Rationale behind vacuum instruments

[Mxsmanic]

Can someone tell me why vacuum power is popular for certain instruments? I
cannot see any special reliability of a vacuum pump as opposed to an electric
motor. The only reason I can think of is historical, in that many small
aircraft have traditionally not had on-board electrical systems beyond what
was required by the engines themselves. However, a vacuum pump seems no more
reliable to me than an alternator. What are the reasons behind it all? I see
lots of descriptions of how the instruments work, but none that explain or
justify the choice of vacuum over electrical power. It also seems that vacuum
is subject to partial failures, whereas an electrical failure is usually much
more obvious.

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[Robert M. Gary]

On Apr 9, 8:17 am, Mxsmanic > wrote:
> Can someone tell me why vacuum power is popular for certain instruments? I
> cannot see any special reliability of a vacuum pump as opposed to an electric
> motor. The only reason I can think of is historical, in that many small
> aircraft have traditionally not had on-board electrical systems beyond what
> was required by the engines themselves. However, a vacuum pump seems no more
> reliable to me than an alternator. What are the reasons behind it all? I see
> lots of descriptions of how the instruments work, but none that explain or
> justify the choice of vacuum over electrical power. It also seems that vacuum
> is subject to partial failures, whereas an electrical failure is usually much
> more obvious.
>
> --
> Transpose mxsmanic and gmail to reach me by e-mail.

If I tell you are you going to tell me I'm wrong??

-robert, CFII

[Maxwell]

"Mxsmanic" > wrote in message
...
> Can someone tell me why vacuum power is popular for certain instruments?
> I
> cannot see any special reliability of a vacuum pump as opposed to an
> electric
> motor. The only reason I can think of is historical, in that many small
> aircraft have traditionally not had on-board electrical systems beyond
> what
> was required by the engines themselves. However, a vacuum pump seems no
> more
> reliable to me than an alternator. What are the reasons behind it all? I
> see
> lots of descriptions of how the instruments work, but none that explain or
> justify the choice of vacuum over electrical power. It also seems that
> vacuum
> is subject to partial failures, whereas an electrical failure is usually
> much
> more obvious.
>

In your case it makes no difference. The vacuum pump in your desk is
electrically driven.

[[email protected]]

On Apr 9, 9:17 am, Mxsmanic > wrote:
> Can someone tell me why vacuum power is popular for certain instruments? I
> cannot see any special reliability of a vacuum pump as opposed to an electric
> motor. The only reason I can think of is historical, in that many small
> aircraft have traditionally not had on-board electrical systems beyond what
> was required by the engines themselves. However, a vacuum pump seems no more
> reliable to me than an alternator. What are the reasons behind it all? I see
> lots of descriptions of how the instruments work, but none that explain or
> justify the choice of vacuum over electrical power. It also seems that vacuum
> is subject to partial failures, whereas an electrical failure is usually much
> more obvious.
>
> --
> Transpose mxsmanic and gmail to reach me by e-mail.

Because your head is an infinite source of vacuum...

[Ron Natalie]

Mxsmanic wrote:
> Can someone tell me why vacuum power is popular for certain instruments?

Driving gyros with air pressure is much simpler, cheaper, and
more reliable from the gyro point of view than using small electric
motors. Venturis and engine-driven wet pumps are real reliable
and not too expensive too. The major problem is engine-driven
dry pumps which have a nasty habit of failing unexpectedly.

> I
> cannot see any special reliability of a vacuum pump as opposed to an electric
> motor.

Your vision is impaired. Spinning a free-in-space gyro (like the AI or
DH) with a motor is complicated. On the other hand, a restrained gyro
like the Turn and Bank is much easier (and these are typically electric).

> The only reason I can think of is historical, in that many small
> aircraft have traditionally not had on-board electrical systems beyond what
> was required by the engines themselves.

The above is only partially true. While it certainly starts there, the
answer is really that electrical gyros are much more expensive and not
that much more reliable.

There are some real nice units coming on the market these days with
a electric Attitude Gyro with a battery backup. But they are still
MUCH more effective. You can actually have two engine driven vacuum
pumps for redundancy in many cases and two independent gyros for what
they cost.


> However, a vacuum pump seems no more reliable to me than an alternator.

A wet pump driving a air gyro is MUCH more reliable than an alternator
driving the entire electrical system driving an electric gyro.

