> Is it possible to use a drone with a balloon on top to help it lift more?
That's essentially a blimp. Due to square/cube scaling, blimps have less lift and more drag relative to their size at small scales than large ones. The extra power needed to overcome the drag would by far negate the power savings from reduced lifting requirements.
Also, helium is for all practical purposes a nonrenewable resource. One drone wouldn't use a lot, but a few million refilling every day would put a dent in the world's helium supply.
I think having what essentially would be small robot controlled fire-bombs flying through the skies would be a tough sell. Even if you managed to make them as safe as possible it's not exactly the kind of thing people would be eager to approve.
It's worth noting that hydrogen is orders of magnitude more energy-dense, by mass, than lithium-ion batteries.
As a benchmark: the DJI Phantom weighs roughly 1kg, and its battery can store about 80kJ of electrical energy. I found a NASA study [1] which estimated that the energy released when a li-ion battery combusts is roughly 2x the usable energy capacity. So let's say that a battery fire would release 160kJ of energy.
In contrast, a balloon capable of lifting a 1kg drone would need about 830 liters of hydrogen, with a mass of 75 grams. That amount of hydrogen, if burned in room-temperature air, would release about 9MJ -- roughly 50x as much energy as a battery failure.
(Of course, most of the hydrogen would burn itself up quickly and harmlessly, assuming the balloon isn't flying near any flammable objects.)
Plus assuming the drone is above the tree line and not next to a tall structure, the actual "fireball" should move fairly skyward and not pose much of a fire threat? I'd be more concerned about the falling drone/battery.
It's not only direct contact with the fireball you have to worry about, a large amount of the energy in the explosion would be coupled into a pressure wave and infrared radiation.
What do you think gasoline powered drones are? Agreed that hydrogen is perceived as being much more dangerous than it is because of the Hindenburg disaster.
But (and I have no reason to think that this is true) if it turned out to be commercially viable, I'm sure that perception could be changed.
Agreed. But there's a perception issue that arises from flammability that requires political skills I don't have. So hydrogen feels like a difficult solution to me. Example headline: "Flying Bombs, Oh My!"
If there were a mini-compressor-pump aboard the drone, is it possible that it could inflate/evacuate a balloon on demand during hover mode? Is the economics of such a thing
even possible?
Assuming there weren't already problems with the balloon idea, what you'd have then is a pressurized vessel, the pump, and of all the compressed helium weighing you down for 99% of your trip just to save a tiny bit of energy (and I'm assuming a day with zero wind here) during the offloading procedure which probably doesn't even last long enough for the balloon to fully inflate.
Also, as far as I know, the cheapest/lightest material to make the balloon out of would be mylar, which is conductive and not something you want around powerlines.
You'll experience the same scaling issues with whatever it is you expect to inflate with. You're going to have a lot of volume dedicated to the pressure vessel and not so much in the pressure vessel, because of scaling issues.
And I'm discarding the pump to put it back, assuming we're just going to vent to the atmosphere when we're done. Things get worse if you want to pump it back in.
No that doesn't really work. High pressure helium pumps are expensive, heavy, and require a lot of maintenance. Plus they require a lot of power to operate. And they produce a lot of waste heat.
Not saying this idea is worth the complexity (sounds over-engineered), but I am pretty sure you could make like a 1"x2" can of compressed helium attached to a 3' balloon with a simple valve to pop open and inflate the balloon. Think of those little air cans that you use for refilling bike tires on the go. Only weigh a few grams, holds a lot of air.
Maybe if we have to dome our cities and thus have no wind to disrupt the drone.
I wonder if it would be cheaper to use a small electric self-driving car like a mobile version of the amazon locker?