AOA Systems - Must They Account for Flap Position?

[maxmirot]

I would think 1/2 flaps would give a margin of safety.

I think the Onspeed folks showed that the RVs have almost the same calibration curves for clean and dirty. That's reassuring in Dynon's case

[rongawer]

Stall speed will be higher clean than dirty, but that is a function of the extra lift the flaps provide. However the angle between wing chord line and relative wind at stall is constant and is irrelevant of speed or flap position. The GAP 26 works on the differential pressures forward of thickest part of the wing (required to be within 25% of the total chord line, measured from the Wing Leading Edge (WLE), but could actually be forward of the WLE by 2"); these differential pressures are completely a function of wing chord line and relative wind. Note that there are four different available calibration points available for the G3X AOA.

Go have some fun with the AOA and you'll find that once calibrated, the alert setpoints will occur at the same stall angle for each of the flap positions, but simply at different speeds.

AOA is a wonderful tool for picking target approach speed, which will change at different aircraft loads and ambient conditions, or making a short approach or up hill landings to places like Johnson Creek (which is simply beautiful, btw). The speeds will change, but the stall angles won't.

[Carlos151]

Originally Posted by RV7A Flyer

This would be one of my very few gripes about the Dynon system...it doesn't use flap position as an input to the AOA indication. I've requested it for years, but it never seems to make it onto the list of improvements.

Pretty sure you can calibrate the AOA for any flap position. Right out the Dynon installation guide:

“Refer to the list below of the stalls recommended to complete the user calibration. The general idea is to record stall data to find the lowest angle of attack stall. The list we have suggested is a starting point and produces a good calibration under most circumstances. However, if there are flight regimes not listed that you suspect would create stalls at lower angle of attack it would be good to record those as well.
 With full power, no flaps
 With no power, no flaps
 With full power, full flaps
 With no power, full flaps”

[rongawer]

Originally Posted by Carlos151

However, if there are flight regimes not listed that you suspect would create stalls at lower angle of attack

Stall will always, always, occur at the same angle of attack for a given wing.

[Carlos151]

Originally Posted by rongawer

Stall will always, always, occur at the same angle of attack for a given wing.

Never said it wouldn’t!!
The given wing changes with the flaps deployed but on our airplanes the change is minimal. Start adding leading edge devices and slotted flaps, now you’re really changing that wing shape and thus the lower stall speed for that different shape. The only thing you’re doing when calibrating the system is setting the AOA window for your airframe.

Totally agree with Lenny that the stall speed on an -8 is virtually identical flaps up or down. Maybe 1 knot difference if I looked at it really close