TruTrak pitch problem RV-6

[flydoc101]

I have an ADI pilot II which after about two hours started having pitch oscillation problems. These tended to be random, but the autpilot tried to stay at the requested altitude. We have adjusted the settings on the autopilot as suggested by Trutrak. We have tried the static lag setting increase. We have disconnected the static lines from the autopilot to see if that was the issue. Trutrak gave us a replacement unit, even though they could find nothing wrong with the first unit. The second unit did the same thing on the 3rd flight after a few hours on the unit. Any suggestions? There is no excess play in the elevator when compared to other RV's on the field.

[Bob Martin]

Do you have any RF problems?
There is a "filter" to install on the rear of the unit as discussed in other posts on this subject. I had a similar problem only when I transmitted. I found my PTT wires were unshielded and running parallel to the Comm antenna coax, A no no!
Good Luck.

[flydoc101]

I did put a filter on it. Before the filter it would climb whenever I keyed the mike. It stopped doing this after the filter was applied.

[patterson]

If memory serves me, there is a small (I mean small) resistor or fusable link embeded in the wiring harness. Make sure that has continuity
Ron

[flydoc101]

Thank you. I'll check on this.

[sharpdoug]

http://parts.digikey.com/1/parts/159...b25ad-250.html

[Bob Martin]

Originally Posted by flydoc101

I did put a filter on it. Before the filter it would climb whenever I keyed the mike. It stopped doing this after the filter was applied.

If the filter worked......then it showed you that you did or do have a RF problem. It might be a good thing to search for the actual problem and correct it so the filter doesn't have to work so hard or maybe it isn't stopping 100% of it. I'm pretty sure you have spoken to Lucas at TT, so they have given you things to look for like he did me.
The comm antenna is pretty close proximity to the panel in the RV-6 as mine was under the seats. Lucas explained the signal goes down the coax and the signal is so strong in the short cable that some of the signal bounces back up the coax and then spreads around the back of the panel.....or something like that. So Lucas suggested I try putting a longer run of coax between the comm and the antenna and then loop the excess up behind the panel to absorb the extra signal. That actually helped my situation 75%. My A/P was an early ADI PII and had a plastic housing so I sent it back for the metal housing update. At some point, it has to be your installation as you said they swapped units and the problem persisted....
for my 2cents, I'd keep looking along the RF line for some unshielded wires, etc. possibly running close to the antenna coax.
Good Luck and let us know what fixes it.

[N661DJ]

I have been involved, trying to solve flydoc,s TT problem. One thing he did not mention, Once the new, replacement controller was installed, the unit functioned perfectly for the first 2 hours or so? Also when the problem did occur, we shut off all the electrical appliances, radios, strobes, alternator, none of this stopped the ocillations. It appears that, after turning the AP off for a short period of time, the problem seems to go away for a while? Thermal problem??
Our next step is to install his AP in my 8, I also have an ADI-II that has been working great. TT has been very helpfull and are as fustrated as we are with this problem.

[Ironflight]

Trying the head in a different airframe is a great idea! We do that between our -6 and -8 all the time when troubleshooting, and it is a good way to narrow down the problem. It pays to have similar "equipment" in the "fleet."

[jeff beckley]

This happened to me. Turned out that I had a intermittent short/open connection at the connector. I reached under the panel while in flight and applied pressure in several directions to the wire loom and found I had something not right. Just a guess