RV8 SV32 and roll trim=> SLIP

[FlyRV8]

Hi everyone,
I installed the SV32 servos (both pitch and roll) in my RV8 and saw that when I engage the autopilot, the roll axis servo is slipping even in calm air when I change the heading.
I suspect this come from the additional torque needed to move the aileron due to the spring system roll trim.
As everyone had this issue before ?
Roll torque is already set at 100%

Should I try moving the servo pushrod to an inner hole of the arm (middle one)? To have a little bit more torque ?
Or
Trying to remove the roll trim system thinking that the additional friction made by the servos could act a little bit as a trim when not engage.
Or
See with my local Dynon avionnics dealer if I should purchase a larger servo .

Thanks

 

[dynonsupport]

That it could be that the servo isn't quite powerful enough for your particular aircraft. We've seen that before. O r, it could be that there's something up with the servo. Try engaging the autopilot on the ground, with the bugs synced to the current heading/altitude so it doens't try to move the stick too much (this can sometime be tough to do, but it's possible. Next, slip the AP in both roll and pitch. Is roll much easier to slip than pitch? If so, that might imply something's up with the servo's ability to deliver power.

 

[DBRV10]

try the middle hole indeed!

Always use the closest hole that you can without the controls going over centre!

 

[FlyRV8]

Thanks for your answers.
Today I tried the closest hole to the servo arm axis and on the ROLL axis, I don't have anymore SLIP indication in calm air but still have it a little when in the French bumpy air.
However, my roll axis controls are a little bit heavier and do not come back to neutral position when releasing the pressure on the stick. The torque on the servo is now more important but the opposite torque (friction) of the servo too.
Tomorrow I will remove the spring trim system and move the pushrod to the middle hole.
I will post the results later

 

[DBRV10]

Just make sure the servo arm does not go over centre on the inner most hole.

If it does it will kill you!

 

[FlyRV8]

Hi,
After further testing on the most inner hole, I found that there is almost no difference between the most outer and inner hole.
The screen is saying that the servo slips even in calm air where there is almost no torque to apply to keep the wings level.
Is this possible that it is rather this servo (SV-32) that is not working properly than a servo that is too small for the plane?

Thanks

 

[dlloyd]

The RV7 & 8 have near identical control linkages, ailerons, forces required. The SV-32 in my 7 set at 50% torque occasionally gives a slip indication on a bumpy day. Using the outer hole suggested in the instructions should work fine. The maximum torque setting would work out to 2-3 pounds of pressure at the stick grip if you were trying to overpower it. That does not sound like much untill you try to move the stick yourself using that much force.
Make certain all your control surfaces and bellcranks move freely and do not bind anywhere. (it is either going to be this or a servo problem)
Did you remove your trim spring? Installed by Van's directions it should have very little effect on the controls when everything is centered. My stick will come to rest a little off center one direction or other.
Did you follow Dynon's suggestion of checking the roll and pitch forces to get a slip indication?
You could swap the servo posititions in your plane and see if the the problem moves. Or could you borrow a servo from someone nearby?
del

 

[FlyRV8]

dlloyd,
All the control surfaces ad bellcranks move freely.
I remove the trim spring but can't report any difference even if I believe it should help a little.
I checked the pitch and roll forces to get the SLIP indication and found that I have to apply at least twice the force I put on the roll to get the pitch servo slip.
Even on ground when I performed some tests to check the problem, the roll servo slips.
I'll try to swap the pitch and roll servo on the next 50hrs and will report the results.

Thanks for your support.

 

[dynonsupport]

FlyRV8 - that's starting to sound like a problem with the servo's ability to sense slip correctly. Do you actually hear/feel it slip, or do you just get the indication? You might get in touch with our tech support directly at 425-402-0433 or support at dynonavionics dot com.

 

[FlyRV8]

Hello support,
The servo do not (really) slip in flight. When it indicates "SLIP" I still have to move the control hard to make it really slip.
I will contact support by e-mail today.
Thanks

 

[DBRV10]

Have you pulled the servo apart by some chance, it sounds like it needs a recalibration

 

[FlyRV8]

As a feedback, I returned the autopilot servo to Dynon Avionics who did the necessary very quickly.
I reinstalled everything and did a first inflight test of the autopilot and it worked perfectly.

Thanks to Dynon for such a customer service.