Hi Gang
I have received an enormous number of responses to my original posting
the use of negative flaps to improve effective aileron control while on
the ground. I think I now have a reasonable understanding of the issues
involved and would like to present a summary of my understandings.
Probably the worst situation occurs with flaperons whereby the flaps
are combined with the ailerons from the wing tips to the root of the
wings. I own 2 gliders - a Stemme S10 VT and a DG800B that have these
flaperons and these 2 ships are difficult to handle in gusty conditions
both on the initial role and breaking on landing. Definitely not entry
level gliders!
So lets make sure we first agree on some of the fundermentals:

1) The angle of attack AOA of the wing is defined by the angle between
the cord of the wing and the effective direction of the flow of the air
that the wing is moving in.

2) The stall of a wing (or a plank of wood) occurs when the AOA reaches
about 17 degrees IRRESPECTIVE, to the first order, of the speed that
the wing is moving through the air whether it be 5mph or 150mph. For
almost all wings ever invented the stall AOA is between 16 and 19
degrees. This is a remarkable fact - not intuitively obvious. Onset of
stall is loosely defined as a dramatic drop of lift.

3) As the AOA of a wing is increased from zero lift also increases
somewhat linearly to an AOA of about 8 degrees. Then the rate of
increase of lift decreases for a further increase of AOA and lift
reaches a maximum at around 12 degrees (minimum sink). At AOAs greater
than 12 degrees lift then diminishes at an ever increasing rate so that
around 17 degrees lift is a small fraction of what is was at 12
degrees. Note that, AND THIS IS EXTREMELY IMPORTANT, except at minimum
sink there are 2 AOA values that will give the IDENTICAL value of lift.
I will show this to be the Archille's Heel for many of our low speed
control problems.

OK now a typical situation with a flaperon ship such as my Stemme on
initial role say with 5 degrees of flaps. The tail wheel is on the
ground and the Stemme, because of its high undercarriage, is pointing
its nose upward. The AOA of the wings are around 12 degrees near
minimum sink. A gust hits me from the side and a wing drops. I react by
full aileron usage and the wing I am trying to lift now has an
effective AOA of 16 or 17 degrees whereas the opposite wing has an AOA
of 7 or 8 degrees. Which wing has the highest lift? The stalled wing
or the one with the AOA of 8 degrees? THE UNSTALLED WING has the
highest lift! In other words the the aileron control has reversed
itself and I am aggravating the problem rather than solving the
problem. If I am unlucky the wing that the gust has hit will itself hit
the runway through my over reaction with the ailerons. What should I
have done? 2 things - the first started off with negative flaps and
secondly have been gentler on the aileron control. In so doing the AOAs
of both wings would have been less than 12 degrees (minimum sink) and
aileron control would be normal not reversed.

Lets recap for a moment. What I am saying is that, if the AOA is
around 12 degrees (minimum sink), and you use use full aileron
deflection, you have a good chance of reversing the operation of the
ailerons. On the ground that means loss of control and in the air the
very real possibility of a spin. All this because there are 2 values of
AOA that give the same value of lift. The only exception is exactly at
minimum sink.

OK What to do? Clearly if you have flaperons use negative flaps for
the initial roll until the tail comes up and then go to whatever the
book says (normally 5 or 8 degrees positive). On landing do what the
book says and then on braking go to full negative flaps. Avoid large
movements of the ailerons. Don't over react!

I would recommend for all gliders that you be aware of the effective
AOA of the wings with the tail wheel on the ground. Some gliders such
as the Mosquito, I am told, are in a stalled condition until the tail
is raised. Again small movements of the ailerons are called for and get
that tail wheel up as soon as possible. Know your glider.
Dave

PS It is claimed that spoilers improve low speed aileron control. Well
maybe. How about someone figuring out in a rational manner if this is
so. I would be real interested in the science if it were shown to be
true.