Anecdotally, I've had perhaps a half a dozen electrical failures in
several different aircraft over the years. I've had one dry pump
go on me.

Evaluating the options. I have the following:

A dry pump feeding the AI.
The vacuum guage prominently located next to the above.
A electric turn coordinator feeding the autopilot.
A real nice IFR GPS with fast update rates.

One major issue with the vacuum failure and transition to parital panel
is realizing that the gyros have failed. While IFR pilots are taught
to contantly verify the indications between the various instruments
a prominate failure flag or annunciator is a big help.

Frankly, the IFR GPS really makes partial panel a lot easier. Zoom
up the thing so you can instantly see any track changes and watch the
altimeter and you'll find it's not too rough maintaining flight.
Punching the autopilot on is almost cheating.

(See what happens when you ask a question nice rather than throwing
out bull****).

[Snowbird]

"Mxsmanic" wrote ...
> Can someone tell me why vacuum power is popular for certain instruments?

Historical. Aircraft electrics tended to be a) more unreliable than today
and b) add unnecessary weight.

[Mxsmanic]

Robert M. Gary writes:

> If I tell you are you going to tell me I'm wrong??

If it conflicts with other information I have, I may question it, but I don't
have much other information. If it sounds odd I may ask for further
explanation.

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[Mxsmanic]

Ron Natalie writes:

> Driving gyros with air pressure is much simpler, cheaper, and
> more reliable from the gyro point of view than using small electric
> motors. Venturis and engine-driven wet pumps are real reliable
> and not too expensive too. The major problem is engine-driven
> dry pumps which have a nasty habit of failing unexpectedly.

Which types of pumps are used in most modern small aircraft?

> There are some real nice units coming on the market these days with
> a electric Attitude Gyro with a battery backup. But they are still
> MUCH more effective. You can actually have two engine driven vacuum
> pumps for redundancy in many cases and two independent gyros for what
> they cost.

How many small aircraft have redundant pumps and gyros?

Are any small aircraft using RLGs?

> Anecdotally, I've had perhaps a half a dozen electrical failures in
> several different aircraft over the years. I've had one dry pump
> go on me.

How hard is it to spot a pump failure? I've gotten the impression from what
I've read here and elsewhere that vacuum pumps may fail gradually and
insidiously, whereas (presumably) an electric motor fails in a much more
obvious way.

> One major issue with the vacuum failure and transition to parital panel
> is realizing that the gyros have failed. While IFR pilots are taught
> to contantly verify the indications between the various instruments
> a prominate failure flag or annunciator is a big help.

Does a failure involve the gyro coming to a stop, or can it just slow down and
thereby cause problems?

> Frankly, the IFR GPS really makes partial panel a lot easier. Zoom
> up the thing so you can instantly see any track changes and watch the
> altimeter and you'll find it's not too rough maintaining flight.
> Punching the autopilot on is almost cheating.

But how does that help you if the AI has failed? The GPS wouldn't tell you
the attitude of your aircraft.

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[Mxsmanic]

Snowbird writes:

> Historical. Aircraft electrics tended to be a) more unreliable than today
> and b) add unnecessary weight.

Since you use the past tense, are you saying that an electrical drive is more
reliable today?

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[Snowbird]

"Mxsmanic" wrote ..
>
>> Historical. Aircraft electrics tended to be a) more unreliable than today
>> and b) add unnecessary weight.
>
> Since you use the past tense, are you saying that an electrical drive is
> more
> reliable today?
>
No, I'm not saying that, although I've observed that recent marketing
activities in aviation publications tend to promote electrical solutions. I
leave that judgment to qualified aviation professionals.

[cavedweller]

On Apr 9, 10:40 am, "Snowbird" > wrote:
> "Mxsmanic" wrote ...
>
> > Can someone tell me why vacuum power is popular for certain instruments?
>
> Historical. Aircraft electrics tended to be a) more unreliable than today
> and b) add unnecessary weight.

Of course, one shouldn't forget that a usable vacuum "supply" was
available without a pump when an external venturi was installed.

[rod]

> Of course, one shouldn't forget that a usable vacuum "supply" was
> available without a pump when an external venturi was installed.
>
I was wondering how long it was going to take for someone to divulge the
REAL reason for vacuum instruments. External venturi tubes were the only
form of energy available to drive gyros on airplanes in the 30'3 and 40's
which had no electrical systems. After WW2 here were so many vacuum
instruments out there nobody had the courage to change.

