Just to start a fire :-) Back Up AI

[M20F]

1 hour ago, Andy95W said:

You should get an STEC autopilot then.  Uses the turn coordinator to keep the wings level.  If you lose everything you can turn on the autopilot and get vectors from ATC.

I have one of those as well.  The vacuum is the redundancy to the electric.  

[MikeOH]

2 hours ago, Andy95W said:

You should get an STEC autopilot then.  Uses the turn coordinator to keep the wings level.  If you lose everything you can turn on the autopilot and get vectors from ATC.

^^^ THIS ^^^.

I have an STEC-30 and, to be honest, if/when I have a vacuum failure you can be damn sure I'll be using the STEC to save my bacon WAAAAY before I think about turning on the backup Precise Flight intake vacuum.

[0TreeLemur]

On 6/22/2022 at 6:36 PM, laytonl said:

Another option is an Av20. Less than 1 amu and only a couple hours to install.  Lee

I always have the AV20 showing the AI when flying in IMC as a second source.  On the plus side, it's got other nice timer functions built in too.  The AV-20S starts a timer when your airspeed tops 40 knots.  Useful for tank switching in case you forgot to note the time you took off.   On the minus side it's AOA function is not worth turning on.

 

 

[carusoam]

The precise flight backup vac system requires reduced MP to work…

So… it works well until….

 a high GW flight…. Or 

over mountainous terrain…

Check what altitude you can maintain with the reduced MP…

Make sure it is above ground level… 

Best regards,

-a-

[cliffy]

4" Venturi new $80

Used AI        $300

Hoses and fittings $100

@ 2 hrs AP  $200

Less than $700  NO electrical requirement, NO engine required, Fail safe- If you're flying it works.  

Polish the venturi for the "cool" looks!  Everyone will ask you what its for :-) Tell them its your life saver

[gmonnig]

I have an RC Allen with an inclinometer in place of the Turn Coordinator. It weighs like 8oz and is just a power and ground. Why mess with vacuum systems?

[Aerodon]

On 6/22/2022 at 8:44 AM, kortopates said:

Many of the early K's didn't have electric standby vacuum from the factory. Some had the "poor man's"  Precise SVS standby vacuum system that worked off of manifold pressure. On a turbo it works much better than on a NA aircraft but still provides marginal capability. The Savvy turbo pilot creates a table of MAP required at different altitudes to know what to use when needed. (In an NA aircraft it was never meant to provide operation for cruise at altitude.) But the easy way to tell which one you have from the cockpit is to check the control. The Precise SVS had a knob you pull out just left the yoke and a red light that comes on with low vacuum as you'll see at at minimum idle rpm. Whereas the electric standby vacuum pump has its own electrical CB Switch on the panel just like all the others electrics and thus works without the engine running. 

Starting with the '86 K, the 252, all K's had electric standby vacuum with most other options like speed brakes and O2.

Both the electric and SVS should be tested on your checklist before takeoff. The Electric is best tested before starting the engine. The SVS is best tested right after startup before the gyro's have fully spun up. Just pull idle back to minimum, see the red light come on, pull the knob and see red light go out. Then push back in and add MAP to bring up to normal idle rpm.

Paul, I thought it was the other way around, they don't work on turbo planes, do work on normally aspirated.  You need to reduce the manifold pressure to 5" below the ambient, so at sea level quite easy to do, at 10,000 feet not so easy.   

Aerodon

[jetdriven]

On 6/21/2022 at 8:38 PM, EricJ said:

My airplane had one when I bought it.   I had to pull the power back so far to make it work that it essentially turned a vacuum failure into a simultaneous vacuum + engine failure.   I guess you'd have been able to stay right-side-up long enough to, hopefully, break out of IMC or land at a nearby field or at least crash right-side-up.    I got rid of it when I did my initial avionics upgrades.

If you need 6" or so of suction to run your instruments, then your MP will need to be 6" or so below ambient to make it work.    That's not a lot of power.

You have to pull the throttle back the same number of inches a vacuum you need which is about 4.5” I don’t see how somebody’s Mooney cannot stay aloft at 4000 feet running 22 inches of manifold pressure that’s still almost 60% power. 

[EricJ]

8 minutes ago, jetdriven said:

You have to pull the throttle back the same number of inches a vacuum you need which is about 4.5” I don’t see how somebody’s Mooney cannot stay aloft at 4000 feet running 22 inches of manifold pressure that’s still almost 60% power. 

In this half of the country the dirt is often higher than that.

[kortopates]

27 minutes ago, Aerodon said:

Paul, I thought it was the other way around, they don't work on turbo planes, do work on normally aspirated.  You need to reduce the manifold pressure to 5" below the ambient, so at sea level quite easy to do, at 10,000 feet not so easy.   

Aerodon

You're right, for some reason I was thinking of UDP rather than ambient, but its pulling a differential against ambient. The system is really only designed to provide vacuum by the pilot initiating a low power descent and then once on the approach, unless its to Leadville, the pilot should have a large enough differential where its really needed. But its a very minimal system.

thanks, I'll correct the above post.

[jetdriven]

29 minutes ago, EricJ said:

In this half of the country the dirt is often higher than that.

