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Ttail
Joined: 24 Jun 2013
Posts: 120
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 Posted: Sun Sep 29, 2019 12:37 pm Post subject: CJ6 Heading Adjustments |
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Seeking info on how to accurately set up the Heading sensor/Flux valve in the CJ6.
After turning on the Gyros then syncing the resultant displayed heading is close to that displayed on the mag compass. If I then line up precisely on Rwy hdg (and re synch) I have around a 7-9 degree heading error. Can this be "biased' out ? If so whats the process How and on what ?
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Clouddog
Joined: 02 Jun 2016
Posts: 119
Location: Lebanon, TN
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| Posted: Sun Sep 29, 2019 2:43 pm Post subject: CJ6 Heading Adjustments |
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I have the same question. My CJ RMI had been spot on for 6 years. All of a suddenly it is 180 degrees out on most flights and on rare occasions (very rare ) it will be accurate. More wrong that right. Yes I know, who uses the RMI?? Well, not much but I like EVERYTHING working in my airplanes! A working airplane us a happy airplane.
Clouddog
On Sun, Sep 29, 2019, 15:42 Ttail <ttail(at)internode.on.net (ttail(at)internode.on.net)> wrote:
| Quote: | --> Yak-List message posted by: "Ttail" <ttail(at)internode.on.net (ttail(at)internode.on.net)>
Seeking info on how to accurately set up the Heading sensor/Flux valve in the CJ6.
After turning on the Gyros then syncing the heading the resultant displayed heading is close to that displayed on the mag compass. If I then line up precisely on Rwy hdg (and re synch) I have around a 7-9 degree heading error. Can this be "biased' out ? If so whats the process How and on what ?
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wlannon(at)shaw.ca
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| Posted: Sun Sep 29, 2019 4:01 pm Post subject: CJ6 Heading Adjustments |
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When was the last time the your runway heading was re-identified? I
believe this is required every ten years for licensed airports but doubt it
is done for my small town runway. And perhaps yours? I actually laid out a
compass rose for ours about 24 years ago which of course by now is currently
useless.
In any case whether the runway headings are currently correct or not is kind
of a moot point at this time. They will be wrong next year!
The North Pole (that has lived in Canada for some centuries) has decided to
move to Russia (actually Siberia!). It is on the way at breakneck speed (in
historical terms) and nobody knows why! Some scientists are suggesting
changes to the flow of liquid iron some hundreds of miles below our feet.
I believe you could find a more intelligent discussion of this phenomena at
NOAA or National Geographic or?.
If you decide to make adjustments to your heading indication it is a
relatively simple process (for a qualified A&P). The primary unit, whether
it is referred to as a flux gate, or whatever, is in fact a master compass
that is adjusted in exactly the same manner as any other aircraft magnetic
compass.
In early CJ's it is located inside the LH wing close to the tip. In later
models in the aft fuselage RH side just fwd. of the horiz. stab.
Cheers;
Walt
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Ttail
Joined: 24 Jun 2013
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markbitterlich(at)embarqm
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| Posted: Mon Sep 30, 2019 9:53 am Post subject: CJ6 Heading Adjustments |
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Actually TTail, I must agree with Walt. In order to adjust a compass, you
need at a minimum a north/south line, and for General Aviation typically an
accurate compass rose. IE. You need an accurate physical reference to
"swing" a compass. If you are only trying to check the accuracy of your
compass it is commonly acceptable to use your GPS True heading, add or
subtract Magnetic Variation (as you said) and then compare your compass
reading with your GPS readings. If you have a WAAS GPS, or perhaps two
built in GPS's this will work, but you have to be moving because GPS has to
derive Heading from movement, and does not compute it sitting still. Thus
if you fly anything but straight and level, GPS heading can also be skewed.
Never-the-less, you can get a pretty good idea of your compass accuracy if
you are flying straight and level and fly right along an Isogonic Line.
With a calibrated North/South line and a calibrated Compass Calibrator it is
possible to park an aircraft on that line, plumb bob it for alignment and
using the calibrator fool the compass into believing any one of the 24
cardinal points and adjust N/S, E/W compensation magnets accordingly, and
create a compensation card as required by the FAA. Very very few facilities
have this device, although the military does. Even then, the North South
line must be surveyed on a regular basis using something like a MC-2000.
What is interesting is that by FAA Regs our compass systems or ... in most
cases a simple magnetic compass... must have an up to date compass
calibration card attached in plain sight. I've always laughed at this,
mainly because FAA Inspectors have not got a clue in this regard.
Supposedly completed by an A&P or better, just how was it done, and how does
the FAA know it was not just made up and never done in the first place? Add
to that what Walt said about a compass rose and not only painting one but to
keep it accurate.
Compass Rose's for many decades were a really big deal on military bases.
So important in fact that no REBAR was allowed in the concrete that the rose
was painted on. Why should be obvious, but suffice it to say there is
natural magnetic deviation and then there is "local influence" and these are
referred to as single and dual cycle errors. Bottom line, any ferrous metal
around you, to include buildings, other aircraft, REBAR, etc., will also
skew magnetic lines of flux, which throw the compass out of accuracy, thus
why the Flux Valve Walt is referring to is generally put as far away from
the engine as possible.
So bottom line, "Swinging a compass" is no small matter, assuming you really
want to do it right, and/or you want an accurate compass calibration
correction card. Doing it on the ground requires special considerations and
an accurate rose which is extremely hard to find, let alone construct. So
in reality there is no way to get there from here and I would venture to say
that most compass's in most GA aircraft fail to meet FAA mandated accuracy
standards, the good news being they have no way to actually prove that!
FYI, the majority of military aircraft today use an Embedded GPS Inertial
Navigation System (or "EGI" for short) that derive Mag Heading using True
Heading from the INS corrected for Mag/Var and tend to ignore the Standby
Compass as regards accuracy.
In the end, given all the very real problems involved, I would be tempted
to calibrate a standby compass using GPS in flight, and if you have an older
model flux valve system, well... good luck with that. You'll need a compass
rose, and someone who really knows what they are doing, and a whole day
doing it. Conversely, I have read about some of the brand new flux valves
that compensate themselves with only a N/S, E/W physical alignment.
In the end, it is highly unlikely that we will be doing any
time/distance/speed navigation these days based on compass heading, ala
Charles Lindbergh ... instead we just pretty much keep the line straight on
the GPS.
Mark
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markbitterlich(at)embarqm
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so applying the latest Mag var should result in an acceptable mag heading. In my part of the world the variation drift is pretty sedate.