Dynon Skyview autopilot

I have an RV-8 with the Dynon Skyview system that I have been flying for three years now and I have a problem with the altitude hold that I've had since day one. In smooth air the autopilot pitch axis pulses and it drives me nuts. I've gone through the tuning procedure many times and tried different setting but still no luck. The only thing the various setting seem to do is speed the pulse up or slow it down just a little. At any rate nothing seems to help I'm starting to wonder if its mechanical or something electronic in the ADAHRS or pitch servo.
Roll axis seems to work fine. Any suggestions would be appreciated.
Matt

I upgraded my -10 to the linear pitch servo before I even flew, so I can't give a before and after comparison, but I can say that through a wide range of weights and conditions, I have been 100% happy with the performance of mine.
You might consider trading up to the linear actuator if you don't have it already.

Same here minor pitch pulses anoying in smooth air.

"In smooth air the autopilot pitch axis pulses.."

This in not normal. Recommend sending Dynon technical support a note. Other than replacing the pitch servo in my RV-10 to the linear actuator (Dynon replaced for free), the Dynon autopilot has been flawless.

Carl

Thanks

I'll give them a call and see what they say
Thanks

I get the same thing with my D-10A (as alluded to in my "pitch up" thread). Its either nervous and jittery like on a caffeine high, or too lazy and hunts for altitude with 100+ foot excursions above or below target. And despite the fact that I have the larger SV-42 and the torque set to 100%, it sometimes cant hold altitude in a 180 degree turn.


Very anoying. As a contrast, the True Track in the -8 is absolutely rock solid.

I used to have the same issue with my TruTrak/4500AFS system. I disconnected the static port on the unit and vented it directly to the cabin. The pulsing in smooth air when away. The only downside that I have experienced, in 10 years, is that the aircraft will bobble a bit if you quickly open an air/heat vent. This simple modification was done on the recommendation of someone else, so long ago that I can not remember all the circumstances but it has worked well since. It would be an easy thing to try and the smart lads in this crowd can then come up with a proper solution!

I never thought of that one either

I'll have to investigate this theory
Thanks

Not sure if my issue is the same but on a recent trip with smooth air, my Dynon SV AP was pulsing some and it was annoying me. I wound up trimming up a couple of hits and it smoothed out.

Exact same issue here, only once in a while, in smooth air.

Tore into the pushrods and linkages to see if there was any slop - none that I could find.

I figured it was just me. Maybe Dynon can look into this?

We have roughly 12 skyview equipped rv's on our airport. Seems that most have had this issue---they are mostly random occurances.

IAS

I think what I'm going to try next when the weather gets better is to put it in expert mode and go through the indicated airspeed control procedure step-by-step I'm wondering if I have an aronious airspeed set in the skyview and the autopilot is pitching up and down trying to achieve the airspeed but the altitude hold is not allowing it to do that so the plane just starts to Oscilate. The other suggestion someone gave me was turned off all electronics like the strobe and the transponder maybe it's getting electronic noise interference. Either way I'll let you guys know what happens.
Matt

Dynon Autopilot - count me in as well

In smooth air I have to add 3 clicks of backstick trim to stop the altitude hunting. I've tried to resolve this for 18 months now, done the tuning / setup numerous times.

D10A

My altitude hold is also twitchy and constantly pulsing in smooth air.
In light turbulent air I have 100ft up and down and have to disconnect.
I tried many different settings in the software menu with little effect.
Have the latest software.

I can feel the little twitches in the stick, and see them at the elevator in flight in smooth air. At first I thought I had something loose to allow the elevator to jitter like I was seeing then realized the autopilot it making those very small adjustments. My altitude hold works well otherwise but I am a little concerned about the wear or stress caused by those little hits on the elevator controls.

Mine is Skyview system on a 7A. I also have the autopilot module and autotrim so not sure I can try the back trim adjustment idea..

Randall in Sedona

This is a cross-post from our own forum, where a similar set of discusssion have been taking place. In any case, from our AP engineer:

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There have already been a number of good suggestions in this thread, so I don't have a lot to add, but I wanted to mention some useful tricks and clarify what people are seeing. If you're having a hard time chasing down a problem, the best thing is to get in touch with Dynon tech support directly at support at dynonavionics dot com or 425-402-0433 so we can give you individual attention.

There are two different issues being discussed here
- Altitude hunting
- Pulsing on the stick

Before I get to those it's important to always check two things when troubleshooting the AP:
- Make sure there are no servo SLIPS (annunciated on the PFD screen)
- Check the linkages from the control surface all the way to the servo arm for SLOP (more on that in a minute)

If you have either of those things you'll save a lot of time by addressing them before trying anything else.

On the pitch axis, the advice to adjust the settings per the settings guide to get airspeed hold right is the key to good performance. One word of advice: don't over do it. If increasing settings stops improving things, stop there and maybe back off a little and you'll be right on.

Low frequency altitude hunting (many seconds per cycle) is usually a result of having ALT_GAIN set too high relative to VSI_GAIN. The default settings work well for the majority of airplanes: ALT_GAIN of 0.6 and VSI_GAIN of 1.5 is pretty close to the middle.

As mentioned, slop can cause hunting too. If you can trim against the servo slightly and the hunting goes away, that's a good indication of slop in the system. When we improved the trim sensing and introduced autotrim a number of airplanes turned up with slop which had previously been hidden by the preload due to being out of trim.

Another cause of low frequency pitch hunting is bumping up against the airspeed limiter. In that case you wont hold altitude well at all.

(Note that the AP either tries to hold airspeed or altitude - it can't do both withtout access to the throttle. Wink )

Higher frequency pitch movements can have a number of causes.
- The AHRS can be bouncing around on a flimsy mount
- The airspeed input is noisy (this will make the AHRS pitch jump around)
- Many of the pitch settings are turned up too high.

The first two are difficult to diagnose without more detailed information; the latter can be addressed by running the airspeed tuning process.

Hope that helps some,

Lawrence Doan
Autopilot Guy