Standby Vacuum?

: 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 *
************************************************** ***********************

I never did get that whole primary secondary stuff to stick in my brain.
Let alone integration...

Obviously, we all have to scan to keep it all on track. No one has ever
figured out a universally applicable optimal procedure for scanning.
And I guess only eyeball scanning will ever tell us what one actually does.

Anyway, after reading several anecdotal references to increased use of
the T&B, I tried it. It worked. Specifically when hand flying the
trimmed out Maule.

Next time you droning along, trimmed out, with Ralph or Bob or whatever
his name is turned off, replace your use of the AI with the TC. Of
course the DG tells you how you are doing and which way to correct, but
try flying with the TC only for longer than you would normally. The
experience changed my scan.

I think Collins wrote something recently where someone was hand flying
on instruments from the right seat. They couldn't see the AI well so
they used the TC instead. Collins had to comment that they were
smoother and straighter than usual and the reason given was use of the TC.

wrote:
...the AI gives you good info, and the heading gyro does
: too, but the best way to keep it all centered in my Maule is definitely
: the T&B. Especially in calm conditions.

I don't know if I'll agree with that. Once you dial in your wind correction
angle, the DG is the primary instrument for bank in straight-level flying.

When I was working on the instrument written, I tried to find easy ways to
remember primary vs supporting instruments for different stages of flight. One of my
conclusions was that for long-term accuracy, the instruments that provide the integral
of the chosen parameter are the most accurate, and thus "primary." For instance,
the result of a pitch change integrated gives you altitude, so it's primary for
straight-level. The result of a bank change integrated yields a heading, so the DG is
primary.

The trouble with direct-read indications is that they are not accurate enough
for long-term useage. The AI is good for radical attitude changes, but you cannot see
a 1/10 stdrad turn on either it or the T&B/TC. You *will* see it on the DG as the
numbers slows roll by.

Of course, to each their own. Just so long as you keep the shiny-side up!...


-Cory

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

Next time you droning along, trimmed out, with Ralph or Bob or whatever his name is turned off, replace your use of the AI with the TC. Of course the DG tells you how you are doing and which way to correct, but try flying with the TC only for longer than you would normally. The experience changed my scan.

I don't know why, but I never did use the AI much. I rely on the TC,
altimiter, DG, and airspeed to give me my picture, and leave the AI sort
of in the background. As a result, when the AI is covered, I fly
equally well. One CFI commented that I fly better on partial panel then
on the full panel.

Jose
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no universe.
for Email, make the obvious change in the address.

Jose wrote:
Next time you droning along, trimmed out, with Ralph or Bob or
whatever his name is turned off, replace your use of the AI with the TC.
Of course the DG tells you how you are doing and which way to correct,
but try flying with the TC only for longer than you would normally. The
experience changed my scan.

I don't know why, but I never did use the AI much. I rely on the TC,
altimiter, DG, and airspeed to give me my picture, and leave the AI sort
of in the background. As a result, when the AI is covered, I fly
equally well. One CFI commented that I fly better on partial panel then
on the full panel.

I have much the same experience. My instrument instructor was a nut
for partial panel practice, so I got really good at it. I miss the DG
when it's covered up, but for the most part, I fly the TC for bank and
the ASI for pitch.

After all these years, I honestly can't tell you how many bars up it
takes to get Vy or what bank angle it takes for a standard rate turn.

Roy Smith wrote:
: I don't know why, but I never did use the AI much. I rely on the TC,
: altimiter, DG, and airspeed to give me my picture, and leave the AI sort
: of in the background. As a result, when the AI is covered, I fly
: equally well. One CFI commented that I fly better on partial panel then
: on the full panel.

: I have much the same experience. My instrument instructor was a nut
: for partial panel practice, so I got really good at it. I miss the DG
: when it's covered up, but for the most part, I fly the TC for bank and
: the ASI for pitch.

