Backup vacuum pump system STC'ed for Cherokee 180

Hi group,

Seems to be a lot of experience out on this list, so I thought I might
ask a question.

I have a Cherokee 180 that is IFR cert, but both A.I. and Turn
Coordinator are vacuum driven. With both driven by vacuum, a pump or
engine failure in IMC will leave you guessing if you're right side up,
turning, or pitching.

I've considered replacing the A.I. or Turn Coordinator with an
electric driven instrument. But either would be expensive and
replacing the Turn Coordinator would break my autopilot. So, I've
decided the cheapest way to provide backup insurance is to put in a
back up vacuum pump.

Does anyone out there have any experience with the STC'ed backup
vacuum pump kits? Is one maker's kit better/easier to install that
others? And is there any information available on reliability? I'd
hate to put in a "backup" system only to have it fail to work!

Thanks guys.



Chuck
N7398W
San Antonio, Tx

Chuck wrote in message . ..

Hi group,

I have a Cherokee 180 that is IFR cert, but both A.I. and Turn
Coordinator are vacuum driven. With both driven by vacuum, a pump or
engine failure in IMC will leave you guessing if you're right side up,
turning, or pitching.

You mean the AI and Directional Gyro, no?

Does anyone out there have any experience with the STC'ed backup
vacuum pump kits? Is one maker's kit better/easier to install that
others? And is there any information available on reliability? I'd
hate to put in a "backup" system only to have it fail to work!

My 172 has the Precise Flight standby vacuum system, which is capable
of providing survival-level vacuum under specified conditions, namely
reduced throttle (less than 2100rpm) and below 8000'. Luckily this is
just what you're doing on an approach, so it works where you need it
to. The installation also typically includes a low vacuum annunciator
light.

http://www.preciseflight.com/standby.html

It's quite simple in and of itself, but there is a recurring
inspection AD that can cost a few hundred dollars depending on the
situation. It works by tapping the vacuum system into the intake
manifold with a bypass valve, so it works a long as the engine's
running.

What I like about this system is that I don't need to change my scan
to use it--I'm still navigating off the same instruments I use all the
time. Typically a backup electric AI is crammed into some odd spot on
the panel.

FWIW it was installed before I bought into the plane so I don't know
what it would cost to put one on. Almost definitely a good deal less
than a second vacuum pump.

Best,
-cwk.

I've owned and flown with various kinds of backup systems, so here's my 2 m$.
I've had 2 vacuum pump failures, one in VMC and one in IMC. I had no backup
equipment installed when I had the IMC failure. I was able to descend a little
to get below the bases into visual conditions. I wouldn't like having to to a
full approach with needle-ball-airspeed.

Precise Flight standby vacuum. Least expensive, least effective. Has a shuttle
valve that selects vacuum from either the primary vacuum pump or the intake
manifold. The shuttle valve tends to stick sometimes. There's a recurring AD to
inspect it. Check it regularly during preflight. Provides vacuum only at low
power settings (when manifold pressure is lowest). As another poster noted, that
is actually exactly what you have during most of an approach. If you have to do
a missed-approach or go-around, be prepared to lose your vacuum instruments as
you add power. Have your mechanic temporarily disable the primary vacuum pump so
you can go out and experiment with it under VMC.

Electric standby vacuum pump. These seem to be a regular vacuum pump with an
electric motor attached. The one I've seen (on a club plane I fly occasionally)
takes up a lot of space under the cowling and looks heavy, but I don't know what
the actual weight is. There is a panel-mounted switch to turn it on. Seems like
it would do the job OK, but at the expense of space, weight, and complexity.

Dual-rotor vacuum pump. I have one of these on my Mooney. Two carbon-vane dry
vacuum pumps on the same shaft, with a clever arrangement that avoids breaking
the shaft for the second pump when the first one fails. The company that owned
the STC has gone out of business, but another company (Phoenix-something?) has
bought the STC but hasn't marketed it yet. They are trying to work out some
failures that occurred on certain engines, suspected to be related to torsional
vibration, I think. Last I knew, they were actively pursuing getting it back on
the market. When it was available, I thought it was good solution, and voted
with my wallet. Google groups will show you some earlier postings from me about
this system.

Electric AI. I have one of these on my Mooney, too. It's unfortunately installed
on the right side of the panel and is too far out of my scan to be useful. It
also seems to have a lot of lag in it, so it's not as nice as the primary AI.
It's required repair/overhaul/replacement a couple of times in the 10 years or
so it's been in the plane.

There's a dry vacuum pump on the market with an inspection window so you can
tell how worn the vanes are and hope to replace the pump before it fails.

I'm sure someone will chime in with "just get a wet pump". I don't have any
experience with those, so I'll just wait for that posting.

DGB

Chuck wrote:
Hi group,

Seems to be a lot of experience out on this list, so I thought I might
ask a question.

I have a Cherokee 180 that is IFR cert, but both A.I. and Turn
Coordinator are vacuum driven. With both driven by vacuum, a pump or
engine failure in IMC will leave you guessing if you're right side up,
turning, or pitching.

