Rag and tube construction and computer models?

On Wed, 7 Apr 2004 18:29:03 -0500, "Harry O" wrote:



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

It is interesting to look at the airframe of the nesmith cougar and
the w8 tailwind together. as you say the wittman uses the one tube for
each longeron. the nesmith steps down in diameter at every cluster.
the tailwind looks to be about half the fiddle factor of the nesmith.

in australia there was an eyeball designed high wing tube and fabric
that was in the run up to production when it hit airworthiness snags.
the CASA engineer determined (it I recall the secondhand info
correctly) that in areas of the fuselage it did not have sufficient
margins of strength. stress checking was then done (dont know what
method was used) to correctly match the tube sizes to the loads.
the second iteration of the design then went into production.

design as I recall was a knock off clone of an avid flyer or a kitfox
but I cant recall the design's name.

so yes there is an instance where a design was optimised by structural
evaluation after initial design.
TLAR only gets it correct is the eye is exceptionally practised.
(tlar - that looks about right)
Stealth Pilot
Australia