AOA seems to be reverse indicating.....

[Henrik]

I thought I had read something about this but I have been unable to find a topic posted relating to this problem.
I have run through the set up sequence in the air.
But I now have one red bar shoing in normal flight, but as I increase AOA the markers go down through yellow to green.
Is this just a matter of changing a couple of feeds arround ?
Look forward to your help,
H

 

[Henrik]

Any help here ???

 

[dynonsupport]

Just to sanity-check what you're doing in the air - can you give a few line overview of what you're doing, step-by-step? Also, how does the AOA bar behave WHILE you perform the calibration?

Also, can you confirm that the beveled AOA port on the pitot is facing down towards the ground?

 

[Henrik]

Firstly the pitot is fitted "the right way up" as your schematic drawings.
Secondly, I have run through the set upprocedure several times. During the set up the indicator bar sits at the bottom of the green and then as soon as the "finish" button is pushed the indicator pops up to the red.
In normal flight the indicator sits at the top of the red. As we increase angle of attack the indicator slides down in to the green.
Does this help diagnose any further?
Look forward to your help.
H

 

[dynonsupport]

Not really, unfortunately. Can you describe, in a few lines, how you calibrated?

Also, make sure that the pitot and AOA lines aren't hooked up in reverse. You can test this by covering the AOA hole on the bottom of the pitot and blowing into the pitot line. You should see airspeed change.

 

[Henrik]

Will try the blow test.(!)
As for the calibation, I followed the instructions set down by yourselves. Raise & lower nose 5 deg four times,
carry out the stalls in various configurations within the count down periods. press finish.

 

[dynonsupport]

What airspeed were you at when you raised/lowered the nose?

 

[Henrik]

We tried this several times....ranging from 150kts to 170kts

 

[Henrik]

The Blow Test:
A gentle blow in the front opening with the lower AOA hole blocked generated an airspeed and sent the AOA bug down to the bottom of the green.
A subsequent fight test had the AOA bug hovering up athe the top of the red!
Any ideas?
Henrik

 

[dynonsupport]

So that test case (all pitot, no AOA pressure) resulted in the correct "low AOA" reading. Can you snap a picture of your pitot/wig installation and attach it to the thread?

 

[Henrik]

Will do.....do you have gudance on how to attach photos?
Any feedback on my other query relating to HSI set up?

 

[dynonsupport]

When you post a message, right below the box where you type the text is "Attach" which allows you to post a picture.

 

[Henrik]

photos as requested

 

[Henrik]

pic inside

 

[Henrik]

pic inside

 

[dynonsupport]

Henrik,
It looks like you have "P" and "S" written on those fittings. The Dynon pitot probe has no static port. I assume these lines run to the "P" and "A" ports on the back of the EFIS and you have a separate static port hooked to the "S" on the back of the EFIS?

Nothing else in the install looks problematic, but I can't see how far back on the wing the pitot probe is from the leading edge. Besides that, we're still stumped.

Have you checked all the tubing for leaks?

 

[Henrik]

The centre of the pitot leg is approx 520mm (21 ins) back from the leading edge.
Our engineer confirms....."I can confirm the pitot head has dynamic pressure (pitot) and AoA. The EFIS is connected to the pitot, AoA and the original static port located in the rear fuselage. This is I believe in line with the latest communication from Dynon. The tubing comprises high quality pneumatic fittings and new plastic hose.".......
We have tested for leaks.
Any clues from the attached?
Henrik

 

[dynonsupport]

No major red flags there. How far back are the actual ports from the leading edge? 2"-12" is our general recommendation based on our testing, but of course that doesn't mean that being out of those ranges is necessarily bad. It looks like the pitot is roughly mid-span, which is desirable.

To cross-check your reported configuration, can you confirm that blowing in both the the pitot or AOA ports produces no altitude change?

 

[meljordan]

In the message, Henrik says the pitot is located 21 inches behind the wing leading edge. I am not an aeronautical engineer, but I have never heard of a pitot being located that far back on the cord of a wing. At that point I seriously doubt that there is any possibility for the AOA to work unless the pitot mast was several feet long. I would also question if the pitot reading at that would not be adversely impacted by the local airflow that far back on the airfoil.

Mel Jordan

 

[khorton]

In the message, Henrik says the pitot is located 21 inches behind the wing leading edge.  I am not an aeronautical engineer, but I have never heard of a pitot being located that far back on the cord of a wing.  At that point I seriously doubt that there is any possibility for the AOA to work unless the pitot mast was several feet long.   I would also question if the pitot reading at that would not be adversely impacted by the local airflow that far back on the airfoil.

The pitot pressure itself should be OK, as it measures dynamic pressure, not static pressure.  Dynamic pressure is the pressure that the air would have if you slowed it to zero velocity with respect to the aircraft.  As the airflow accelerates and decelerates around the wing, the static pressure and velocity changes, but the dynamic pressure remains constant - Bernoulli's Law.

But, I agree that if the ports on an AOA probe are too far aft of the leading edge that this could greatly reduce the sensitivity of the probe to AOA changes.  I can't imagine that it would lead to reverse sensing though.