Rod

[ktbr]

Aircraft of old use venturies mounted on the fuselage to
power vacuum gyros. They were fairly reliable and did not
require any source of electrical power. The disadvantage
was that the AC had to be moving before the gyros would
spin up.

Later on vacuum pumps replaced the venturies for more
consistant vacuum, but one could argue the reliability
over a venturi... other than icing up perhaps.

The advantage of Vacuum instruments is that you could
still have a venturi as a backup vacuum source in case the
pump failed. Alternatively you could use some manifold
pressure (vacuum) as a backup source.

Until recently electrical instruments and electrical
systems were not considered as reliable. Nowadays you
can easily have battery backed up electrical gyros.

Either way, if a gyro-power source fails there are
systems that can immediately identify that fact to the pilot.
The gyros of course would spin down slowly and without
some immediate way to alert the pilot hwe my get erronious
information until the fail in an apparent way.

Usually, a gyro will show signs of needing a rebuild before
is actually "fails" such as slow to spin up/recet, excessive
precession, etc., but not always.

[Mxsmanic]

ktbr writes:

> The advantage of Vacuum instruments is that you could
> still have a venturi as a backup vacuum source in case the
> pump failed. Alternatively you could use some manifold
> pressure (vacuum) as a backup source.

Why not use manifold vacuum as the primary source, instead of a separate
vacuum pump that provides an additional point of failure? The manifold vacuum
would be there as long as the engine were running, without the need to rely on
a pump.

> Usually, a gyro will show signs of needing a rebuild before
> is actually "fails" such as slow to spin up/recet, excessive
> precession, etc., but not always.

What type of bearings do the gyros use, and how long do the bearings last?

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[Bertie the Bunyip[_2_]]

Mxsmanic > wrote in
:

> Can someone tell me why vacuum power is popular for certain
> instruments? I cannot see any special reliability of a vacuum pump as
> opposed to an electric motor.

Of course you can't


Bertie

[Bertie the Bunyip[_2_]]

Mxsmanic > wrote in
:

> Robert M. Gary writes:
>
>> If I tell you are you going to tell me I'm wrong??
>
> If it conflicts with other information I have, I may question it, but
> I don't have much other information. If it sounds odd I may ask for
> further explanation.

Send me fifty bucks and I'll explain it to oyu.


bertie

[Bertie the Bunyip[_2_]]

"rod" > wrote in
:

>> Of course, one shouldn't forget that a usable vacuum "supply" was
>> available without a pump when an external venturi was installed.
>>
> I was wondering how long it was going to take for someone to divulge
> the REAL reason for vacuum instruments. External venturi tubes were
> the only form of energy available to drive gyros on airplanes in the
> 30'3 and 40's which had no electrical systems. After WW2 here were so
> many vacuum instruments out there nobody had the courage to change.

No, actualy, that's not it.


Bertie

[Bertie the Bunyip[_2_]]

Mxsmanic > wrote in
:

> ktbr writes:
>
>> The advantage of Vacuum instruments is that you could
>> still have a venturi as a backup vacuum source in case the
>> pump failed. Alternatively you could use some manifold
>> pressure (vacuum) as a backup source.
>
> Why not use manifold vacuum as the primary source, instead of a
> separate vacuum pump that provides an additional point of failure?

God you;'re an idiot.
No wonder you can't fly.



Bertie

[kontiki]

Mxsmanic wrote:
>
> Why not use manifold vacuum as the primary source, instead of a separate
> vacuum pump that provides an additional point of failure? The manifold vacuum
> would be there as long as the engine were running, without the need to rely on
> a pump.
>

It sounds like a free lunch doesn't it? :^O Well, tt works in a pinch
of course, but having to maintain a power setting that produces a
manifold pressure difference (between MP and outside static pressure)
just so that the gyros can spin sort of limits your flexibility.

[Mxsmanic]

kontiki writes:

> It sounds like a free lunch doesn't it? :^O Well, tt works in a pinch
> of course, but having to maintain a power setting that produces a
> manifold pressure difference (between MP and outside static pressure)
> just so that the gyros can spin sort of limits your flexibility.

Yes. I guess I got confused, thinking there would always be vacuum available
from the engine.

