Switch to Alt Static causes attitude changes

[bkthomps]

Dynon- I was test flying with my new alt static port, and I decided to hand fly the AP for ALT and let it just hold a HDG.

When I enabled the ALT static which uses my cabin pressure, of course as expected the altimeter started to climb and settled out to about 9180 (i was level at 9000)

What is concerning to me is that the attitude indicator indicated a dramatic nose up attitude and a slight left roll. (I was VMC, holding steady heading)

What is going on with that?

 

[TRCsmith]

To start with you were at the wrong altitude.

As required by 14 CFR Section 91.159(a), the appropriate VFR altitudes for aircraft (not in a holding pattern of 2[ch8201]minutes or less, or turning) operating more than 3,000[ch8201]feet above the surface to and including 18,000 feet MSL:

Magnetic courses 0-179- odd cardinal altitudes plus 500[ch8201]feet; e.g., 3,500, 5,500.

Magnetic courses 180-359- even cardinal altitudes plus 500 feet; e.g., 4,500, 8,500. 

It's there for everyone's safety.

 

[bkthomps]

I only fly IFR- I was correct for my direction of flight.

 

[dynonsupport]

You caused a dramatic and sudden change to airspeed when you changed to alt static. We use airspeed changes as part of the attitude algorithm, so this will cause a short term error that will fix itself over a few seconds.

 

[bkthomps]

You caused a dramatic and sudden change to airspeed when you changed to alt static. We use airspeed changes as part of the attitude algorithm, so this will cause a short term error that will fix itself over a few seconds.

Thanks! This makes sense and answers my question. Are there any other variables involved in the attitude algorithm?

 

[dynonsupport]

Attitude is involved

Nothing else really is. Actual attitude is used plus airspeed. Airspeed can be sourced from pitot, or in the case of pitot failure, GPS. Altitude, and magnetic heading are not used.