AP oscillation

[lfussell]

I am running a D100 and AP units in an RV7A without any of the add on modules. The unit flys great much of the time but on occasion will start to Oscillate on the roll axis. I can stop the oscillation by putting light pressure on the stick but would rather find the issue and correct as it can become pronounced if not arrested. All settings are as recommended for RV-7. Any ideas or help would be very appreciated.
Thanks
Larry

 

[rvmills]

Larry,

What roll mode do you have engaged when this happens? (Or does it happen in HDG, TRK and NAV?)

If it's in HDG, a compass cal might help, as it may be that the heading is drifting occasionally. If its in all modes, it could be your Torque and Sensitivity settings. I've been running at 100% and 8, and it works pretty well. In bumpy air, I'll lower it a little, though I usually just adjust the pitch setting in bumps (the pitch servo seems a little more sensitive to bumps than the roll). Of course, each aircraft is different, and you may have found your sweet spot already.

One other thought. As I'm flying a X-C, I'll occasionally get a slight wing-rock, or slight bump in the ailerons. If I disconnect, I usually find I've gone out of trim on the ailerons due to fuel burn. The bump is the servo telling me "re-trim the ailerons, knucklehead".   You may have already tried this, but it'd be cool if it were as simple as that, eh!

Best of luck, and if you find another bogey, please post it, so we can all look out for it!

Cheers,
Bob

 

[Chunky]

I am getting the same thing. Have the two servo's fitted to my RV6. The problem seems to be more apparent during the NAV Function. It starts rocking its wings and seems to get worse and worse. Have checked for play between the servo and connecting rods etc and have found nothing.

 

[dynonsupport]

There are a couple of possibilities here, as rvmills points out.

For lfussel, the fact that light stick pressure stops the oscillation suggests that there is some slop in the system.  The best way to check for this on the ground is to go into SETUP->AP->SERVO TEST.  When the servos are engaged, use the stick to slip them to the center, then go move the ailerons.  They should have less than 1deg of total motion (up + down) before the servo slips.

For Chunky, it's less clear.  If wing rock occurs in  NAV/VOR mode it may be the magnetic compass, If it lags or leads in turns the AP will chase it.  To see if your compass is OK, fly towards a prominent point on the horizon and bank the airplane, but keep the nose on the point with the rudder.  The compass should not show a heading change.  If it does, you need to recalibrate your compass.

Hope that helps!