Good AI backup, wish me luck

After having both a vac pump failure and an AI failure (not on the
same flight ) I decided its really time for a backup. I always
consider my Mooney to be an "IFR anytime" type of plane, in that I
consider it a solid IFR platform. When the vac pump goes out alarms
starting sounding, my voice annunicator starting saying "check vac
pressure" and the needle goes to 0. It's pretty obvious. I do a
voluntary IPC every 6 months with a local DE and always do partial
panel approaches so I'm as comfortable as you can be with that. A
couple weeks ago I had my AI go out. WOW, that's another story!! The
thing slowly rolled 30 degrees off and REMAINED RESPONSIVE!! When I
banked, it banked, when I pitched, it piched. Figuring out that it was
dead could be hard and it would be easy to miss it. I decided I need a
back up and those vac backup systems are a waste of money(Precise
Flight, electric vac, etc). After getting it back from overhaul my
partner reported that it did it again! I called a couple gyro places
and they said the vac AIs don't last very long because they have a
stream of "dirty" air running through them. The electrics last much
longer. So I'm getting an electric AI installed as my backup. I
noticed that the non-TSO'd electric AIs are almost $1000 less than the
TSO'd ones. I asked my mechanics and the FSDO and they said I could
probably get a 337 approved by the FSDO for a non-TSO'd unit as long
as it wasn't in the "T" area of the panel. One FSDO guy said I might
need to label it "VFR only" and I'd have to promise not to do 135. In
either case I'll end up having an electric backup AI for under $1500.
That's less than the price of a backup electric vac pump installed
about about the same price to put a Precise Flight in a Mooney (with
California labor rates of $95/hr ) with twice the redundency.

-Robert

Robert M. Gary wrote:
After having both a vac pump failure and an AI failure (not on the
same flight ) I decided its really time for a backup. I always
consider my Mooney to be an "IFR anytime" type of plane, in that I
consider it a solid IFR platform. When the vac pump goes out alarms
starting sounding, my voice annunicator starting saying "check vac
pressure" and the needle goes to 0. It's pretty obvious. I do a
voluntary IPC every 6 months with a local DE and always do partial
panel approaches so I'm as comfortable as you can be with that. A
couple weeks ago I had my AI go out. WOW, that's another story!! The
thing slowly rolled 30 degrees off and REMAINED RESPONSIVE!! When I
banked, it banked, when I pitched, it piched. Figuring out that it was
dead could be hard and it would be easy to miss it. I decided I need a
back up and those vac backup systems are a waste of money(Precise
Flight, electric vac, etc). After getting it back from overhaul my
partner reported that it did it again! I called a couple gyro places
and they said the vac AIs don't last very long because they have a
stream of "dirty" air running through them. The electrics last much
longer. So I'm getting an electric AI installed as my backup. I
noticed that the non-TSO'd electric AIs are almost $1000 less than the
TSO'd ones. I asked my mechanics and the FSDO and they said I could
probably get a 337 approved by the FSDO for a non-TSO'd unit as long
as it wasn't in the "T" area of the panel. One FSDO guy said I might
need to label it "VFR only" and I'd have to promise not to do 135. In
either case I'll end up having an electric backup AI for under $1500.
That's less than the price of a backup electric vac pump installed
about about the same price to put a Precise Flight in a Mooney (with
California labor rates of $95/hr ) with twice the redundency.

FWIW, I have an electric AI in my Mooney and I wouldn't do it again. It's
expensive, failure prone, and too far out of my scan to be useful as a backup.

I've had the Precise Flight system in a previous airplane, and it was OK, but
has some drawbacks. Since it depends on the intake manifold as a vacuum source,
the vacuum available is dependant on throttle setting. In order to maintain
vacuum for the instruments, you may need a throttle setting that's not what
you'd prefer.

