First the AI, then the DG, then...?

[Jay Honeck]

A couple of months ago our AI, which had been "coming and going", finally
went. We replaced it with a rebuilt unit from "The Gyro House", which had
the dual effect of getting our autopilot working properly again.

Last month, our DG failed completely and suddenly, after a normal landing in
Pella, IA. Before that landing it worked, after that landing it didn't.
And the autopilot -- connected to the DG, too -- stopped working again.

So, I've just received a rebuilt unit from the Gyro House. As a precaution
(I'm assuming some sort of contamination caused the second failure), I've
ordered new vacuum hoses -- enough for my A&P to replace all the hoses, from
the vacuum pump to the firewall, and from the firewall to the two vacuum
instruments. I'm also having him replace all the filters.

Short of replacing the vacuum pump itself (which is still working fine), is
there anything else I should be watching?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[rip]

Intake filter, regulator, vac gauge accuracy....

Rip

Jay Honeck wrote:
> A couple of months ago our AI, which had been "coming and going", finally
> went. We replaced it with a rebuilt unit from "The Gyro House", which had
> the dual effect of getting our autopilot working properly again.
>
> Last month, our DG failed completely and suddenly, after a normal landing in
> Pella, IA. Before that landing it worked, after that landing it didn't.
> And the autopilot -- connected to the DG, too -- stopped working again.
>
> So, I've just received a rebuilt unit from the Gyro House. As a precaution
> (I'm assuming some sort of contamination caused the second failure), I've
> ordered new vacuum hoses -- enough for my A&P to replace all the hoses, from
> the vacuum pump to the firewall, and from the firewall to the two vacuum
> instruments. I'm also having him replace all the filters.
>
> Short of replacing the vacuum pump itself (which is still working fine), is
> there anything else I should be watching?

[Paul Tomblin]

In a previous article, "Jay Honeck" > said:
>Short of replacing the vacuum pump itself (which is still working fine), is
>there anything else I should be watching?

Practice partial panel much lately?


--
Paul Tomblin > http://xcski.com/blogs/pt/
You know the saying, every time you develop an idiot proof system they
develop a better type of idiot... and now you know who "they" are.
-- Matthew Malthouse

[Stu Gotts]

Do you have a wet pump or dry pump? You may give the place you traded
your old one into a call and ask what they found while repairing it.
Regular wear or contaminants. Then again, you just may have been
unlucky. What did the Gyro House hit you up for the A/P DG?


On Fri, 28 Nov 2003 03:32:13 GMT, "Jay Honeck"
> wrote:

>A couple of months ago our AI, which had been "coming and going", finally
>went. We replaced it with a rebuilt unit from "The Gyro House", which had
>the dual effect of getting our autopilot working properly again.
>
>Last month, our DG failed completely and suddenly, after a normal landing in
>Pella, IA. Before that landing it worked, after that landing it didn't.
>And the autopilot -- connected to the DG, too -- stopped working again.
>
>So, I've just received a rebuilt unit from the Gyro House. As a precaution
>(I'm assuming some sort of contamination caused the second failure), I've
>ordered new vacuum hoses -- enough for my A&P to replace all the hoses, from
>the vacuum pump to the firewall, and from the firewall to the two vacuum
>instruments. I'm also having him replace all the filters.
>
>Short of replacing the vacuum pump itself (which is still working fine), is
>there anything else I should be watching?

[EDR]

In article <1lzxb.331132$Tr4.1006704@attbi_s03>, Jay Honeck
> wrote:

> A couple of months ago our AI, which had been "coming and going", finally
> went. We replaced it with a rebuilt unit from "The Gyro House", which had
> the dual effect of getting our autopilot working properly again.


Hmmmm... Your landing or Mary's? :-)

[Jay Honeck]

> What did the Gyro House hit you up for the A/P DG?

