M20C no PC & vacuum system deletion

[Don Gates]

Howdy;

I am going all fancy and installing dual Garmin GI-275 electronic attitude and HSI instruments.  Thus, other than to run the Positive Control wing leveler and the step retract,  I have no need for a vacuum system anymore.  I have no other autopilot.

Will I miss not having PC installed if I delete the vacuum system altogether?  I suspect I will have to maintain left - right wing fuel balance a bit more vigilantly to avoid a “heavy wing”, mainly meaning switching g left / right tanks more often.  I am interested in any PIREPS from guys that have done this.

In my case the PC turn coordinator is in the tailcone. Thus, pull the vac pump, vac regulator, filter, various hoses that used to power the AI and DG, wing and rudder servos, step servo. (I have an electric step retraction to replace this).  Remove servo vac lines as practical. Weigh and re-do airplane W&B, as accounting for all the removed parts and their moment arms would be both painfull and likely inaccurate. 

Another driver for going no-vacuum is after deletion it frees up space on the firewall to mount the engine monitor controller box (EI CGR-30 combo) which will then be primary, removing tach and it’s flex shaft cable, fuel press, manifold press, oil press, CHT / EGT, fuel level, (the whole cluster gauge six-pack)…. Lots of stuff.  It will be interesting to see how much weight comes off the plane.

[Browncbr1]

If I were you I would keep the PC.   If you come across a Brittain accuflite, then you’ll have a nice AP.     Or it is possible to hook up a porchine device if you can get an bi805 valve.   The PC is a big helper in turbulent IMC.  

[Don Gates]

9 minutes ago, Browncbr1 said:

If I were you I would keep the PC.   If you come across a Brittain accuflite, then you’ll have a nice AP.     Or it is possible to hook up a porchine device if you can get an bi805 valve.   The PC is a big helper in turbulent IMC.  

Thanks for the opinion!  Given the vintage of anything Brittain I would not be inclined to go that way, mainly due to ongoing support being problematic going forward. 
 

I am going to disconnect and cap off the vac line to the system and go fly the plane and see how it handles before committing to the surgery…..

 

Don

[cferr59]

I have flown with a broken vacuum system and did not miss the PC in VFR conditions.  If you fly VFR only, I would say this is a reasonable enough thing to do.  If you are flying in IMC and the PC otherwise works, I would leave it alone.  The PC is pretty simple, but is good at keeping you out of unusual attitudes.

[takair]

I think it depends how you fly.  As others have discussed, are you flying IFR or VFR.  The GI-275 gives you great IFR capability, but without the PC you will be full time, in the loop.  High workload, even with the 275.  Another consideration, the vacuum system gives you a dissimilar source of attitude, in the form of the PC.  There is another thread or five on failures of a single technology to provide attitude, with various results to the occupants and the aircraft.  For hard IFR, it seems you cant have enough redundancy….  It’s all about compromises with how you intend to use the plane and how long you intend to have it.

[Browncbr1]

1 hour ago, Don Gates said:

Thanks for the opinion!  Given the vintage of anything Brittain I would not be inclined to go that way, mainly due to ongoing support being problematic going forward. 
 

I am going to disconnect and cap off the vac line to the system and go fly the plane and see how it handles before committing to the surgery…..

 

Don

removing PC makes VFR flying around sight seeing more fun... the controls are a little lighter...  you will want it for IFR though.

the good thing about brittain is that you don't need support.    All you need is some electrical tape every 5 years or so...  

Edited December 7, 2021 by Browncbr1

[David Lloyd]

Since you have the remote gyro, nothing you do on the panel right now will interfere.  There are other places to put the box for the EIS that will be better than the cramped area right behind the engine.  If you get 275s, an inappropriate amount of time will be spent while flying looking at them rather than out the window.  You will be glad you left the PC in place until later.  Pump, regulator, filter and plumbing weigh about 5 pounds.  PC servo, remote, piloted valve and the plastic lines about the same.

[DCarlton]

I flew without my Brittain PC tracking my DG heading bug for about two years and definitely missed it.  Finally got around to troubleshooting it (DG needed overhaul).  I'll install a single G5 in the AI position at some point but keep my TC and vacuum system just to run my PC.  I don't see myself going all in on digital avionics for this airplane and I'm a fan of the Brittain system.  

If you do remove the PC system, please pass or sell the parts to other Mooney owners that may need them.  

Edited December 7, 2021 by DCarlton

[Don Gates]

1 hour ago, David Lloyd said:

…….   There are other places to put the box for the EIS that will be better than the cramped area right behind the engine. ……..

Ok, where? EI requires the EIS EDC box to be installed on the cabin side of the firewall and that is a bit of a head scratcher, just looking and trying to plan.  
 

The consensus seems to be about 50 / 50 on deleting the PC system. I shall evaluate more and try a flight test with PC disabled also.  

[Don Gates]

1 hour ago, DCarlton said:

If you do remove the PC system, please pass or sell the parts to other Mooney owners that may need them.  

Indeed, once removed the parts will go on the block for sure, once removed cannot see ever putting them back in. I will post them here on MS at that time. 

[Schinderhannes]

Having an Aspen and attitude indicator with battery backup the PC system is the only device connected to my vacuum system as well. With the Accutrac connected to the 430W the airplane tracks perfect. Considering the high cost or unavailability of the new autopilot systems I would keep the PC system and add the Accutrac. The PC system is very simple and used parts are available to keep it working for a fraction of the cost of a new system.   

[Schinderhannes]

7 hours ago, Browncbr1 said:

If I were you I would keep the PC.   If you come across a Brittain accuflite, then you’ll have a nice AP.     Or it is possible to hook up a porchine device if you can get an bi805 valve.   The PC is a big helper in turbulent IMC.  

Is there a way to step op the 150mW signal from the porchine device to drive the bi805?

[Browncbr1]

1 hour ago, Schinderhannes said:

Is there a way to step op the 150mW signal from the porchine device to drive the bi805?

I’m sure.  The porcine just converts a digital signal to analog with max +/-150mV..  The b805 uses a max +/-4.5v signal from the accuflite iirc.  You would just need to amplify the signal, then you can fine tune gain on the porcine.