"Oliver Arend" wrote in message
...
After reading

http://www.faa.gov/aircraft/gen_av/l...dia/Zodiac.pdf

I'm wondering how much trouble is hidden in other kitplane designs?
Obviously, the RV fleet seems to be rather untroubled, but the others?
How much design work is really going into kit planes? Or is it
eyeballing/judging from experience for the most part?

Oliver

Often the designs are performed by well meaning backyard designers that
borrowed a design from another ship that they saw flying and assumed it to
be good. In fact a noticeable test for reliability has been noticed
occurring so often that I've coined an ancronym for it: NHFY. None Have
Failed Yet. That is exactly the statement I've heard when reliability was
questioned. I've heard people say things like "Herby has been flying his
ship with that design for 5 years" A closer check shows that yeah Herby has
been flying on the average 10 hrs/yr. and has accumulated the total of 50
hrs on that design. In some cases the shafts had very sharp stress risers
machined into them but the NHFY said they were reliable. In one case a
simple seal w/o the normal spring insert, chewed a 0.020 jagged groove in
the shaft. The designer was aware of this problem for several years but
elected to use the NHFY reliability test.
It pays to look into the specifics of the design and might even pay to have
an experienced engineer take a close look. Vans anodizes the RV wing spars.
Anodizing aluminum reduces the fatigue life by as much as 50%. Van knows
this and takes it into account in his design to achieve a safe aircraft.
Other designers see the use of anodizing and use it without having the
technical skills evidenced by the RV crew. Numerous examples of violation
of "Good Practice" can be seen in numerous aircraft at various fly-ins. If
some of the judges used at these events could be of higher technical and
experience background, some of these things could be found and pointed out.
E.G. A Oshkosh Grand Champion rotorcraft had anodized aluminum control
tubes that failed in fatigue. The pilot survived. Up until then NHFY
worked.