Separating models, controllers, etc. into subdirectories

I’d like to organize my models, controllers, helpers, and even toplevel
view directories into subdirectories. There are so many files in my
rails app that it is getting unwieldy to find files in a list. Is there
a correct way to do this so that things don’t break? I tried putting
the model files in subdirectories; some pages seemed to work (models
loaded fine), while others did not.