: After all these years, I honestly can't tell you how many bars up it
: takes to get Vy or what bank angle it takes for a standard rate turn.

Whew... I thought I was the only one! In straight/level, I rarely look at the
AI except once in awhile to cross-check. For straight/level it's useless, just as the
T&B/TC is for bank. It's really only good for setting up an attitude (whether it be
intentional transition or an "Oh crap... I busted my altitute/heading!")

-Cory

--

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

Jose wrote:
I don't know why, but I never did use the AI much. I rely on the TC,
altimiter, DG, and airspeed to give me my picture, and leave the AI sort
of in the background.

When I mostly flew an Archer, I did the same. Somehow in the transition to the
Mooney, I've becomre more fixated on the AI. Not sure why. I think my scan now
looks like that classic diagram in the training manuals where you look at the
AI, then some other instrument, then back to the AI, then some other instrument,
etc.

I've wondered whether the change is a function of performance / stability of the
airplane. The Archer was so stable it was easy to follow along just using the
result-based instruments. In the Mooney, it became necesary to be more aware of
slight changes in attitude that would affect the performance instruments in a
few seconds.

It also could be a better-quality AI in the Mooney that's easier to read.

The Mooney is the highest-performing airplane I've flown, but I've noticed that
people that fly jets seem to talk / write more about the importance of the AI.

....but I think you are experienced in higher-performance airplanes, right, Jose?

Dave

When I mostly flew an Archer, I did the same. Somehow in the transition to the
Mooney, I've becomre more fixated on the AI. Not sure why.

Because the Mooney demands more precision in your attitude control.
The cleaner the airplane, the more true that is. Once you reach the
ultimate clean airplane (a transport jet), there is no way to fly
partial panel. No jet crew that lost all attitude indicators in IMC
has ever survived. That's why the airlines have given up on teaching
partial panel. On the other hand, an old, slow, draggy ragwing can be
flown with no gyros at all, using just airspeed (or sound) for pitch
and compass for roll. I know someone who has over an hour of IMC time
in a ragwing with no gyros at all, doing it exactly that way. I've
done it at night under the hood in the TriPacer.

The Archer was so stable it was easy to follow along just using the
result-based instruments. In the Mooney, it became necesary to be more aware of
slight changes in attitude that would affect the performance instruments in a
few seconds.

Exactly correct.

This is why I teach the control-performance model of the scan - my
students are generally either flying slippery airplanes or are planning
to move up to them. For someone who will fly his entire career in an
Archer or Skyhawk, the FAA primary-secondary model works fine, and then
the AI is just a way to crosscheck.

Michael

...but I think you are experienced in higher-performance airplanes, right, Jose?

I've flown in transport category jets, but in the back seat. Way back.

I do have a little experience in high performance singles, but not very
much. And you are probably right about the AI being more critical in
high performance aircraft. Things happen faster.

Jose
--
Quantum Mechanics is like this: God =does= play dice with the universe,
except there's no God, and there's no dice. And maybe there's no universe.
for Email, make the obvious change in the address.

Michael wrote:

First off, with dual AI's next to each other, I believe that following
a dying AI into an unusual attitude becomes far less likely, and thus
while the chances of recovery from the unusual attitude are reduced
slightly, the chances of encountering it in the first place are reduced
dramatically.Â*Â*NotÂ*soÂ*withÂ*aÂ*backupÂ*vacuum *-Â*youÂ*haveÂ*toÂ*engageÂ*it.

This is the first of my two major reasons for preferring the backup AI. It
helps with problem detection. A backup vacuum doesn't.

And even if you do, half the time (in my experience more) the problem
is the AI, not the power source, so backup power for the AI does you no
good.

And this is #2.

Some people to whom I've spoken about this have made a big deal about the
fact that the backup AI does nothing for a HI during a vacuum failure. My
response is typically "who cares?". Given a compass and a GPS, the HI has
plenty of backup already.

- Andrew

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.