Vacuum pump economics

[PT20J]

1 hour ago, RobertGary1 said:

That's basically where I am. So even though I have no shortage or AHRS (I think your 345 will also provide AHRS to your G3X if it detects a failure) having a mechanical backup doesn't seem like a bad idea.

In the G1000 I have had the AHRS reboot in flight with a message "hold wings level". What if some bug in the AHRS handshaking the Garmin products do (they constantly compare each other) that causes them all to reboot you'd be dead without another backup.

 

-Robert

It’s a consideration. I had the AHRS go buggy in the GTX 345. Garmin support told me it’s the same AHRS used in other products. It got replaced under warranty. The failure mode was not obvious. After about 180 degrees of a constant rate turn it would indicate a bank angle opposite the true bank angle and a pitch down even though level. Had I been using it IMC, I would have never figured it out before losing control. 

Skip

[RJBrown]

5 hours ago, Stetson20 said:

“100,000 miles of drinking…”

Freudian slip? 

Dang spell check, driving.

last drink I had was in another century.

here is 33.3 average mph over the last 746.7 miles. Haven’t used it for years.

Edited May 17, 2021 by RJBrown
Add gps image

[jlunseth]

I have a 231. As it comes from the factory, the six pack instruments are mainly (not all) vacuum driven and there is only one vacuum pump. The TC is electric and is part of the backup system. The HSI is also electric dependent, it functions best when the flux gate is operational. There is a backup method in the event the flux gate fails, (unslave the HSI, set it with the compass) but it is not very good. There is only one alternator and the alternator system is vulnerable to failure because of the coupler. So none of it is the greatest in terms of backup if the vacuum pump fails, and I have had a pump fail, just not in IMC.

Lots of pilots seem to think that there is a big weight savings if the old avionics are removed and replaced with new electronics. I had my ADF, KNS80 and old King comm removed and replaced with a GTN750Xi and lost a pound in useful load. The vacuum system is still in, but the vacuum system is not very heavy it turns out, and the people who stand to gain useful load by having it removed are aircraft that already have two alternators and two batteries, so they have a backup alternator.

One useful addition is a GI275 in place of the TC. The 275, with a temp probe, is certified primary for the TC, but better than that, it is an AI, so you have a very good backup AI if the vacuum AI craps out.

In my own opinion, substituting electronics that have a half hour or one hour internal backup is not good enough. There are plenty of occasions in my K where I am up high and out west where the airports are spaced wide apart, and in the wrong circumstances, if I were above the tops, I would not have enough backup to get down. You need to take the rated backup and cut it in half as far as I am concerned, because that is what you would have when that backup battery has been in place for several years.

The best solution is to have two alternators, then, with other internal backups, I would feel comfortable taking out the vacuum system. I would expect to lose useful load doing this, not gain it, but the difference would not be much. Then you could put in as much new electronic gear as you want and still be safe.  Expect to lose useful load with new electronics, not gain it, the putative gains are way overblown.

Covid backups in the FSDO system are impairing getting a quick answer on this, it requires FSDO approval (337) but seems possible. I don’t know what the solution would be for Lyc’s, but it seems to me there must be a way.

[steingar]

One of these days soon I'm going to have some math to do.  I'm either going to plumb in a backup vacuum or get some glass.  $400 sounds like not much of anything, a really paltry price to pay to not die when the main pump fails.

[RobertGary1]

Just now, steingar said:

One of these days soon I'm going to have some math to do.  I'm either going to plumb in a backup vacuum or get some glass.  $400 sounds like not much of anything, a really paltry price to pay to not die when the main pump fails.

But you still have to backup the indicator in that case. Its one reason I have two electronic attitudes and one vacuum. Odds of all failing via any failure mode are nearly impossible.

-Robert

[A64Pilot]

Didn’t we train for partial panel?

[RobertGary1]

3 hours ago, A64Pilot said:

Didn’t we train for partial panel?

In theory. Although as a CFII I'm not sure how realistic it is for the average pilot to keep the plane upright in real IFR turbulence based on the turn coordinator bouncing back and forth.

[carusoam]

4 hours ago, A64Pilot said:

Didn’t we train for partial panel?

My training assumed I was living in an ideal world...

Where the TC would always operate as if it was brand new...

In the middle of my IR training... we went partial panel as expected...

It was a bumpy day in December over the hills of NJ.... and the TC looked more like a metronome wagging delightfully...

Worn TCs lose their stability in the bumps...

So... select your back-up AI wisely...  select two if you have the funds...  have them powered independently from each other

and... no.... an AHRS in a portable, connected to an iPhone... is a horrible idea for a serious plan B...  plan C sure...  Plan B no...

TCs were an economical Plan B...  mechanical gyros were too expensive, so nobody could afford another AI....

Electric AIs were incredibly expensive and heavy compared to their vac powered counterparts...

Losing a vac pump as expected... leaves a ship relying on the TC in IMC...

If  you survive recognition of the failure... and transition to the TC for primary roll control... everything is good... unless you are not living in an ideal world...

 

Test: Wait for a bumpy day... and see what the TC does... 

Expect the TC to be like a mag compass... it hardly gets looked at during most flights...

PP thoughts only, I probably missed a point somewhere...

Best regards,

-a-

[jlunseth]

10 hours ago, RobertGary1 said:

In theory. Although as a CFII I'm not sure how realistic it is for the average pilot to keep the plane upright in real IFR turbulence based on the turn coordinator bouncing back and forth.

Yeah, that is the problem. I think I am pretty good without the AI, I spent a good part of my first IFR years essentially not using the AI and relying on the other instruments. But I have been in some incredible turbulence once or twice during approaches and would not want to lose the AI at those times. Things can get out of hand.