Intermittent excessive pressession of DG

[rozenfeld57mh]

Hello,

I fly a 1977 Cessna R172K with the G502-A vacuum driven DG. This DG has a weird tendency to presses excessively while my vacuum gauge is still in a green arc. Sometimes it gets so bad - I have to adjust it every 5 minutes. Other times it may work as it should. I am puzzled. The DG was overhauled less than 2 years ago. Should I send it out for another overhaul?

 

[flyingmoose]

Most likely yes. If you have good vacuum like you said above, then the only other thing is the DG itself. You could check the tubing and verify there is no obstructions.

 

[hindsight2020]

Yep. Welcome to vacuum wonky POS gyros. Mechanical friction wear makes these things about as good as flying with a vertical compass card. Use makes them wear. Even lack of use makes them wear. It Sounds like another OH for you.

Unfortunately the FAA in all its wisdom has made the switch to AHARS an expensive venture for non-experimentals, making the option of spending 400 bucks per OH much cheaper than a 10-15K installation of even the most basic PFD. Experimentals have us beat by decades and 10K in installation costs. If owner-experimental was here today I would buy a full Dynon PFD suite tomorrow and install it and never experience DG inaccuracies again.

 

[Silvaire]

FWIW vacuum gauges are not very good indicators of system problems, they aren't much better than a glorified idiot light. So change the filters and have the lines cleared before yanking the instrument and sending it off.

Basic troubleshooting technique, if you're going to use a shotgun shoot the cheap stuff first.

 

[GCA319]

I have had this happen in a 182 I recently started flying for work. I'd be curious to know why yours is acting up.

 

[Marauder]

I had a DG like your's a number of years back. Sent it out twice to have it overhauled, only to have the issue come back within a year or so. I eventually bought a high end DG which was more robust and gave me 10 years of solid service before I pulled it for an Aspen.

At issues with the AI? If not, you should be able to rule out the vacuum pump.

 

[rozenfeld57mh]

Thanks for replies everyone. Someone locally suggested that I may simply have a sticking heading bug which may be disengaging the plate from the gyro. I think I will test this theory on my next flight. Seems like the least expensive option.

On a separate note, did anyone have any experience with slaved vacuum DG G502-B? It seems like an inexpensive option for certified plane (assuming I can find one).