Altitude Hold no holding

[N91CZ]

I have a IIVS in a Lancair 360. Occasionally it is unwilling to hold altitude. I have to dial in a climb rate of a few hundred fpm to maintain level flight. Usually cycling power resolves the issue and I forget about the problem until it happens on another flight. Is there any known cause or cure for this?

Chris Zavatson

[PhantomPholly]

Hi Chris,

Check your PMs & give me a call. I should be around any time tomorrow.

Bill

[TrutrakTech]

Hi Chris,

I think Bill is a good guy to know. I would definitely heed his advice as he's usually spot on.

From my end, what are you current vertical settings? Thanks!

[N91CZ]

Lucas,
Settings are:
vrt activity = 0
vrt torque = 12
static lag = 0
microactivity = 0
half step = Y
With these settings the auto pilot does a nice job flying the plane througout all normal flight maneuvers, SL to 17.5k.

Only one of the last five flights presented a condition where alt hold did not hold, but rather produced a slow steady descent of a few hundred fpm. Disengaged and reengaged at it held after that. It happens so infrequently that it is hard to diagnose.
I did notice some of those vertical lines in the display coming back when it switched to night time lighting.
Chris

[TrutrakTech]

Lucas,
Settings are:
vrt activity = 0
vrt torque = 12
static lag = 0
microactivity = 0
half step = Y
With these settings the auto pilot does a nice job flying the plane througout all normal flight maneuvers, SL to 17.5k.

Only one of the last five flights presented a condition where alt hold did not hold, but rather produced a slow steady descent of a few hundred fpm. Disengaged and reengaged at it held after that. It happens so infrequently that it is hard to diagnose.
I did notice some of those vertical lines in the display coming back when it switched to night time lighting.
Chris

I am surprised you're able to fly it well with an activity setting of 0. The half step option reduces the available torque by a considerable amount. My suggestion would be to try the vertical activity at 3 and turn the half step off. See what you get at that setup. Thanks!

[PhantomPholly]

I agree - anything less than 3 in my 320 seemed to "wallow" (corrections smooth, but too slow creating a very slow porpoise).

You want it high enough so that in chop it reacts fairly quickly, but no so aggressively that it feels like it is "stirring the stick" in smooth air.

[N91CZ]

Lucas,
I arrived at these settings after speaking with someone at Trutrak on the phone right after my first test flight. I had a continuous stick shake I was trying to remove. Vrt act. just made it worse. Half step was suggestested as the cure. I then flew on a 1,400 mile cross country and the plane flew like an airliner the whole way. Altitidue never budged more than a needle width. It also does really well in turbulence.
The issue is that every so often it decides -400 fpm, or similar, is level when selecting alt hold. For example, after a climb at say 700 fpm, I hit alt hold. Instead of leveling off, the plane starts a decent. When it does this, it is a continuous steady decent. Turning the unit off/on has always reset alt hold to be zero fpm.
Chris

[TrutrakTech]

Chris,

Since this is intermittant, it will be hard to see if this suggestion helps, but let's try it anyway. Disconnect the static line from the AP. See if the problem repeats, just be aware that changes in air vent settings will cause fluctuations in pitch until the pressure stabilizes again.

If you're comfortable with your settings, go ahead and leave them as is.