[icegreentea]

I think the net change in fuel consumption would be largely dependent on a lot of factors - but mostly on the speed of the truck. Since rolling friction tends to dominate at lower speeds, and a quadcopter expends a lot of energy to stay afloat, then it's likely that for most truck - quadcopter configuration, there exists a critical speed where net fuel (or energy) consumption flips over. My wildass guess is that for most configurations, it would be somewhere above residential speeds (~40km/h), but far below highway speeds (~100km/h).

[acveilleux]

That's what I think too.

I've seen the figures on the aerodynamic roof air deflectors they put on semi-trailers and they can get as much as ~8-10% fuel saving at highway speed (ideal size/fit) where the aerodynamic drag is dominant.

Semis average around 6.5 mpg these days (flat, highway) so a 10% saving is close to 1 gph of diesel fuel or about 2.80-3.00$/h.

So I'd guess drones would add about 1-1.50$/h in fuel cost or so when they latch on. Enough to be noticeable.