Bill Daniels wrote:


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

Yikes! I don't know what you are flying, but it takes my ASH 26 about 27
seconds to make one turn (50 kts IAS, 8000' msl, 8.2 lb/sq ft wing
loading). That's measured from a flight trace. My ASW 20 was a little
quicker, flying at 7.5 lb/sq ft, but nothing like 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.

How did the 302 compare, what did you have the time constants set at,
and where you judging by the needle or the audio?


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.

At least with my glider and my vario, it seems to be less than 20
degrees, and I can ignore it, since the glider doesn't respond quickly
enough. Flying small gliders (11 meter SparrowHawk, 12 meter Russia,
etc.) will surely change the equation.


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.

I'm guessing the hard part for an inertial vario would be ignoring stick
thermals.


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Eric Greenwell
Washington State
USA