I am currently trying to build an aircraft with contra-rotating propellers. I have an idea of what my horsepower should be. The question is should i dived the horsepower between the propellers or not?
If you do not know what contra-rotating propellers are:
https://i.makeagif.com/media/10-28-2015/9ao8rq.gif
It depends on how fast you want the plane to be. First just build the plane and fly it, and you can change engine stuff after that.