I'm designing a copter and trying to decide if the propellers should be ducted or open axial flow. I've read some theory on ducted and open air flow but I can't find any where that compares the two. I would prefer to use ducted over open for safety (ie put a safety guard round the propellers so they can't be run into with fingers etc). So are there any major advantages or considerations I should take into account, with ducted vs open axial flow before ploughing ignorantly ahead with one or the other type of flow?
Actually, ducted fan propeller are much less efficient than open blade propeller soif efficiency is your priority, open propeller is your option