Hi Neal

Your statements are not in contradiciton with mine... And I already mentionned the limits of this sooner in the thread:

The key factors to assume that flaps have little influence on stall AoA of the aircraft a

1)simple airtight whole span flaps, I could add small chord ratio, the kind of flaps we only have on gliders, in summary...

2)low deflection angle, say lower than +-10 degrees to give indicative numbers

3)experimemtal data with a side string: I haven't noticed a significant difference of the side string angle when buffeting and loss of control starts through the whole flaps position range.

There is relatively few publications regarding the above conditions... Please let me know if you find some.

The idea behind the AoA indicator is to help setting the flaps in the right position during normal transition flight, so the first expected pilot's reaction is to adapt the flaps to stay at the right angle whatever could be the wing loading and other factors.

Another useful AoA value corresponds to the lowest sink rate, as you can see on speed polars the lowest sink speed range in relatively narrow and there is about a 10km/h margin between the lowest sink and the complete stall, where the sink rate increase abruptly... If you want to climb, you must avoid this range... And the only instrument that can give you an idea when you are thermalling with a continously changing speed and load factor is the AoA... And this is also in this configuration that safety comes into play.

In the case my sidestring had shown a different critical angle for different flaps position, I would have set the stall point with the maximum positive position before landing postions. So I have a right idea of my margin when thermalling. For any lower flaps position, the stall AoA could only be a few degrees higher... So I'm on the safe side through the whole flight envelope, except maybe with flaps in landing position...

At the recommended approach speed, the AoA with landing flaps is very low, giving a huge margin to reach stall, and in this configuration the goal isn't to be near stall angle, it's to stay at or above approach AoA. And on most if not all gliders the recommended flaps position in gusty contitions is not landing, ist last positive to keep more ailerons control... And this is where the AoA should have been tuned for stall...

And finally, for most of the gliders, you have no flaps to worry about... And the AoA remains a precious helper, specially at low speed when thermalling.

In practice, I think that this simple and cheap AoA indicator is much more than an additional gadget, it gives more significant information than the ASI through the whole flight envelope and an accurate stall warning.

So I don't know if I measure the true AoA... Maybe by chance the instrument gives the same indication as the sidestring only because it sustains the same perturbation and that by chance this perturbation compensate exactely the difference of critical AoA with the flaps for my DG-800B glider only.

But I'm confident that it should work on any glider. I will check this soon on my club's ASK21 and a Ventus 2cxa...