$515, plus tax and shipping.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Jay Honeck]

> > A couple of months ago our AI, which had been "coming and going",
finally
> > went. We replaced it with a rebuilt unit from "The Gyro House", which
had
> > the dual effect of getting our autopilot working properly again.
>
>
> Hmmmm... Your landing or Mary's? :-)

Mine. Funny thing was, it was one of my better landings! :-)

A friend of mine says that the gyros inside ride on some sort of a "ruby
bearing" -- and that they eventually wear out. Sometimes the rotor (or
whatever) even falls right off the bearing. When that happens, everything
just stops -- like mine did.

Or something like that. Either way, it's just more money...
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Aaron Coolidge]

Jay Honeck > wrote:
: Short of replacing the vacuum pump itself (which is still working fine), is
: there anything else I should be watching?

As others have said, check the accuracy of the vac gauge, because extra-high
vacuum will make the gyros "over-rev" and wear their bearings quite quickly.

You might want to look at the inline filter STC that inserts a filter in the
suction line between the regulator and the vacuum pump. The theory is that
if the pump fails, the carbon vanes blow up into dust which gets sucked back
into the lines and instruments by residual vacuum. This in-line filter
supposedly traps all of that carbon dust, preventing the lines, regulator,
and instruments from becoming contaminated. When the pump is replaced, the
filter needs to be replaced as well.

As I recall, the same fellow that holds the M-20 air/oil seperator STC holds
this in-line vacuum filter STC.

--
Aaron Coolidge (N9376J)

[David Lesher]

"Jay Honeck" > writes:

>As a precaution
>(I'm assuming some sort of contamination caused the second failure), I've
>ordered new vacuum hoses -- enough for my A&P to replace all the hoses, from
>the vacuum pump to the firewall, and from the firewall to the two vacuum
>instruments. I'm also having him replace all the filters.

A somewhat dumb question. Each vacuum-driven instrument has its
own input filter, correct? The hoses and pumps are then all downsteam
of the instrument.

Does garbage really migrate upstream into the expensive toys? (And
if so, you'd thunk someone would add a inline filter between the
toy and the common vacuum line..)

Education welcomed.
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Jim Weir]

David Lesher >
shared these priceless pearls of wisdom:

->
->A somewhat dumb question. Each vacuum-driven instrument has its
->own input filter, correct? The hoses and pumps are then all downsteam
->of the instrument.

Sometimes. More often there is one very large filter with two outlets (or a
single outlet with an installer's T fitting) for both vacuum gyros.


->
->Does garbage really migrate upstream into the expensive toys? (And
->if so, you'd thunk someone would add a inline filter between the
->toy and the common vacuum line..)

Not really. The carbon dust that comes off of a normally operating pump gets
ported overboard and the big chunks that come off of a pump in failure mode get
thrashed about until they are small enough to be blown overboard OR remain in
the pump as mute testimony to the advantages of a wet pump.


->
->Education welcomed.

And is generally expensive, but not as expensive as ignorance (Twain).


Jim
Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

[G.R. Patterson III]

David Lesher wrote:
>
> Does garbage really migrate upstream into the expensive toys?

If a dry pump fails, the carbon vanes may turn into powder. When this happens,
the pressure on the instrument side is lower than atmospheric pressure, and you
may wind up with some of this powder being blown back into the instruments. In
normal use, however, garbage does not migrate back upstream.

> (And if so, you'd thunk someone would add a inline filter between the
> toy and the common vacuum line..)

Some people do this as a preventative measure. Alternatives include prophylactic
replacement of the dry pump to attempt to ensure it never fails, using a wet
pump, and cleaning the instruments before using them after a pump fails. The
filter is cheap insurance.

George Patterson
Some people think they hear a call to the priesthood when what they really
hear is a tiny voice whispering "It's indoor work with no heavy lifting".

[Stu Gotts]

Was that with the exchange? I'm looking for an a/p DG, but have
nothing to trade.

