Skyview AP anomaly

[RVDan]

I was flying with the AP engaged and the FD roll mode in Nav, tracking the GPS-250 flight plan.  The pitch mode was set to vertical speed (-500FPM) as I was descending from my cruise altitude.  The altitude preselect was set about 2500 ft below my present altitude. Speed hit the max limit (envelope protection) for pitch (ASPD HIGH annunciation) and the aircraft pitched up maybe 10 degrees, then pitched down to somewhere around -10 degrees with a max vertical speed of about -1200FPM before I intervened by reducing power.  It then pitched up again overshooting less and eventually settled on the proper vertical speed. It had perhaps 3 overshoots before getting back to the set vertical speed.  This was in smooth air.

Since I had plenty of altitude and safety wasn't an immediate concern, I let the AP go to see how it handled the situation. 

The AP has been functioning properly other wise, but this was the first time I hit the max speed protection. 

I was wondering if I should expect that behavior when hitting the max speed protection?  The aircraft is a RV-6A.  This was with V14 SW.  This was in the last 30 minutes of flight, so I should be able to download the diagnostics file if you want it.

 

[Dynon]

So that's definitely not what it's supposed to do. A few thoughts:

1) Did the servo slip when it started to limit on airspeed? You would have seen that as a yellow message near the autopilot status area.
2) If you're not experiencing slips: fundamentally, the AP is in an airspeed mode when it's limiting on airspeed. Improving the performance you get from this mode can be done by going through the the Autopilot In-Flight Tuning Guide available at http://docs.dynonavionics.com.

 

[RVDan]

There were no servo slips noted and the pitch up was gradual, I assume following G limiting, as was the pitch over. I have never had a problem with airspeed hold after I did my initial AP tuning, although I did have the pitch go divergent on a glide slope capture one time back at version 12 or so.

I will save the diagnostics file before next flight just in case, and next flight I will try to duplicate this.