Standby Vacuum?

Ron Natalie wrote:
: Redundant engine driven vacuum pumps.
: Quite common on twins and some of the bigger singles. The rub on
: singles is having a place to mount the second one.

Now, even *I* say that's silly for a single. For a twin, sure... since it's likely already in place.
There's still a single point of failure (instrument itself)... An electric AI is more effective. Too bad they're
extra-ridiculously aviation priced.

-Cory
--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

Mitty wrote:
Our club is looking at upgrading a couple of airplanes to Garmin 430s, etc.

It seems to me that standby vacuum would be a good thing to add, too.

1) Good idea? Do these systems really work?

2) Recommendations on type/brand/model?

TIA

Electric attitude. Vacuum pumps are going away.

Scott Moore wrote:

Electric attitude. Vacuum pumps are going away.

Or electronic AI (ie. solid state; not a gyro).

My club's fleet all have what used to be the precise flight standby vacuum.
It's not bad, but I'd prefer something else.

One important consideration is preflight. Be sure that you follow the
procedure, lest you find yourself in the clouds with no backup and no
awareness that you've no backup.

- Andrew

Scott Moore wrote:
Mitty wrote:

Our club is looking at upgrading a couple of airplanes to Garmin 430s, etc.

It seems to me that standby vacuum would be a good thing to add, too.

1) Good idea? Do these systems really work?

2) Recommendations on type/brand/model?

TIA


Electric attitude. Vacuum pumps are going away.

But, can't an electric attitude indicator fail? Bearings wear out.
I've suffered that on a hard disk. Are there any MTBF numbers for the
two systems?

If your attitude indicator fails and you have a back up, you just look
at the other attitude indicator (this is what the airlines and military
teach).
If your attitude indicator fails and you have precise flight, you learn
to fly with the turn coordinator alone.

-Robert

Stubby wrote:

Scott Moore wrote:

Mitty wrote:


Our club is looking at upgrading a couple of airplanes to Garmin 430s, etc.

It seems to me that standby vacuum would be a good thing to add, too.

1) Good idea? Do these systems really work?

2) Recommendations on type/brand/model?

TIA


Electric attitude. Vacuum pumps are going away.


But, can't an electric attitude indicator fail? Bearings wear out.
I've suffered that on a hard disk. Are there any MTBF numbers for the
two systems?

I have heard that EAIs have better fail numbers than vac, but sure, its
nonzero.

The reason why all electric panels are becoming common is because
electrical systems are more reliable than vacuum, and backup is easier to
provide for everything, a second battery. It also makes more sense to
unify around a single system, instead of having a hodge-podge of two
different systems.

I would go all electric and remove my vac pump, but I blew it and
got an NSD-360. The first repair bill for that utter piece of defective
junk easily pushed the total cost above what an all electric solution
would have cost (i.e., $5000 for the NSD360, and $4000 to get it to
work correctly).

: The reason why all electric panels are becoming common is because
: electrical systems are more reliable than vacuum, and backup is easier to
: provide for everything, a second battery. It also makes more sense to
: unify around a single system, instead of having a hodge-podge of two
: different systems.

Easier is relative. Designing a truly redundant electrical system is
nontrivial and expensive in both money, weight, and complexity. Strictly speaking,
you should have dual alternators, dual busses with crossover breakers, etc, etc. It's
not as simple as "throwing another battery" in the tail. If the system isn't designed
properly or is improperly operated, a failed system can break the other system.

The nice thing about the standard six-pack is that there's redundancy built
into the instruments and sources. Yes, vacuum systems are less reliable, but short of
something catastrophic, they are *completely* independent. It would probably be
better to transition to an electric AI and vacuum TC as "standard equipment"... or
maybe electric DG and vacuum TC. Still redundancy, but the likelihood of failure goes
down with the electric replacements. A vac pump going out on a standard plane (and
losing *all* bank except TC) is "unpleasant" and not that uncommon. Change 2 out of 3
bank instruments to be electric, rather than vacuum and one failure isn't nearly so
bad.

-Cory

--

************************************************** ***********************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
************************************************** ***********************

wrote:
: The reason why all electric panels are becoming common is because
: electrical systems are more reliable than vacuum, and backup is easier to
: provide for everything, a second battery. It also makes more sense to
: unify around a single system, instead of having a hodge-podge of two
: different systems.

Easier is relative. Designing a truly redundant electrical system is
nontrivial and expensive in both money, weight, and complexity. Strictly speaking,
you should have dual alternators, dual busses with crossover breakers, etc, etc. It's
not as simple as "throwing another battery" in the tail. If the system isn't designed
properly or is improperly operated, a failed system can break the other system.

The nice thing about the standard six-pack is that there's redundancy built
into the instruments and sources. Yes, vacuum systems are less reliable, but short of
something catastrophic, they are *completely* independent. It would probably be
better to transition to an electric AI and vacuum TC as "standard equipment"... or
maybe electric DG and vacuum TC. Still redundancy, but the likelihood of failure goes
down with the electric replacements. A vac pump going out on a standard plane (and
losing *all* bank except TC) is "unpleasant" and not that uncommon. Change 2 out of 3
bank instruments to be electric, rather than vacuum and one failure isn't nearly so
bad.

-Cory


I agree with most of what you say, but this mystical belief by pilots that because
VAC is a "different" system than electrical it is more secure to have both.
Electrical systems can be made fully redundant, with separate generator, battery
and even distribution system and breakers. The fact that your airplane is not
comletely redundant may or may not degrade its reliability to LESS than the
inferior reliability of a vac pump.

For my own part, I'll be glad to see the vac components go. I'm tired of worrying
about the low replacement times on the vac pump, the posibility of contamination,
the lower general reliability of the components, etc.

Airplanes: We have 4 different flavors of PA-28s, six total, plus a Cherokee
Six. The two being upgraded right now are Archers.

Type of Flying: We do not fly a lot of hard IFR, panel space is limited as is
money. Hence, we are not looking at backup horizons, etc. Also, one of the
airplanes will be getting an S-TEC 2/ or 30, which replaces the TC.

Hence, something like the Precise Flight at $400-500 kind of numbers is the
candidate. Possibly an electric pump, though I don't know anything about the cost.

On 8/17/2005 12:41 PM, Mitty wrote the following:
Our club is looking at upgrading a couple of airplanes to Garmin 430s, etc.

It seems to me that standby vacuum would be a good thing to add, too.

1) Good idea? Do these systems really work?

2) Recommendations on type/brand/model?

TIA

Mitty wrote:

WeÂ*doÂ*notÂ*flyÂ*aÂ*lotÂ*ofÂ*hardÂ*IFR

That's good. My "scary thought" about the precise-flight is losing vacuum
pressure on the missed approach.

- Andrew