DG Questions

[Jay Honeck]

Six weeks ago my attitude indicator gave up the ghost, after slowly dying
over a period of several months. It's been replaced with a re-built unit
that's working fine.

Two days ago my directional gyro abruptly failed. It worked fine flying
into Pella, and it didn't work at all flying out. The thing wouldn't spin
up at all -- as if the gyro failed catastrophically, or, perhaps, a vacuum
line had come detached. The setting button would pop out, and the thing
would momentarily spin (10 degrees or so), but nothing would happen from
that point on.

My A&P says all the lines look fine, so the cheap fix is apparently out
(naturally). This leaves the DG -- and, of course, it's the real expensive
one with the heading bug for my autopilot...

Doesn't it seem just a little weird to lose both vacuum instruments in a six
week period? Is there any way my vacuum pump could still be putting out 5
inches of suction, and somehow sending junk into the instruments? Could the
AI failure last month have influenced the DG failure this month?

Or is it just bad luck that they've failed together? Any opinions?
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Ron Natalie]

"Jay Honeck" > wrote in message news:xdvnb.50697$HS4.232433@attbi_s01...

> Doesn't it seem just a little weird to lose both vacuum instruments in a six
> week period? Is there any way my vacuum pump could still be putting out 5
> inches of suction, and somehow sending junk into the instruments? Could the
> AI failure last month have influenced the DG failure this month?
>
> Or is it just bad luck that they've failed together? Any opinions?

You do have a vacuum filter on the intakes to these things? When we lost both
our gyros (other than finding one and a $5 price tag on the top of it), we found
that the gyro inputs were just open to the crumbling insulation behind the panel.

[Jim]

Exactly my thought. Remember that the vacuum sucks air through the
instrument, check the inlet to see if the filter is on it. Could be just as
Ron described, insulation, dust and other crud could be getting sucked into
your gyros from behind the panel.
--
Jim Burns III

Remove "nospam" to reply


"Ron Natalie" > wrote in message
m...
>
> "Jay Honeck" > wrote in message
news:xdvnb.50697$HS4.232433@attbi_s01...
>
> > Doesn't it seem just a little weird to lose both vacuum instruments in a
six
> > week period? Is there any way my vacuum pump could still be putting out
5
> > inches of suction, and somehow sending junk into the instruments? Could
the
> > AI failure last month have influenced the DG failure this month?
> >
> > Or is it just bad luck that they've failed together? Any opinions?
>
> You do have a vacuum filter on the intakes to these things? When we lost
both
> our gyros (other than finding one and a $5 price tag on the top of it), we
found
> that the gyro inputs were just open to the crumbling insulation behind the
panel.
>
>

[[email protected]]

On 28-Oct-2003, "Jay Honeck" > wrote:

> Six weeks ago my attitude indicator gave up the ghost, after slowly dying
> over a period of several months. It's been replaced with a re-built unit
> that's working fine.
>
> Two days ago my directional gyro abruptly failed.


In close to 2000 hours over 34 years I have never seen a vacuum instrument
suddenly die like that, except when associated with vacuum failure (pump or
vacuum line breakage or disconnection). I suppose it could happen, but
usually it's a slow death like you experienced with your AI.

I'd check to make sure that there is suction to the instrument, not just
visual inspection of the hoses, before I removed it from the plane.

--
-Elliott Drucker

[Jay Honeck]

> I'd check to make sure that there is suction to the instrument, not just
> visual inspection of the hoses, before I removed it from the plane.

How would you recommend going about doing that?

I've not seen what's up there for myself -- how are the hoses attached to
the instruments? How do you check for vacuum? Detach the hose and stick
your finger over it?

Thanks for the advice!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Jay Masino]

Jay Honeck > wrote:
>> I'd check to make sure that there is suction to the instrument, not just
>> visual inspection of the hoses, before I removed it from the plane.

> How would you recommend going about doing that?
> I've not seen what's up there for myself -- how are the hoses attached
> to the instruments? How do you check for vacuum? Detach the hose and
> stick your finger over it?

You could removed the line from your panel mounted vacuum gauge and attach
it directly to the suction hose going into your DG (remove the hose
completely from the DG, don't use a "T" at first). This way you're
isolating the vacuum comming from the regulator. You may need an adapter,
because I believe they're generally use a smaller hose to the gauge than
the hose to the instruments. A decent avionics shop, or even a well
equipped maintenance shop should be able to apply a vacuum to the
instrument using a bench mounted vacuum pump to check it out. I agree
that most vacuum instruments die slowly, not suddenly.

The hoses are generally hooked to the instrument with either a barbed
adapter, or an adapter with a single "ridge" flaired into it. This type
is the type where you'd use a hose clamp. It's generally not needed with
the barbed adapter, although it's often used anyway.

