Failing airspeed, D180

[DaleB]

We have a Dynon D180 panel in a 2011 RV-12. Unti recently everything worked perfectly fine. Recently, though, it has developed a problem. Some time after takeoff, the airspeed indicator will read low by a wide margin, and I had a report from one of the partners about it dropping to zero. The last time I flew I was at 3500 AGL 5000 RPM, with GPS ground speed showing 120+ kt and the Dynon showing the correct altitude but airspeed decaying until it eventually reached about 34 kt. This morning (after a new pitot tube) one of the other partners flew it; he saw 119 kt on the GPS and 74 kt indicated (winds aloft were maybe 5-6 kt).

I tested the pitot system; we had a leak that I traced to a bad pitot tube, so I installed a new stainless pitot tube and tested for leaks. The system held 150 kt indicated for an hour with no loss. This morning after my partner flew it and saw the problem again, we blocked off one static port and pulled vacuum on the other to get 150 kt indicated. After clamping the external rubber hose I used to pull the vacuum, it held airspeed +/- 3 kt and altitude +/- 80’ for a couple of minutes. So no significant leaks in the pitot or static system.

The system will hold a steady airspeed reading on the ground for at least an hour. I haven't been able to get it to fail at all onthe ground. In the air, airspeed is Ok for a few minutes then after a few minutes reads way low. AoA still works, altimeter works, no other weird things going on that we've noticed. The last time I had the avionics bay open I checked to ensure there were no loose or damaged electrical connectors.

I’d like to hear any theories about where this problem might be coming from. I have my own, but what do I know?

 

[Majorpayne317641]

Go to an avionics shop to get the system tested. If you can rule out the tubes then the next step would be to send out the D180 to Dynon. They are very good at turning around a nice overhauled unit. I’ve done it twice for screen issues.

 

[DennisRhodes]

Could there be water or moisture in a low loop somewhere in the tubing system?

 

[springer]

We have a Dynon D180 panel in a 2011 RV-12. Unti recently everything worked perfectly fine. Recently, though, it has developed a problem. Some time after takeoff, the airspeed indicator will read low by a wide margin, and I had a report from one of the partners about it dropping to zero. The last time I flew I was at 3500 AGL 5000 RPM, with GPS ground speed showing 120+ kt and the Dynon showing the correct altitude but airspeed decaying until it eventually reached about 34 kt. This morning (after a new pitot tube) one of the other partners flew it; he saw 119 kt on the GPS and 74 kt indicated (winds aloft were maybe 5-6 kt).

I tested the pitot system; we had a leak that I traced to a bad pitot tube, so I installed a new stainless pitot tube and tested for leaks. The system held 150 kt indicated for an hour with no loss. This morning after my partner flew it and saw the problem again, we blocked off one static port and pulled vacuum on the other to get 150 kt indicated. After clamping the external rubber hose I used to pull the vacuum, it held airspeed +/- 3 kt and altitude +/- 80’ for a couple of minutes. So no significant leaks in the pitot or static system.

The system will hold a steady airspeed reading on the ground for at least an hour. I haven't been able to get it to fail at all onthe ground. In the air, airspeed is Ok for a few minutes then after a few minutes reads way low. AoA still works, altimeter works, no other weird things going on that we've noticed. The last time I had the avionics bay open I checked to ensure there were no loose or damaged electrical connectors.

I’d like to hear any theories about where this problem might be coming from. I have my own, but what do I know?

I loved my D-180 especially the simple screen presentation over the newer units from various avionic suppliers. Only ever had one issue with the screen going black. Sent it back for repair and a new internal battery. This is on an 16 year old RV-8. Airspeed indications were always dead on.