On Fri, 28 Nov 2003 15:29:52 GMT, "Jay Honeck"
> wrote:

>> What did the Gyro House hit you up for the A/P DG?
>
>$515, plus tax and shipping.

[Mike Rapoport]

How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
600,000,000 times in 1000hrs.

Mike
MU-2

"Jay Honeck" > wrote in message
news:1lzxb.331132$Tr4.1006704@attbi_s03...
> A couple of months ago our AI, which had been "coming and going", finally
> went. We replaced it with a rebuilt unit from "The Gyro House", which had
> the dual effect of getting our autopilot working properly again.
>
> Last month, our DG failed completely and suddenly, after a normal landing
in
> Pella, IA. Before that landing it worked, after that landing it didn't.
> And the autopilot -- connected to the DG, too -- stopped working again.
>
> So, I've just received a rebuilt unit from the Gyro House. As a
precaution
> (I'm assuming some sort of contamination caused the second failure), I've
> ordered new vacuum hoses -- enough for my A&P to replace all the hoses,
from
> the vacuum pump to the firewall, and from the firewall to the two vacuum
> instruments. I'm also having him replace all the filters.
>
> Short of replacing the vacuum pump itself (which is still working fine),
is
> there anything else I should be watching?
> --
> Jay Honeck
> Iowa City, IA
> Pathfinder N56993
> www.AlexisParkInn.com
> "Your Aviation Destination"
>
>

[Tom S.]

"Mike Rapoport" > wrote in message
link.net...
> How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
> 600,000,000 times in 1000hrs.
>

I hate to think how many revolutions my 7200RPM hard drive makes in a year
(24/7).

[Jay Honeck]

> Was that with the exchange? I'm looking for an a/p DG, but have
> nothing to trade.

Yep. They charged my card $2100, and they will credit me back the
difference when I return the old DG.

How's THAT for a good incentive to get that thing in the mail? :-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Mike Rapoport]

But you HDD was sealed in a cleanroom. Vacuum gyros are constantly
injesting grit.

Mike
MU-2


"Tom S." > wrote in message
...
>
> "Mike Rapoport" > wrote in message
> link.net...
> > How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
> > 600,000,000 times in 1000hrs.
> >
>
> I hate to think how many revolutions my 7200RPM hard drive makes in a year
> (24/7).
>
>

[Stu Gotts]

WOW, sure is! Isn't the new STec DG around $2300?

On Sun, 30 Nov 2003 01:52:49 GMT, "Jay Honeck"
> wrote:

>> Was that with the exchange? I'm looking for an a/p DG, but have
>> nothing to trade.
>
>Yep. They charged my card $2100, and they will credit me back the
>difference when I return the old DG.
>
>How's THAT for a good incentive to get that thing in the mail? :-)

[Jay Honeck]

> WOW, sure is! Isn't the new STec DG around $2300?

Yeah, for some reason electric DGs are outrageously more expensive than
vacuum ones.

Anyone know why?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Kevin]

Jay Honeck wrote:
>>WOW, sure is! Isn't the new STec DG around $2300?
>
>
> Yeah, for some reason electric DGs are outrageously more expensive than
> vacuum ones.
>
> Anyone know why?


Probally a dumb question, but I have to ask. would a GPS not be more
accurate than a DG ?

[Jay Honeck]

> Probally a dumb question, but I have to ask. would a GPS not be more
> accurate than a DG ?

Yes, but many autopilots are "slaved" to a "heading bug" on your DG. This
set-up pre-dates GPS by decades, and is much cheaper than the (seemingly
simpler) GPS-autopilot connection.

Again, there is no logic to this -- but what else is new?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Stu Gotts]

Yes, but in this instance he needed a DG to drive the autopilot for
flying desired or assigned course headings.

