On Sep 28, 10:45*am, Chris Nicholas wrote:
This is pure speculation, but I wonder if Prof Frank Irving’s
preference for the probe pointing downwards is because in his day, and
particularly in the UK, cloud flying was commonplace.

It follows that accumulation of water droplets on the probe was also,
common. *After only a few minutes in cloud, it is usual to find that
the vario starts misbehaving. (I find that typically, it suddenly
stops displaying rate of climb accurately, and then flicks to a
different reading, then settles back to something sensible for a few
seconds, and then repeats the cycle. I put this down to water droplets
accumulating, to the point that they block the tiny holes in the
probe, then suddenly get freed, then repeat the cycle. I have no means
of knowing whether my speculation in this respect is accurate.)

*Anything that can delay that, or at least get rid of surplus water
droplets so that the vario returns to functionality for a few seconds
at a time, is probably worth doing.

If you're not flying where water droplets are likely to accumulate on
the probe, other things being equal it seems to me that keeping it as
far from disturbed air over the wings as possible is a good thing,
hence up.

Just my two cents worth.

Chris N

Gliders with short rear fuselage mounted TE probes often suffer from a
flickering and false vario reading when flown at high angles of
attack, as in a thermalling turn. I assume that this is because of
interference from turbulent air coming off the wings. I have also
experienced this effect with some fin mounted probes. I would point
the probe upwards to keep it as clear as possible from any wing
turbulence.

Derek C