Re: Space Age

[XURQ03A@prodigy.com ( LEE A HART)]

Chris Pollard wrote:
> it has been shown that the drag coefficient can be reduced below
> that of birds and fish.  Sailplanes have better glide ratios and
> fish aren't that good.

This is the conventional wisdom. If you assume that a rigid shape is "best",
then look for that shape, you find that a teardrop shape is best. If you
assume that laminar flow is "best", then hard, smooth surfaces are best.

The trouble is, what if these assumptions are wrong?

When Captain Cook discovered the Hawaiian Islands, he reported in his log that
the natives saw his ships coming, sailed out in their dugout canoes, circled
his ship, and returned to land ahead of him.

Cook was a taciturn man, not inclined to put frivilous "tourist" information
in his log. Why did he make this note? Because he was sailing what he believed
to be the best sailing ship in the world, absolutely state-of-the-art. He knew
that the bigger the ship, the more sail she could carry and the faster she
could go. So how in hell could these natives sail rings around him in one-man
canoes?!?! It's because they *****BRRRIIINNNGGGGG****  sorry, there goes my
off-topic alarm. :-)

Anyway, conventional aerodynamics theory isn't the whole story. Towing a dead
fish does say it has a higher drag coefficient. But a live fish is a different
story; it uses far less energy to swim than its drag coefficient would
indicate. Look for an article in Scientific American about a year ago on
"Robo-Tuna", an attempt to understand this phenomenon. It has the details and
references on this phenomenon.

Also check the "Experimenter", the monthly journal of the Experimental
Aircraft Association. An article within the last 6 months reports on propeller
shapes that are not airfoils, and yet produce more thrust for a given
horsepower, and make less noise doing it. They have an odd step that
deliberately creates turbulence. The results have been independently confirmed.

EAA also reported within the year on the result of deliberately dimpling
surfaces, like a golf ball. Briefly, they say that dimpling right at the
widest part of the body, where the airflow would detach, increases drag
coefficient but reduces the thrust needed to push the aircraft forward through
the air.

If it's worth my while I can dig up exact references (but hey, you gotta do
some things for yourself :-)

> PS Why would you want a practical vehicle that rode on the bow wave of a
> ship or the vortices of a sailplane?

Imagine that you could ride the "bow wave" of a tractor-trailer to save energy.

Suppose a race car could ride it to *lead* instead of follow an opponent's car?

Or a method so military aircraft could achieve longer flight distances by
flying in just the right formation?

Lee Hart                     If you would not be forgotten
4209 France Ave. N.          Soon as you are dead and rotten
Robbinsdale, MN 55422 USA    Either write things worth the reading
phone (612) 533-3226         Or do things worthy of the writing
e-mail XURQ03A@prodigy.com   (Ben Franklin, Poor Richard's Almanac)