"John" wrote in message
om...
Bill,

Are you still using the AOA indicators made from yaw strings? Which
glider type is it mounted on?

I have tended to use them with new gliders to calibrate my seat of the pants
feel near a stall. Once my senses are atuned to the glider the strings are
no longer neccessary. I have tried them on a Lark IS28, Blanik L-23 and a
Nimbus 2C. The string indications were simular on all.

I assume these strings would be forward, so you visualize them at the
same time you see the normal yaw string. Is that correct?

The strings need to be as far forward as possible to get away from the
near-field flow over the wing. If I recall my Aerodynamics 101, the perfect
place for an AOA sensor would be about 10 wing chord lengths ahead of the LE
on a nose boom. The best practical position is near the forward end of the
canopy side frames. This happens to put them in the pilots field of view.

The 3D flow over the glider's nose seems to amplify the response of the
strings to changes in AOA so don't expect the string angles to represent the
actual AOA. While the absolute accuracy is terrible, the indications are
very repeatable and once calibrated to the three critical AOA's, they do
give useful data.

The biggest problem is that they are highly sensitive to yaw angles but if
both strings are giving the same indication, the yaw error is cancelled out.
Another nuisance issue is that the strings tend to get sucked under the
canopy frame as it is being closed trapping the strings.

Bill Daniels