Do you use your magnetic compass?

A recent compass swing on our plane has turned up some opinions about
magnetic compasses that are surprising to me..

A club member has asked me why we spent money to have a 14 degree error
removed from our compass since it is just a back up instrument if everything
else quits. He just sets the DG to the runway heading on takeoff and uses
that. A couple of 360 in our 172 to look at something on the ground will
put our DG 15 -20 degrees off and it drifts about that much each hour. That
doesn't seem to concern him.

An A&P I asked in another forum said he hopes his customers don't expect him
to get the compass closer than about 10 degrees. Our shop says 10 degrees
is what is allowed.

I used to do a lot of sailing and a degree or two in a compass is a big deal
to me. Even though I can do direct to with the Loran or GPS, I like to be
able to start out in the right direction. If I'm looking for an airport or
landmark, knowing pretty accurately where the aircraft is pointed helps. If
everything else quits, I'd really like to know where the plane is pointed
while I try to find a place to land.

I agree that the compass is pretty fuzzy in an airplane. By the time you
get it to settle down, set the DG, and add in the difficulty of figuring out
exactly where the axis of the airplane is, 10 degrees may be the best you
can do. However, my experience with both navigation and engineering tells
me that it's still worth being precise where you can. If you accept a 10
degree error in the compass itself and then add the 10 degrees of other
factors, you could be up to 20 degrees. That seems like a lot to me.

Am I being overly compulsive about this? I know that everything the
magnetic compass tells you has to be verified with all other available
information but it is still the primary source of direction information in a
simple aircraft like our 172.

Are these casual attitudes towards compass accuracy I'm encountering common?


--
Roger Long

VFR I don't see the big deal about having a working compass and stable
DG. Most of us have a GPS these days, and in the Midwest we can
navigate by the 'grid' road system.

IFR a working compass and DG is a lot more important. If the DG
precesses, it can make long vectors a real pain. Since an accurate
compass is the only easy way to get magnetic heading aloft, it is
necessary to figure the winds aloft, which is fairly important while
beginning an approach.

I'm assuming your club members fly both IFR and VFR, so you should
maintain the plane to what makes sense for the IFR members.

-Nathan


On Sat, 15 May 2004 12:33:25 GMT, "Roger Long"
om wrote:

A recent compass swing on our plane has turned up some opinions about
magnetic compasses that are surprising to me..

A club member has asked me why we spent money to have a 14 degree error
removed from our compass since it is just a back up instrument if everything
else quits. He just sets the DG to the runway heading on takeoff and uses
that. A couple of 360 in our 172 to look at something on the ground will
put our DG 15 -20 degrees off and it drifts about that much each hour. That
doesn't seem to concern him.

An A&P I asked in another forum said he hopes his customers don't expect him
to get the compass closer than about 10 degrees. Our shop says 10 degrees
is what is allowed.

I used to do a lot of sailing and a degree or two in a compass is a big deal
to me. Even though I can do direct to with the Loran or GPS, I like to be
able to start out in the right direction. If I'm looking for an airport or
landmark, knowing pretty accurately where the aircraft is pointed helps. If
everything else quits, I'd really like to know where the plane is pointed
while I try to find a place to land.

I agree that the compass is pretty fuzzy in an airplane. By the time you
get it to settle down, set the DG, and add in the difficulty of figuring out
exactly where the axis of the airplane is, 10 degrees may be the best you
can do. However, my experience with both navigation and engineering tells
me that it's still worth being precise where you can. If you accept a 10
degree error in the compass itself and then add the 10 degrees of other
factors, you could be up to 20 degrees. That seems like a lot to me.

Am I being overly compulsive about this? I know that everything the
magnetic compass tells you has to be verified with all other available
information but it is still the primary source of direction information in a
simple aircraft like our 172.

Are these casual attitudes towards compass accuracy I'm encountering common?

