Precession

[tsuttles]

How much precession in the DG do you feel is normal? Over time and Degrees.

[N201MKTurbo]

Mine drifts about 5 degrees an hour, it depends on the turbulence to some degree. I have had DGs rebuilt probably 5 times in my flying life. I have had some that would drift 5 degrees in 5 min before I got it fixed.

 

I have found that if you set the vacuum regulator to the minimum setting your gyros will last a lot longer between overhauls.

[Dale Logsdon]

Mine drifts about 5 degrees an hour, it depends on the turbulence to some degree. I have had DGs rebuilt probably 5 times in my flying life. I have had some that would drift 5 degrees in 5 min before I got it fixed.

 

I have found that if you set the vacuum regulator to the minimum setting your gyros will last a lot longer between overhauls.

Your vacuum pump will last longer too.

[N601RX]

I asked an instrument shop this question last year and I believe they told me less than 4 deg in ten minutes when on their test table which moves back and fourth.  Setting the pressure low may make them last longer, but they also slows them down and will increases the precession.

[Mooneymite]

Precession seems to be affected by the amount of turning I do. Go out and practice steep turns and the DG will be off in no time. Straight and level, hardly at all.

The shops I've dealt with seem to think 10 degrees an hour is okay, but I've never seen anything written.

I had a DG overhauled three times with no improvement. The shop finally agreed to exchange it. The new one has worked fine ever since, but I pity whoever got that original one!

[tsuttles]

I probably got your original one mine seems to drift 10degrees in 10mins on a flight and then the next flight maybe 5 degrees every 10 mins. That still seems excessive to me. It makes using the heading bug almost a joke. It has been rebuilt twice now. 

[omega708]

I have no idea how long it takes for the gyro to fully spin up to normal operating speed, but it seems that if I wait until I'm doing my normal run-up procedures to make the initial adjustment to the DG things seem to work out better for me.  If I set it shortly after startup, 15 minutes into the flight it seems to have drifted considerable more.

[Mooneymite]

I probably got your original one mine seems to drift 10degrees in 10mins on a flight and then the next flight maybe 5 degrees every 10 mins. That still seems excessive to me. It makes using the heading bug almost a joke. It has been rebuilt twice now. 

 

Except that mine didin't have a heading bug, it sounds just like the one I got rid of!!!

[WardHolbrook]

If it's drifting enough for you to be asking the question "is this normal", it's probably time to do something about it. 

[MARZ]

Definitely tied to running ROP or LOP

[Marauder]

I'm so happy I don't use the "P" word anymore! I think I was fortunate with my old DG with heading bug. It was precessing less than 5 degrees in an hour of flying. The one before that could have been used as a sun dial considering the amount of precession it was doing. It was the reason I installed the Precision magnetic compass.

[Mooneymite]

In this day and age, I'm not sure why ATC does not vector using magnetic track instead of heading!

[Bob - S50]

In this day and age, I'm not sure why ATC does not vector using magnetic track instead of heading!

Because the DC9 still did not have RNAV, GPS, or glass until the day it was retired.  Steam gauges all the way.

[N33GG]

I have had old DG's that just kept working great for years, and have bought brand new ones that were horrible.  Very annoying.

[larryb]

Aspen

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[cliffy]

Levers and steam guages Can anyone say  B727-100, -200, 737-200, -300, DC-9-10, LR23, 24, 25  :-)  :-)

Vectors all the time, didn't know from GPS, we don't need no stinkin GPS  HAW HAW HAW