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[EridanMan]

IIRC, the FAA mandates a fully redundant electrical system (two
completely separate electric buses, each with its own alternator and
battery) before they'll allow you to run your primary gyros off
electric power. The added weight of such is often substantially more
than just a vacuum system alone.

Also, in almost every aircraft I've flown, Only the AG and DG run off
the vacuum system, while the Turn coordinator is electric. This way,
if either the vacuum or the electrical systems fail, you still have
enough of a partial panel to get you through a cloud layer, at the
very least.

[Dave[_1_]]

Sometimes there is MX..

My aircraft has a "standby Vacuum system" using the manifold pressure
in the engine..

It is for emergency use only, and , of course, will NOT supply enough
vacuum if the altitude is too high or if the engine is operating at
too high a power setting..

But could sure be useful in a vacuum pump failure situation...

In some instances, thehigh flying pilot was able to reduce power
(producing vacuum) and decend safely on the manifold vacuum system
to an altitude that the system was able to produce enough vacuum for
continued operation.

Dave


On Mon, 09 Apr 2007 23:20:07 +0200, Mxsmanic >
wrote:

>kontiki writes:
>
>> It sounds like a free lunch doesn't it? :^O Well, tt works in a pinch
>> of course, but having to maintain a power setting that produces a
>> manifold pressure difference (between MP and outside static pressure)
>> just so that the gyros can spin sort of limits your flexibility.
>
>Yes. I guess I got confused, thinking there would always be vacuum available
>from the engine.

[Mxsmanic]

Dave writes:

> My aircraft has a "standby Vacuum system" using the manifold pressure
> in the engine..
>
> It is for emergency use only, and , of course, will NOT supply enough
> vacuum if the altitude is too high or if the engine is operating at
> too high a power setting..

So you have the unenviable choice between crashing into a mountainside and
knowing you are about to do so, or staying safely above the mountain but
without any means of knowing it.

> In some instances, thehigh flying pilot was able to reduce power
> (producing vacuum) and decend safely on the manifold vacuum system
> to an altitude that the system was able to produce enough vacuum for
> continued operation.

Why don't vacuum pumps run out of vacuum at high altitudes? When the air gets
thin enough I should think it wouldn't be possible to maintain the necessary
pressure differential to keep things spinning.

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[Mxsmanic]

EridanMan writes:

> IIRC, the FAA mandates a fully redundant electrical system (two
> completely separate electric buses, each with its own alternator and
> battery) before they'll allow you to run your primary gyros off
> electric power. The added weight of such is often substantially more
> than just a vacuum system alone.

If you're flying a twin that already has two engines and two alternators, what
would it add?

What's the backup for vacuum?

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[EridanMan]

> If you're flying a twin that already has two engines and two alternators, what
> would it add?

At most an extra battery. But most of us don't fly twins;)

> What's the backup for vacuum?

If you want to be fancy about it, a venturi or a second vacuum pump
(equal in weight to an extra electrical system I suppose). If your
goal is to just get yourself on the ground in one piece, an Electric
Turn Coordinator, compass and ASI will get you through a cloud layer
and to an airport in short order if you have basic partial panel
skills (and recognize the problem early enough).

[Ron Natalie]

Mxsmanic wrote:

> Which types of pumps are used in most modern small aircraft?

Dry engine-driven pumps followed by wet engine-driven pumps.
Electric pumps and direct electric driven come last.

There's also the manifold-powered suction backup unit (Precise Flight).

>
>
> How many small aircraft have redundant pumps and gyros?

There are a lot with the backup systems either manifold or
electric. As for dual gyros, air-driven gyros rarely fail.

>
> Are any small aircraft using RLGs?

I don't know of any certificated ones suitable for light aircraft.

> How hard is it to spot a pump failure? I've gotten the impression from what
> I've read here and elsewhere that vacuum pumps may fail gradually and
> insidiously, whereas (presumably) an electric motor fails in a much more
> obvious way.

Nope you have the wrong impression. The dry pump fails instantly. A
flag, light, or well place gauge will tell you instantly. The issue
is that if it fails and you don't notice the lack of vacuum, it takes
a few minutes as the gyro slowly spins down and becomes unstable to
notice.
> Does a failure involve the gyro coming to a stop, or can it just slow down and
> thereby cause problems?
Precisely.

