Flat pattern bodies for curved archway

I am currently trying to model a curved archway frame (c channel made from 3 off 10mm plates) around a cylindrical brick wall. I have managed to model this however I am having difficulty in creating flat patterns for the 3 plates required. I have managed to create one flat pattern (web of the flange around the arch) however the remaining 2 off I cant seem to get. Any help would be greatly appreciated.

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