Here is the detailed picture I meant to send. The built up "beam" has round tubes top and bottom with round tube shear web bent and smashed so to allow riveting to the top and bottom tubes. This was a very early 80s design and the problem at SunFun was that it could not fly all with the other ULs during the UL Show Case where none of the ULs were supposed to pass each other. In 80 and 81 etc lots of the ULs were still flying 15 and 20 hp motors... This was before Rotax. The empty weight was 188 and max speed was 85 with a 25hp motor. Take another look at that spar and MARVEL. I once talked to the designer and at the showIt looks [to me] like the spars are rectangular bar?!
1) The ratio of moment of inertia to weight per unit length should be optimized.I expect there are several unspecified assumptions among those making the negative statements about tube spars. I have the following questions.
What are those assumptions?
Well that certainly discourages low fly-bys.I've got your proper engineered tube spar, right here. ;-)
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That's the counterweight arm for a 10' X 30' one piece door. The 6" irrigation tubing had a bit more flex than my redneck TLAR engineering felt would be safe. So there's a 10' run of 5 quarter X 6" treated deck board on edge inside, centered at the top hinge point. If memory serves, there's about 90 lbs of lead & steel up at the top. The door is classic tube (irrigation) and gusset (road signs) construction. I could write a book about the things that are wrong with it. An actual 2nd year engineering student could probably fill a semester. But it's survived about 15 years, so far. The bigger door in the background actually had some calculations (back of envelope) go into it.
Works fine to put a plane in; not recommended to put in a plane.
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IIRC they even managed to etch a taper in the wall thickness by standing the spar on end and either slowly filling or slowly draining the etching acid. I forget which.Contrary to popular opinion, the Gossamer Condor used an aluminum main spar, chemically etched in a pipe to thin the outboard sections.
That is because Volksplane rudder tubular spars serve two functions: structure and hinge. Using one component to serve two functions often simplifies construction and weight.The T/S-18 stabilator uses an aluminum tube for the spar.
The Evans VP’s use an aluminum tube for the spar of the flying rudder.