Like I said, wingtips are a magnet for eccentric aerodynamics (and
aerodynamisysts).

One I particularly liked was a ram air turbine that popped out of the
wingtip when needed. It spun like a pinwheel in the tip vortex. The
inventor claimed it generated electricity from energy that would have been
wasted.

At about the same time as the red smoke photo shown on the minix site was
taken, I was working on a similar project to get some good air velocity
measurements in a wingtip vortex. Our idea was to fly an airplane through a
cloud of small helium balloons and track their 3D motion with an array of
35mm film cameras known as cine-theodolites.

As expected, the balloons became entrained within the vortex flow. What we
didn't expect was that the balloons spiraled inward to the vortex center in
a plane at right angles to the vortex axis. (The lighter than air balloons
were moving up the air density gradient.) When they reached the vortex
core, they raced away after the airplane in two parallel streams. The
balloons were moving at more than half the speed of the airplane. It was
fascinating to watch and we got some good data.

Bill Daniels


"Bob Salvo" wrote in message
news
Has anyone tried this? http://www.minix.fr/

Bob Salvo

"Bill Daniels" wrote in message
news:zTPfd.321990$3l3.156113@attbi_s03...

"CV" wrote in message
...

Another aerodynamic bone to toss around and chew on:

Instead of carefully crafted, expensive winglets, wouldn't
straightforward flat end plates serve nearly as well in
reducing wingtip vortices and improve performance.

Have they ever been tried, and with what results ?
CV



Wing end plates were a big fad in the early 1950's. It was found that
the
same or better improvement could be obtained by simply adding the same
area
to the wingtip as additional wingspan.

Messing with wingtips has a long and somewhat eccentric history. They
have
been bent up and down, swept forward and back, made wider and narrower,
sliced off at an angle or square, slots added and removed. Until
Whitcomb
developed winglets, everything else people tried had a huge drag
penalty.
Airflow around the wingtip is complicated. You really have to
understand
it
to extract any gain.

Winglets produce a real gain especially if the glider must remain within
a
span-limited competition class. They have the advantage of increasing
the
lift inboard of the winglet without increasing the bending force on the
wing
as much as additional span would. They also convert some of the energy
in
the wingtip vortex into thrust which is seen as a general drag reduction
in
the wingtip area. Think of the winglet as a sailboat sail that catches
some
of the inward flow on the upper surface and converts it into thrust.

Bill Daniels