Rhino has some tools in it for working with developable surfaces, some info here:

http://www.rhino3.de/design/modeling/developable/

http://wiki.mcneel.com/labs/devsrf

http://docs.mcneel.com/rhino/5/help/en-us/commands/unrollsrf.htm


Here you'll see how a complex curved surface made from bent planks does not really happen with a single bent piece, rather it's a set of strips with each individual strip being a developable surface:
http://www.boatdesign.net/forums/boat-design/designing-developable-surfaces-rhino-45275.html#post592264

Just any curved surface is not likely to be developable, especially a fillet going around a curved shape is not going to have a straight line shape to it in any single direction, in order to unroll a surface it has to have that straight line on it which is where it would be bent at in order to roll it up.

- Michael

Thanks Michael, your explanation makes perfect sense ...



bz