Precession of 10 degrees in 10 minutes too much?

I need to find out if there is an official maximum amount of precession
for a Directional Gyro. My aircraft precesses 10 degrees in 10 minutes
during mostly straight and level flight with only a few shallow banks.

One avionics tech told me that it depends on the gyro manufacturer as to
what is acceptable. He also told me that an out of the box unit tested
on the table should not precess more than ONE degree in four minutes.

Jay Moreland

I don't know about any official maximum amount of precession, but 10 degrees
in 10 minutes during mostly straight and level flight would be beyond my
tolerance for safely in instrument flying.

"Jay Moreland" wrote in message
...
I need to find out if there is an official maximum amount of precession
for a Directional Gyro. My aircraft precesses 10 degrees in 10 minutes
during mostly straight and level flight with only a few shallow banks.

One avionics tech told me that it depends on the gyro manufacturer as to
what is acceptable. He also told me that an out of the box unit tested
on the table should not precess more than ONE degree in four minutes.

Jay Moreland

Jay Moreland wrote:

I need to find out if there is an official maximum amount of precession
for a Directional Gyro. My aircraft precesses 10 degrees in 10 minutes
during mostly straight and level flight with only a few shallow banks.

One avionics tech told me that it depends on the gyro manufacturer as to
what is acceptable. He also told me that an out of the box unit tested
on the table should not precess more than ONE degree in four minutes.

Jay Moreland

Its too much. I had a new gyro that precessed about 3 degrees in 15, even
though the installer told me it would be better than that. I marked it
up to salesmanship. Later, the gyro developed a problem because of
manufacturing defect that was covered by the maker. Maker gets the gyro,
and pronounces its precession out of range. I told them then it had
allways been out of range, I had no way to know it should have been
better. They told me to pound salt, since the product was out
of warranty. I had it fixed by a third party shop, now it gets less
than 1 degree per 15 or less -- basically inperceptable.

By the way, it was Century, and they can pound salt the next time I buy
avionics of any kind. Their customer support policy sucks, and the
person there dealing with me was nasty about it as well. Besides, their
quality control is obviously suspect, since they let the unit go with
out of tolerance precession in the first place.

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In article , Jay Moreland
wrote:

I need to find out if there is an official maximum amount of precession
for a Directional Gyro. My aircraft precesses 10 degrees in 10 minutes
during mostly straight and level flight with only a few shallow banks.

One avionics tech told me that it depends on the gyro manufacturer as to
what is acceptable. He also told me that an out of the box unit tested
on the table should not precess more than ONE degree in four minutes.

Jay Moreland


I've heard 3 degrees/ 15 minutes as the max. One degree per minute is certainly
too much.

An airplane I used to fly had a lousy old DG in it...it precessed at a rate that
if you maintained the heading on the DG you were in about a 1/2 standard rate
turn. G

--
Dale L. Falk

There is nothing - absolutely nothing - half so much worth doing
as simply messing around with airplanes.

http://home.gci.net/~sncdfalk/flying.html

In defense of Century, the gyro may well have been in spec when it left
the factory. Shock during transit or sitting too long on the shelf can put
flat spots in the bearings that will cause precession. All it takes is
someone
dropping the shipping carton, or even sitting on the avionics shop shelf (or
in
your airplane) without spinning for more than a month or two.

Scott Moore wrote:

Besides, their
quality control is obviously suspect, since they let the unit go with
out of tolerance precession in the first place.

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

In article , Jay Moreland
wrote:

I need to find out if there is an official maximum amount of precession
for a Directional Gyro. My aircraft precesses 10 degrees in 10 minutes
during mostly straight and level flight with only a few shallow banks.

One avionics tech told me that it depends on the gyro manufacturer as to
what is acceptable. He also told me that an out of the box unit tested
on the table should not precess more than ONE degree in four minutes.

Jay Moreland


I've heard 3 degrees/ 15 minutes as the max. One degree per minute is
certainly
too much.

An airplane I used to fly had a lousy old DG in it...it precessed at a rate
that
if you maintained the heading on the DG you were in about a 1/2 standard rate
turn. G

I've heard the same. IIRC, the max was actually 10 degrees per hour. 3
degrees in 15 minutes was the short timer check.

No Spam

Scott Moore wrote:

By the way, it was Century, and they can pound salt the next time I buy
avionics of any kind.

To be fair, since there are a couple businesses called Century,
are you talking about Century Instruments in Wichita, KS or
Century Flight Systems in Mineral Wells, TX?

Thanks,
Sydney

Ray,
Respectfully, that is the reason gyros ought to be shipped in special
packaging, to prevent damage in transit.
I work with gyro product of another ilk, and we consider the packaging part
of the quality control process and mark it so it wont get discarded before
the units go in the vehicle. And we got shockmounts inside too, something
the GA gyros lack.

Javier


"Ray Andraka" wrote in message
...
In defense of Century, the gyro may well have been in spec when it left
the factory. Shock during transit or sitting too long on the shelf can
put
flat spots in the bearings that will cause precession. All it takes is
someone
dropping the shipping carton, or even sitting on the avionics shop shelf
(or
in
your airplane) without spinning for more than a month or two.

Scott Moore wrote:

Besides, their
quality control is obviously suspect, since they let the unit go with
out of tolerance precession in the first place.

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930 Fax 401/884-7950
email
http://www.andraka.com

"They that give up essential liberty to obtain a little
temporary safety deserve neither liberty nor safety."
-Benjamin Franklin, 1759

3° every 15 minutes is what I remember from training. That's what some may
consider ultimately manageable in the cockpit under IFR/IMC workload
conditions (YMMV), and is an 'human factors' limitation.
This is not to say that this is the acceptable tolerance for an instrument
out of the factory. They should be much, much better than that. The
avionics shop can tell from the gyro overhaul manual.

HTH

javier

"Jay Moreland" wrote in message
...
I need to find out if there is an official maximum amount of precession
for a Directional Gyro. My aircraft precesses 10 degrees in 10 minutes
during mostly straight and level flight with only a few shallow banks.

One avionics tech told me that it depends on the gyro manufacturer as to
what is acceptable. He also told me that an out of the box unit tested
on the table should not precess more than ONE degree in four minutes.

Jay Moreland

I learned the max was 3 degrees / 15 minutes. My understanding was that if
your gyro precesses more than 3/15, you should not fly IFR with it.

I always thought was too strict given my experience with different gyros; I
don't think any of the planes I've flown in would have passed.

The only source I found for this is the answer to a question in the Gleim
study guide, and it claims the reference is the FAA's "Instrument Flying
Handbook, chapter V".

"Jay Moreland" wrote in message
...
I need to find out if there is an official maximum amount of precession
for a Directional Gyro. My aircraft precesses 10 degrees in 10 minutes
during mostly straight and level flight with only a few shallow banks.

One avionics tech told me that it depends on the gyro manufacturer as to
what is acceptable. He also told me that an out of the box unit tested
on the table should not precess more than ONE degree in four minutes.

Jay Moreland