Unable to Test Batteries ; "Residual" Airspeed?

[Sportsman7064]

All,

I have been flying my Skyview system for a few hours now, and decided it was time to conduct the annual battery test for the two back-up batteries. When I try to use the procedure outlined in the manual, nothing happens.

When I cut the power to the units, I get the message "Aircraft Power Lost", but no countdown of 30 seconds. I also get three soft keys, one says Stay On, the next says Power Off, and the third is Test Bat, but that one is greyed-out.

I think the issue may be that when parked, my Skyview always shows an intermittent airspeed of 15-20 knots, even when parked in the hanger with no wind. When the airspeed momentarily drops to zero, the system appears to start the 30 second countdown, but the airspeed jumps back up to 20 in a fraction of a second and it goes away...

So, is there a remedy for the phantom airspeed indications?

Thanks, as always.

Russ

 

[Dynon]

Check out SETUP MENU > HARDWARE CALIBRATION > ADAHRS CALIBRATION > ZERO PRESSURE AIRSPEED CALIBRATION for the adjustment that'll fix this. You'll want to be in the hangar when you do it though.

 

[dynonsupport]

Before you do that however, you should really disconnect the pitot and static lines from your AHRS and see if it goes away. The units are calibrated here, and 20 knots is about 4X how far off they are allowed to be when they ship. You don't want to use airspeed zero to cover up water in your lines or some other issue.

 

[Sportsman7064]

I'll try that.  Looking at the data logs, the difference between the IAS and GPS Groundspeed converge pretty quickly once I start a take-off roll, ending up with a difference that seems to agree with the prevailing surface winds on my last flight...

I've attached a short segment of the data from that flight so you can see the IAS bounce from 20-21 to zero every few seconds or so.

Thanks

Russ

 

[dynonsupport]

Airspeed is logarithmic against PSI. So a 0.02 PSI error is 20 knots at 0 knots, but it's only a knot at 100 knots. It's expected that small errors down low won't cause issues once you are really flying. Jumping from 20-21 knots is a change of less than 1/1000th of a PSI!

 

[Sportsman7064]

Worked perfectly! No issues. I can now do the battery test and calibrate the autopilot servos. Thanks for the help!

I'll post an autopilot question on that branch of the forum, as I'd like to see if anyone with a Glastar Sportsman 2+2 is using settings different than the default settings she came with...

Russ