On 07 Apr 2004 22:31:51 GMT, (BllFs6) wrote:

Mr Hoover

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

Let me take another stab at this....

Take some "typical" rag and tube design that your "cost challenged"
homebuilders are building these days with minimal tools and skills....

Most likely (IMHO) it is of a design that was not computer
optimized....somebody long ago probably just eyeball/rule of thumb/comparision
with previous successful designs engineered it till it seemed light enough,
simple enough, and when given the static loads it was likely to encounter it
didnt break.....at which point the designer said "praise the lord" and moved on
to other tasks....

Now, take THAT design, and do the modeling (of course the modeler needs to KNOW
what they are doing)....

Look at the computer results....the model might show some areas that have ALOT
of stress.....which at the very least tells the builder "make sure THOSE welds
are damn good".......

or the model might show some tubes are under very low tension compared to its
strength .....so you realize you can spec out those tubes one or two standard
sizes down in diameter/thickness.....without any penalties

Or the model might show an area prone to buckling which when fixed with an
extra brace adds only a little weight to the overall structure but makes the
entire structure significanty stronger (ie high rewards to cost ratio there)...

Or by playing with the model you might find out that you can leave out this
tube here, that tube there, and those over yonder and you've lost little or
nothing in the strength of the design.....

I understand what your saying about the big projects....you optimize the design
in a biggggg way and then special material or sizes are no big deal.....

I'm asking/proposing the opposite....take a standard design....and see if you
can tweak it and still use standard materials and parts....and with a little
luck you might end up with something that is a bit lighter or stronger or if
you are really lucky has a lower part count....

The good thing about that kinda project is the only thing its gonna cost you is
your computer time (assuming your using free software)....

Just some wonderings on my part....

take care

Blll

Bill, my understanding of the most certified tube and fabric airplanes
is that they WERE structurally engineered using the old methods of
analysis. I would guess that you might save a pound or two off the
J-3's fuselage but then again, maybe not.

I'm building a Christavia Mk 4. The designer, Ron Mason, deliberately
overdesigned it. It's way heavier than it needs to be but he has his
reasons for doing it that way. I'm not happy with the extra weight
but I'm not a structural engineer and I'm not about to second guess
him. He designed the airplane with missionary use in mind and
pictured it pounding along in jungle thermals over gross. Then he
added a fudge factor for idiot/unskilled builders and you end up with
a really really stout airplane, but heavy.

Like I said, he had his reasons.

Corky Scott