Design Nomenclature / Form & Geometry
Developable surface
Also called ruled surface, single curvature, developable, unrollable
This entry has not been translated yet and is shown in English.
A surface with zero Gaussian curvature everywhere, so it unrolls flat without stretching or tearing. The classification is complete and short: planes, generalized cylinders, generalized cones, and the tangent surfaces of space curves. Every developable is ruled — a straight line lies in it through each point — but the converse fails: a hyperboloid or a helicoid is ruled and not developable.
In practice
The test for whether a panel can be rolled or a pattern cut flat. 'Single curvature' is the shop word; 'double curvature' means you are into darts, stretch-forming, or breaking the panel into pieces.