I've considered replacing the A.I. or Turn Coordinator with an
electric driven instrument. But either would be expensive and
replacing the Turn Coordinator would break my autopilot. So, I've
decided the cheapest way to provide backup insurance is to put in a
back up vacuum pump.

Does anyone out there have any experience with the STC'ed backup
vacuum pump kits? Is one maker's kit better/easier to install that
others? And is there any information available on reliability? I'd
hate to put in a "backup" system only to have it fail to work!

Thanks guys.



Chuck
N7398W
San Antonio, Tx


--
Dave Butler, software engineer 919-392-4367

Your AI and TC are vacuum powered? What kind of autopilot? Most the
Cherokees came with electric powered TCs/autopilots.

-Nathan


On Fri, 17 Sep 2004 05:17:36 GMT, Chuck wrote:

Hi group,

Seems to be a lot of experience out on this list, so I thought I might
ask a question.

I have a Cherokee 180 that is IFR cert, but both A.I. and Turn
Coordinator are vacuum driven. With both driven by vacuum, a pump or
engine failure in IMC will leave you guessing if you're right side up,
turning, or pitching.

I've considered replacing the A.I. or Turn Coordinator with an
electric driven instrument. But either would be expensive and
replacing the Turn Coordinator would break my autopilot. So, I've
decided the cheapest way to provide backup insurance is to put in a
back up vacuum pump.

Does anyone out there have any experience with the STC'ed backup
vacuum pump kits? Is one maker's kit better/easier to install that
others? And is there any information available on reliability? I'd
hate to put in a "backup" system only to have it fail to work!

Thanks guys.



Chuck
N7398W
San Antonio, Tx

The worst thing about a vacuum failure is not knowing it!!!
My suggestion is to put in a idiot light indicating that there is a
vacuum failure. It's an easy arrangement with a vacuum switch and a bulb.
When the light is on, go into partial panel mode.

My next suggestion is to put in a wet vacuum pump. The life spans on
these are usually in the thousands of hours not the 500 hrs as in the
dry pumps.

The next thing I'll hear is that my "belly has a little oil on it", "I
don't want to get a wet pump".

When it really gets down to it, whats more important, a clean belly or a
working vacuum system?

It doesn't get much more simple than that.





Nathan Young wrote:
Your AI and TC are vacuum powered? What kind of autopilot? Most the
Cherokees came with electric powered TCs/autopilots.

-Nathan


On Fri, 17 Sep 2004 05:17:36 GMT, Chuck wrote:


Hi group,

Seems to be a lot of experience out on this list, so I thought I might
ask a question.

I have a Cherokee 180 that is IFR cert, but both A.I. and Turn
Coordinator are vacuum driven. With both driven by vacuum, a pump or
engine failure in IMC will leave you guessing if you're right side up,
turning, or pitching.

I've considered replacing the A.I. or Turn Coordinator with an
electric driven instrument. But either would be expensive and
replacing the Turn Coordinator would break my autopilot. So, I've
decided the cheapest way to provide backup insurance is to put in a
back up vacuum pump.

Does anyone out there have any experience with the STC'ed backup
vacuum pump kits? Is one maker's kit better/easier to install that
others? And is there any information available on reliability? I'd
hate to put in a "backup" system only to have it fail to work!

Thanks guys.



Chuck
N7398W
San Antonio, Tx

I presume you mean that your DG and AI are vacuum driven. Virtually all
TC'c are electric.

We have a backup electric AI in our Arrow, and it works very well. To
extend its life, we have an on/off switch for it, and only turn it on when
in IMC. It is mounted in an otherwise unused space on the right side of the
radio stack. But many owners are ditching their ADFs these days, and the
hole where the ADF head was makes a good home for an electric AI. Ours has
not required any maintenance in 1700 flight hours over 8 years. I think
installed cost for such an instrument today would be around $2300 or so.
One big advantage of the electric AI is that it provides backup for the
vacuum AI instrument as well as the vacuum system as a whole.

Another thing to remember for vacuum system backup is that most portable GPS
units have an HSI function that works quite well as a DG. Not perfect,
since it displays magnetic track rather than magnetic heading, but a whole
lot better than nothing.

Finally, vacuum failure in IMC is an EMERGENCY, and should be treated as
such. As soon as you can do so safely, let ATC know of your problem. Know
ahead of time whether your AP will be affected. If so, turn it off
IMMEDIATELY upon detecting vacuum failure. If not, use it to help keep
wings level.

--
-Elliott Drucker

wrote:
I presume you mean that your DG and AI are vacuum driven. Virtually all
TC'c are electric.

We have a backup electric AI in our Arrow, and it works very well. To
extend its life, we have an on/off switch for it, and only turn it on when
in IMC. It is mounted in an otherwise unused space on the right side of the
radio stack. But many owners are ditching their ADFs these days, and the
hole where the ADF head was makes a good home for an electric AI.


Since TC's are no longer required you can mount the elctric AI right
next to the vacuum AI.