"John" wrote in message
om...
Here is a thought:

Was in the back yard making thousands of soap bubbles (Mr. Bubbles)
for the baby. Slight breeze. Clearly could tell the entire airflow
pattern in the back yard....even a little ridge lift over the glider
trailer!

Wonder if you could add a soap bubble machine to a sailplane? Turn it
on when you first hit a thermal and a trail of bubbles is created.
After one circle, just fly toward the highest bubbles and that is
where the thermal's core is.

I could see the bubbles about 200 feet away, but might could add a
color die to enhance visibility further.

Any thoughts on this?

Sounds maybe a little silly but it's sound thinking. Way back in the 1960's
I worked for Paul McCready at a little company called Meteorology Research
in Pasadena, California. One of my projects was to develop techniques to
map boundary layer turbulence.

We had made the same observation you did that soap bubbles trace airflow
very well. The first idea was to generate a bunch of bubbles, film them
with a pair of carefully calibrated movie cameras to get 3D data and then
analyze the film to plot the individual bubble trajectories. We thought we
could do a lot of interesting science with this data. (With the Lawrence
Welk TV show the rage, you can imagine the reputation this project quickly
developed - Welk was a band leader who used soap bubbles on his set to
highlight his "champagne music")

There were several problems. First, soap bubbles don't last very long -
maybe 20-30 seconds outdoors. (It seems UV degrades the soap films.)
Second, even with dye in the soap solution, bubbles are nearly invisible.
We tried filling them with colored smoke which reduced the average bubble
lifespan to about a second.

Tackling the bubble half life problem head on, I sought the help of some
chemists at CalTech who recommended adding polyvinyl alcohol to the bubble
solution. With PVA in the solution, a solid PVA film formed as the PVA was
polymerized by UV. The PVA+soap film seemed to be pretty gas tight and the
bubbles lasted a long time, but now they were heavy and quickly sank to the
ground.

Back at the drawing board, we dreamed up a modified bubble machine that
allowed the introduction of a carefully controlled amount of helium. With
this device pouring out bubbles, we could adjust the helium needle valve
until the bubbles showed neutral buoyancy. Now the bubbles traced the
airflow streamlines perfectly, we just couldn't see them very well and the
cameras didn't see them at all. Welk wasn't impressed.

Now we were delving into bubble optics. We knew that tiny glass spheres
would reflect light back to the source since that is what is used in
reflective paint on highway signs. Would bubbles do the same? Yes, but
altogether too well. The little glass spheres in reflective paint are
deliberately flawed. Our bubbles were perfect so they reflected a
searchlight beam directly back into the searchlight. If you were standing
next to the searchlight, you saw no reflections.

Now we built a camera mount with a huge beamsplitter so the cameras could
look right down the axis of the searchlight beam. Success! Our little
bubbles shown like stars tracing every little twist and turn of the airflow.

So here's the scene, high noon in downtown Pasadena with a couple of rented
Hollywood carbon arc searchlights, 35mm movie cameras and billions of
bubbles drifting around the buildings. It took several hours and the
company attorney to convince the authorities we weren't filming a movie and
didn't need a permit to do so.

We moved the project to the desert. It expanded from bubbles to Mylar
balloons, dozens of cameras and produced mountains of data. Unfortunately,
the IBM 360 punch card computer we used wasn't up to the task of analyzing
all the data. Last I heard, the data were still being re-analyzed by each
new generation of supercomputer.

So, would your idea work? I proved it would but all that heavy gear will be
pretty hard to get into a glider. Throwing out bits of toilet paper
probably works better. Hmmm, Lets see.....what would a toilet paper
dispensing machine look like...

Bill Daniels