Sharing a thermal

"Nyal Williams" wrote in message
...
How much of this depends on the reaction time of the
vario?


A lot.

Most vario's have a time constant of about 2-3 seconds or more. I put a
bunch of different varios on a test bench last winter and found some were as
bad as 11 seconds. The average 45 degree bank thermalling turn takes about
13 - 14 seconds so a 3 second delay can be a quarter turn. Some vario's
respond more quickly with the onset of lift but can take much longer to
return to zero after the lift ends.

FWIW, Mike Borgelts varios were the best of the lot on my test bench.

This means that you have to pay attention to the "whack it the back" (or
"whump in the rump" in the case of a 2-33) feel as you enter a thermal. If
you must watch the vario, figure a 60 degree of turn correction for vario
lag.

All this points up the need for an "inertial vario" that integrates the
vertical acceleration to display rate-of-climb. An inertial vario would
have no lag, no noise since it is damped by the mass of the glider and
should be dead accurate. UAV MEMS AHRS (Attitude Heading Reference Systems)
with three orthogonal gyros and accelerometers are in the $1000 range.
They'd make a fabulous vario. I'd love to have an instrument with a 1:1
correlation with the seat-of-the pants feel.

Bill Daniels