> But how does that help you if the AI has failed? The GPS wouldn't tell you
> the attitude of your aircraft.
>

The altimeter/vsi tells me if I am climbing or descending. The GPS
tells me if I am turning (as does the Turn Cordinator, but the turn
coordinator is a bit more finicky, and turns are more difficult because
you can't really count on the whisky compass while turning, you do
timed turns, but with the GPS you just watch it's simulation of
the HSI).

Instrument pilots do a decent amount of practice with the gyros
simulated failed.

[Mark Hansen]

On 04/09/07 17:48, Ron Natalie wrote:
> Mxsmanic wrote:
>
>> Which types of pumps are used in most modern small aircraft?
>
> Dry engine-driven pumps followed by wet engine-driven pumps.
> Electric pumps and direct electric driven come last.
>
> There's also the manifold-powered suction backup unit (Precise Flight).
>
>>
>>
>> How many small aircraft have redundant pumps and gyros?
>
> There are a lot with the backup systems either manifold or
> electric. As for dual gyros, air-driven gyros rarely fail.
>
>>
>> Are any small aircraft using RLGs?
>
> I don't know of any certificated ones suitable for light aircraft.
>
>> How hard is it to spot a pump failure? I've gotten the impression from what
>> I've read here and elsewhere that vacuum pumps may fail gradually and
>> insidiously, whereas (presumably) an electric motor fails in a much more
>> obvious way.
>
> Nope you have the wrong impression. The dry pump fails instantly. A
> flag, light, or well place gauge will tell you instantly. The issue
> is that if it fails and you don't notice the lack of vacuum, it takes
> a few minutes as the gyro slowly spins down and becomes unstable to
> notice.
>> Does a failure involve the gyro coming to a stop, or can it just slow down and
>> thereby cause problems?
> Precisely.
>
>> But how does that help you if the AI has failed? The GPS wouldn't tell you
>> the attitude of your aircraft.
>>
>
> The altimeter/vsi tells me if I am climbing or descending.

and the airspeed indicator... The altimeter tells you where you
are; the VSI and ASI tell you where you are going.

> The GPS
> tells me if I am turning (as does the Turn Cordinator, but the turn
> coordinator is a bit more finicky,

Finicky? It's very accurate, if that's what you mean. It's provides an
easy way to determine if your wings are level (assuming coordinated
flight) among other things. I think it's a wonderful back-up for an inop
DG.

> and turns are more difficult because
> you can't really count on the whisky compass while turning,

Really? I can. I can turn to a heading using the wet compass. You just
have to know how to use it.

> you do
> timed turns, but with the GPS you just watch it's simulation of
> the HSI).
>
> Instrument pilots do a decent amount of practice with the gyros
> simulated failed.

Well, instrument pilots are required to show proficiency. Some practice
more than that though...


--
Mark Hansen, PP-ASEL, Instrument Airplane, USUA Ultralight Pilot
Cal Aggie Flying Farmers
Sacramento, CA

[Roy Epperson]

Robert,
You as a mere CFII are no match to Mxmanic the seer and no all...
Roy CFII, PGl

Robert M. Gary wrote:
> On Apr 9, 8:17 am, Mxsmanic > wrote:
>> Can someone tell me why vacuum power is popular for certain instruments? I
>> cannot see any special reliability of a vacuum pump as opposed to an electric
>> motor. The only reason I can think of is historical, in that many small
>> aircraft have traditionally not had on-board electrical systems beyond what
>> was required by the engines themselves. However, a vacuum pump seems no more
>> reliable to me than an alternator. What are the reasons behind it all? I see
>> lots of descriptions of how the instruments work, but none that explain or
>> justify the choice of vacuum over electrical power. It also seems that vacuum
>> is subject to partial failures, whereas an electrical failure is usually much
>> more obvious.
>>
>> --
>> Transpose mxsmanic and gmail to reach me by e-mail.
>
> If I tell you are you going to tell me I'm wrong??
>
> -robert, CFII
>

[G. Sylvester]

Mxsmanic wrote:
> Can someone tell me why vacuum power is popular for certain instruments? I
> cannot see any special reliability of a vacuum pump as opposed to an electric
> motor. The only reason I can think of is historical, in that many small
> aircraft have traditionally not had on-board electrical systems beyond what
> was required by the engines themselves. However, a vacuum pump seems no more
> reliable to me than an alternator. What are the reasons behind it all? I see
> lots of descriptions of how the instruments work, but none that explain or
> justify the choice of vacuum over electrical power. It also seems that vacuum
> is subject to partial failures, whereas an electrical failure is usually much
> more obvious.

