Fairly new to Rhino. Project is R/C airplane design. I have a partial vertical side (the pink shaded closed polysurface) that I wish to Bend (so that it has a smooth surface) and follow the open curve shown selected in the snippet . It seems to me that Bend is a bit too free-form and lacks constraint snaps. I tried the “Flow along curve” function but the resulting shape looked terrible and had a lot of distortion at each of the bulkhead intersections and overall was smooth.
GDK
Upload your file as this would help us show you the best way do what your trying here. There are a few ways to do what I think your trying that are quite easy.
All my best … Danny
@GDK31216 As lopacki suggested upload the model or at the parts of the model relevant to your question, and we’ll suggest how to do it.
In general creating a curved surface using curves is more productive then trying to distort a flat surface to match curves. It may then be possible to flatten the curved surface and determine the portion of it which matches a particular shape.
There are some major differences in underling concepts between building a model in (say) wood and building one in a computer, even though the end products can look very similar in photos. 
Learning Rhino not only consists of “which buttons to push” but also best practices for getting the results you want.
You have come to the right place for help on that. Just click the icon that looks like a horizontal bar with an up pointing arrow at the top of discourse editing screen. This will allow you to upload your Rhino .3dm file so potential helpers can see what you’re doing.
Thank you for the assistance, apologies for not getting back sooner. Project has my attempt at forming the vertical polysurface to follow a curve. A side note, I did have some success with having a longeron follow the arch of a polyline in another test project so I think I understand the functionality of the “Flow Along Curve” menu item now.
With the project open, what I am trying to achieve is to have the red closed curve (and a subsequent solid extruded from it) follow the smooth arch of the cyan colored curve fore to aft and thereby represent a portion of the fuselage surface.
AIW - Yup, not everything on the 1:1 can be modeled at a smaller scale, but I need to at least attempt to replicate the appearance of such features within the limits of the medium being used. There is always concessions. If I can learn a new skill or method to add to my repertoire at model design the better.
Red curve, cyan curve, where, where, where ?
Have you considered using ‘loft’ 
on the bulkheads?
@Luc - Guess my upload wasn’t too successful. S’pose there is an upload file size restriction? I just did a “Save Small”. Here is the missing upload. Sorry.
McNeel Forum Prj.3dm (574.4 KB)
@Luc - Yes. I am well versed with lofting - and some will be. I am trying a different way.
I actually don’t see the problem. Flow (along curve) seems to work nicely.
Here McNeel Forum Prj 001.3dm (408.9 KB) I built the green line on the level of the cyan curve (apparently for some reason - or accidentally? - you moved the CPlane down relative to the World origin). This curve will serve as ‘base curve’ in the Flow command . The cyan curve was cut up (3 segments) and truncated to (kind of) fit the length of the green reference curve. ‘Flow’ is then execute with following option-settings : Copy=Yes Rigid=No Line Local=No Stretch=Yes PreserveStructure=No.
Stretch=Yes compensates the difference in length between ‘base curve’ (green) and ‘target curve’(cyan).
When a surface (using PlanarSrf) is made out of the red curve previous to Flow you get a nice bend (“flowed” actually) surface McNeel Forum Prj 002.3dm (445.3 KB) … Then you can use ‘OffsetSrf’ to make it a solid.
Using ‘Rebuild’ on the cyan curve hence reducing the number of control points (e.g. 9) makes the result even smoother.
PS. The polysurface below in you model doesn’t look that bad. Does it not comply?
@Luc - Deepest apologies for not getting back to you sooner than this. This project has been on a back seat to life… CPlane was intentionally moved down for the wing design based on side profile of the subject aircraft 3-View. I appreciate the assistance and affirmation what I did using the Flow command - albeit may not be textbook clean, adequately worked. I wasn’t aware of the ‘Rebuild’ command to soften the curve, thanks for that.
As for the polysurface below the wire frame model; it was my first attempt resulting in undesired surface undulations in spots and too flat through the center section over the wing airfoil cutout.
Again, appreciate your time and time expended with providing clarifying examples.
No problem. Life is one’s top priority project.