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I tried making a 31' arc for the top of my minivan (as described in a previous thread as a 5.64x ht). Found that it was very hard to define the correct shape. First tried string. I was fighting string stretch and gravity. My second attempt was to use a steel tape measure. Not much better. My attempts have been thwarted to get any kind of accurate shape.
A different approach is required. I could calculate the saggita of the chord that I wanted and then flex a 1/4" x 6' rod to give me that much sag.It would give me an approximation of the curve at least of the central regions of the flexed rod. The sag formula is s=r-sqrt(r^2 - l^2).
One method of construction would involve flexing 1/4" steel rods into the shape and then welding them together to form a removable frame work that could be covered with dacron fabric like a light airplane fuselage
The curve of a 2 foot long piece only has about 3/4" of saggita.
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