Foolishly tempted fate...

[PhantomPholly]

Ok, so I swung by the TruTrak kiosk and said hi to Lucas, and foolishly told him "nothing is wrong with my autopilot." :(

Not half way home, it pitched hard left for no apparent reason. No, I didn't see what the screen said. Re-engaged and worked ok for a while, happened again later a couple of times.

Where should I look first - ARINC wires or servo?

[TrutrakTech]

Bill, good to meet you in person finally!

Let's start with a gyro set. With the system powered up but not engaged, press and hold the knob in for about 30 seconds. The display will show GYRO SET. Do this before your next flight while the aircraft is stationary.

Also, if this reoccurred with a pretty consistent time interval, try flying the AP in the track selector mode and see if it repeats. Let me know. Thanks!

[PhantomPholly]

I'll do it Lucas - good to meet you too!

I do remember seeing one thing. I am certain I was flying in GPSS track mode (love my GNS 480), and somewhere during my frantic grab to put the aircraft heading somewhere back towards where it should be, I noticed that the display on the TT showed a heading that was varying rapidly. Yes, I still have the magnetometer version, thought it was pretty stable in heading mode but maybe not so much.

So, if it was losing signal from the GPS (or the GPS was losing satellites, which I really haven't seen much with the antenna mounted outside the cabin) it would revert to magnetic heading, and if the heading info was erratic could have caused the aggressive turn....

Best case is that the GPS lost signal - though that would be disturbing as I have all the updates and even got a brand new antenna for free from Garmin. Can't fix that. Second best / worst would be a loose ARINC wire.

[TrutrakTech]

Ok, more info is always good. If the GPS lost signal completely (including the RS232 feed) then the AP would revert to the magnetometer. Have you calibrated the magnetometer? If not, that would certainly cause it to possibly jump off course.

Let me know.

[PhantomPholly]

No, I haven't calibrated the magnetometer (always seemed to read good on the ground, didn't bother) and when you told me the "upgrade" would cost me money I balked... :o

So, at this point I'm thinking calibrate and then live with it, until I'm ready to pony up for the newfangled defaults-to-heading version.

[ian.orrman@gmail.com]

Hi Lucas,

I have posted to this thread as I have experienced the same left turn phenomenon. In my case it was extreme and without my intervention, would have resulted in the aircraft going into an inverted attitude!

As you know, I recently upgraded from the Trutrack VSVGII to the AF Pilot. Prior to the upgrade I had about 40 hours on my aircraft and the Autopilot had worked well without any apparent problems other than the screen lines failing. Therefore a new screen and an upgrade to the AF Pilot.

On a long trip I came back from last week, I had the following experience.
On the first day of travel, I was flying in smooth air at 8500 to 9500 feet. I was getting a slow wing roll associated with smooth air. So I was making slight adjustments to the settings in flight to see if I could reduce the slow roll (micro motion). Every once in a while the Auto pilot would roll left and not self correct. So I was disengaging, getting back on track and re-engaging. All this time I was operating in manual and not through the EFIS.

I assumed it was the super smooth air I was flying in that was causing the left roll problem. I also wondered if it was the changes in the settings in flight that had caused some kind of problem. So I set everything back to the original settings and continued the rest of the distance flying the aircraft with the AP off.

The next day I was heading off on my next leg, got to 5500 feet, levelled off and turned the AF Pilot onto manual. Within about 5 minutes it commanded a left roll input for no apparent reason, even though I was exactly on track. I decided to see how far it would go off track before it started to correct with some right aileron input.

On this occasion, the roll input increased in severity to the left and if I had let it continue I would have been inverted before long. I disengaged and had to wrench the joy stick right, and in the process I suspect I sheared the shear screws on the pulley. Despite disengaging the AP, it did not let go of the controls. My roll slightly exceeded 90 degrees! Not a pleasant experience and quite a fright for me. Fortunately I was on my own.

I completed the rest of the trip (40 hours flying) without ever engaging the AP again as I was in very remote locations without the time or resources to do anything to fault find.

I am about to do my first 100 hour inspection, so the AP mechanicals are the first area I will investigate.

However, if is interesting to note that another owner has had an unexpected left turn signal. Possibly more than a co-incidence. I will keep you updated on my progress.

Any suggestions on a process of elimination would be appreciated.

Regards,


Ian Orrman
Perth, Australia.
Glasair Sportsman GS-2, TD, IO 390, VH - ZIF

[TrutrakTech]

Ian,

Do you power this unit up on the ground while stationary?

[ian.orrman@gmail.com]

Lucas, yes I did. I always power up the AP on the ground while the engine oil warms up.

[PhantomPholly]

Follow up:

I calibrated the magnetometer; removed the filter temporarily to eliminate it as a potential source of "bad connection;" lightly squeezed the female pins between the AP and the GNS 480; and went flying.

The AP performed flawlessly; however, it should be noted I only flew for 30 minutes. My last problem occurred 2 hrs into a 3 hr flight after more than 50 hrs total time since AP install. Will report back once the economy improves and I fly more - but I do optimistically believe the "problem" is gone. Next step will be to re-install the filter (actually a new, lighter filter) so I don't have to grab the stick and wrestle every time I key the mic...

[TrutrakTech]

Let's see if you find anything at your condition inspection. Check that the servo cables are tight. Check that the servos move in the correct direction. Let me know what you find. Thanks!