetic force vector to be projected onto the plane that is
perpendicular to apparent gravity. Under those assumptions you
get standard turning errors regardless of the technology used to
sense the magnetic field.
But as Larry Dighera pointed out in a previous posting, a
plane that is referenced to a "gyro-stabilized platform that is
maintained parallel to the earth's surface at all times, regardless
of pitch and/or bank of the aircraft" would have no turned errors.
And if there were an easier way to identify up and down, then
we wouldn't need gyros in our attitude indicators. But since
we do have gyros, it stands to reason that a compass with
no turning errors cannot be made without using a gryo or
equivalent (like a laser ring gyro). Without such a reference
there is no way to identify the proper plane onto which the
magnetic force vector is to be projected.
Then Larry goes on to say:
> A Hall-Effect compass mounted directly to the aircraft will
> have essentially the same *turning* errors (due to magnetic dip)
> as would a Whiskey compass.
I assume that by "mounted directly to the aircraft" he means that
the Hall-effect compass is measuring the magnetic field projected
onto a plane that is always parallel to the wings and
perpendicular to the yaw axis. Under coordinated flight this
compass will indeed behave like a whiskey compass, since the
plane perpendicular to apparent gravity is the same as the
plane of the airframe. But consider what happens in a slip.
If you are flying due north in a constant slip with the right
wing low and plenty of left rudder, the whiskey compass will
continue to indicate due north, while the Hall-effect compass
mounted to the now-tilted airframe will display turning error
(even though you are not turning). By the way, most of the
commercial electronic compasses that I have seen are equiped
with sensing elements floating in a liquid. They are not
mounted rigidly, so they do respond to apparent gravity.
Everett M. Greene
> Larry Dighera (LDig...@worldnet.att.net) wrote:
> : While the statement below may be true of mechanical compasses, an
> : electronic compass based on the Hall Effect should not have errors
> : associated with geomagnetic dip nor acceleration.
>
> This is true only if the compass is mounted on a gyro-stabilized (or
> at all times, regardless of pitch and/or bank of the aircraft. A
> essentially the same *turning* errors (due to magnetic dip) as would a
> Whiskey compass.
Trivia question: Why is it called a whiskey compass? I thought
the fluid was something akin to kerosene? Do or did they contain
alcohol?
Larry Dighera
Charles Lindbergh on his non-stip New York to Paris flight:
http://www.tsrcom.com/neatstuff/eb2271-1.jpg
As you indicated, it was mounted in gimbals to overcome "rolling and
pitching or the plane." The chief advantage of the Earth Inductor
Compass over a magnetic compass is its freedom from oscillation error.
On Thu, 16 Jul 1998 02:17:25 GMT, mmal...@netcom.com (Mark Mallory)
wrote:
>Larry Dighera (LDig...@worldnet.att.net) wrote:
>: While the statement below may be true of mechanical compasses, an
>: electronic compass based on the Hall Effect should not have errors
>: associated with geomagnetic dip nor acceleration.
>
>This is true only if the compass is mounted on a gyro-stabilized (or
>equivalent) platform that is maintained parallel to the earth's surface
>at all times, regardless of pitch and/or bank of the aircraft. A
>Hall-Effect compass mounted directly to the aircraft will have
>essentially the same *turning* errors (due to magnetic dip) as would a
>Whiskey compass.