For once I agree with MXmoron. Vacuum instruments completely suck.

Gerald

[Maxwell]

"G. Sylvester" > wrote in message
t...
> Mxsmanic wrote:
>> Can someone tell me why vacuum power is popular for certain instruments?
>> I
>> cannot see any special reliability of a vacuum pump as opposed to an
>> electric
>> motor. The only reason I can think of is historical, in that many small
>> aircraft have traditionally not had on-board electrical systems beyond
>> what
>> was required by the engines themselves. However, a vacuum pump seems no
>> more
>> reliable to me than an alternator. What are the reasons behind it all?
>> I see
>> lots of descriptions of how the instruments work, but none that explain
>> or
>> justify the choice of vacuum over electrical power. It also seems that
>> vacuum
>> is subject to partial failures, whereas an electrical failure is usually
>> much
>> more obvious.
>
> For once I agree with MXmoron. Vacuum instruments completely suck.
>

Then you would be wrong, just like MX usually is. Vaccum pumps suck!!!!

[Bertie the Bunyip[_2_]]

Mxsmanic > wrote in
:

> EridanMan writes:
>
>> IIRC, the FAA mandates a fully redundant electrical system (two
>> completely separate electric buses, each with its own alternator and
>> battery) before they'll allow you to run your primary gyros off
>> electric power. The added weight of such is often substantially more
>> than just a vacuum system alone.
>
> If you're flying a twin that already has two engines and two
> alternators, what would it add?


You're an idiot.


>
> What's the backup for vacuum?

In your case, you put the feed tube into your mouth.


Bertie
>

[Bertie the Bunyip[_2_]]

Mxsmanic > wrote in
:

> Dave writes:
>
>> My aircraft has a "standby Vacuum system" using the manifold
>> pressure in the engine..
>>
>> It is for emergency use only, and , of course, will NOT supply enough
>> vacuum if the altitude is too high or if the engine is operating at
>> too high a power setting..
>
> So you have the unenviable choice between crashing into a mountainside
> and knowing you are about to do so, or staying safely above the
> mountain but without any means of knowing it.

you're an idiot.


Bertie

[[email protected]]

On Apr 9, 4:17 pm, Mxsmanic > wrote:
> Why don't vacuum pumps run out of vacuum at high altitudes? When the air gets
> thin enough I should think it wouldn't be possible to maintain the necessary
> pressure differential to keep things spinning.

Aircraft certificated for flight above 18,000 feet use pressure
intead of vacuum. Same pump, same instruments, different plumbing,
more filters to prevent carbon dust from the pump getting into the
gyros. The differential at altitude does diminish with vacuum, making
the pressure system necessary.
Dry pumps fail mostly because they're allowed to wear too far.
We only buy the Rapco pumps that have the inspection hole in the case.
The pump comes with a small plastic gauge that will tell you how much
vane is left, and if you replace the pump when the gauge tells you to,
the system gets very reliable. The vanes get short when they wear and
begin to cock and jam in their slots. Enough of that and they break
the whole rotor. The plastic drive coupling also ages and needs to be
replaced every few years in aircraft that don't fly much. New pumps
come with new couplings. Another way to wreck a pump is to never
replace filters, especially the relief valve filter, which degrades
and lets bits of rotten foam into the line to the pump. I don't know
how many airplanes in which I've found that filter rotting off. Or
washing the engine down and getting solvent into the drive end of the
pump. Or having a gyro experience a catastophic failure and releasing
bits of metal debris into the pump. Or letting the vacuum hoses get
old and brittle, whereupon they will release bits of hardened rubber
junk into the system. Seen that far too often.
Poor maintenance is false economy: it ends up costing big time
in the end. Check the pump wear every 100 hours. Replace the filters
when the manufacturer says to. Replace the hoses every five years. The
airplane is aging whether you fly it or not.

Dan

[Mxsmanic]

Danny Deger writes:

> The Boeing 787 has done away with using bleed air and is using electricity
> for everything. It takes some massive generators to do this
> (airconditioning, pressurization, anti-ice, etc.), but it saved weight and
> reduced fuel burn.