I now have the Aero-Advantage STCed dual-rotor vacuum pump and think it is
overall the best solution. It offers more redundancy and more reliable backup
for a reasonable price. http://www.aeroadvantage.com

Including installation it will be less than your electric AI, and a better
solution, IMO.

Dave
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Dave Butler wrote in message ...
I now have the Aero-Advantage STCed dual-rotor vacuum pump and think it is
overall the best solution. It offers more redundancy and more reliable backup
for a reasonable price. http://www.aeroadvantage.com

Including installation it will be less than your electric AI, and a better
solution, IMO.

I'm not so worried about losing the vac. What I'm worried about is
lossing the AI.

BTW: What is the purpose of the dual rotor pump. When my pumps have
gone out its always been because a vain got stuck and sheared off the
pump shaft. My mechanic said that's how they usually fail. Wouldn't
that kill both rotors?
-Robert

Robert M. Gary wrote:
I'm not so worried about losing the vac. What I'm worried about is
lossing the AI.


Am I missing something? How is installing a 2nd AI going to solve
the problem of identifying an inaccurate indication? The old saying
goes, "A man with one watch knows the time, a man with two watches
is never sure." If you have two AIs and they disagree, how will you
determine which one is correct? You will have to cross check against
the DG and TC, same as you would if you had only one AI. Seems to me
a better approach would be to practice cross-check in a simulator,
where you can practice with an erratic AI rather than simply covering
it up.


Ross Oliver

If you have two AIs and they disagree, how will you
determine which one is correct?


You at least know one has gone south, and you can go PP. With only one AI, you
could be leaning first.

Jose



--
(for Email, make the obvious changes in my address)

(Ross Oliver) wrote in message ...
Robert M. Gary wrote:
I'm not so worried about losing the vac. What I'm worried about is
lossing the AI.


Am I missing something? How is installing a 2nd AI going to solve
the problem of identifying an inaccurate indication? The old saying
goes, "A man with one watch knows the time, a man with two watches
is never sure." If you have two AIs and they disagree, how will you
determine which one is correct? You will have to cross check against
the DG and TC, same as you would if you had only one AI. Seems to me
a better approach would be to practice cross-check in a simulator,
where you can practice with an erratic AI rather than simply covering
it up.

I think you are missing something. If both AIs start showing different
results you will be suspecious and start asking questions. As I noted
a realistic AI failure situation can be very difficult to detect.

In article ,
(Robert M. Gary) wrote:
I think you are missing something. If both AIs start showing different
results you will be suspecious and start asking questions. As I noted
a realistic AI failure situation can be very difficult to detect.

How is this fundamentally different than if one AI disagrees with the DG
and turn coordinator? I try not to stare at the AI the entire time, and
it seems that a scan would pick up a discrepency regardless of whether
it included a second AI. Now, flying the plane with a second AI may be
easier once the failed AI is identified, but I don't see how a second AI
would make identifying the failure any easier, because it would be a
required scan item just like the DG and turn and bank.


JKG

Robert M. Gary wrote:
Dave Butler wrote in message ...

I now have the Aero-Advantage STCed dual-rotor vacuum pump and think it is
overall the best solution. It offers more redundancy and more reliable backup
for a reasonable price. http://www.aeroadvantage.com

Including installation it will be less than your electric AI, and a better
solution, IMO.


I'm not so worried about losing the vac. What I'm worried about is
lossing the AI.

BTW: What is the purpose of the dual rotor pump. When my pumps have
gone out its always been because a vain got stuck and sheared off the
pump shaft. My mechanic said that's how they usually fail. Wouldn't
that kill both rotors?
-Robert

I understand your skepticism, but AeroAdvantage claims that they have a
mechanical arrangement that allows each rotor to fail independently. Check the
web site for more details, but if my memory serves it amounts to providing weak
points (necking) in the shaft in such a way that the shaft for each rotor can
fail independently. I have had trouble visualizing what the mechanical
arrangement is and would like to take one apart or see an exploded drawing to
see how they do that. I can't explain exactly how it's done, but they convinced
me to my satisfaction that they had solved the problem.