The "schematic" for your vacuum system is likely the following:

+----- DG ------+
| |
filter < > regulator ----- vacuum pump
| |
+----- AI ------+
|
+----- vacuum gauge

direction of air flow ------------>

Note that both the filter, and the firewall mounted regulator have two
ports on them. The vacuum gauge is often driven by an auxilary port
on either the AI (as pictured) or the DG. I think you can also have it
fed by a "T" off the normal lines to one of the instruments.

-- Jay


__!__
Jay and Teresa Masino ___(_)___
http://www2.ari.net/jmasino/ ! ! !

Checkout http://www.oc-adolfos.com/
for the best Italian food in Ocean City, MD and...
Checkout http://www.brolow.com/ for authentic Blues music on Delmarva

[Jay Honeck]

Thanks, Jay.

I have no idea how I'm going to climb under there to actually see all
this -- but if my 60 year old, 220 pound A&P can do it, so can I, dang it!
:-)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[[email protected]]

On 28-Oct-2003, "Jay Honeck" > wrote:

> How would you recommend going about doing that?


I really don't know how easy it is to determine the presence of suitable
suction at the end of a vacuum tube just by putting your finger over it, but
certainly your A&P should have a vacuum gauge that will remove all doubt.

There should be two hoses attached to the back of the DG. One (the air
outlet) comes from the vacuum regulator and the other (the air inlet) goes
(probably through a "T" connector) to the filter.

First remove the air inlet hose. With the engine running (vacuum gauge
registering) check if there is suction at the inlet port to the DG (where
you just removed the hose). BTW, if the DG now seems to be working, the
problem is an obstruction on the inlet side.

Then remove the air outlet hose from the DG. Check if there is suction at
the end of this hose.

If there is suction in both places your DG is bad. The airflow is not
spinning the gyro.
If there is no suction at the air outlet there is a leak or obstruction
between the regulator and the DG.
If there is suction at the air outlet but not at the air inlet your DG is
bad, but it may just be a relatively simple internal obstruction.

--
-Elliott Drucker

[Michelle P]

Jay,

Two can die close together if you lost or the previous owner lost a
vacuum pump and did not check for backwash in the lines from the
intruments to the pump. Carbon has been know to get sucked back into the
lines and make it into the instruments.

Michelle

Jay Honeck wrote:

>Six weeks ago my attitude indicator gave up the ghost, after slowly dying
>over a period of several months. It's been replaced with a re-built unit
>that's working fine.
>
>Two days ago my directional gyro abruptly failed. It worked fine flying
>into Pella, and it didn't work at all flying out. The thing wouldn't spin
>up at all -- as if the gyro failed catastrophically, or, perhaps, a vacuum
>line had come detached. The setting button would pop out, and the thing
>would momentarily spin (10 degrees or so), but nothing would happen from
>that point on.
>
>My A&P says all the lines look fine, so the cheap fix is apparently out
>(naturally). This leaves the DG -- and, of course, it's the real expensive
>one with the heading bug for my autopilot...
>
>Doesn't it seem just a little weird to lose both vacuum instruments in a six
>week period? Is there any way my vacuum pump could still be putting out 5
>inches of suction, and somehow sending junk into the instruments? Could the
>AI failure last month have influenced the DG failure this month?
>
>Or is it just bad luck that they've failed together? Any opinions?
>
>

--

Michelle P ATP-ASEL, CP-AMEL, and AMT-A&P

"Elisabeth" a Maule M-7-235B (no two are alike)

Volunteer Pilot, Angel Flight Mid-Atlantic

Volunteer Builder, Habitat for Humanity

[G.R. Patterson III]

Jay Honeck wrote:
>
> Is there any way my vacuum pump could still be putting out 5
> inches of suction, and somehow sending junk into the instruments?

No.

George Patterson
You can dress a hog in a tuxedo, but he still wants to roll in the mud.

[G.R. Patterson III]

Jay Honeck wrote:
>
> I have no idea how I'm going to climb under there to actually see all
> this -- but if my 60 year old, 220 pound A&P can do it, so can I, dang it!

I haven't tried it in a Piper, but the procedure in my Maule is to wriggle into
a position in which my head is lying against the rudder pedals and my legs are
over the back of the pilot's seat. Removing the pilot's seat helps a lot, but
it's a real pain in a Maule.

My biggest problem these days is raising my head in this position far enough
for my old eyes to focus on the back of the panel. You shouldn't have that
problem (yet).

George Patterson
You can dress a hog in a tuxedo, but he still wants to roll in the mud.

[Mark Mallory]

Jay Honeck wrote:
> Doesn't it seem just a little weird to lose both vacuum instruments in a six
> week period? Is there any way my vacuum pump could still be putting out 5
> inches of suction, and somehow sending junk into the instruments? Could the
> AI failure last month have influenced the DG failure this month?

If the (dry) vacuum pump fails catastrophically, it can barf chunks of vane
material back into the regulator and instruments (the instrument cases act as
vacuum reservoirs, and will suck air back into them if the outlet pressure jumps
back to ambient.)