I notice you mention weight and fuel economy, but not reliability. I suppose
time will tell.

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[Danny Deger]

"Mxsmanic" > wrote in message
...
> Can someone tell me why vacuum power is popular for certain instruments?
> I
> cannot see any special reliability of a vacuum pump as opposed to an
> electric
> motor. The only reason I can think of is historical, in that many small
> aircraft have traditionally not had on-board electrical systems beyond
> what
> was required by the engines themselves. However, a vacuum pump seems no
> more
> reliable to me than an alternator. What are the reasons behind it all? I
> see
> lots of descriptions of how the instruments work, but none that explain or
> justify the choice of vacuum over electrical power. It also seems that
> vacuum
> is subject to partial failures, whereas an electrical failure is usually
> much
> more obvious.
>

If you have some instruments powered by electricity and some by vacuum, then
you have redundancy to keep the airplane flying if one or the other fails.

Danny Degr

[Danny Deger]

"Snowbird" > wrote in message
. fi...
>
> "Mxsmanic" wrote ..
>>
>>> Historical. Aircraft electrics tended to be a) more unreliable than
>>> today
>>> and b) add unnecessary weight.
>>
>> Since you use the past tense, are you saying that an electrical drive is
>> more
>> reliable today?
>>
> No, I'm not saying that, although I've observed that recent marketing
> activities in aviation publications tend to promote electrical solutions.
> I leave that judgment to qualified aviation professionals.
>

The Boeing 787 has done away with using bleed air and is using electricity
for everything. It takes some massive generators to do this
(airconditioning, pressurization, anti-ice, etc.), but it saved weight and
reduced fuel burn.

Danny Deger

[Dave[_1_]]

On Tue, 10 Apr 2007 00:17:42 +0200, Mxsmanic >
wrote:

Snip..
>So you have the unenviable choice between crashing into a mountainside and
>knowing you are about to do so, or staying safely above the mountain but
>without any means of knowing it.

Not at all....


Reduce power, get lots of vacuum, turn away from mountain, land at
nearest available...

I don't have to get much lower than the max altitude my airplane can
climb to to have enough vacuum to operate the system...

In other words, I can't get up to where I shouldn't be, where your
example would be a concern.

I have no business or desire to take my plane IFR into mountains
that high..

No way.... EVER.

Dave

>
>Why don't vacuum pumps run out of vacuum at high altitudes? When the air gets
>thin enough I should think it wouldn't be possible to maintain the necessary
>pressure differential to keep things spinning.


Correct....See post below re: pressure systems, good explaination....

[Mxsmanic]

Danny Deger writes:

> One plus on reliability is a bleed air duct failure can distroy a plane in a
> few minutes. The air is REALLY hot. We lost an F-4 in the squadron I was
> in due to a bleed air duct failure.

True, although I don't recall ever reading about a bleed duct failure in a
commercial airliner. I think it's very rare.

--
Transpose mxsmanic and gmail to reach me by e-mail.

[Danny Deger]

"Mxsmanic" > wrote in message
...
> Danny Deger writes:
>
>> The Boeing 787 has done away with using bleed air and is using
>> electricity
>> for everything. It takes some massive generators to do this
>> (airconditioning, pressurization, anti-ice, etc.), but it saved weight
>> and
>> reduced fuel burn.
>
> I notice you mention weight and fuel economy, but not reliability. I
> suppose
> time will tell.
>

One plus on reliability is a bleed air duct failure can distroy a plane in a
few minutes. The air is REALLY hot. We lost an F-4 in the squadron I was
in due to a bleed air duct failure.

Danny Deger

> --
> Transpose mxsmanic and gmail to reach me by e-mail.

[Danny Deger]

"Mxsmanic" > wrote in message
...
> Danny Deger writes:
>
>> One plus on reliability is a bleed air duct failure can distroy a plane
>> in a
>> few minutes. The air is REALLY hot. We lost an F-4 in the squadron I
>> was
>> in due to a bleed air duct failure.
>
> True, although I don't recall ever reading about a bleed duct failure in a
> commercial airliner. I think it's very rare.

I can't think of one either, and I have followed airline accidents fairly
close for many years.

Danny Deger
>
> --
> Transpose mxsmanic and gmail to reach me by e-mail.

