Robert Ehrlich wrote:
Mark James Boyd wrote:
...
I did a few calculations of an imaginary glider with a stall speed
of 32 knots, a min sink speed of and
a wingspan of 87 feet.

In a 50 degree bank at 54 knots (good thermalling speed if you
believe)

www.stolaf.edu/people/hansonr/soaring/spd2fly/

the fuse and ASI says you are at radius 180 ft circling every
7 seconds. The inner wingtip is 3/4 of that distance, and
3/4 of that airspeed, and should be stalled. The outer
wingtip is 5/4 of that distance from center, and 5/4
of that airspeed, and producing excellent lift.
...

I don't completely agree with your computations. I agree with
the 54 knots, i.e. 43 knots multiplied by the square root of
the load factor at 50 degree bank. However the radius I find
for this speed and bank is 66 m (sorry, I prefer to do my
calculations in metric, because I know the formulas for metric
data), i.e 216.5 ft. A wingspan of 87 feet translate into 26.5 m,
the inner wingtip is inside the circle by an amount which is
the half wingspan multiplied by the cosine of 50 degree, this is
8.5 m or 27.8 ft. The ratio of the two radii is .87 rather than
.75 and the speed at the inner wing tip is 37.4 kt.

I forgot to change the wingspan to 90 feet to make the
math easy. Sorry. I was really just trying to make the
point that the wings have different airspeeds, and this is significant
at high bank angles and low speeds with long wings. If
this is untrue please let me know.

The bigger error of mine that you pointed out
was that I did the radius calculations assuming the wings
were level. This was incorrect on my part, and resulted
in a fairly large discrepancy....


Anyway even with your values tis doesn't implies the inner wing tip
is stalled, because stall depends on AOA rather than speed. Of course
you need an increase of AOA in order to compensate for the
lower speed in order to keep an equal lift on both wings. Some difference
in AOA between both wings is already provided by the simple fact that
the glider is sinking, i.e. both wings have the same vertical component
of velocity but different horizontal ones. The complement is provided
by aileron deflection, which change not only the AOA but the whole
airfoil shape, so that the action is an increased Cl due to both changes
in AOA and shape. The stall case would be if the needed Cl would be higher
than the maximum achievable Cl, but this can't be decided just from the
value of the speed at wing tip.

Exactly why I think AOA indicators halfway+ down the wings
would be nice. I've never heard of them on any gliders.
Why is this?