In article ,
Edmond Dantes wrote:

Fred,
The thermal is giving you "free lift". Since the wing now doesn't
produce as much lift, induced drag is simultaneously reduced. With
reduced drag, airspeed increases.
Hope this helps,
Brad

There is no such thing as "free lift". The wing/tailplane produces lift
-- all of it. If you feel a push upwards, it is the wing doing it. As
you enter the updraft you get an increased angle of atack, increased
lift, increased drag, and upwards acceleration.

As noted by others, if you leave the stick in the same place then the
speed will increase due to stability making the glider pitch down, but
thsi will only be a very temporary effect and will dissappear soon after
the glider's vertical speed has equalized with the updraft -- which is
only a matter of a second or two. Consider that it's pretty common to
feel a half-G surge on entering a strong thermal, that a G is 10 m/s per
second, and that strong thermals are 4 - 7 m/s, and and it's clear that
the glider gains the upwards velocity of the thermal pretty quickly.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------