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<DIV><FONT face=Arial size=2>If a pilot can't break an airframe - it's too
<STRONG>heavy</STRONG>. That being said, I've used 3/4" o.d. 0.027"
wall 6061-T6 aluminum tubes in 7-8# 60 size pattern planes without problems. I
tested these by supporting on the ends and adding barbell plates in the
middle (more severe than in normal installation), and measured about 1/4"
deflection @100#. Failure was about 110#. The 7/8" x 0.035" tube normally
used deflects about 1/16" with 100#, I've not loaded one to failure. So -
even the small tube would handle 10G's in a 10# airplane. It would be
interesting (and maybe exciting) to load a 7/8" CF tube to failure. I'm not
surprised that the failure point is the tube mount in the wing foam. It would
also be interesting to use a G-force sensor with a data logger to get some real
load data.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>Earl</FONT></DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=bob@toprudder.com href="mailto:bob@toprudder.com">Bob Richards</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=discussion@nsrca.org
href="mailto:discussion@nsrca.org">discussion@nsrca.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Saturday, January 08, 2005 7:56
PM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> Re: Wing building</DIV>
<DIV><BR></DIV>
<DIV>IHMO, if wing tubes are being bent (and there are reports to that effect)
then the plywood support ribs are a moot point.</DIV>
<DIV> </DIV>
<DIV>If we go to stronger wing tubes, then the weak point will move somewhere
else, probably the ribs or whatever is used to support the wing tubes.</DIV>
<DIV> </DIV>
<DIV>It appears to me that over the last 10 years, a lot of effort has been
put into designing weight out of our planes. It all started, or certainly
escalated, when the engine size restriction was lifted. I remember
thinking at the time that people would use the biggest engines they could
shoehorn into the plane, and the airframe strength was going to be compromised
to stay under the weight limit as a result.</DIV>
<DIV> </DIV>
<DIV>There have not been, to my knowledge, very many in-flight structural
failures, so we keep shaving stuff off our airframes. Now we have a schedule
with a real stresser of a maneuver. Snap -- literally! Guess we need to put
something back in the plane!</DIV>
<DIV> </DIV>
<DIV>I also think it was interesting that none of the pattern planes were 2m
UNTIL there was a 2m limit. Nevermind that we did not have the horsepower to
effectively fly a plane that size, or that a 2m airframe was even optimal, all
of a sudden everyone had to have a 2m plane.</DIV>
<DIV> </DIV>
<DIV>The F8F Bearcat from WWII had wingtips that were designed to blow off if
the stress limit of the plane was exceeded. Maybe that is what we need now.
:-)</DIV>
<DIV> </DIV>
<DIV>Bob Richards.</DIV>
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