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Artificial Horizon slow to wake up

TheTurtle

By TheTurtle
in General Mooney Talk

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TheTurtle Experienced

TheTurtle

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My artificial horizon will sometimes hang out cocked sideways until after my runup.  Vacuum gauge is showing vacuum even at idle.  The runup itself doesnt usually wake it up but sometime between runup and takeoff it will start working.  Sometimes it comes alive on startup but not usually.  Once it wakes up it seems to be accurate in flight and isnt lagging behind turns or climbs.

Does this sound like a vacuum pump going bad or the gauge?  The DG seems to hold as well as the cessnas I trained on and those are vacuum operated.  I dont have a low vacuum light and the gauge is showing 4ish.

Ive only flown this plane 4 or 5 times so just getting the feel of all her kinks.

Edited by TheTurtle
gsengle Grand Master

gsengle

Posted
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What model AI? DG is probably electric, should say on the face? It's prob the AI, if the vacuum gauge is reading normally

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jetdriven Grand Master

jetdriven

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I think the AI.  IT should be erect and reliable within a minute or so.  The vacuum gauge often reads case vacuum from a port on the DG. In this case, a bad or loose hose going ot the AI will cause a vacuum leak and low vacuum to the AI gyro, and the gauge looks normal. So, inspect the hoses to the AI, and go from there.

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TheTurtle Experienced

TheTurtle

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Just now, jetdriven said:

I think the AI.  IT should be erect and reliable within a minute or so.  The vacuum gauge often reads case vacuum from a port on the DG. In this case, a bad or loose hose going ot the AI will cause a vacuum leak and low vacuum to the AI gyro, and the gauge looks normal. So, inspect the hoses to the AI, and go from there.

great thanks.  That rats nest of wires back there is scarey, but Ill take a look ;)

mooniac15u Veteran

mooniac15u

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Just now, gsengle said:

What model AI? DG is probably electric, should say on the face? It's prob the AI, if the vacuum gauge is reading normally

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Most standard DGs are vacuum driven. 

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jetdriven Grand Master

jetdriven

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the DG and AI have black rubber hoses going to them. Its not so bad one you figure out how to lay on the pilots floor board and look up. Bring a good flashlight.

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gsengle Grand Master

gsengle

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Every airplane I've flown has an electric DG paired with a vacuum AI. True on a Cessna 152/172, and a Piper (I've flown a few) and on my Mooney. Not sure what you're basing that on...

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mooniac15u Veteran

mooniac15u

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I've never seen a trainer or entry level aircraft with an electric DG. My M20D had a vacuum DG, as does my M20J. I think you may be mistaken about the Cessna 172. For example here's a 1998 model with a vacuum DG:

http://www.controller.com/listings/aircraft/for-sale/1394301/1998-cessna-172-skyhawk-td

Are you perhaps thinking of the TC?  The standard partial panel in IFR training is to cover the DG and AI to simulate a vacuum failure.

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TheTurtle Experienced

TheTurtle

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Looking at pics of the panel it doesnt look like theres any brand names visible.  Im going to look through the W&B and see if it lists the model there.  Anybody have any idea on the model AI in a 67 F model?

mooniac15u Veteran

mooniac15u

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6 minutes ago, gsengle said:

Maybe. But my arrow and Mooney both had electric DG.... Hmmm

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Electric DG or electric HSI?

mooniac15u Veteran

mooniac15u

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Just now, TheTurtle said:

Looking at pics of the panel it doesnt look like theres any brand names visible.  Im going to look through the W&B and see if it lists the model there.  Anybody have any idea on the model AI in a 67 F model?

You are more likely to find the model number in the logbooks. Changing out an AI probably wouldn't affect W&B. 

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gsengle Grand Master

gsengle

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One of each...

In any case the op could just tell us :)

But if the vacuum were the problem my guess is you'd see it in a vacuum AI before you'd notice it in the DG

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TheTurtle Experienced

TheTurtle

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Just now, mooniac15u said:

You are more likely to find the model number in the logbooks. Changing out an AI probably wouldn't affect W&B. 

I thought I saw all the panel items listed in the W&B booklet when I was going through it but ill look at the logs as well.  I dont think its ever been changed.

gsengle Grand Master

gsengle

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Does it say DC OR AIR or anything else like that on the bezel? Any pics? Don't know if we are talking a C model or an Acclaim

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mooniac15u Veteran

mooniac15u

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Just now, TheTurtle said:

I thought I saw all the panel items listed in the W&B booklet when I was going through it but ill look at the logs as well.  I dont think its ever been changed.

Based on the panel picture you posted when you bought the plane that looks like a fairly new AI. The 60s vintage AIs often had a white "sky" instead of the blue you see now.  There should be a logbook entry with the details of the replacement. 

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TheTurtle Experienced

TheTurtle

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heres the AI.  you are right, some of the other planes I looked at had the white and black realllllly old school AIs.

Ill check the logbooks.

 

20160815_173959.jpg

Mooneymite Grand Master

Mooneymite

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Reading the original post, it sounds like a classic case of a vacuum driven A.I. that's about ready for overhaul.  They'll take longer and longer to erect until they don't.

However, if the plane has been sitting a lot, sometimes frequent use can get 'em going again.

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TheTurtle Experienced

TheTurtle

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4 minutes ago, gsengle said:

Is there a fuse or CB marked DG? Just a thought...

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nope just a T&B CB.  Pretty sure its vacuum.   Ill look under the panel when i get out there.

TheTurtle Experienced

TheTurtle

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Just now, Mooneymite said:

Reading the original post, it sounds like a classic case of a vacuum driven A.I. that's about ready for overhaul.  They'll take longer and longer to erect until they don't.

However, if the plane has been sitting a lot, sometimes frequent use can get 'em going again.

it was only flown monthly for the last year or so.  Im hoping to kick her back to life!

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