I've an efficiency fantasy of them piggybacking on the roofs of trucks going in the right direction in order to save fuel, then hopping off when the truck starts to head in a different direction. Techno parasitism.
A truck on the freeway could be even harder, a drone would need to hold 55mph, throw in a headwind of say 15mph and you'll need a 70mph drone. Even on a highway at 40 + 15mph you're looking at 55mph in an environment with overhead lines, other vehicles, people.
Takeoff would be harder still, once the drone is released from a truck then it's instantly doing 55mph, or more if there is a tailwind. Should there be a failure during this mavouvre, there's no safety mechanism: the drone would become a 55mph+ projectile heading straight towards the following car's windshield.
So it's insanely dangerous.
Indeed. I believe the design is called "trucks" ;-)
One could of course have stackable drones and fit them in an open lorry, and program the route, order the drones so that the could take off in sequence... I'm not sure it'd be worth it though. I could definitively see fleets of "drone hangar lorries" driving around, slowing down to let drones off with deliveries, and taking on returning drones. I suppose you could set up a couple of circuits in big cities, guaranteeing a flightpath of, say no more than n kilometres from any one address to the nearest circuit -- and the drones might hop from circuit to circuit -- possibly even with a charge-station in the lorries.
Or change the lorries with purpose-build/modded electrical trains... (and fill in dead-zones with electrical trolleybuses).
Come to think of it, fitting trolleybuses with a "roof hangar" and charging station might be best: they typically don't go very fast -- and even if they do, they regularly stop to take on/let off passengers. Sounds like a good match.
The net result would be lawsuits and damaged drones I'm afraid. At least until a drone operator enters into an agreement with a hauling company.
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.
Except that it might be the last thing you'd see, before the drone fails and comes crashing through your windshield. Seriously though, if you're in the car behind a drone trying to land on a car ahead when it fails, there's no failsafe.
Or what if the drones hide on the back of the truck instead of the top?
And fuel consumption concerns are negligible. Sure, there likely would be a net increase in fuel used, but the premium is on drone electric charge capacity, battery weight, and drone range. A coordinated network of drones hopping onto trucks would greatly increase total per-drone range and make it possible to centralize drone freight depots even more (making them more sparsely distributed). This would push down costs a lot. The drone actually flies only "the last mile" and delivers only higher-valued goods.
The fuel was never an issue, sure there's a net increase in fuel consumed but not a net increase in energy as the drone is less efficient than the truck at transporting the same load.
A "last mile" drone is a pretty good idea, not just because it increases range, but because it avoids the need for the for the drone to return to the depot after each delivery. On the other hand, if the deliveries are tightly clustered it might sill be more efficient to just deliver them using the truck, as drones waste a lot of energy working against gravity.
Well, even crossing a highway with a large number of drones, is bound to lead to some of them failing and falling down into traffic? I suppose in some way there's some safety margin, having the drone do a controlled crash as soon as one engine fails -- but there must be scenarios in which the (presumably rather cheap) devices suffer sudden failure (eg: battery pack failure?).
I also wonder whether delivery trucks are in and of themselves as prevalent in China as they are in America, versus, say, bicycle carriers or other forms of delivery.