Tools on Surfaces is a good choice. You could do it with native tools by drawing an arc as a 'D' shape and extruding that through the cylinder. Then delete the flat side and use Intersect Faces to create the intersection. Delete the rest of the extrusion and you'll be left with the arc on the cylinder. [image: Vqta_arconcyl.png]

ExtrudeEdgesbyRails or CurviLoft ? Perhaps adding a central curve across the form and making it in two halves...[image: DczX_Capture.PNG]