On Sun, 30 Nov 2003 16:35:46 GMT, Kevin > wrote:

>Jay Honeck wrote:
>>>WOW, sure is! Isn't the new STec DG around $2300?
>>
>>
>> Yeah, for some reason electric DGs are outrageously more expensive than
>> vacuum ones.
>>
>> Anyone know why?
>
>
>Probally a dumb question, but I have to ask. would a GPS not be more
>accurate than a DG ?

[Dan Thomas]

"Jay Honeck" > wrote in message news:<%Hpyb.172161$Dw6.663993@attbi_s02>...
> > Probally a dumb question, but I have to ask. would a GPS not be more
> > accurate than a DG ?
>
> Yes, but many autopilots are "slaved" to a "heading bug" on your DG. This
> set-up pre-dates GPS by decades, and is much cheaper than the (seemingly
> simpler) GPS-autopilot connection.
>
> Again, there is no logic to this -- but what else is new?

A DG gives heading, a GPS gives track. Two very different things.

Dan

[Dan Thomas]

"G.R. Patterson III" > wrote in message >...
> David Lesher wrote:
> >
> > Does garbage really migrate upstream into the expensive toys?
>
> If a dry pump fails, the carbon vanes may turn into powder. When this happens,
> the pressure on the instrument side is lower than atmospheric pressure, and you
> may wind up with some of this powder being blown back into the instruments. In
> normal use, however, garbage does not migrate back upstream.
>
> > (And if so, you'd thunk someone would add a inline filter between the
> > toy and the common vacuum line..)
>
> Some people do this as a preventative measure. Alternatives include prophylactic
> replacement of the dry pump to attempt to ensure it never fails, using a wet
> pump, and cleaning the instruments before using them after a pump fails. The
> filter is cheap insurance.
>
> George Patterson
>
A failed vac pump isn't likely to send garbage back up the line.
The instruments represent a significant vacuum leak, and the pressure
will drop off almost instantaneously when the pump fails. The filters
between the gyros and pump are more likely to keep garbage from a
failed instrument from gettingn into the pump, failing it as well.

Dan

[Dan Thomas]

"Jay Honeck" > wrote in message news:<E7nyb.369913$Fm2.367716@attbi_s04>...
> > WOW, sure is! Isn't the new STec DG around $2300?
>
> Yeah, for some reason electric DGs are outrageously more expensive than
> vacuum ones.
>
> Anyone know why?

So few made. Most general aviation aircraft use vacuum or air-driven
attitude and heading indicators, and an electric turn coordinator to
provide some redundancy if the vacuum fails. Electric DGs and horizons
would be used as backups in much larger airplanes, like the small
electric attitude indicators in the centre of most airliner panels.

Dan

[Dan Thomas]

"Jay Honeck" > wrote in message news:<fXJxb.334160$HS4.2853565@attbi_s01>...
> A friend of mine says that the gyros inside ride on some sort of a "ruby
> bearing" -- and that they eventually wear out. Sometimes the rotor (or
> whatever) even falls right off the bearing. When that happens, everything
> just stops -- like mine did.
>
> Or something like that. Either way, it's just more money...

Little wee tiny ball bearings. The lube dries out from all
the air going through the instrument, cold weather hardens it,
airborne pollutants get through old/cracked/nonexistent filters
(cigarette smoke is a bad one) and bearings can't take it anymore.

Dan

[Dan Thomas]

"Mike Rapoport" > wrote in message . net>...
> How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
> 600,000,000 times in 1000hrs.
>
> Mike
> MU-2

I think it's a lot higher than that, maybe as much as two or three
or four times. Plenty, anyway.

Dan

[Jay Honeck]

> > Again, there is no logic to this -- but what else is new?
>
> A DG gives heading, a GPS gives track. Two very different things.

True. However, the illogic I was referring to is the incredible difference
in price between an autopilot that is slaved to a DG, versus an autopilot
that is connected to a GPS. The former is MUCH more difficult to achieve
than the latter, yet the GPS connection is much more expensive to buy.

