Are you talking about varients of stock aircraft? That I think you will. I believe those are saved within the program itself, and will dissappear if you uninstall/reinstall. I think the restore defaults option just resets all of the things under settings to factory, so you probably won't lose your planes doing that. Don't quote me on this though, cause I am not 100% sure. The only thing I am pretty sure of is you won't lose any aircraft you downloaded from somewhere else as they are stored in a folder elsewhere in your computer.