Chris Nicholas wrote:
Now, why does opening the airbrake (usually called spoilers in the USA
for some unknown reason) help on some gliders? And did it ever help on
gliders that really did have spoilers (UK-speak for things that spoil
lift but don't add much drag, unlike airbrakes [in UK-speak], which do
both in spades)?

The best argument FOR this technique was presented in Soaring magazine
quite a few years ago.

At low speed the wing is producing some lift over the entire span.
This provides a damping effect to any rolling tendency. Imagine a
whole bunch of weak springs attached to the spar every few inches and
attached to the ceiling. The plane will resist a wing drop. Now,
remove the springs in the spoiler region and the glider will tip more
easily, as there are fewer springs working to keep it level.

So with the spoilers extended, the wing is easier to pick up as the
aileron has a little bit less force to fight.

Another argument is that on some wings, the turbulence caused by the
spoiler might help attach some flow to the aileron.

In any case, then next time you're sitting in the glider waiting for a
tow and there's a bit of a breeze on the nose, try some experiments.
Have someone hold your wing level, then do some slight rolls with and
without spoilers. I have found that there is a slight but noticeable
increase in response with the spoilers open.

-Tom