This is due to demand, I suppose?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Dan Thomas]

(Dan Thomas) wrote in message >...
> "Mike Rapoport" > wrote in message . net>...
> > How old were your gyros? At 10,000 rpm (just a guess) a gyro revolves
> > 600,000,000 times in 1000hrs.
> >
> > Mike
> > MU-2
>
> I think it's a lot higher than that, maybe as much as two or three
> or four times. Plenty, anyway.
>
> Dan

Looked it up just now: 25,000 RPM. Bearings are typically .031" (1/32") diameter.

Dan

[Doug Vetter]

Jay Honeck wrote:
>>>Again, there is no logic to this -- but what else is new?
<snip>

Jay,

I joined this thread a bit late...after my local server flushed the
original message, but I believe your original question was "what could
cause premature gyro failure"?

In my experience, two things:

1) If it fails within a few hours of being new, that's typically because
of manufacturing, long-term storage, or shipping damage -- all of which
can cause the bearings to "flat spot". Apparently the bearings are
*that* soft.

2) If it fails after a few hundred (as opposed to a few thousand) hours,
improper mounting or excessive vibration is usually the culprit. The
problem is most severe in aircraft whose panels aren't shock mounted AND
when those same aircraft don't have their props properly (dynamically)
balanced.

Our gyros were so damn expensive that when we had our panel apart last
time I had the shop replace the mounts. Not only does the panel NOT sag
like it used to, but as we encounter various (normal) harmonics in our
particular engine/prop combination, the shock-mounted instruments simply
don't shake like some of the other fixed mounted units (fuel gauges, etc).

I forget if your airplane has a fixed or shock-mounted panel, but if
it's shock mounted, I'd recommend replacing the shock mounts and getting
the prop redressed / painted, then dynamically balanced for good measure.

HTH,

-Doug

--
--------------------
Doug Vetter, CFIMEIA

http://www.dvcfi.com
--------------------

[David Lesher]

"Jay Honeck" > writes:

>Yeah, for some reason electric DGs are outrageously more expensive than
>vacuum ones.

>Anyone know why?

They ARE direct drive, are they not?

My guess is as follows. The air/vacuum motor is trivial; a series
of vanes and a jet tube from the intake filter. Easy to make go
fast.

But a tiny DC motor is difficult; the rotor windings will want to
fling themselves out at high speeds. The brushes and commutator
will be near watchmaker-skill level.

A new design would have a AC inductor motor with a squirrel-cage
motor, and a small internal inverter. But does anyone make them
like that?


--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Aaron Coolidge]

David Lesher > wrote:
<snip>

: A new design would have a AC inductor motor with a squirrel-cage
: motor, and a small internal inverter. But does anyone make them
: like that?

The DC-powered electric gyros are actually as you describe: a three
phase, 400Hz motor with an inverter. See www.chiefaircraft.com -> aircraft
-> flight instruments -> gyros -> RC Allen Electric Gyros.

The 400Hz models, of course, have no inverter.
--
Aaron Coolidge (N9376J)

[David Lesher]

Aaron Coolidge > writes:

>: A new design would have a AC inductor motor with a squirrel-cage
>: motor, and a small internal inverter. But does anyone make them
>: like that?

>The DC-powered electric gyros are actually as you describe: a three
>phase, 400Hz motor with an inverter. See www.chiefaircraft.com -> aircraft
>-> flight instruments -> gyros -> RC Allen Electric Gyros.

Hmmm. Thanks..I was thinking something far higher in frequency{...as he tries
to recall the relationship between frequency, rotor poles and RPM...}

--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

[Greg Copeland]

On Tue, 02 Dec 2003 04:33:59 +0000, David Lesher wrote:

>
> But a tiny DC motor is difficult; the rotor windings will want to
> fling themselves out at high speeds. The brushes and commutator
> will be near watchmaker-skill level.
>

Wow! I assumed they used a brushless motor.