AOA Calibration

[David_Prince]

I have been flying my Glasair 1TD for about 15 hours now with the Dynon D-180, heated AOA/Pitot, HS34, Garmin SL30, Garmin 296. I tried to calibrate the AOA two days ago but was unable to get it to work.

Starting at cruise airspeed 200 mph
Entered AOA calibration menu
Pitched aircraft up and down several times

From a level cruise, pushed the stall button
Slowed the aircraft and stalled, clean power off
Recovered from the stall and returned to cruise airspeed
I then let the timer finish the countdown

From a level cruise, pushed the stall button
Slowed the aircraft  and stalled, clean power on
Recovered from the stall and returned to cruise airspeed
I then let the timer finish the countdown

From a level cruise, pushed the stall button
Slowed the aircraft and stalled, flaps down power off
Recovered from the stall and returned to cruise airspeed
I then let the timer finish the countdown

I pressed the Finish button

Exited all menus


After the calibration in cruise flight the AOA meter only  shows a Red triangle with a single red chevron blinking below it.

If I load up the aircraft +2g's or so the chevrons increase to show red, yellow and green.

Returning to level cruise shows single red triangle and blinking single red chevron.

It seems to be displaying in reverse???


Yesterday I re-read the installation manual and re flew the calibration sequence with similar results.

Any insight into what I might be doing wrong would be helpful.

David Prince
N238SH

 

[dynonsupport]

David,
My first guess would be that you have the AoA and Pitot lines connected backwards. If you're getting the AoA going more towards the green as you pull G's, that's about the only way it could happen.

 

[David_Prince]

I have verified the pitot and aoa lines are connected properly. The aoa line is the rear line in the pitot head and connected the the left most connector on the D-180 looking from the rear. Airspeed indication seems to be right on based on chase aircraft and GPS 3 way ground speed.

I have again tried to calibrate with out success. Any other ideas?
David Prince

 

[David_Prince]

Should I press the stall button at cruise airspeed and then slow and stall before the countdown timer reaches zero or should I press the stall button once slowed and just prior to stalling? Perhaps the speed change from 200 mph cruise to 50 mph for the stall is causing my issue.

 

[dynonsupport]

That last thought isn't a bad one. It may be recording some data erroneously, but we haven't seen that before. Also, the reversed behavior is something which is truly bizarre that is stumping us. It just shouldn't be possible unless the pressure inputs were the reverse of what we were expecting them to be.

Also, try doing just the power off, dirty stall and see what that produces.

 

[David_Prince]

I have attempted several more times to calibrate the AOA. I have finally turned off the AOA display and moving on with other testing. I will revisit this after my 40 hours of flight testing. It is still strange how the indication seems to be reversed. Is there any chance that the internal pressure sensor is reading backwards?

 

[dynonsupport]

Your situation is really odd. It isn't possible that the sensor reads backwards. We'd catch this in our calibration process.

The only thing I can think of is the AoA and Pitot lines being swapped inside. This seems tremendously unlikely, but anything is possible I guess. It is easy to check and see if the ports inside are swapped.

Take the D-180 out of the panel, and power it up. This is really easy if you have the battery, admittedly harder if you don't.

Once turned on, press your finger over the "P" port (the middle one). Make sure it seals the port completely, and then press hard. You should be able to get 100-200 MPH on the display.

If you can't, try the same thing on the AoA port. If you get airspeed on the AoA, the tubes are swapped.

If you get airspeed on the pitot, port, try something for us:

Apply some pressure on the pitot port to get 100-ish MPH. You need to hold this speed semi-constant.
You should have max green AoA.
Press another finger on the AoA port. You should be able to vary the AoA toward red as you press on the AoA port harder.

If you can increase the AoA by pressing on the AoA port, then it is almost a 100% chance that you have the AoA and pitot tubes swapped somewhere in the plane.

 

[ffaww]

Okay, I have exactly the same problem with my AOA reading reversed. I checked the lines from the pitot and everything seems correct. I even reversed the tubes deliberately and tried it but no luck yet. What was the answer to your problem? My mechanical airspeed and the EFIS don't agree either. Normally I would suspect the mechanical gauge is in error but it tends to agree closer with the gps than the numbers from the EFIS. Could that be related to the problem? Otherwise, everything seems to work fine.

 

[David_Prince]

I never did find a solution to the AOA calibration issue. The airspeed accuracy seems very good on my Dynon and tracks closely with the mechanical airspeed indicator.

 

[vlittle]

I never did find a solution to the AOA calibration issue. The airspeed accuracy seems very good on my Dynon and tracks closely with the mechanical airspeed indicator.

David, try checking for a blocked AoA line.

Vern