Tecnam Eaglet: unstable heading control

[jmfarto]

We are installing a Dynon autopilot system on a Tecnam's Eaglet. It exhibits an unstable heading control in HDG mode. It only seems to be corrected by setting a very high roll sensitivity (20 to 25) and a turn rate limit of 1,5 deg/s or less but, when ALT mode is also engaged, random heading wandering (more than +-10 deg, sometimes stable, sometimes gradually increasing) appears. Also when performing AP-commanded 90 deg turns, it always overshot. This can be corrected by setting turn rate limit to 0 and bank limit to >=20 deg, but then random heading wandering and/or unstable behavior occurs.

Installed system:

- An EFIS-D100 unit
- An EMS-D120 unit
- A HS34 unit
- An AP74 unit
- Two SV32 servos
- Firmware 5.4 (upgraded from a 4.x version in D100, D120 and HS34)

 

[dynonsupport]

HI,

How is performance in TRK mode?  If it's OK, then your roll mode settings are correct and the compass is most likely the problem.  (Setting turn rate to zero and choosing a suitable bank angle is probably the best place to start.)

The best way to verify the compass is to fly towards a point on the horizon, and then bank while keeping the nose on that point.  The compass should show no heading change with bank angle.  

If the compass does swing with bank, it may be misaligned to the D-100 or it may need recalibration.