Calibrating the AoA System

andresmith76

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How do most pilots calibrate their Skyview AoA system - with no flaps, partial flaps or full flaps? I have an RV-6 with a new Skyview install and am ready to calibrate.
If I calibrate using full flaps, wouldn't the visual & aural AoA indicators be skewed/offset when landing without any flaps or partial?
Andre'
 

andresmith76

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What is a "full" calibration?

I spoke to David at Dynon Tech support this week and he told me these 2 rules for calibrating the AoA system:

1) Every time you perform and SAVE a stall calibration, it over writes and replaces what was in Skyview's memory. Performing more and more stalls and saving the data after each one is not an additive process. The last one performed is all Skyview retains in memory.

2) If you perform a series of stalls prior to pressing the SAVE button (such as no flaps, partial and full flaps), all Skyview stores in memory is the highest angle of attack sensed during all those combined stalls. Again, it is not an additive process. In my example, since the highest angle of attack would be experienced with full flaps, only that stall/AoA would be written into Skyview.

The installation guide, pilot user's guide and on-screen instructions (see attached) don't really make the above 2 rules very clear.

Which is why I asked in my 1st post, how do pilots calibrate their AoA system - no, partial or full flaps and why?

Andre'
 

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Carl_Froehlich

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To answer the specific question, I calibrate the AOA with full flaps.

If I land with something other than full flaps I find the AOA still works, but tends to not be as critical as no flap landings are done at increased airspeed.

I also note AOA is much more informative with a nose gear plane than with a tail dragger when doing wheelie landings. But very nice indication when doing a three point.

Carl
 

andresmith76

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I heard an interesting debate that calibrating the AoA with no flaps might give the pilot better warning when performing maneuvers, such as circling tightly over a point, alerting the pilot before a sudden "moose stall" occurs and might be least expected. The flipside being as Carl mentioned, in a tail wheel full flaps are most likely used during landing, where a stall is most imminent and expected.

All in all, I suppose the calibration point isn't that critical. Dynon gives us the ability to fine-tune when the AoA tone starts and when the tone turns steady in the Setup menu (see pictures). Also - if a no flap calibration occurs when the chevrons 1st turn from yellow to red, then a full-flap stall might occur at the 2nd or 3rd red chevron. After some practice, the pilot would become aware at which flap setting these indications would appear when approaching a stall.
 

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sunfish

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I am getting a little confused here regarding the idea that the stall angle of attack changes with speed and / or flap configuration.

I was taught that the angle of attack at the stall is always the same, no matter what the load or speed or configuration.

While the speed at stall will vary with loading, G or configuration, the angle of attack does not. It is constant.
 

andresmith76

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I am getting a little confused here regarding the idea that the stall angle of attack changes with speed and / or flap configuration.

I was taught that the angle of attack at the stall is always the same, no matter what the load or speed or configuration.

While the speed at stall will vary with loading, G or configuration, the angle of attack does not. It is constant.
Adding flaps alters a wing's camber, changing the shape of the wing and increases the AoA:
 

sunfish

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Such is the over confidence of a new builder! Thank you for this thread! I am now totally confused as to what configuration to put the aircraft in and the power setting for AoA calibration. I thiiiink I may have had an incident a few weeks ago but didn’t realise until just now how close I may have come to disaster! I may be an accident waiting to happen.

Firstly, the aircraft is a zenith stol with fixed leading edge slats. It doesn’t really have a well defined stall “break”, it just starts mushing down rather fast. It’s easily recoverable from this situation - I think. It may have modes to “bite” an unwary pilot but I haven’t found one yet.

‘I calibrated the AoA IAW Dynon instructions and with flaps up and power set a bit above idle. I have not heard the AoA tone at all except for a second or two on rotation at takeoff with half flaps. Never heard it at all in flight, not even on landing flare.

‘’I’ve been thinking to myself “how great is this airplane!” “I can throw it around and it won’t bite because of those leading edge slats - and I haven’t even had a stall warning!”. Now it’s dawned on me that I may have just been very lucky so far.

My first error is thinking my “party trick” is safe - that is saving a high approach by closing the throttle - which results in an immediate, elevator like, high rate of descent until I open the throttle when I’m back on profile. I’m now not sure how close to the stall that condition is.

‘’My possible incident was a few weeks ago. I had a heavy passenger and was at close to rearmost CG. On landing I closed the throttle at about fifty feet and the aircraft dropped like a stone - no AoA tone either. I added power and saved the landing. It has just dawned on me that I must have stalled it without even noticing.

‘’From reading here and the reference I think I need to recalibrate the AoA and this time do it with full flaps and power right off at low idle. Does this sound safer?
 

andresmith76

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Absolutely sounds safer. Is there a manufacturer guideline or someone else's POH matching your plane that you can reference for their stall figures? That would at least get you in the ball park for your stall numbers.

Don't forget you should be doing these stall calibrations at a high altitude so you can recover safely.

As I posted earlier, when calibrating Dynon's AoA system the on-screen instructions mention you can perform a series of stalls before pressing the SAVE button. This way you can stall with the no/partial/full flaps scenario and you will save the highest AoA the system measured. Are you also using the Dynon pitot probe?

You story has a silver lining as you seem to have actually been flying your plane rather than depending on your avionics to tell you when and how to fly and land. Well done! Now you have a great hangar story to tell your pilot friends . . . or not ;>)
 
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swatson999

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I have to question why, after all these years, Dynon doesn't simply utilize flap position in the AoA indicator. Then it wouldn't be a problem, would it? (Of course, then I'll have to actually install one, but it's pretty straightforward :)).
 

Carl_Froehlich

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Keep in mind many builders use the “look out the window” flap position indicator.

I also suggest if you calibrate at full flaps you are covered for most applications.

Carl
 

GalinHdz

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FWIW My airplane only has two flap settings, 12 & 24 degrees. I calibrated my AOA at 1/2 flaps (12 degrees), set my audible tone to start beeping at the yellow zone and go solid at the red zone. I always land with full flaps so I use the tones to tell me how much to pull back on the stick. I keep the tones slowly beeping until just before the mains touch. An instant before the mains touch, I pull the stick back until the tone just turns solid and hold this attitude until the mains touch. With this AOA calibration and technique I can "grease" it in 99% of the times and my airplane is not known to be an easy airplane to "grease" it in. It works very well for me but YMMV

:cool:
 
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