I wonder if there is any rule for how closely you can put engine nozzles to each other. Are there any vibration, heat, etc. constraints when you are assembling two or more engine bells together?
Saturn I had four central engines very close, with the external gimballing engines more distant. I know that the outboard ones were placed there, among other things, to allow better pitch, yaw, and roll authority. But are there any limits for clustering engine nozzles?