> The watt hours needed to fly a medium sized VTOL uav of any type for any reasonable amount of time can't be collected by the size of pv panel that can be reasonably carried by the same craft.

Drones aren't limited to quadcopters.

> Not unless it sits still for a week in a sunny spot.

So do that?

Humans are persistance predators, or so I'm told. We didn't domesticate horses by running faster than them, but by because they had to rest, and when they stopped we'd catch up, and then they'd run again, a cycle that repeated until they couldn't run any more.

But these days, we humans are no longer nomadic: we live in predictable homes, and most of us who work do so at predictable locations.

A drone that takes a year to get to one of us? We could outrace it, or shoot it down… but only if we know it's there.

> A drone that takes a year to get to one of us? We could outrace it, or shoot it down… but only if we know it's there.

As someone in the IRA once told Margaret Thatcher, "We only need to be lucky once. You need to be lucky every time".

> sits still for a week

Why would that be an issue? Planners have to think further ahead, but the threat is only marginally decreased.

So called “vampire drones” have the capacity to identify electrical transmission lines and leech off them

This is still speculative tech, no?

I bet it won't by next month or so.

I remember seeing a demo. It doesn’t honestly seem very hard.

I don’t think induction alone would cut it. Having the drone make contact and step down hundreds of kilovolts seem pretty hard to me. Plus the EM interference on the drones systems would be a challenge under the best circumstances.

You can have other drones swap in fully charged batteries when needed.

Find an outdoor wall socket?

they don't need to be constantly flying. as long as work is not done, there isn't much energy being burned. and most of the energy burned is not with the rotors

If you mean something that is put in place with a full charge and just uses PV to trickle charge keep itself awake and alive, sure. I was thinking a scenario where something is dropped off, flies 10-15 minutes and lands somewhere to await a target. It would need many days to charge before it could fly again for ten minutes.

What about those drones that charge via power lines?

For the curious: https://www.youtube.com/watch?v=C-uekD6VTIQ

Drop a charging pad on a roof somewhere

> Not unless it sits still for a week in a sunny spot.

Isn’t that the answer to your question, then?

Kind of, but it seems such things would be obvious and exposed to being easily located if just sitting around idle in sunlight collecting charge. Not exactly like a landmine.

A drone sitting on a roof where no one ever goes isn't exactly obvious

Will militaries or civilian operators soon operate fleets of drones that scan rooftops and other exposed sunny locations for charging drones?

Even if they do, can still be camouflaged as e.g. a bunch of leaves, or other detritus.

Sounds like an arms race to me.

In any case, the solar cells should still be visible.

(solar cells can be non-reflective black, the reflectivity is just to double-dip the suns rays)

I had no idea, thank you!

Such cells would be half as efficient I suppose, so would need to be twice as large and probably at least twice as heavy. I wonder how that might affect design and payload constraints as it scales.

Or you just wait twice as long, which seems fine for sleeper drones parked on a rooftop waiting for the target to come in range.

How many drones would it take to do that? We’re talking potentially thousands of square miles. The resources required to scan all those areas—and scan them often enough to catch all the drones slowly working their way through—would be monumental.

It would be not unlike scanning all US aircraft passengers to the extent that it is done. At the time, that looked quite infeasible and expensive as well. You would be surprised at how much resources can be diverted to security firms under guise of national security.

My assumption is that it would be several orders of magnitude more than that, but, maybe we’ll find out.

power lines are AC, same tech as wireless phone charging, you just need to coil wires properly

Not usefully like wireless charging, but also there are easier ways such as touching the exposed wire.

Tram lines could be a target.