AN gyro wandering

How to keep the Cessna 170 flying and airworthy.

Moderators: GAHorn, Karl Towle, Bruce Fenstermacher

Post Reply
User avatar
rickyricky2
Posts: 50
Joined: Wed Oct 01, 2014 1:33 am

AN gyro wandering

Post by rickyricky2 »

Hello All
My AN style Direction Gyro was wandering. I sent it to KC for rebuild and reinstalled. It still wanders. They will check it out for me but before I send it back i want to know if there is something I should be doing first.
It is plumbed exactly like the Cessna parts book shows except that I am using a 8" venturi and I have filtered air going the back of the D/G and the Artificial Horizon.
I am showing 5" vacuum at cruise and don't usually climb above 2500 feet. I have all the proper fittings and 3/8 hose to the vacuum source.
I removed the filtered air and the fittings and now have 5.75" vacuum and no change.

Dick Bryant
N2704C
Plymouth MA
User avatar
GAHorn
Posts: 20968
Joined: Fri Apr 12, 2002 8:45 pm

Re: AN gyro wandering

Post by GAHorn »

Don’t know what you men by “wandering” but I suspect it may be precession and that may be due to a poor re-build.

Also don’t know who “KC” is… but I highly recommend “Aircraft Quality Instruments” in Wichita for gyro repair: http://flyaqi.com/
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
User avatar
rickyricky2
Posts: 50
Joined: Wed Oct 01, 2014 1:33 am

Re: AN gyro wandering

Post by rickyricky2 »

I am sorry.
AQI did the rebuild in KS not KC.

Dick
User avatar
Bruce Fenstermacher
Posts: 10313
Joined: Tue Apr 23, 2002 11:24 am

Re: AN gyro wandering

Post by Bruce Fenstermacher »

Perhaps the problem is your running to much vacuum, An AN gyro was designed to be run on 3" of vacuum hence they are able to be used nicely with a 4" venturi vacuum system. I'd check with the overhauler for their opinion.
CAUTION - My forum posts may be worth what you paid for them!

Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
User avatar
GAHorn
Posts: 20968
Joined: Fri Apr 12, 2002 8:45 pm

Re: AN gyro wandering

Post by GAHorn »

It’s Sunday, Bruce…. you’re probably thinking of a 3-1/8” gyro…. AN gyros are expecting 3.5” vacuum….. 3-1/8” gyros expect 4.5” vacuum.
But in any case, that is a design minimum…. not a maximum….and the 5” he’s experiencing should operate either type. (In fact, my AN types work perfectly even at “high” altitude (10K+) where less than 3.5” occur on my system because (I suspect) they are already spooled up.

viewtopic.php?f=24&t=8660&p=77192&hilit ... uum#p77192
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons. ;)
Post Reply