Altimeter Fluctuations

I'm using Van's altimeter as well as a Dynon D-10A. I see Van's altimeter fluctuating += 40 feet, but the Dynon is dead on. I'm told by Dynon that their
EFIS does some internal dampening which may be hiding the fluctuation in that unit.

I cannot seem to find a leak in my static system. Has anyone else seen this problem with Van's altimeter?

(I have a good reason for asking. )

Jamie said:

I'm using Van's altimeter as well as a Dynon D-10A. I see Van's altimeter fluctuating += 40 feet, but the Dynon is dead on. I'm told by Dynon that their
EFIS does some internal dampening which may be hiding the fluctuation in that unit.

I cannot seem to find a leak in my static system. Has anyone else seen this problem with Van's altimeter?

(I have a good reason for asking. )

Click to expand...

Fluctuating like vibrating shaking needle? Or at a slower frequency?
Does the fluctuation change with manifold pressure? RPM?
What does it do air born with the prop stopped?

I've had three planes with Dynons and Van's Altimeters.
I experienced the same fluctuations in the altimeters but not the Dynons.
The fix for me on my current RV8 was to leave out the airspeed and altimeter and go with just the Dynon.

Jamie said:

...I see Van's altimeter fluctuating += 40 feet, but the Dynon is dead on...

Click to expand...

I had an altimeter that developed a fluctuation over time. It got to the point that it would fluctuate hundreds of feet at times. There would be a cycle on the order of every one or two seconds. I don't know what kind of altimeter it was or where I got it (possibly Van's). The cure was a new altimeter.

At the same time I had a RMI digital altimeter display, teed off the same plumbing that was completely steady.

Larry's description is close to what I'm seeing. I have seen it gradually grow larger over time. It's moving at about 2-3hz so it doesn't seem to be good old fashioned vibration. I have not noticed any differences.

The reason I'm asking is because I'm trying to track down a problem with my Dynon autopilot (in pitch). The roll axis works great, but the pitch is deviating slowly. I''ve been talking to the Dynon folks about the issue and they suggest I try to narrow down the cause of the altimeter fluctuations first.

This weekend I will fly with the Dynon static connection vented into the cockpit to see how it performs.

The altimeter itself could be leaking. Perhaps popping off the hose from the altimeter and capping it off. Then fly with only the Dynon and see what the AP does.


Just a guess.

Static vent in cockpit

If you vent the Dynon static inside the cabin and it is driving the autopilot, changes in pressure inside the cabin will make the autopilot deviate in pitch. Things like open/close vents, turn on heater, etc. Chased this one down with a TT A/P that was vented inside instead of from the external static system.