DG That Spins

HeyEng

NAHB Doesn't Give a Crap
So what might cause a DG to spin almost continuously? Basically I have a vacuum DG that as soon as the pressure gets up, it starts spinning. Sometimes real fast, sometimes slow and sometimes not at all. When you cage it, it will work OK for about 5-10 seconds and starts spinning again. Any thoughts or am I going to be out a chuck of change for a new one? Oh yeah, vac pressure is good and the AI works just fine. Thanks!
 

Cessnaflyer

Wooooooooooooooooooooooooooooooo
So what might cause a DG to spin almost continuously? Basically I have a vacuum DG that as soon as the pressure gets up, it starts spinning. Sometimes real fast, sometimes slow and sometimes not at all. When you cage it, it will work OK for about 5-10 seconds and starts spinning again. Any thoughts or am I going to be out a chuck of change for a new one? Oh yeah, vac pressure is good and the AI works just fine. Thanks!
We had an airplane that did the same and the mechanics told me that when they popped it open that it looked like it was due to dirty air and it caused an imbalance on the gyro.
 

SpiraMirabilis

Possible Subversive
From a service manual for a DG:

Trouble: Dial spins continuously in one direction
Cause: Defective mechanism
Remedy: Replace.
 

HeyEng

NAHB Doesn't Give a Crap
We had an airplane that did the same and the mechanics told me that when they popped it open that it looked like it was due to dirty air and it caused an imbalance on the gyro.
Hmmm....interesting. Guess I need to have a look at the filter, although it was changed fairly recently. Speaking of which, do any of you fancy A&Ps recommend changing the filter more often than the service manual calls for?

Also, were they able to clean out the dirt and return it to service or did it require rebuild?
 

Cessnaflyer

Wooooooooooooooooooooooooooooooo
I'm not sure what they did with it because we had such a stockpile of instruments and things were always changed in and out to different aircraft.
 

SpiraMirabilis

Possible Subversive
Hmmm....interesting. Guess I need to have a look at the filter, although it was changed fairly recently. Speaking of which, do any of you fancy A&Ps recommend changing the filter more often than the service manual calls for?

Also, were they able to clean out the dirt and return it to service or did it require rebuild?
You have to have a repair station (instruments) air agency certificate to legally return a repaired flight instrument like a DG to service.

A good rule of thumb is to replace the filter every 500 hours and it should be part of your 100 hour inspection to inspect the filter for damage/etc.
 

SpiraMirabilis

Possible Subversive
One of the more common proximate causes for gyro failure in training aircraft are hard landings causing the primary bearings to create an impression inside the bearing race. A dent like this on inner race will increase friction which in turn causes wear on the bearing, which in turn causes increased friction which in turn causes increased wear, you get where I am going. Eventually the unit will fail.
 
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