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Comment by jpollock | Hacker News Reader

Didn't I just see a story about quadcopter design, and how helicopters were actually more efficient due to the single large rotor?

Here it is: http://www.geek.com/science/weve-been-designing-quadcopters-...

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Traditional helicopters are also far more efficient in normal cruising forward flight. They can glide quite well, which is how you can safely land in the case of engine failure [0]

[0] http://en.wikipedia.org/wiki/Autorotation_(helicopter)

I wonder if, at larger scales like this, electric motors and batteries are unable to efficiently power a tradition helicopter design (one main rotor and a small tail rotor).

Batteries are less energy dense (J/kg) than fossil fuels at any scale. For flight applications this makes batteries not so great because reducing weight is so critical. This becomes especially pronounced for larger aircraft sizes. You also don't get the weight reduction as you burn off fuel. For tiny RC aircraft the short flight times are fine, you can use cheap electric motors and they're safer. Larger RC aircraft are gas powered though.

the advantage here is the ability to have several (like 8-16 motors) so the failure of one motor isn't leading to a crash). It is the same paradigm shift as when horizontally scaled commodity hardware systems with expected multiple points of failure have almost everywhere replaced the highly-reliable Big Iron systems.

Another advantage is the possibility to have the propellers in ducts/shrouds (eVolo didn't do it, yet nothing prevents it) that is not doable for one big helicopter's propeller, thus such machine can fly near buildings/trees/etc... where helicopter can't. There is also issue of control in tight quarters where air flow is hard to predict and is affected by near by objects - multiple electric motors are much more flexible and faster reacting than one big engine+propeller.

Like with electric cars, the main issue is "range". It is solvable by having a series hybrid drive (especially once new gas engines specifically developed for series hybrids - ie. higher efficiency and lighter weight at the cost of power band - come to market). While such system willn't beat efficiency of 787 or fly transatlantic, it would be unbeatable for Santa Cruz to Mountain View commute.

Helicopters are pretty crash proof - the autorotation system is simple and very effective.

the autorotation requires a highly trained pilot and it is an emergency situation. Failure of 1 motor/propeller out of 16 is like a "low gas" warning, time to think about where to conveniently and casually land, instead of immediately autorotating down to whatever lake or heavy forested mountain you happened to be flying over.

I suspect it is more the availability of motors. Bigger than that and you are going to want to build them yourself because the price will be astronomical and nearly everything you will be able to get will be for the marine industry and weigh a ton.

http://www.yasamotors.com and similars. 75kw/27kg

Exactly what I thought of the moment I saw this.

Not only that, but the range for a battery-powered helicopter is going to be severely limited.

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