Stanby Vacuum Requirement?

[Rage]

First of all, thanks for the great advice and input everyone provides on this forum.  I just purchased my first Mooney (two weeks ago), a '67 20F, and ya'll were extremely helpful.  I have not posted yet, because so far I've found every answer to any question I've had somewhere on the forum.  So here I am with my first of many questions.  The plane I bought had the standby/backup vacuum system removed a few years ago (I believe it ran off of the Manifold system) and I kind of like the idea of redundancy in that area.  First, is that necessary in a GA aircraft for a lot of IFR flying...I would assume so?  If so, what are some good options for a standby system?  Do you add a second vacuum pump or do you go with an electric backup ADI?

[Ned Gravel]

Rage:

In answer to your first question:  Is it necessary to have a standby vacuum source for flying IFR?  The answer is, it depends.  On you.  

Loss of the vacuum pump may cause you to lose the TC, AI and DG if they are vacuum based.  If they are not, no worries.

If you lose the attitude indicator and DG in hard IFR, do you have a way to keep your aircraft upright and on course without them?  If you have an autopilot, and you use it a lot, from where does it draw its attitude and course information?  If the answer to that question is "my vacuum based gyros" then it too is gone. If not, then at least the A/P might be relied upon to hold the aircraft upright and on course for you while you have no other method of determining which way is up, while you figure out what to do next.

My solution in my E model is an electric TC that feeds an STEC-50 A/P.  Between these two and my compass, I should be able to keep things going until a bolt hole appears out of the murk. My panel mounted GPS can drive the A/P and I have a control column mounted GPS providing situational awareness.  I practice partial panel  a lot because this is not the best solution. Backups to keep the primary reference instruments operating is the one I would like to have in place.

Here are some options for standby systems - and you already mentioned one approch. Getting electrically driven gyro instruments is a good one - but can be expensive.  One step further along that line is little bit of glass in the Aspen Evolution, but you still need backup instruments to go with that.  As well, these may require some electrical power backup.

The old Precise Flight standby vacuum system (SVS) that was probably the one previously on your F model, is now manufactured by The Vacuum Source (http://www.thevacsource.com/).  Aero Safe (http://www.aerosafe.net/) manufactures an electrically driven vacuum system that we can install in the battery compartment.  Both have their advantages and disadvantages.  SVS is $1000 cheaper and one third the price of the electrical option.  It also causes a little bit of loss of MAP when it is engaged (or so I am told).

Choices are now yours.   I will probably put the SVS system in my aircraft during its next annual, because I really dislike having to sweat partial panel in hard IFR.  Someday, when I win the bijillion, I will probably replace everything vacuum related with electrical and then install a Turbo Alternator BAE-14/28.  See http://www.basicaircraft.com/turbo-alternator-bae-14-28.asp

 

[Guest Anonymous]

Quote: edgargravel

Loss of the vacuum pump may cause you to lose the TC, AI and DG if they are vacuum based.  If they are not, no worries.

 

One possible correction - if you have the Brittain TC used with the PC system, it will work on a vacuum failure. The gyro is powered by either vacuum or electic sources according to the Brittain AFM supplement. The TC will continue to work, BUT you will lose the rest of the PC system, so don't count on it to keep the wings level.

But you will have Altitude, Airspeed and TC (Needle, Ball and Airspeed), which is the minimum reversionary requirement for IFR under FAR 91.

Vacuum backup, necessary?  -- no, but probably a very good idea for "a lot of IFR".

RFB

[Ned Gravel]

Thanks SagemGuy:

I am obviously not familiar with the Brittain systems and the Mooney PC and I appreciate your insight.

[Rage]

Thanks, that's great info.  Most of my time the past 7 years has been in higher-end aircraft that I don't have to pay for or maintain, so getting back into GA aircraft is requiring a lot of learning...but I'm loving it.  I'm still too big of a wimp to do too much VFR out here in the Utah mountains so everywhere I go I at least file IFR...putting in the standby sounds like a good idea. 

[carusoam]

When considering the manifold pressure  based back-up vacuum systems...

Take a look at their limitations.  At wide-open throttle they may not have the pressure differential required to drive the instruments.  On the east coast, this might not be as important.  At high altitudes, partially open throttle to acheive acceptable vacuum differential may not be enough power to maintain altitude.

My plane was originally delivered with an engine driven back-up pump and subsequently been changed to an electric motor driven back-up pump.  When all else fails, I have electric TC and compass for traditional partial panel.

In 500 hours of flying, I have not experienced loss of vacuum.  I have lost electricity twice. (1 controller failure, 1 generator failure)

-anthony-

[danb35]

To be more accurate--at WOT they will not have the pressure differential required.

[Piloto]

If you loose the vacuum pump that drives your AI and DG you can still fly the plane in IFR by using the turn coordinator, compass and altimeter/VSI to keep it level. I had this situation twice (once overwater at night) and found no problem coping with it. Just don't do abrupt maneuvers. The standby vacuum system that works of the engine intake is not reliable. To get any vacuum you practically needs to idle the engine in-flight like in a descent. But when you are 400nm offshore that option is not practical. The vertical card compass is a low cost good idea as a HDG backup

José