Half a Catenary Curve?
- This topic is empty.
-
'Half' a cantenary curve will have no measurable difference than a 'whole' cat curve with less curvature. The catenary curves used in tarps and tents are just a tiny piece of the bottom of a very large catenary curve and are nearly identical to a circular arc (blue in picture below). As such, it doesn't matter which piece of the circle you use, they are all the same.
When I developed my catenary curve spreadsheet, I plotted a number of cat curves vs circular arcs and the differences were tiny( in the range of 1/64"). Keep in mind that the deflection in 'half' a curve is not half of the deflection of the 'whole' curve. In the picture below the first drawing shows 3" deflection over 96" with a cord drawn to the midpoint to accentuate what half a curve would look like. The bottom drawing shows 1.5" deflection over 48". Hope this helps.Derrick, I used 1.5"-2" of deflection on mine (I use a 14' pole that I bend and tie guy line to both tips to hold it's shape, then trace along the pole to mark my lines) and I've been really happy with out it turned out.
After reading about spread sheets here for many years, am so glad to have read Jordo's post and his photo that illustrates the success of his method. Catenary cuts have always been a nightmare for me, and while there were some successes, the wasted time spent on the failures was frustrating. An early attempt that mostly worked was the zip seam joining the front vestibule covers of this tent:
But the curve on the back side of the inner net on this tent was difficult to tailor, and a short 6" sewn in carbon spar was needed at the floor to keep it taut: 
The result of Jordo's method should be no different than the result of flexing a hoop or dome tent pole into an arc; namely, a parabolic curve, or one that arcs slightly more at its center. Beyond me is the math and physics that produces the parabola, and determines which parabola is best for a tent ridge where two sloping tent walls are joined. Having seen commercial tents with a more pronounced arcs in the parabola near the top, or highest point, some have occasionally wondered here if a symmetrical parabola will work when tipped up on a steep angle. The arcs on Aarn tents appear symmetrical (scroll down): http://www.aarnpacks.com/#!pacer-tents/c204h With others, not so sure, as with this Black Diamond vestibule with an arc that appears more pronounced near its bottom: http://blackdiamondequipment.com/en/tents-and-bivys/ahwahnee-tent-vestibule-BD8101370000ALL1.html#cgid=shelter&start=22 All the wonderers here seem to have come away from their threads reassured, but their reasons expressed for being so never seemed entirely convincing. But think I'll go with Jordo's m/o for now. Thanks for a simple alternative to spreadsheets.I agree with Jordan that 1.5-2" deflection is pretty good for a mid. I just made a 9×9 foot mid with 1.5" deflection on the ridges and 2" deflection along the bottom. I haven't been able to properly pitch it (just one pitch inside out in my garage to seal the seams, without the best anchors), but it seems good so far:
When I developed my 
Hope this helps.
But the curve on the back side of the inner net on this tent was difficult to tailor, and a short 6" sewn in carbon spar was needed at the floor to keep it taut: 
The result of Jordo's method should be no different than the result of flexing a hoop or dome tent pole into an arc; namely, a parabolic curve, or one that arcs slightly more at its center. Beyond me is the math and physics that produces the parabola, and determines which parabola is best for a tent ridge where two sloping tent walls are joined. Having seen commercial tents with a more pronounced arcs in the parabola near the top, or highest point, some have occasionally wondered here if a symmetrical parabola will work when tipped up on a steep angle. The arcs on 
- You must be logged in to reply to this topic.
