I remember using one of the first finite element programs outside of the
aerospace industry. Back then, you did not have a nifty program to create
all the "bricks" something was made up of. You had to define each node in
three dimensions -- and then define the end conditions at each node in 9
ways (3 for each dimension). Took a lot of work. Then it was sent by
telephone to St. Louis (to McDonnell-Douglas I believe) for processing. The
results were sent back by telephone in one or two days. No graphs. No
colors. Just numbers. The last finite element program I used was on a PC
about 10 years ago. Much easier. As you may have guessed by now, I am a
registered structural engineer.

Anyway, to get back to your question, it depends. I have run some tube and
fabric designs through finite element analysis. If you were to check the
Tailwind design, you will not find ANY reductions in tube size or thickness.
You will undoubtedly find some suggested tube increases. I checked the
design on one of the later programs and also built a Tailwind airframe. I
believe that he probably used every tube size and wall thickness there is
available in that design. There are little itty-bitty tubes branching all
over the place. I know Steve's design has a long history of troublefree
use, so I would be suspicious of the finite element model. I did not have
the inclination or time to refine the model any more.

If you were to check just about any of the EAA airplanes (such as the EAA
Biplane or the EAA Acro Sport), you will find many reductions in size or
thickness. I believe that the Poberezny designed airplanes were made
"hell-for-stout" for beginners and also to minimize the number of different
tube sizes needed. BTW, I looked carefully at the designs for these, but
did not do an analysis of them.

I doubt that optimizing the EAA airframes (metal tubes only) would cut more
than 10 pounds from them. If you were to race airplanes (like Wittman did),
any improvement would be worth the work. If you don't, is it really that
important? Each designer decides that himself.

"BllFs6" wrote in message
...
Mr Hoover

Another good/interesting point by you as always and I "grok" what your
saying....

snip

Just some wonderings on my part....

take care

Blll