Dave
Remove SHIRT to reply directly.

Dave Butler wrote:
Robert M. Gary wrote:

Dave Butler wrote in message
...

I now have the Aero-Advantage STCed dual-rotor vacuum pump and think
it is overall the best solution. It offers more redundancy and more
reliable backup for a reasonable price. http://www.aeroadvantage.com

Including installation it will be less than your electric AI, and a
better solution, IMO.



I'm not so worried about losing the vac. What I'm worried about is
lossing the AI.

BTW: What is the purpose of the dual rotor pump. When my pumps have
gone out its always been because a vain got stuck and sheared off the
pump shaft. My mechanic said that's how they usually fail. Wouldn't
that kill both rotors?
-Robert


I understand your skepticism, but AeroAdvantage claims that they have a
mechanical arrangement that allows each rotor to fail independently.
Check the web site for more details, but if my memory serves it amounts
to providing weak points (necking) in the shaft in such a way that the
shaft for each rotor can fail independently. I have had trouble
visualizing what the mechanical arrangement is and would like to take
one apart or see an exploded drawing to see how they do that. I can't
explain exactly how it's done, but they convinced me to my satisfaction
that they had solved the problem.

Following up my own posting: here's what it says in the FAQ at
http://www.aeroadvantage.com (to visualize, the pump is mounted so that the
drive shaft is pointing forward):

1.) How can the rear pumps chamber continue to operate after the forward pump
chamber has failed?

The Dual Rotor Vacuum Pump incorporates a shear coupling between the forward
rotor and the driveshaft. The forward rotor’s shear coupling can shear away from
the driveshaft without causing the driveshaft to fail. Similarly, the rear rotor
also incorporates a shear coupling. As an Additional safeguard, the shaft has a
necked down area between the two rotors. Either the rear rotor’s shear coupling
or the necked area in the driveshaft can shear away from the forward rotor
without effecting the forward rotors continued operation.

and also:

6.) When a vacuum pump fails it can contaminate the vacuum system how do you
prevent one vacuum pump chamber from contaminating the other in the event of a
failure?

The Dual Rotor Vacuum Pump incorporates an intake manifold with dual check
valves. When a rotor disconnects from the driveshaft the check valve for that
chamber closes, preventing contamination of the other pump that is still
operating. Also, since the pump's chambers share a common exhaust, the exhaust
from the operating pump helps contain the contamination to the failed chamber by
applying positive pressure to the failed chamber.

Dave
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Robert M. Gary wrote:
After having both a vac pump failure and an AI failure (not on the
same flight ) I decided its really time for a backup.

I had a similar revelation recently, after a challenging IPC at night
and a quiet reflection on a AI that did fail one me, albeit on a nice
day. Did lot of soul searching and decided to postpone a GPS upgrade
in favor of some attitude information backup first.

Dave Butler wrote:

FWIW, I have an electric AI in my Mooney and I wouldn't do it again. It's
expensive, failure prone, and too far out of my scan to be useful as a backup.

Did you have a lot of problems with the electric AI ? I am also
considering one (the dual pumps sound promising, but still don't back
up the gyro...), so I am curious how they hold up (the RCA-26 series
or the non-TSO'd Falcon, the AIM / Midcontinet stuff is just too
expensive). I heard mixed reviews on the RC Allen, some people have
had them for years without any problems and some claim they they don't
hold up as well as quality vacuum gyros.

Re Falcon, I strongly considered the possibility (337 or not), but
with a custom tilt they are over $1100 (Chief), not *that* cheap
considering a brand new RCA goes for $1650 at the discounters (like
Spruce), factory tilt included and less paperwork hassle. Still, $500
is money, so if they are OK, might be worth considering. There seems
to be very little info on them besides the manufacturer,
unfortunately....

Thanks,

Martin