Dynon AoA calibration

[Chuck]

New CTSW owner here.

 

I've been getting familiar with my '06 CTSW over the last couple months and am a little confused by the AoA indication on the Dynon D100 I'm flying behind.  I'm curious to hear if others are using it and if so, how.

 

I read through the calibration sequence that Dynon requires and went out and did it in the plane.  They ask for the pilot to fly a series of stalls in different configurations (power on, power off, all the flap settings) as part of this calibration.  Having done this, it seems to me now that the AoA readout reads very differently at different flap settings.  When I'm at -6 or 0 degrees flaps the indicator will go deep into the red as I'm approaching the stall, but at 15 or 30 or 40 degrees flaps I have to be right at the edge of a stall before it even gets into the yellow. 

 

My guess on this is that a flap setting of -6 the overall pitch attitude of the plane (and therefore the wings with the dynon AoA probe) is more nose-up so the AoA probe sees a higher angle of attack and gets higher into the red.  Conversely, when I go to 30 or 40 degrees flaps the overall pitch attitude of the plane is more nose down, so the AoA probe is at a lower angle of attack so it stays more in the yellow.  Does this logic hold up?

 

In my other plane (a 1941 Interstate Cadet) I have a thing called a Lift Reserve Indicator, which works off the same kind of probe and is essentially a non-electronic angle of attack gauge, and after installing it I found that it was a very powerful tool when maneuvering close to the ground and getting into short fields, especially with different weight conditions, but that plane doesn't have flaps so it's a little easier to understand.  The behavior I'd like to see out of the Dynon in my CTSW is that it beeps at me if I'm getting close to a stall when I'm in the pattern or doing maneuvers.  I thought maybe I could trick it by just flying the calibration in the 30 degree flap setting, but when I did that it now is deep into the red when I'm not close to the stall in a -6 degree flap setting.  I don't want to have it beeping at me when I'm in cruise flight.  It seems like if I do the full calibration with all the flap settings, it's going to give me close-to-stall information for the -6 degree flap setting, but what I really care about is the close-to-stall information at 30 and 40 degrees, and that gets washed out by the -6 degree calibration.

 

Am I missing something about how to use this system with the different flap settings?

 

Thanks in advance for any advice,

Chuck

[Anticept]

First, disconnect the lines from the back of the panel (ensuring you got the lines going out to the wing and no instruments are attached) and blow them out. A lot of water entrapment happens.

Then, go out and try again. Then test the stalls. If it's still off, try the full power full flaps stall portion with one notch less of flaps and try again. If no go, try 0 instead of -6.

The AoA system works by monitoring the pressure difference between the ram air inlet and the AoA inlet. The stall calibration is looking for the part where that difference is at its lowest.

When you do the stalls, you want to be right there at the edge. If you aggressively stall, it's going to calibrate to a point briefly past, and cause faulty calibration.

[Chuck]

Thanks so much for the reply! 
 

So if I understand you correctly, the calibration is going to look for the stall with the lowest pressure differential between the two ports - am I correct that this should be a full-flap power off stall?

If so, then I assume the Dynon will set the scale so that the AoA indicator gets into the red as the pressure differential nears this value correct? 
 

And then wouldn’t it get to the red well before an actual impending stall when you’re in a no-flap or negative-flap setting? 
 

im still trying to figure out what’s going on behind the curtain…

 

[Towner]

The D100 manual says to adjust a dirty stall to the top of the red. Clean configuration stalls should should be between yellow and red.

It really doesn’t take much to change the stall location on the AoA. Even if you have it set for a power off, full flap stall at the top of the red, simply adding some power or changing the flap setting changes the location of where the plane stalls on the graph.

I ended up taking the AoA off of the screen as I didn’t find it that useful. While it would be nice to have an audible stall warning, I’ve found you won’t really need either after getting familiar with the plane.

Have fun!

[Anticept]

12 hours ago, Chuck said:

Thanks so much for the reply! 
 

So if I understand you correctly, the calibration is going to look for the stall with the lowest pressure differential between the two ports - am I correct that this should be a full-flap power off stall?

If so, then I assume the Dynon will set the scale so that the AoA indicator gets into the red as the pressure differential nears this value correct? 
 

And then wouldn’t it get to the red well before an actual impending stall when you’re in a no-flap or negative-flap setting? 
 

im still trying to figure out what’s going on behind the curtain…

 

As you approach stall, more pressure is applied to the bottom of the tube. The dynon unit can detect that and the pressure in the ram air inlet. I just know that it is a differential AoA system.

It should go into the red and start warning BEFORE the actual stall, but not all stalls are like that. Just get it the best you can.