Heavy wing and autopilot

[N74846]

I'm flying a new rv-12 and slowly diagnosing a heavy wing problem. The question is: will the constant corrections need by the A/P to compensate for a heavy wing in flight cause damage to the servo unit over time? The A/P is able to keep a course but the stick is always wobbling.

 

[Dynon]

No, it won't cause damage - even if you didn't have an out of trim or heavy wing, the autopilot will fairly constantly move the stick subtly while it's flying the airplane.

 

[DHeal]

You really should find the basic cause of your heavy wing and fix it aerodynamically - Van's plans offer advice in this regard (TE adjustment, rigging, etc.).  I have rigged my RV-12 to fly hands-off with me and an average load of fuel (say 15 gallons).  A heavy passenger and more fuel will result in the need for some slight additional left aileron.  My SV AP (ROLL function) will compensate for this slight additional aileron requirement for most operations.  However, I will occasionally get ROLL SLIP warnings indicating that the ROLL servo is working at its limits.  Be careful that you don't inadvertently apply too much corrective aileron input in this situation because you might shear the ROLL servo's shear pin.  While the shear pin is easily replaced, the servo itself is a bear to access being behind the rear bulkhead. :'(

 

[mmarien]

I do agree that the plane should be adjusted to fly straight and level but with a small plane the weight distribution can make a big difference. My Glasair II is heavy on the left when I'm solo. It's fine with a passenger. Since I fly 50% of the time solo the AP holds the left wing up quite a bit. I have 350+ hours on the AP and have never seen a roll slip warning. The roll is an SV32 and is the original. The original SV32 pitch servo burn out within a hundred hours so I replaced it with a SV42. I do see lots of pitch trim warnings but rarely a pitch slip indication.

Be careful that you don't inadvertently apply too much corrective aileron input in this situation because you might shear the ROLL servo's shear pin.

I believe you can overpower the servo without breaking the shear pin.