"tango4" wrote in message ...
On an aircraft like the ventus there are several sections of control surface
along the T/E of the wing resulting in several 'breaks' in the trailing
edge. My question is - Are the breaks or corners of a deflected control
surface the source of their own little vortices and therefore additional (
very small) drag? I know that the inboard end of flaps is an area that
causes a lot of problems, my ventus has fences fitted there and some people
fit fences to the aileron joints. Just how much drag difference do aileron
fences make given that they increase the wetted area by several square
inches themselves?

Ian

The outboard end of a deflected flap can produce a very strong vortex.
You can see this from the ground (or the back of the cabin) when
alomst any transport category aircraft is on approach to land on a
humid day.

As you correctly point out, the addition of a fence is a tradeoff.
Since the flap is not always deflected, there is an additional duty
cycle tradeoff, because the fence is always in the flow.

There is also a safety tradeoff, since the fence can fail and jam the
control surface. A jammed flap is manageable, but a jammed aileron is
not.

My general understanding is that aileron fences are usually added to
enhance aileron authority, not to reduce drag directly. There may be
an incidental reduction in drag by using a smaller control surface
with fences, however.