Erratic Airspeed (IAS) on HDX

[pacecapt]

I have a dual screen Dynon HDX system with Dynon Pitot, ADAHRS, etc. I have been flying this system for 3 years and during that time I have always had a erratic or bouncy airspeed indication (2-3 MPH up and down) while in flight. I have done all the calibration that I can with this system, in fact I have had to recalibrate it several times as for no apparent reason it will just start acting goofy when on or sitting at idle (bounces around 0 to 25 mph) and no motion of the aircraft. Any thoughts or is this normal?

 

[GalinHdz]

This is not normal. If both screens give the same erratic indication then I doubt it is with the equipment.

My initial thought; there is an issue with the Pitot or Static system. Does the altimeter and/or the VSI also bounce around at the same time? If so then the culprit is with the static line or port. If only airspeed bounces around, then the culprit is with the pitot line or probe.

Less probable is the AOA line and sensor. If you have the AOA connected, check that line too. If not connected, make sure the AOA port on the ADAHRS is closed off and not open. Good luck on finding this and let us know when you find.

 

[pacecapt]

This is not normal. If both screens give the same erratic indication then I doubt it is with the equipment.

My initial thought; there is an issue with the Pitot or Static system. Does the altimeter and/or the VSI also bounce around at the same time? If so then the culprit is with the static line or port. If only airspeed bounces around, then the culprit is with the pitot line or probe.

Less probable is the AOA line and sensor. If you have the AOA connected, check that line too. If not connected, make sure the AOA port on the ADAHRS is closed off and not open. Good luck on finding this and let us know when you find.

Yes, it does it on both screens and neither the VSI nor Altitude have erratic readings and yes, I do have the AOA attached. I have never thought it was the HDX screens but probably the ADAHRS or the lines. I have checked all line with no leaks...

 

[Rhino]

Could be the location of the tube or static port. Unexpected air currents around either one can cause this. Temporarily run your static tube inside the cockpit and see if it settles down.

 

[GalinHdz]

Yes, it does it on both screens and neither the VSI nor Altitude have erratic readings and yes, I do have the AOA attached. I have never thought it was the HDX screens but probably the ADAHRS or the lines. I have checked all line with no leaks...

Do you have one ADAHRS or two?

 

[pacecapt]

Do you have one ADAHRS or two?

Do you have one ADAHRS or two?

I only have one.

 

[pacecapt]

Could be the location of the tube or static port. Unexpected air currents around either one can cause this. Temporarily run your static tube inside the cockpit and see if it settles down.

I did that and no change. I also moved the static ports further aft as I was getting a high IAS but now that seems to be a better location.

 

[GalinHdz]

Have you done the "Zero" pressure calibration? Pg 5-22 of the installation manual.

ZERO PRESSURE IAS/AOA CALIBRATION
"This calibration routine samples Pitot, Static, and AOA pressures in a windless environment to allow SkyView to provide the best possible Indicated Airspeed (IAS) readings at very low airspeeds, and the best possible Angle of Attack (AOA). Ideally, perform this calibration before performing an (in-air) AOA calibration. After performing these two steps, in the future, performing a ZERO PRESSURE IAS/AOA CALIBRATION should restore both airspeed and AOA performance without requiring a full AOA calibration.

It is important that this calibration is done in an absolutely windless environment, such as a closed hangar. Additionally, before performing this calibration, cover the Pitot, Static, and AOA ports with a sock or cloth to minimize airflow WITHOUT putting any air pressure on the Pitot, Static, or AOA ports."

 

[pacecapt]

Have you done the "Zero" airspeed adjustment to the ADAHRS?

Yes, many times...

 

[GalinHdz]

Yes, many times...

It is sounding like your ADAHRS may have a problem. But to eliminate installation issues, run a "temp" line from the Pitot tube to the ADAHRS. If this doesn't fix the issue then the ADAHRS is the problem and you need to contact DYNON support to get it checked. I sent you my phone number so we can talk. Easier than these back-n-forth posts.

 

[jimalexander]

@pacecapt I'm having this same behavior in my Skyview Touch with a similar configuration (single ADAHRS but no AOA). Cleared the pitot tubes and did multiple calibrations, no joy. I'm wondering if you reached a resolution. I also put in a call to DYNON support today, waiting for callback to discuss with them.

 

[pacecapt]

@pacecapt I'm having this same behavior in my Skyview Touch with a similar configuration (single ADAHRS but no AOA). Cleared the pitot tubes and did multiple calibrations, no joy. I'm wondering if you reached a resolution. I also put in a call to DYNON support today, waiting for callback to discuss with them.

Yes, I did get it fixed but it turned out to be a defect and upgrade was needed on my ADAHRS module.

 

[jimalexander]

@pacecapt Thanks for the update. I worked with Dynon to get the debug on/off scripts and we determined that my pitot pressure sensor was failing. ADAHRS has been pulled and sent for service.