On Mon, 24 Feb 2020 23:21:59 -0800, Bret Hess wrote:

These are journalists describing science. I think more accurate would be
"these vortices are a consequence of the process of generating lift with
that wing". They create drag, which we don't want, but they come with
the lift which we want.


Yes, that's fair. A wing can't generate lift without generating tip
vortices. The energy used in spinning them up adds to the aircraft's
sinking speed, but clever wing design, which may include winglets and/or
wingtip shaping as well as a carefully designed wing planform can reduce
the energy that goes into spinning up tip vortices and hence will reduce
the sinking speed of the aircraft.

For a very readable account, try "Affandi Darlington on winglets", which
first appeared on PPrune but may have vanished unless The Wayback Machine
has a copy. I have a local copy I can send if you can't find it anyplace
else.

Peter Masak's "Winglet Design for Sailplanes" and Wil Schuemann's "A new
wing planform with improved low-speed performance" are both worth
reading. A web search will find the Masak paper and Wil Schuemann's paper
is in the Soaring Symposium archive.

When I developed my 'Delta-G' series of F1A class competition free flight
gliders, I used a combination of Wil Schuemann's planform ideas, first
seen by glider pilots on the S-H Discus, combined with Hoerner wingtips,
also common on gliders from the first glass airframes until winglets took
over, and had decent competition results with this series of models.


--
Martin | martin at
Gregorie | gregorie dot org