I did, last Wednesday

Not long after leaving the airport northbound, the Garmin III+ popped
up a message: Battery Low. Then it went off, and after one more rep it
stayed off. Happily there was not much wind, and the position of the
compass (there is no gyro in the Cub) was well-remembered as between N
and 3 outbound and between S and 16 on the return trip, which enabled
me to go and return with reasonable accuracy. (Viz was about 10 miles
so I couldn't steer by the mountains as I prefer to do.)

It made me realize that it had been a very long time since I'd checked
my progress on the chart.

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

Dan...

I'm so disappointed... You actually use a GPS in a Cub...
Blastphemy!!!!

John Price
CFII/AGI/IGI
http://home.att.net/~jm.price


"Cub Driver" wrote in message
news

I did, last Wednesday

Not long after leaving the airport northbound, the Garmin III+ popped
up a message: Battery Low. Then it went off, and after one more rep it
stayed off. Happily there was not much wind, and the position of the
compass (there is no gyro in the Cub) was well-remembered as between N
and 3 outbound and between S and 16 on the return trip, which enabled
me to go and return with reasonable accuracy. (Viz was about 10 miles
so I couldn't steer by the mountains as I prefer to do.)

It made me realize that it had been a very long time since I'd checked
my progress on the chart.

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

I'm so disappointed... You actually use a GPS in a Cub...

I wouldn;t leave home without it!

The big problem was where to mount it, given that the Cub is soloed
from the back seat. For the solution (actually, two solutions) see
www.pipercubforum.com/garmin.htm

all the best -- Dan Ford
email: (put Cubdriver in subject line)

The Warbird's Forum www.warbirdforum.com
The Piper Cub Forum www.pipercubforum.com
Viva Bush! blog www.vivabush.org

On Mon, 17 May 2004 17:05:30 -0400, Cub Driver
wrote:


I'm so disappointed... You actually use a GPS in a Cub...

I wouldn;t leave home without it!

The big problem was where to mount it, given that the Cub is soloed
from the back seat. For the solution (actually, two solutions) see
www.pipercubforum.com/garmin.htm


where to mount it actually has some worthwhile considerations.

most are up in the windscreen slung from the roof, these typically
need the rubber diaphragms replaced every year since they perish in
the uv and start to leak.
the old pilot who built my aircraft put it at the base of the panel.
its bobbing around isnt distracting down there out of the field of
view and being at the bottom of the panel keeps it cool enough that
the diaphragms last over 5 years.

never realised the significance until an instrument overhauler pointed
out what it achieved.
Stealth Pilot

while in class B airspace you need a working compass / DG , otherwise what are
you going to do when told to make all those turns.

Nathan Young wrote:

VFR I don't see the big deal about having a working compass and stable
DG. Most of us have a GPS these days, and in the Midwest we can
navigate by the 'grid' road system.

You would have to be allowed into Bravo airspace for that to matter.
In 8 years of flying VFR and IFR in the Chicago area, I've been inside
the Bravo probably less than 5 times, and those were at odd hours.




-Nathan

On Thu, 20 May 2004 18:47:20 -0700, Jeff wrote:

while in class B airspace you need a working compass / DG , otherwise what are
you going to do when told to make all those turns.

Nathan Young wrote:

VFR I don't see the big deal about having a working compass and stable
DG. Most of us have a GPS these days, and in the Midwest we can
navigate by the 'grid' road system.

"Roger Long" wrote:
Am I being overly compulsive about this?

Not at all, IMO.

I know that everything the magnetic compass tells you has
to be verified with all other available information

It's the other way around, isn't it? Once you're airborn, the compass
is the only thing you have that directly displays your heading. The HI
is not much use if you have no way to remove its precession.

Are these casual attitudes towards compass accuracy I'm encountering
common?

I don't know, but to me the compass is as important as any other flight
instrument. I definitely want to know which way the nose is pointed.
--
Dan
C172RG at BFM

Am I being overly compulsive about this?

Maybe. Although I still religiously set the DG to the compass in flight,
it's more from habit than from need.

I've got two moving map GPSs, two VORs, DME, and the road grids to navigate
with -- any one of which is far more accurate than my whisky compass. And
the odds of losing all of those tools (including battery back-ups) are
almost nil.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"