Garmin AOA calibration-different flap settings

116TP had its first light today. All went pleasantly smoothly.
Shortly, I'll be calibrating my AOA linked to Garmin g3x touch( dual screens).
I have flap position indication on my PDF.

Does the Garmin system (all Garmin avionics) store the settings dependent on flap position? Obviously, the stall speed is higher clean than full flaps.
So if I calibrate the AOA at each flap position does the AOA give stall indications based on flap configuration?

Thanks
Tom H

Pondering calibration myself. Did anyone find the answer to this question?

tomhanaway said:

Does the Garmin system (all Garmin avionics) store the settings dependent on flap position? Obviously, the stall speed is higher clean than full flaps.
So if I calibrate the AOA at each flap position does the AOA give stall indications based on flap configuration?

Thanks
Tom H

Click to expand...

Stall speed is higher clean, because flaps add lift. But the stall angle of attack of the main wing doesn?t care about the flaps. That?s why a conventional stall vane works for all flap settings. Same for AOA.

Thanks, Bob, I had to read that three times to understand such a simple thing. So, this means I can run the calibration clean and it will still be valid for various flap settings. Right?

That makes it much better.

Thanks again.

AOA

I looked this up recently and it?s my understanding that the Advanced Flight Systems AOA stores two data sets. One for cruise and one for flaps. It monitors the flap sensor (if one is installed) and uses the more conservative data set for reporting the AOA for flap settings in between clean and full deflection. I know you asked about Garmin but here is some documentation that might help. The manuals are a pretty good source of info on AOAs in general.

http://advanced-flight-systems.com/Support/AOAsupport/aoasupport.html

dhmoose said:

I looked this up recently and it?s my understanding that the Advanced Flight Systems AOA stores two data sets. One for cruise and one for flaps. It monitors the flap sensor (if one is installed) and uses the more conservative data set for reporting the AOA for flap settings in between clean and full deflection. I know you asked about Garmin but here is some documentation that might help. The manuals are a pretty good source of info on AOAs in general.

http://advanced-flight-systems.com/Support/AOAsupport/aoasupport.html

Click to expand...

That is certainly the case as I had Advanced AOA and you had to preform the calibration twice, one time with the flaps up (clean) and a second set of calibration with the flaps down. My GRT AOA which did not have sensor/calibration for flap up or down, was calibrated only with the flaps down and did not produce the same result when you approached stall clean.

Flaps add lift, but they also change the airfoil of the wing. Different airfoils stall at different angles of attack. When performing the calibration of the Garmin AOA, multiple power off stalls are flown at different flap settings. The G3X system will automatically use the most conservative value for the warning, but it doesn't distinguish between flaps up or down. Since the flaps on RV's are fairly simple, there is not a lot of difference in the angle of attach at which the airflow separates and a stall occurs. Once my G3X AOA was calibrated, I flew stalls at all flap settings and found that it gave me a warning before an impending stall at all settings. The AOA indicator may not tell me precisely when a stall is going to happen, but it is effective enough to tell me it's getting close.

The Garmim G3X AOA configuration page is found in section 34.4.7 of the G3X installation manual.

BobTurner said:

Stall speed is higher clean, because flaps add lift. But the stall angle of attack of the main wing doesn?t care about the flaps. That?s why a conventional stall vane works for all flap settings. Same for AOA.

Click to expand...

I know this is an old thread, but Im asking myself the same question and thought I correct the record. Flap position does decrease the wing critical angle of attack. Flaps also significantly increase Cl for a given wing AoA, in other words increasing lift at a given airspeed.

If your AoA indicator only provides for one calibration curve you have to decide which configuration you want it referenced to. Calibrating the curve with flaps extended is more conservative. With flaps retracted you would still have a few degrees of margin when your system is indicating stall AoA.

Power setting can also have a significant effect on critical AoA. A windmilling propeller will reduce critical AoA by nearly as much as extending the flaps. So again, a conservative approach (no pun intended) would be to calibrate your AoA indicator with a windmilling fine pitch prop and flaps extended.

One might also consider where to se the green "donut" or other flags in the AoA indicator. I plan to set the green "donut" at max L/D with flaps retracted, engine windmilling, and prop at coarse pitch to give me a target AoA if I had to glide the plane to a distant airfield. Another good choice would be to set it at the AoA corresponding to 1.3Vso at max gross, or or some other target approach AoA.

Quick Reference:
http://www.n91cz.net/AOA/AoA_Article_Web.pdf