If two or more quadcopters are aligned, would the effect of drag due to the lead quadcopter's slipstream lead to measurable energy savings? And if so, how would one determine the optimal distance between the quadcopters?
My thought are that some energy savings are possible, but that there must be some distance between the quadcopters to avoid the high pressure air behind the lead quadcopter interfering with the quadcopter that's behind. How great this distance is depends on the tilt of the lead quadcopter. Since the drag force is proportional with the square of the velocity this means that energy savings should be larger at high velocity, but unfortunately the tilt of the quadcopters will also be higher causing the minimal distance needed between the quadcopters to increase.