Having half-built a large curved viaduct in N gauge I think the prototype approach as suggested by 34C will look wrong on a model due to the tighter than prototype cuves that we use.
My effort was built with stripwood and will eventually be clad in embossed styrene. In the meantime I have built some Plastikard sides to stop the trains falling off, and these also have the shape of the main arches. My viaduct is on a 1m radius and is about 65mm wide, the arches are at about 120mm centres on the inside and about 8mm more on the outside IIRC. I thought piers tapering from maybe 10mm on the inside to 18mm on the outside would look strange, so I have made the piers parallel and the arches are circular on the inside and slightly elliptical outside. Also I have made the sides on a continuous curve because making each arch straight in plan, as I think 34C is suggesting, would just look wrong. Either the parapets would overhang by a large amount or the whole thing would resemble a giant 50p piece!
My effort was built with stripwood and will eventually be clad in embossed styrene. In the meantime I have built some Plastikard sides to stop the trains falling off, and these also have the shape of the main arches. My viaduct is on a 1m radius and is about 65mm wide, the arches are at about 120mm centres on the inside and about 8mm more on the outside IIRC. I thought piers tapering from maybe 10mm on the inside to 18mm on the outside would look strange, so I have made the piers parallel and the arches are circular on the inside and slightly elliptical outside. Also I have made the sides on a continuous curve because making each arch straight in plan, as I think 34C is suggesting, would just look wrong. Either the parapets would overhang by a large amount or the whole thing would resemble a giant 50p piece!