And all over the whole country you can make an M20J sustain level flight at about 15 inches of manifold pressure. You’re not getting anywhere very fast, but you’re still flying. Here’s a quote from the POH at 12,000 feet there’s still 5 inches available there. Now just depends on the exact model airplane you have whether it’s turbo charged and where you live but for a large part of the country it’s doable.

[Aerodon]

I have a spare 28V electric standby pump if anyone is looking to install.  I'll have to look at the parts manual, I think you need a different vacuum manifold too, 

 

Aerodon

[201er]

53 minutes ago, jetdriven said:

And all over the whole country you can make an M20J sustain level flight at about 15 inches of manifold pressure. You’re not getting anywhere very fast, but you’re still flying. Here’s a quote from the POH at 12,000 feet there’s still 5 inches available there. Now just depends on the exact model airplane you have whether it’s turbo charged and where you live but for a large part of the country it’s doable.

Still faster than most fixed gear GA airplanes. And a lower fuel flow to boot! I'm pretty sure it will at least stay level on 40% power.

[M20F]

6 hours ago, jetdriven said:

You have to pull the throttle back the same number of inches a vacuum you need which is about 4.5” I don’t see how somebody’s Mooney cannot stay aloft at 4000 feet running 22 inches of manifold pressure that’s still almost 60% power. 

The standby system is really designed to be used in the approach phase where you are using minimal power.  For cruise it’s partial panel time which for straight and level isn’t terribly hard.  

There are dozens of cheap options today thanks to technology.  I still keep my precise flight and my vacuum gyros as back up to all the electrical whiz bang stuff.  You can never have too many tools when things go sideways. 

[jetdriven]

3 hours ago, M20F said:

The standby system is really designed to be used in the approach phase where you are using minimal power.  For cruise it’s partial panel time which for straight and level isn’t terribly hard.  

There are dozens of cheap options today thanks to technology.  I still keep my precise flight and my vacuum gyros as back up to all the electrical whiz bang stuff.  You can never have too many tools when things go sideways. 

It’s not advertised or it was not sold to be a standby system only for the Approach Phase of flight it was a standby system for all phases of flight. That’s why there’s a Placard on the instrument panel showing Max usable manifold pressure per altitude.  But generally I agree, we have better technology now get AHRS electronic gyros and let the standby vacuum drive your vacuum attitude indicator for your century auto pilot. Or just rip everything out and put in a standby alternator which is really the best way to go here

[Mooney in Oz]

On 6/23/2022 at 2:11 PM, MikeOH said:

^^^ THIS ^^^.

I have an STEC-30 and, to be honest, if/when I have a vacuum failure you can be damn sure I'll be using the STEC to save my bacon WAAAAY before I think about turning on the backup Precise Flight intake vacuum.

My previous autopilot was an STEC and the only criticism I had was its instability in turbulence, however I understand this is a limitation of a rate base system.

Provided there is electrical power, it offers great redundancy.

[M20F]

8 hours ago, jetdriven said:

Or just rip everything out and put in a standby alternator which is really the best way to go here

Having had a full electrical failure (prior to G5), I remain forever a fan of a redundancy that is not electric.  

[201Mooniac]

11 hours ago, jetdriven said:

Or just rip everything out and put in a standby alternator which is really the best way to go here

I agree I just wish there was an STC to put a standby alternator on the vacuum pad.  The alternator exists and I know there is a 337 for it being installed on an M20K at Lasar but I can't get anyone interested in trying to get a field approval for my M20J.

[jetdriven]

There are M20J’s flying around with standby alternators on the vacuum pad. How’d they do it?

[Marauder]

There are M20J’s flying around with standby alternators on the vacuum pad. How’d they do it?

Illegally.

My guess they got a field approval. I approached Philly FSDO about installing one in my Mooney. I would have better luck asking the guy if I could date his wife.


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[Marauder]

There are M20J’s flying around with standby alternators on the vacuum pad. How’d they do it?

Takair and I spoke about a Mooney that was approved to have one installed. I approached B&C about seeing if they would seek approval for the Mooney series. There was interest but not a lot of commitment. I would love to have a standby alternator on my naked vacuum pad.

If perhaps there is enough requests, maybe they would pursue it.


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[tmo]

A field approval was done for a TB20, so I don't see why one couldn't be done for a M20...

See this post / thread for reference.

 

[201Mooniac]

There was also one done for an M20K (337 attached) but I can't find a shop around here that will take it on.  I was told by my MSC (in northern CA) that the FSDO told them they will no longer handle field approvals.  I was also turned down by a shop in OR.  337_BC410_Mooney_M20K_N44CG.pdf

[EricJ]

6 minutes ago, 201Mooniac said:

There was also one done for an M20K (337 attached) but I can't find a shop around here that will take it on.  I was told by my MSC (in northern CA) that the FSDO told them they will no longer handle field approvals.  I was also turned down by a shop in OR.  337_BC410_Mooney_M20K_N44CG.pdf

I like that they just cite STC installations in other aircraft as the basis.

[201Mooniac]

3 minutes ago, EricJ said:

I like that they just cite STC installations in other aircraft as the basis.

I couldn't even get Lasar to reply to my request to do the same with my plane even though they did it here.  I guess there was concern that without a Lycoming based STC there would be structural data needed for the vacuum pad housing (or so I was told).