Skyview autopilot IFR approaches

[Jrskygod]

In my RV 9 I have a Garmin 430 hooked up to my skyview system. I have a SV42 Roll servo and a SV 32 pitch servo installed per the manuals with Dynon install kits. I've been doing practice approaches while VFR trying to dial in my system. The roll function works very well with my current settings but not so much for the pitch.

When I'm going down the hill on final and slowing the plane to 90 MPH for flaps the pitch servo starts intermittently slipping and asking for trim up. I do have the auto trim feature and it will eventually catch up early on on final. However by the time I get to 800 feet AGL or so and start putting in some flaps the annunciation is steadily indicating trim up and pitch servo slip situation worsens to the point where you can feel the servo banging the controls to the point that I just disconnect the autopilot and hand fly it on in. The trim function also does not respond to my stick switch input while the autopilot is flying so I cant even give it what it needs.

I have tried several different settings per the "autopilot in flight tuning guide" for sensitivity etc. and some seemed to help a little. I'm thinking I either don't have the correct combination of settings or the servo just is not strong enough for the application.

Anyone have any input on this?

 

[dynonsupport]

The first thing to figure out is your trim system. The buttons for trim always override the autopilot. If you truly aren't getting trim motion when you press the buttons, AP on or off, then you have a problem.

How are you verifying the trim is not moving? Do you have a trim position sensor with a display, or are you just waiting for the "TRIM UP/DOWN" indication to go away? If you hand fly the plane on an approach, can you actually get it into trim in all the various configurations, at the CG you are flying now?

The auto trim is purposely not very fast, so it is possible to yank power, pull flaps, and pitch the airplane up so quick that it will get behind and slip. It should eventually catch up.

Also, the trim system does a timeout after a few seconds so if you are just holding the button for a long time expecting trim motion, make sure you release and re-press.

 

[Jrskygod]

If I hand fly the approach, lower the flaps and use the trim manually all is well. I do have trim indicators on my skyview so I can visually tell the trim position.

On the approach I slowly reduce power to slow the plane down inbound to the final approach fix. By the time I am at the fix I am on airspeed or pretty close and everything is stable. The autopilot is doing just fine unless I reduce power too quick. After starting downhill form the fix I have to reduce power some to maintain my airspeed below flap operating speed and begin to bring in flaps. After I get 1/2 flaps in things begin to get funky. The servo begins to slip and wants trim but it seems the trim is too slow to respond so the clutch on the servo banging banging the controls. At that point I disconnect the autopilot and hand fly.

It seems that the trim rate is just too slow or the servo does not have adequate force. I must make all power reductions or flap inputs very slow or I get this slip condition.

Is there a setting I may be missing? How can I get the trim speed faster in autopilot mode when the plane is slow?

 

[dynonsupport]

There is an adjustment for trim speed under HARDWARE CALIBRATION. You may have your trim speed set really slow, and that will slow down the AP as well.

However, there is still the serious concern that you cannot trim with the AP engaged, which should never be true.

 

[Jrskygod]

I will confirm the trim issue and my trim speed settings and get back to you. I do know the wiring is correct and verified. Thanks for your help on this as i do want to get this resolved before I poke my head in the clouds.

 

[Jrskygod]

Flew the plane yesterday and did several approaches. I confirmed the trim settings at 100% speed at all airspeeds. The trim does respond to the trim switch in autopilot mode. The situation remains the same when the plane is slowed down on final and you slowly add 15 deg. flaps the auto trim just cant keep up with the changes in the plane configuration and starts slipping then banging the controls while asking for more trim. Operating the trim switch does help but you have to do it early on or the time out function occurs. If I do the approach without flaps the system works well with only very minor changes in power to keep everything stabilized. Oh well - I guess I'll just have to throw the flaps out at the bottom of the hill. I sure don't like making large changes like that at the bottom of the approach but it works.

 

[Dynon]

To be clear - is it correct that you CAN actually manually trim at regular speeds while the AP is engaged (subject to the timeout)? So the main issue here is that the auto-trim feature does not move fast enough to keep up with your flight profile changes - is that essentially true?

 

[Jrskygod]

Yes that is correct I can manually trim the plane when the autopilot is engaged. The problem seems to be that the trim cannot keep up with the configuration changes. (trim motor is too slow even at 100% speed)

Does the trim time out work when the autopilot is controlling the trim and no manual input is being made?

I currently have a SV32 pitch servo installed. Will going to a SV42 help this situation? It would seem that perhaps a stronger servo would have enough torque to handle the load until the trim can catch up.

 

[Dynon]

The MANUAL trim (when you push a trim button) time-out is active regardless of whether the AP is on or off. IE, if you press and hold a button, it has the time-out always.

However, the auto-trim feature doesn't work by pressing the trim button for any continuous length of time, so there isn't a time-out that is applicable in the same way as when you manually actuate trim. When the Autopilot is engaged, and auto-trim is enabled, the auto-trim is constantly evaluating the trim / out-of-trim condition. But, it only actually commands the trim every so often - I think it's on the order of once a second - and then waits to see if it's trimmed enough or not to satisfy the trim requirements. It's possible that for your aircraft dynamics, that might not be getting there fast enough.

 

[timfwalsh01]

Wire Connections for the SV-AP-Panel Trim.

I have read the forum, and the installation manual.  I am sorry if this has been covered – just want to get it right.

I currently have an electric pitch trim, and trim switch on the control stick.

On page 18-7 “Trim control wiring diagram” (Installation Guide – Revision U) - Do I just splice the wires from Pin 7 Motor Trim Up, and Pin 8 Motor Trim Down, to the wires already connected from the trim switch? 

Meaning – I leave the current wires alone on the control stick, and splice into the wires by the motor.

Hope this makes sense.  Thanks  Tim

 

[dynonsupport]

Tim,
You don't just splice the wires.

The motor output from the trim controller must be the ONLY thing going to the trim motor.

Your stick trim switches now need to go to the trim controller. They make a request to the trim controller and it moves the trim, rather than powering the trim motor directly.

If you have trim on your stick grips, you likely have a relay somewhere in the plane that gets replaced by the trim controller.

 

[timfwalsh01]

Dynon,

Makes perfect sense, just want to confirm.  Thanks!!  Tim