title_body: Why are larger propellers generally more efficient than smaller ones? In almost every case, long-range drones use larger propellers than other drones that don't need to travel very far or don't need to fly for very long. I have heard that a major reason for this is because a drone with larger props can be much more efficient than a drone with smaller props. If this is the case, what is the reason that larger props are generally more efficient to use?
upvoted_answer: Thrust is proportional to the change in momentum of the air passing through the prop - i.e. how much the prop speeds it up. 
  
  The power required to do this is proportional to the kinetic energy of the air, which is proportional to speed squared. That 'squared' is the problem.
  
  A smaller prop acts on less air, so it has to speed it up more to generate the same thrust. Half as much air moving twice as fast generates the same thrust, but takes twice as much power.
  
  This explains why helicopters can hover relatively economically, propeller planes only if they're powerful aerobatic models, jets only if they're extremely powerful and carrying a minimum of weight, and no one uses rockets unless they have to.