In article ,
Robert Ehrlich wrote:

If you consider
two polars, e.g. for zero setting and the first negative setting,
they intersect each other at some point. At speed above the
speed of this point, clearly the negative setting is better,
at speed below this point, the zero setting is better. But it
is not optimal to switch the setting juste when you cross this
speed. Above the intersection, the two polars have a common
tangent which meets each polar at some point, corresponding
to some speed, a low one for zero setting and a high one
for negative setting. You should never fly a speed between these
both speed

Another alternative is to use a flap setting between the detents while
in that speed range.

The performance difference is likely to be minor in any case.

When I fly the Janus -- the only flapped ship I fly, and which (as you
note) gives individual polars in the manual -- I tend to choose between
the lower and higher flap setting based on what I and the air are likely
to be doing. For example, when flying in the 50 - 60 knot range, if the
air is smooth (e.g. in wave) I'll fly in zero flap. If the air is bumpy
and I'm turning from side to side looking for a thermal then I'll use +6
becasue I figure that the better response and performance at the higher
AOA in a gust will outweigh the little extra drag the rest of the time.

At the other end, it was I think the Dick Johnson report that claimed
that there was no speed range in which -4 was better than both 0 and -7,
so don't use it.

-- Bruce