jcarlyle wrote:
I've never flown a plane with an AOA meter, so I don't understand how
it would respond during changing conditions:

I haven't either, so the below is all theoretical, take it with a grain of
salt.

(1) In landing through a wind gradient, I assume the AOA suddenly
increases as you drop into the slower wind? I assume this because I
know you're closer to a stall when the wind suddenly slows and the ASI
decreases, but I don't understand the relative wind change needed to
cause an AOA change in this situation.

Right, the AOA increases. On a very short timescale, when you drop into
slower wind, your airspeed decreases. This then decreases the amount of
lift your wings are developing. The lift they create is now less than your
weight, so you begin to drop. As you drop, the relative wind becomes more
vertical, increasing your AOA and the lift created by the wings. Once the
AOA increases to the point where the lift balances out your weight, you
reach a steady state again at a slower airspeed and higher AOA. If the AOA
reaches the stall angle before the lift increases to match your weight,
you'll stall, and this is why you should carry plenty of extra speed in
that situation.

(2) What happens in a turbulent thermal? When you fly a thermal using
a constant attitude it's common to see fairly definite ASI changes -
what would an AOA meter show during this situation? I assume the AOA
would change as the relative wind changes, and that you would still
fly a constant attitude much as you do with an ASI.

Turbulence would bounce it around similar; if you get hit with a gust from
below the AOA will momentarily become larger, increasing the lift from the
wings. You then begin to climb until your vertical speed matches the gust
and your AOA goes back to what it was. Similarly with a gust from above,
where you start to drop.

In both of these situations the ultimate question is: why would an
AOA meter be better than an ASI? I'm guessing the AOA would be good
upon entry so you would know what attitude to maintain, but I think it
wouldn't necessarily be any better than an ASI once you were into the
changing situations described in (1) and (2).

I think the advantage in a thermal is that the optimal airspeed changes
with bank, whereas the optimal AOA doesn't change. Instead of trying to
figure out the best airspeed to track as you keep altering your bank to
center the thermal, you can just track a single AOA all the time.

For landing I think the advantage is just that you can stick a warning
signal around the stall AOA to remind you to stop hauling back on the
stick when you get too close to a stall.

--
Michael Ash
Rogue Amoeba Software