Also, some vacuum hoses are prone to deterioration with age and can shed junk
into the instrument inlets (especially if the hoses are flexed and/or wiggled,
as happens when an instrument is replaced):

http://www.avionicswest.com/myviewpoint/vacuumarticle.html

[Ross Richardson]

George,

You have the visual problem also??? I thought it was just me.

"G.R. Patterson III" wrote:
>
>
> I haven't tried it in a Piper, but the procedure in my Maule is to wriggle into
> a position in which my head is lying against the rudder pedals and my legs are
> over the back of the pilot's seat. Removing the pilot's seat helps a lot, but
> it's a real pain in a Maule.
>
> My biggest problem these days is raising my head in this position far enough
> for my old eyes to focus on the back of the panel. You shouldn't have that
> problem (yet).
>
> George Patterson
> You can dress a hog in a tuxedo, but he still wants to roll in the mud.

[Jay Honeck]

> You have the visual problem also??? I thought it was just me.

Just in the last year, I have developed this issue -- and I discovered it
the LAST time I was under the panel.

I was trying to re-route my GPS antenna wire, and after turning myself
upside down and sideways, I realized that I couldn't focus well enough to
see what I was doing. Taking my glasses off -- usually the solution --
didn't help, cuz my clear-focal length is about 7 inches.

I also discovered that I could not extricate myself from under there without
experiencing grave pain. Next time, the seat IS coming out. I'm afraid
bi-focals are in my near future. (Mary started needing reading glasses a
couple of years ago, but still has 20/20 distance vision...)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Jay Honeck]

> http://www.avionicswest.com/myviewpoint/vacuumarticle.html

Thanks, Mark -- great article.

It sure sounds like my A&P inadvertently cashed in my DG -- but we'll never
know for sure.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[G.R. Patterson III]

Jay Honeck wrote:
>
> I'm afraid bi-focals are in my near future.

Bifocals are not an optimal solution (though they seem to be the best the eye
docs can give us). However, I have a set of single-vision glasses that are
made especially for work at computers. They focus in the area between about two
feet and four feet away and have a special coating for dealing with glare. They
work fine for under the panel.

George Patterson
You can dress a hog in a tuxedo, but he still wants to roll in the mud.

[Nathan Young]

"Jay Honeck" > wrote in message news:<afXnb.57745$Fm2.35151@attbi_s04>...
> > You have the visual problem also??? I thought it was just me.
>
> Just in the last year, I have developed this issue -- and I discovered it
> the LAST time I was under the panel.
>
> I was trying to re-route my GPS antenna wire, and after turning myself
> upside down and sideways, I realized that I couldn't focus well enough to
> see what I was doing. Taking my glasses off -- usually the solution --
> didn't help, cuz my clear-focal length is about 7 inches.
>
> I also discovered that I could not extricate myself from under there without
> experiencing grave pain. Next time, the seat IS coming out. I'm afraid
> bi-focals are in my near future. (Mary started needing reading glasses a
> couple of years ago, but still has 20/20 distance vision...)

Definitely take out the seat! Assuming the Pathfinder's seat tracks
are like my 180's - it takes all of 2 minutes to do. 4 screws and
slide the seat.

-Nathan

[COUGARNFW]

The vision problem. I have had the glasses that have the upper half capable of
swinging down to add to the correction of the glasses and then a few years ago
my optometrist listened and found an item called an "opticaid", by Elroy
Products of Nyack NJ.

They attach to glasses and there are five powers one can get which give you
various working distances.

The protective packet the folded devices come in is about 3 X 4 inches and
maybe 5/8ths thick. Handy.

Even with bifocals, everyone forgets that, looking up you are still blind.

With these devices, you have your normal glasses, either simple or bifocal, and
the aid these give you.

One of those very handy devices I won't go under the "dash" without.

Neal

[Jay Honeck]

> Definitely take out the seat! Assuming the Pathfinder's seat tracks
> are like my 180's - it takes all of 2 minutes to do. 4 screws and
> slide the seat.

Actually 8 screws, but you're right -- it's an easy thing to do.

I just thought I could pop under there like I was 25 again. BIG mistake. ;)
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"

[Nathan Young]

"Jay Honeck" > wrote in message news:<vnfob.65164$e01.218689@attbi_s02>...
> > Definitely take out the seat! Assuming the Pathfinder's seat tracks
> > are like my 180's - it takes all of 2 minutes to do. 4 screws and
> > slide the seat.
>
> Actually 8 screws, but you're right -- it's an easy thing to do.
>
> I just thought I could pop under there like I was 25 again. BIG mistake. ;)

Ditto that, and I don't think 25 has anything to do with it - Just not
enough space. I spent several nights last week installing Nulites in
the panel of my 180. A few hours of that made me wonder how one could
be an avionics tech without first being a contortionist.

-Nathan