> They don't have to be efficient

Thats the point, the more efficient the less supply line you need, which means more autonomy.

I cant find the source but in Afghanistan a large proportion of the Allied casualties were from protecting supply lines.

The thing about quad copters is that they work at small scale because the rotor have almost no inertia. When you scale that up to 2m, then inertia is a bitch. That means you need tilting blades to make up for that lack of control.

BUT

You also need something to be powerful enough to alter the speed of the rotors to get yaw.

Plus you then also need to get them all to rotate so that you can get the efficiency of normal flight.

The reason why the osprey exists is because it has longer range than a helicopter (~1200 miles vs 400) its also faster.