[Bertie the Bunyip[_2_]]

Mxsmanic > wrote in
:

> Danny Deger writes:
>
>> One plus on reliability is a bleed air duct failure can distroy a
>> plane in a few minutes. The air is REALLY hot. We lost an F-4 in
>> the squadron I was in due to a bleed air duct failure.
>
> True, although I don't recall ever reading about a bleed duct failure
> in a commercial airliner. I think it's very rare.
>

Not too rare, and it wouldn't lead to any real damage unless you were
very unlucky.. Anyhow, bleed is not used to powere gyros!



bertie

[Bertie the Bunyip[_2_]]

"Danny Deger" > wrote in
:

>
> "Mxsmanic" > wrote in message
> ...
>> Danny Deger writes:
>>
>>> One plus on reliability is a bleed air duct failure can distroy a
>>> plane in a
>>> few minutes. The air is REALLY hot. We lost an F-4 in the squadron
>>> I was
>>> in due to a bleed air duct failure.
>>
>> True, although I don't recall ever reading about a bleed duct failure
>> in a commercial airliner. I think it's very rare.
>
> I can't think of one either, and I have followed airline accidents
> fairly close for many years.
>

that's because they don't usually cause accidents..


bertie

[Thomas Borchert]

Mxsmanic,

> Why not use manifold vacuum as the primary source, instead of a separate
> vacuum pump that provides an additional point of failure?

Because Manifold Pressure sucks (and that is a serious and true answer).

>The manifold vacuum
> would be there as long as the engine were running, without the need to rely on
> a pump.

Wrongo!

--
Thomas Borchert (EDDH)

[[email protected]]

In rec.aviation.piloting Thomas Borchert > wrote:
> Mxsmanic,

> > Why not use manifold vacuum as the primary source, instead of a separate
> > vacuum pump that provides an additional point of failure?

> Because Manifold Pressure sucks (and that is a serious and true answer).

> >The manifold vacuum
> > would be there as long as the engine were running, without the need to rely on
> > a pump.

> Wrongo!

This was written by someone obviously too young to have ever driven a
car with manifold vacuum powered windshield wipers and little to no
understanding of real engines.

--
Jim Pennino

Remove .spam.sux to reply.

[[email protected]]

In rec.aviation.piloting Thomas Borchert > wrote:
> > This was written by someone obviously too young to have ever driven a
> > car with manifold vacuum powered windshield wipers and little to no
> > understanding of real engines.
> >

> This was written by someone running his AIRCRAFT engine at full
> throttle at the altitudes used by many of us. A throttle setting that
> will yield no usable manifold "pressure". A car is operated
> differently.

I was talking about the other guy, not you.

If you too are too young to have had the experience, vacuum windshield
wipers did something different everytime you changed throttle setting;
sometimes they stopped totally, sometimes they went like hell.

--
Jim Pennino

Remove .spam.sux to reply.

[[email protected]]

On Apr 12, 4:25 pm, wrote:
> In rec.aviation.piloting Thomas Borchert > wrote:
>
> > > This was written by someone obviously too young to have ever driven a
> > > car with manifold vacuum powered windshield wipers and little to no
> > > understanding of real engines.
>
> > This was written by someone running his AIRCRAFT engine at full
> > throttle at the altitudes used by many of us. A throttle setting that
> > will yield no usable manifold "pressure". A car is operated
> > differently.
>
> I was talking about the other guy, not you.
>
> If you too are too young to have had the experience, vacuum windshield
> wipers did something different everytime you changed throttle setting;
> sometimes they stopped totally, sometimes they went like hell.

My 1951 International pickup has the vacuum wipers. The young folks
think they're hilarious. Stomp on the gas, they quit. Let up, they go
like mad. Actually something of a pain, and I'm thinking of adapting
an electric wiper motor to it.

Dan

[tony roberts]

Robert M Gary wrote bs, bs, bs
Roy Epperson wrote bs, bs, bs
Deanwil wrote bs, bs, bs

What does it take for you people to understand that we are all sick and
tired of your pathetic attempts at humour/sarcasm/whatever you think it
is.
We are sick and tired of it.
Can you understand that?
You are not funny!

can we please please please have a respite from this crap?

Thank you

Tony
--

Tony Roberts
PP-ASEL
VFR OTT
Night
Cessna 172H C-GICE